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Yinghui Pu, Yiming Niu, Yongzhao Wang, Qing Liang, Lei Zhang,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06345

Abstract:
Metal–support interaction (MSI) has been extensively investigated regarding its structural and catalytic modification in heterogeneous catalysts. Herein, we reveal how facet-dependent MSI impacts on the structure and performance of Pd/ZnO in the CO oxidation reaction. ZnO nanosheets with orthohexagonal shape which are exposed mainly with {001} facets exhibit remarkable thermal stability under air atmosphere until 600 °C, while ZnO nanorods bounded with {100} facets transform at 400 °C and totally change after calcination at 600 °C. Thus, the Pd species supported on ZnO nanorods and nanosheets also display different sintering behaviors after thermal treatment, and the particle size of Pd grows from 1.1 to 5.7 nm on {100} facets while it keeps high-dispersion on {001} facets after 600 °C calcination. In situ transmission electron microscopy was used to visualize the sintering process, demonstrating that Pd displays the Ostwald ripening and particle migration coalescence mechanism on ZnO {100} facets, while shows extraordinary stability on ZnO {001} facets. Therefore, Pd supported on ZnO nanorod exhibits deactivation behavior after high temperature treatment in CO oxidation, during which the T50 delays from 106 to 120 and 145 °C after 200, 400, and 600 °C calcination. Interestingly, Pd on ZnO nanosheet shows obvious activity enhancement from 137 to 90 and 75 °C of T50 after the same treatment, which is ascribed to the synergy between Pd and ZnO {001} facets during catalysis. This work gives in-depth understanding of the facet-dependent MSI of Pd/ZnO catalysts, and it sheds light on the rational design of heterogeneous catalysts with high efficiency and sinter resistance.
Ting-Hsiang Hung, Qiang Lyu, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05959

Abstract:
Metal–organic frameworks (MOFs) are an emerging class of materials for membrane gas separations. The pore limiting diameter (PLD) of a MOF, i.e., the aperture size of the material, is often used as a key structural property to evaluate its size exclusion capability for a gas mixture. The current computation of a PLD is based on the van der Waals radii outlined by the Cambridge Crystallographic Data Centre (CCDC), and this set of van der Waals radii may fail to capture the strong repulsion exerting on a guest molecule when passing through the bottleneck of a channel. In this work, we propose a new set of van der Waals radii for the framework atoms, whose values are smaller than the existing ones to describe the repulsive adsorbent-adsorbate interaction. The PLD of a MOF computed using this more transport-relevant radius set is referred to as PLDt-r, and that computed based on the widely used set outlined by CCDC is referred to as PLDCCDC. We evaluate the relevance between PLDt-r/PLDCCDC and the transport properties of MOF compounds including their diffusivity as well as diffusive and permeative selectivities for various binary mixtures. From our investigation on approximately 400 MOF structures, the results show that PLDt-r can more effectively identify highly selective MOFs for membrane gas separations. In this work, we also demonstrate the applicability of PLDt-r when the framework flexibility is considered.
Swati J. N. Dixit, Ankur A. Awasthi, , , Neeraj Agarwal
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05709

Abstract:
The correlation between molecular structure and its photophysics is well reported, and organic chemistry is blessed with the freedom of substitution to obtain the desired photophysical property, suitable to control the functional aspects of materials. Despite the fact that the photodynamics of perylene has been studied in depth, its bay and peri aryl-substituted derivatives have not been studied to that extent. Herein, the ultrafast photodynamics of two anisyl perylene derivatives (peri-OCH3 and bay-OCH3) is presented. Isomers of anisyl perylene were designed to study the positional effect of substitution on their molecular packing and excited-state photophysics. The fluorescence spectra of nanoaggregates of peri-OCH3 showed excimer formation, while monomer emission is dominated in bay-OCH3. These features are consistent with the solid-state α-phase and β-phase of perylene, respectively, which are grown in a very precise and controlled manner. Excited-state dynamics studies show that in peri-OCH3, the monomeric free excitons undergo a relatively faster decay to populate the self-trapped monomeric excitonic state and E-state. In bay-OCH3, the contribution of emission from the Y-state and E-state is much less. The molecular structure alteration and different packing are also observed to have an impact on the exciton diffusion rate. The bay-OCH3 isomer is observed to have an almost-double diffusion length, which is attributed to the slightly faster diffusion and longer lifetime of free excitons. The present report indicates the structural modulation effect on the exciton-to-excimer transition dynamics and exciton diffusion properties, which can be beneficial in designing perylene-based materials for organic electronics.
Huijie Tian,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04495

Abstract:
We present a machine learning-based formalism to correct the mean-field assumption in microkinetic models to incorporate adsorbate interactions and surface inhomogeneity at the fast diffusion limit. Lattice Monte Carlo simulations are used to compute the macroscopic reaction rate in the presence of adsorbate interaction at different values of surface coverage. This dataset is then used to train an artificial neural network to compute precise reaction rates as a function of surface coverage of intermediates, and the underlying microkinetic model of the reaction system is modified by correcting the typical mean-field rate terms with these data-driven functions. An example of CO oxidation on the square ordered lattice is used to illustrate the speed, accuracy, and robustness of this approach, vis-à-vis a full-fledged kinetic Monte Carlo simulation. In particular, we show that while the traditional mean-field model completely misses the bistability of this system under certain conditions, the neural network-modified formalism correctly captures this phenomenon. We posit that this method scales well to larger reaction systems and is a cost-effective means to improve the accuracy of differential equation-based microkinetic models.
, , O. A. Stonkus, N. A. Kharchenko, , A. M. Gorlova
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05529

Abstract:
The structural features and reduction-induced structural evolution of Ni/Ce1–xZrxO2 catalysts for the methanation of carbon oxides were investigated. The catalysts prepared by the impregnation technique were investigated by ex situ and in situ X-ray diffraction (XRD) analysis, atomic pair distribution function (PDF) analysis, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction by H2. The main part of nickel was established to exist on the support surface as bulk NiO and Ni0 nanoparticles in as-prepared and reduced under reaction conditions catalysts, respectively. The metal–support interaction with incorporation of Ni2+ ions into the Ce1–xZrxO2 crystal lattice was also revealed. In situ XRD and XPS studies allowed one to monitor the structural evolution of the Ni/Ce1–xZrxO2 catalysts during their heating under H2 atmosphere in the temperature range of 25–450 °C. The formation of Ni0 nanoparticles was shown to favor reduction of Ce1–xZrxO2 oxide via hydrogen spillover. In situ XRD results revealed reversible expansion and contraction of the Ce1–xZrxO2 crystal lattice in reductive and oxidative atmospheres, which are associated with Ce4+ ↔ Ce3+ transitions and redistributions of oxygen vacancies. The elucidated metal–support interaction and synergism of redox properties of the Ni/Ce1–xZrxO2 catalysts are relevant for high activity in the CO2 and CO methanation reactions.
, Brenden W. Hamilton, Alejandro Strachan
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05599

Abstract:
Hot spots are local regions of high temperature that are widely considered to govern explosive initiation. Hot spot dynamics rests on a delicate balance between heat generation due to chemical reactions and heat loss through thermal conduction, making accurate determinations of the conductivity under extreme conditions a key component of predictive explosive models. We develop here an approach to directly determine the thermal transport properties of explosive hot spots with realistic initial structures through a combination of molecular dynamics (MD) and diffusive heat equation (HEq) modeling. Effective thermal conductivity values are determined by fitting HEq models to MD predictions of long timescale hot spot relaxation. The approach is applied to model hot spots in the molecular crystalline explosive 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) for a range of shock strengths and two limiting cases for impact orientation. Isotropic and anisotropic HEq models yield similar results, despite TATB exhibiting some of the largest and most anisotropic thermal conductivity values for explosive near normal conditions. The conductivity is found to be a strong function of density, which parametrically captures dependence on temperature, pressure, and material state. The associated root-mean-square errors of the fitted HEq models are approximately 5% of MD predicted final equilibrium temperatures. The conductivity values determined here for TATB hot spots are considerably larger than those used in a prior hot spot criticality study, which may significantly impact predictions for critical hot spot sizes. The approach provides a convenient foundation for determining the effective thermal conductivity for hot spot problems in other explosives and directly yields information on reasonable approximations that might be taken in higher-level models for those materials.
Guillermo Gutierrez, Emma M. Sundin, Paul Gaurav Nalam, Vishal Zade, Rebecca Romero, Aruna N Nair, , Debabrata Das, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04005

Abstract:
We report the structural chemistry and optical properties of tin (Sn)-mixed gallium oxide (Ga2O3) compounds, where the interfacial phase modulation-induced structural distortion in turn induces variations in the band gap and nonlinear optical activity. The Sn incorporation into Ga2O3 causes significant reduction in the band gap and induces nonlinear optical activity upon chemical composition tuning. Detailed investigation performed on the structural chemistry, phase stabilization, surface morphology, and optical and electrochemical properties of Sn-mixed Ga2O3 compounds (Ga2–2xSnxO3, 0.00 ≤ x ≤ 0.3, Ga-Sn-O) indicates that the Sn-incorporation-induced effects are significant. To produce Ga-Sn-O materials of high structural and chemical quality, we adopted a simple solid-state chemical reaction route involving first calcining and then sintering the material at higher temperatures. Structural chemistry analyses of sintered Ga-Sn-O compounds by X-ray diffraction (XRD) showed solid solution formation at lower Sn concentrations (x ≤ 0.10). The XRD analyses indicate the SnO2 secondary phase formation at higher (x > 0.10) Sn concentrations. Surface morphology analysis using scanning electron microscopy (SEM) also showed a positive relationship between phase separation and Sn concentration. Optical absorption spectra showed a substantial redshift in the band gap (Eg), which would allow Ga-Sn-O compounds to have wide spectral selectivity. At higher Sn concentrations (x = 0.25–0.30), corroborating with structural/chemical analyses, an additional lower-energy sub-band transition that explicitly corresponds to SnO2 appears in the optical absorption data. Importantly, the evidence of nonlinear optical activity in Ga-Sn-O, which is otherwise not traditionally known for such an activity, as well as dipolar- and quadrupolar-shaped dependence of activity with the polarization angle of the excitation source was detected. At higher concentrations (x ≥ 0.15), Sn was found to be insoluble, which can be attributed to Ga2O3 and SnO2 possessing different formation enthalpies and cation (Ga3+ and Sn4+) chemistries. The fundamental scientific understanding of the interdependence of synthetic conditions, structure, chemistry, and optical and electrochemical properties could be useful to optimize Ga-Sn-O inorganic compounds for optical, optoelectronic, and photocatalytic device applications.
, Aaron C. Y. Tay, Jonathan L. Falconer, S. J. Lee,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06227

Abstract:
Two Cu(II) metal–organic frameworks (MOFs) were prepared on the nanoscale at room temperature using a microemulsion method, namely, [Cu3(BTC)2(H2O)3] (BTC = benzene-1,3,5-tricarboxylate), known as HKUST-1 (1), and [Cu2(OH)(BTC)(H2O)]·2H2O (2). Thermochemical and gas sorption properties of the microporous topologies were characterized by mid- and far-infrared vibrational spectroscopy, supported by periodic density functional theory calculations. The mid-infrared profile of 1 appeared altered in response to gas sorption under variable temperature and pressure conditions. Vibrational mode analysis indicated the most sensitive infrared peaks were associated with the internal vibrations of organic linker moieties indirectly coupled to the Cu(II)–gas coordination site, activated by a lowered symmetry induced by guest interactions. Synchrotron far-infrared spectroscopy was shown to be a useful diagnostic for the microstructure of 1 and 2 where different temperature dependences were displayed in the low-frequency region. The loss of residual water during the activation of 2 at elevated temperature coincides with peaks indicative of free paddle-wheel moieties emerging in the far-IR spectra. As demonstrated for both materials 1 and 2, vibrational mode analysis was effective in screening MOF materials for their propensity toward gas uptake and, inversely, the diffusion of guest species such as adsorbed water from the microporous environments.
Xinpeng Guo, Yongquan Guo, Linhan Yin
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04280

Abstract:
Valence electron structures (VESs) and mechanical and thermal properties of single-phase refractory high-entropy alloys (RHEAs) have been investigated with the empirical electron theory (EET) of solids and molecules. The calculated bond lengths agree well with the experimental ones. The physical properties of RHEAs, which include the hardness, yield strength, melting point, and cohesive energy, are strongly related to their VESs. It shows that the hardness and yield strength of RHEAs are enhanced with increasing linear density of covalence electron pair ρL along the direction of the strongest bond and the covalence electron number per atom nc/atom. The melting points of RHEAs increase with increasing covalence electron pair nA and the average of the covalence electron number nc/atom. The cohesive energies for RHEAs significantly depend upon the average of the covalence electron number per atom. It is suggested that the mechanical and thermal properties of RHEAs are modulated by their covalence electrons.
Xianxian Kong, Qianqian Pan, , Zhiqiao He, , Yan Yu
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05866

Abstract:
The development of low-cost, high-performance, and stable photocatalytic materials is vital to achieving highly efficient solar-to-fuel conversion. We report the fabrication of a metal-doped Zr-UiO-66-NH2 ((M/Zr)-UiO-66-NH2) catalyst using a one-pot hydrothermal method via a single-step reaction. The optimized 0.5(Co/Zr)-UiO-66-NH2, 0.5(Ni/Zr)-UiO-66-NH2, and 0.5(Fe/Zr)-UiO-66-NH2 photocatalysts exhibit significant hydrogen evolution performance approximately 35.22, 13.84, and 1.58 times higher than Zr-UiO-66-NH2 under simulated solar light. The enhanced hydrogen production efficiency can be ascribed to the metal-to-metal charge-transfer excitation between Co (Fe or Ni) and Zr species and the improved light harvest. Their cooperating function favors the excitation and separation of photogenerated carriers, which leads to a marked increase in catalytic activity.
Manuel Meusel, Afra Gezmis, Simon Jaekel, , Andreas Bayer, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06613

Abstract:
We deposited defined amounts of [C1C1Im][Tf2N] on Au(111) at different temperatures and investigated the morphology and wetting behavior of the deposited films by atomic force microscopy. For multilayer coverages, we observe a drastically different growth behavior when comparing deposition at room temperature (RT) and deposition below 170 K followed by slow annealing to RT. Upon deposition at RT, we find the formation of 2–30 nm high and 50–500 nm wide metastable 3D droplets on top of a checkerboard-type wetting layer. These droplets spread out into stable 2D bilayers, on the time scale of hours and days. The same 2D bilayer structure is obtained after deposition below 170 K and slow annealing to RT. We present a statistical analysis on the time-dependent changes of the shape and volume of the 3D droplets and the 2D bilayers. We attribute the stabilization of the 2D bilayers on the wetting layer and on already formed bilayers to the high degree of order in these layers. Notably, the transformation process from the 3D droplets to 2D bilayer islands is accelerated by tip effects and also X-ray radiation.
Shengxia Zhang, Peipei Hu, Lijun Xu, Hailong Chen, Khan Maaz, Pengfei Zhai, Zongzhen Li, Li Liu, Wensi Ai, Jian Zeng, et al.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04724

Abstract:
The emergence of monolayer transition metal dichalcogenides (TMDCs) has provided a favorable platform for exploring a broad range of novel optoelectronic device applications and quantum phenomena due to their remarkable physical and chemical characteristics. Understanding the transition and motion of excitons in TMDCs is of fundamental interest for their optoelectronic devices. Here, we demonstrate the exciton transition in monolayer WS2 that can be fine-tuned by swift heavy ion (SHI) irradiation. The dependence of trion and exciton emissions on SHI irradiation in the as-transferred and as-grown monolayer WS2 was investigated by micro photoluminescence (PL) spectra where different PL responses were monitored. The trion-to-exciton transition in the as-transferred WS2 monolayer was ascribed to SHI irradiation that resulted in charge localization and pre-existing defect annealing, whereas the exciton-to-trion transition in the as-grown WS2 monolayer was attributed to the competition of charge localization and charge transfer caused by SHI irradiation. Femtosecond transient absorption measurements were performed to study the exciton relaxation dynamics in SHI-irradiated WS2, and it was shown that defect-assisted recombination dominates the exciton relaxation process for SHI-irradiated WS2. These results open up new opportunities to manipulate and tune the optical properties of two-dimensional TMDCs, which are of special importance for the development of optoelectronic and valleytronic devices.
Huan Li, Tomoya Taguchi, Yanan Wang, Hidenori Goto, Ritsuko Eguchi, Hirofumi Ishii, Yen-Fa Liao,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06207

Abstract:
Herein, the pressure dependence of the electrical resistance R of superconducting 4d and 5d transition metal compounds, CaRh2 and CaIr2, with superconducting transition temperatures, Tc’s, as high as 6.09 and 6.04 K at ambient pressure, respectively, is investigated to depict their Tc–pressure (p) phase diagrams. The superconductivity of these samples is investigated based on plots of R vs temperature (T) over a wide pressure range. It is demonstrated that the Tc of both compounds decreases slowly as pressure increases but saturates in a high pressure range. This behavior is similar to that of SrIr2 reported previously, suggesting that it may be a unique behavior of the 4d and 5d transition metal compounds investigated. The crystal structures of CaRh2 and CaIr2 are determined based on powder X-ray diffraction patterns generated via synchrotron radiation at high pressures, and no structural phase transitions are observed up to ∼20 GPa. The magnetic field dependence of R–T plots recorded at 12.2 and 7.98 GPa for CaRh2 and CaIr2, respectively, is analyzed using three pairing models. Consequently, the superconductivity of CaRh2 and CaIr2 could not be explained merely based on s-wave dirty limit and s-wave clean limit models but rather the p-wave polar model. We fully analyzed the magnetic behavior of the superconducting phases of CaRh2 and CaIr2 at ambient and high pressures using three different methods: the Werthamer–Helfand–Hohenberg/Maki, empirical, and Ginzburg–Landau models. This report provides a systematic study pertaining to the pressure dependence of superconductivity in binary-element compounds comprising alkali-earth and 4d or 5d transition metal atoms.
Siyuan Weng, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06291

Abstract:
One of the most interesting structures of organic photodetectors (OPDs) is the bulk heterojunction (BHJ), which can be achieved by mixing electron donors and electron acceptors in a suitable solvent and then spin-coating. BHJs have proven to be a very useful method to overcome the short diffusion length of organic semiconductor excitons. However, this structure enhances disorder and hinders the collection of photogenerated carriers. Therefore, it is very important to prepare OPDs with this structure. In this paper, we show how to use conjugate polymer donor poly(3-hexylthiophene) (P3HT) and fullerene derivative acceptor 6,6-phenyl C61-butyric acid methyl ester (PC61BM) to form a binary BHJ active layer by spin-coating to improve the performance and detector wavelength of a ZnO ultraviolet (UV) photodetector (PD). Compared with the ZnO UV PD, the responsivity of the OPD can reach 0.58 A W–1, which is increased by about 7.14 times. Furthermore, the OPD shows improved absorption, high photocurrent to dark current ratio (1.63 × 104), and excellent detection capability (3.67 × 1012 Jones). The preparation of a new OPD by this work shows strong performance and provides a new idea for the research of OPD. Therefore, it is very important to design and manufacture ZnO UV PD to form a BHJ OPD with organic polymers P3HT:PC61BM.
Craig Waitt, Audrey R. Miles,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05917

Abstract:
Adsorption free energies are fundamental to surface chemistry and catalysis. Standard models combine some assumed analytical form of the translational potential energy surface, often parametrized against density functional theory (DFT) calculations, with an analytical expression for the resultant translational densities of states (DOS), free energy, and entropy. Here we compare the performance of such models against numerical evaluations of the DOS and thermodynamic functions derived from solutions to the translational Schrödinger equation. We compare results for a translational potential energy surface (PES) derived from nudged eleastic band calculations with those obtained from adsorbate rastering across a series of monatomic (O, S, C, N, and H) and polyatomic (NHx) adsorbates on (100) Pt and Au facets. We find that analytical models as commonly parametrized have mixed performance for describing the translational PES and that the consequences for computed free energies are modest but potentially significant in microkinetic models. Numerical solutions are possible for modest to no additional computational cost over analytical models and thus should be considered when reliable free energy estimates are needed or translational potential energy surfaces are available.
Nora C. Buggy, Yifeng Du, Mei-Chen Kuo, Soenke Seifert, Ryan J. Gasvoda, Sumit Agarwal, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06036

Abstract:
Performance of polymer electrolyte-based energy systems is significantly impacted by transport within the electrode catalyst layer, where ionomer thin films coat catalyst particles. Proton exchange ionomer thin films have been thoroughly characterized, but few studies have critically examined anion-exchange ionomer (AEI) thin films. Further, none have reported nanoscale phase separation for hydrocarbon AEIs, which is critical to mitigate transport resistances. In this work, a set of hydrocarbon-based AEIs with nanoscale phase separation are developed from tunable block copolymer systems composed of polyisoprene (PIp) and polychloromethylstyrene (PCMS). The effect of the PIp/PCMS ratio, architecture, and thickness on the thin-film morphology of the neutral block copolymer precursors on silicon and silver substrates is investigated using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM). AEIs are prepared by quaternizing with trimethylamine or methylpiperidine and their cation-dependent morphology is characterized at 60 °C and 95% RH. A perpendicularly aligned morphology is observed on silver, while no phase separation is observed on silicon, indicating that silver–polymer interfacial interactions drive phase separation. After quaternization, dipole–dipole interactions induce some disorder, but nanoscale phase separation is still maintained. GISAXS patterns are modeled using a Unified Fit approach to understand water uptake and swelling, and recommendations for AEI design are presented.
Marie-Paule Pileni
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05115

Abstract:
Here we use a water dispersive 3D suprastructure of ferrite (Fe3O4) nanocrystals called colloidosomes. They are a shell of one or few layers of hydrophobic nanocrystals with a very high flexibility, deformability, and low Young modulus. We propose a strategy to modulate the intralysosomal distribution of nanocrystals through colloidosomes. This suprastructure displays an increase cellular uptake by tumor cells compared to the same nanocrystals used as building blocks, coated with a hydrophilic agent and consequently dispersed in aqueous solution. Moreover, an increase of the nanocrystal density close to the lysosome membrane takes place. Importantly, nanocrystals remain assembled in cells whereas dispersed nanocrystals are randomly aggregated. By subjecting the internalized colloidosomes to a magnetic field they align and form long chains. We decorticate the fate of colloidosomes within the tumor microenvironment in comparison to their nanocrystal building blocks. We highlight that self-assemblies trigger local photothermal damages that are inaccessible for isolated nanocrystals and not predicted by global temperature measurements.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05037

Abstract:
Bridging ligands play a crucial role in design of luminescent dinuclear metal complexes. Bis-cyclometalating ligands gave rise to a large family of highly efficient emitters. Herein, we investigate the effect of switching the cyclometalating function of the bridging (chromophoric) ligand on photophysical properties of dinuclear Ir(III) complexes. The new dinuclear Ir(III) complex (Ir-1), comprising a bridging chromophoric ligand with two terminal cyclometalating phenyl derivatives, conjugated to the central twice nitrogen-coordinating thiazolo[5,4-d]thiazole derivative, displays red phosphorescence of decent efficiency in CH2Cl2 solution at room temperature (ΦPL = 12%, τ = 1.5 μs, and λ = 635 nm). This is several times more efficient compared to the properties of the earlier reported dinuclear Ir(III) complex IrIr, with a bridging ligand comprising terminal nitrogen-coordinating pyridine derivatives and a central cyclometalating thieno[3,2-b]thiophene derivative, under the same conditions (ΦPL = 3.5%, τ = 2.9 μs, and λ = 714 nm). This “C/N swap” within the bridging ligand caused blue-shifted and improved efficiency of phosphorescence of Ir-1. The origin of this effect is the significantly reduced exchange interaction in state T1 and, consequently, smaller ΔE(S1 – T1) energy gap. According to the density functional theory calculations, this comes from the more even (wider) distribution of the highest occupied molecular orbital within the bridging ligand and increased participation of the metal centers and halide atoms in the formation of states S1 and T1. Modulation of the substituent pattern on the bridging ligand in complex Ir-2, analogous to Ir-1, afforded selective tuning of the phosphorescence rate, whereas other properties of phosphorescence remained similar under the same conditions (ΦPL = 15%, τ = 3.1 μs, and λ = 632 nm).
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04823

Abstract:
The confinement and the enhancement of optical fields near metallic nanostructures provide unique tools for versatile applications in nanoscale devices and spectroscopies. It is therefore of great importance to investigate plasmonic properties of metallic nanostructures, such as the distribution of optical fields and the wavelength dependence of localized surface plasmon resonance on the nanometer scale. In this article, we demonstrate nanoscale visualization of the distribution of optical fields and the wavelength dependence of localized surface plasmon resonance of gold nanostructures by means of a tip-enhanced Raman spectroscopy (TERS)-based technique, which is a novel application of TERS to visualize the plasmonic properties at the nanoscale. Owing to the capability of fetching frequency-resolved optical information in Raman spectroscopy and an innovative molecular-functionalized metallic probe that we previously developed, intrinsic features of both the field confinement and the wavelength dependence of localized surface plasmon resonance of gold nanostructures are successfully visualized with a spatial resolution as high as 11 nm. Our present results enable one to comprehensively understand inherent plasmonic properties of metallic nanostructures, which would help to study the nature of plasmonic nanostructures and develop a wide range of plasmonic applications, such as molecular sensing, energy transfer, or optical storage.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05859

Abstract:
Gallium-based liquid metals have gained plenty of attention in the scientific community due to their extraordinary properties. The most intriguing properties of liquid metals are high surface tension, density anomaly, high electrical and thermal conductivity, phase transition, and their temperature and low viscosity in combination with their low toxicity. Though there are many reports of the physical properties of gallium-based liquid metals, some of these are highly scattered and inconsistent. Therefore, we compile literature data of these aspects of gallium-based liquid metals, point out general relationships of these physical parameters, and unravel inconsistencies in the literature. Subsequently, we state reasons for the observed scatter and recommend science-based values researchers should employ. Furthermore, we discuss important dependencies between the physical parameters, introduce methods to alter the physical parameters, and introduce selected applications based on changing the physical properties. Finally, we point out open questions concerned with the physical parameters of liquid metals, which should be investigated in the future.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06807

Abstract:
The developed generalized analytic model of charge transport in disordered matter describes self-consistently the drift and diffusion of charge carriers, includes the nonequilibrium regime, and incorporates both energy and off-diagonal (structural) disorder. The model makes it possible to accurately describe the anomalously wide transient current “tails” observed in time-of-flight experiments over wide ranges of temperature and electric field strength. Explicitly considering the off-diagonal disorder provides a more accurate description of the energy distribution of states and other parameters of the materials. The disorder contains information about the ratio of carrier diffusion coefficient to carrier mobility and characterizes the fraction of deeper localized states that inhibit mobility.
Ashley T. Smith, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06670

Abstract:
We investigate the influence of acidity and confinement for different aluminum T-site substitutions in H-ZSM-5 using reactions related to the methanol-to-olefin (MTO) process as examples. We use density functional theory at the PBE-D3 level to study all 12 different T-sites existing in the MFI framework. We find that transition-state energies vary by about 20 kJ/mol with the commonly employed T12 site having some of the lowest barriers. A large part of the energetic differences can be ascribed to differences in dispersion forces due to the surrounding framework, as also evidenced by smaller and uncorrelated differences in calculated heats of adsorption of ammonia. Our analysis shows that taking the T12 site as a computational active site model will yield reaction barriers that are among the lowest of all T-sites available.
Yi-Jung Tu,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05698

Abstract:
The differential capacitance profile of electrochemical interfaces reflects the physical properties of the double layer. For carbon electrodes and ionic-liquid-based electrolytes, these capacitance profiles are not fully understood. In this work, we utilize constant voltage molecular dynamics simulations to compute differential capacitance profiles of ionic liquids [BMIm+][BF4–] and [BMIm+][TFSI–] mixed with acetonitrile and 1,2-dichloroethane, at model graphene electrodes. We find that both pure and 10% mole fraction ionic liquid electrolytes exhibit camel-shaped capacitance profiles with two peaks on either side of a minimum centered at the potential of zero charge. This profile shape results from the electric-field-induced rearrangement of ion structure within the inner layer closest to the electrode interface. At a low potential, the ionic liquid inner layer is concentrated with nonpolar trifluoromethyl and butyl functional groups of the anions and cations, corresponding to the minimum of the capacitance profiles. With increasing voltage, electrostatic interactions of polar/charged functional groups with the electrode surface compete with these nonpolar interactions, leading to ion rearrangement that increases the inner-layer charge density and results in higher capacitance. After the ion restructuring is complete, the response saturates and capacitance diminishes. The presence of organic solvent significantly changes the composition of the inner layer. For example, strong nonpolar interactions between dichloroethane molecules and the graphene surface substantially block ion/electrode contact at moderate potentials. Overall, our simulations highlight the dynamic nature of the inner region of organic electrolyte double layers and the sensitive dependence on electrolyte composition and applied voltage.
Pan Yin, Jun Yu, Lei Wang, Jian Zhang, Yao Jie, Li-Fang Chen, Xiao-Jie Zhao, Hai-Song Feng, Yu-Sen Yang, Ming Xu, et al.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06381

Abstract:
Au supported on TiO2 (Au/TiO2) catalysts have shown excellent activity in low-temperature water-gas-shift (LT-WGS) reaction; however, the effects of different crystalline phases of the support, the oxygen vacancies (Ov) on the support, and the metal-support synergy on the catalytic performance still remain indistinct. In this work, a combination of density functional theory (DFT) calculation, microkinetic modeling, and experimental investigation for the LT-WGS reaction mechanism over the Au8 cluster supported on TiO2 with three crystalline phases (Au/ana-Ov, Au/rut-Ov, and Au/bro-Ov) is systematically performed. Notably, Au/ana-Ov gives the lowest energy barrier at each step of the WGS reaction, indicating a superior catalytic activity, and a redox pathway is confirmed: H2O undergoes the dissociation adsorption on Ov while interface Au serves as an active site for CO activation. The microkinetic modeling results confirm the favorable operating condition (pH2O/pCO ≤ 4) for this reaction. Furthermore, experimental researches verify that the Au/ana-Ov sample exhibits the optimum catalytic activity, which accords well with the prediction conclusions of theoretical calculation. This work provides the detailed information on the metal-support synergistic catalysis as well as the in-depth understanding of the reaction mechanism of LT-WGS over the Au/TiO2–x system, which would pave a way for the development of heterogeneous catalysts toward interface sensitive reactions.
, Xinyuan Ke, , Susan A. Bernal
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c07328

Abstract:
Alkali-activated materials are promising low-carbon alternatives to Portland cement; however, there remains an absence of a fundamental understanding of the effect of different activator types on their reaction products at the atomic scale. Solid-state 27Al and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy and 1H–29Si cross-polarization MAS NMR spectroscopy are used to reveal the effect of the activator anion on the nanostructure, cross-linking, and local hydration of aged alkali-activated slag cements. The main reaction product identified is a mixed cross-linked/non-cross-linked sodium-substituted calcium aluminosilicate hydrate (C–(N)–A–S–H) gel with a structure comparable to tobermorite 11 Å. Analysis of cross-polarization kinetics revealed that a higher content of soluble silicate in the activator promoted the incorporation of Al into the aluminosilicate chains of C–(N)–A–S–H gels, charge-balanced preferentially by protons within the gel interlayer. In sodium carbonate-activated slag cements, aluminosilicate chains of C–(N)–A–S–H gels are instead charge-balanced preferentially by Ca2+ or AlV ions. Hydrotalcite was observed as a secondary reaction product independent of the activator used and in higher quantities as the content of sodium carbonate in the activator increases. The presence of soluble silicates in the activator promotes the formation of an Al-rich sodium aluminosilicate hydrate (N–A–S–H) gel which was not identified when using sodium carbonate as the activator. These results demonstrate that the anion type in the activator promotes significant differences in the nanostructure and local hydration of the main binding phases forming in alkali-activated slag cements. This explains the significant differences in properties identified when using these different activators.
Siyuan Weng, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06405

Abstract:
Compared with the electron donor of the bulk heterojunction (BHJ) organic/inorganic photodetectors (OPDs), there is less development in the field of electron acceptors that have strong absorption capacity in the visible light and near-infrared (NIR) region, which hinders the further research and development of OPDs. As a traditional acceptor, fullerene has limited electronic tunability and weak visible light absorption, which limits the optical absorption and electron tunability properties required by the donor. In this work, a novel low-band-gap nonfullerene acceptor (NFA) sodium indocyanine green (Ir-125) is introduced, blended with a fullerene derivative acceptor [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) and a conjugate polymer donor poly(3-hexylthiophene) (P3HT), to form ternary BHJ-active layers, forming a high-performance BHJ OPD with ultrawide spectral response from the ultraviolet (200 nm) to visible light to NIR (1050 nm) region. Here, the high-performance OPD exhibits complementary absorption on the scale of exciton diffusion length and is uniformly mixed with the pure phases. The OPD has high external quantum efficiency (132%) and high detectivity (9.07 × 1012 Jones), which is much higher than those of P3HT:PC61BM, which are 58% and 3.62 × 1012 Jones, respectively, and also, OPDs show an increase in the photocurrent to dark current ratio (Iphoto/Idark) by one order of magnitude. The generation of the balanced photocurrent between the donor and NFA eliminates the undesirable limitation on the donor imposed by fullerene derivatives and expand the response range of the BHJ OPD, which opens up a new avenue toward a higher efficiency and wider response range for the OPDs.
Dan Wu, Xinyi Shen, Xiaokang Liu, Tong Liu, , Dong Liu, Tao Ding, , Lan Wang, Linlin Cao, et al.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05148

Abstract:
Development of high-efficiency and inexpensive oxygen evolution reaction (OER) catalysts is highly desirable for water electrolysis devices and rechargeable metal–air batteries. Herein, we report novel one-dimensional (1D) Fe-doped α-Ni(OH)2 nanobelts as OER-active electrocatalysts. In-depth characterizations revealed that Fe atoms are incorporated into the lattice of Ni(OH)2, resulting in the strong electron interaction with active Ni sites. Moreover, a contraction of Ni–O bond distance induced by Fe is revealed by operando X-ray absorption fine structure spectroscopy under OER working condition, which leads to a near-optimized adsorption of oxygen intermediates. Consequently, the Fe-doped α-Ni(OH)2 nanobelts deliver significantly promoted OER activity in alkaline solutions with a low OER overpotential of 236 mV at 10 mA cm–2 along with good stability. This work provides a strategy for developing efficiently non-noble metal catalysts, gives insights to the Fe doping effect and the dynamic evolution of disturbed atomic and electronic structure of Ni active sites.
, Juan Fernandez, Samuel Hevia, Eduardo Cisternas, Marcos Flores
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c01774

Abstract:
Self-assembled monolayers are a promising opportunity to control the electrochemical reactions taking place on electrodes of lithium-ion batteries. Such control is relevant to diminish the aging process and to improve the performance of these energy storage devices. From this point of view, the adsorption of para-aminobenzoic acid on vanadium pentoxide, an attractive high-capacity cathode material, is investigated with the combination of experimental angle-resolved X-ray photoelectron spectroscopy as well as dispersion-corrected density functional calculations. Our results show that the molecules prefer a lying-down or up-standing configuration depending on their concentration. The comparison between experiment and simulation indicates a high coverage of the surface and hence the formation of a self-assembled monolayer of up-standing molecules.
, , , Denisa Kubániová, Claudio Cara,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06211

Abstract:
Understanding the complex link among composition, microstructure, and magnetic properties paves the way to the rational design of well-defined magnetic materials. In this context, the evolution of the magnetic and structural properties in a series of oleate-capped manganese-substituted cobalt ferrites (MnxCo1–xFe2O4) with variable Co/Mn molar ratios is deeply discussed. Single-phase ferrites with similar crystallite and particle sizes (about 10 nm), size dispersity (14%), and weight percentage of capping oleate molecules (17%) were obtained by an oleate-based solvothermal approach. The similarities among the samples permitted the interpretation of the results exclusively on the basis of the actual composition, beyond the other parameters. The temperature and magnetic field dependences of the magnetization were studied together with the interparticle interactions by DC magnetometry. Characteristic temperatures (Tmax, Tdiff, and Tb), coercivity, anisotropy field, and reduced remanence were found to be affected by the Co/Mn ratio, mainly due to the magnetic anisotropy, interparticle interactions, and particle volume distribution. In addition, the cobalt and manganese distributions were hypothesized on the basis of the chemical composition, the inversion degree obtained by 57Fe Mössbauer spectroscopy, the anisotropy constant, and the saturation magnetization.
Katrín Blöndal, Khachik Sargsyan, , ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04009

Abstract:
A new method for computing anharmonic thermophysical properties for adsorbates on metal surfaces is presented. Classical Monte Carlo phase space integration is performed to calculate the partition function for the motion of a hydrogen atom on Cu(111). A minima-preserving neural network potential energy surface is used within the integration routine. Two different sampling schema for generating the training data are presented, and two different density functionals are used. The results are benchmarked against direct state counting results by using discrete variable representation. The phase space integration results are in excellent quantitative agreement with the benchmark results. Additionally, both the discrete variable representation and the phase space integration results confirm that the motion of H on Cu(111) is highly anharmonic. The results were applied to calculate the free energy of dissociative adsorption of H2 and the resulting Langmuir isotherms at 400, 800, and 1200 K in a partial pressure range of 0–1 bar. It shows that the anharmonic effects lead to significantly higher predicted surface site fractions of hydrogen.
Christoph Schiel, Maximilian Vogtland, Ralf Bechstein, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c06305

Abstract:
Mobile molecules on surfaces can arrange into stripes due to directional attractive interactions such as π–π stacking, hydrogen, or covalent bonding. The structural arrangement of the stripes depends on the underlying substrate lattice and omnipresent long-range electrostatic interactions. To model the impact of the interplay of short-range attractive and long-range interactions on the molecular arrangements, we study a coarse-grained theoretical approach, where the attractive interaction is described by an anisotropic Ising model. As for the long-range electrostatic interaction, we focus on repulsive dipole–dipole interactions. An efficient Monte Carlo algorithm is developed by which even stripe patterns with very long stripes can be equilibrated. Using this algorithm, we assess the limits of a previously developed mean-field theory, which provides analytical predictions for stripe-to-stripe distance and stripe length distributions. This theory allows one to extract interaction parameters by fitting respective distributions to experimental data. We determine the limits of the applicability of the mean-field theory and beyond its limits suggest a combined approach of mean-field analysis and simulations. The power of this approach is demonstrated by applying it to experimental observed stripe pattern of 3-hydroxybenzoic acid (3-HBA) on the calcite (10.4) surface.
Hirak Chatterjee, Dorothy Bardhan, Sudip Kumar Pal,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04839

Abstract:
Plasmonic aspects of anisotropic nanostructures have been a subject of considerable interest over the proposition of electromagnetic scattering theories in the past century. Since an accurate description is not possible in the polar coordinates, Gans modified Mie scattering theory for metal spheres assuming the shape of a rod-like scatterer as an approximated case of infinitely elongated ellipsoid (R ≪ L) so that the contributions of end-caps can be neglected. Due to prudent sophistication in the nanoscale synthetic strategies, a plethora of correlated rod-like nanostructures with diverse end-cap geometries have been synthesized. Experimental measurements have elucidated that a seemingly minor change in end-cap morphology of the nanorods imbues distinctly different optical characteristics; therefore, the consideration of adequate contributions is obvious to the electromagnetic modeling of realistic geometry of the nanorods. Since the basic philosophy of science is to dissect similar observations into diverse magnification, we focus to enumerate the pragmatic change in shape toward scattering characteristics employing topology as a general description of the realistic rod-like nanostructures. Two widely different structures, nanodumbbells (extreme case of dogbone-like nanorods) and nanobars have been considered as the two extremities of rod-like geometries. The geometries have been described through proper functional assignment of their shape functions that have been adopted for electromagnetic simulations. These methodologies lead to achieve a general solution to substantiate the observed plasmonic response of the realistic rod-like nanostructures.
, Mariem Louhichi, Amel Ben Fredj, Samir Romdhane, Daniel Ayuk Mbi Egbe, Habib Bouchriha
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c07065

Abstract:
We report on the enhancement in the efficiency of inverted polymer solar cells because of increased open-circuit voltage and short-circuit current by using an electron collecting an interfacial layer of an aluminum-doped zinc oxide (AZO). The efficiency of polymer solar cells comprising a bulk heterojunction photoactive film of an anthracene containing poly(p-aryleneethynylene)-alt-poly(p-arylenevinylene)/1-(3methoxycarbonyl)propyl-1-phenyl[6,6] and phenyl-C60-butyric acid methyl ester has increased from 3.6% to 4.6% from the standard to the inverted architecture with Al concentrations of 0.6%, respectively. After this concentration, the efficiency starts to decrease. The reasons for these results are discussed based on the AC electrical process and magnetoconductance (MC) measurements under open-circuit conditions at room temperature. The frequency (f) dependence of the real part (Z′) and the imaginary part (Z′′) of the complex impedance with various Al concentrations at open-circuit conditions at room temperature show three f regimes: low, mid, and high f. The Cole–Cole plots (Z′′ vs Z′) demonstrate an increase in the semicircle radius from the standard to the inverted architectures for Al concentrations of 0.2% and 0.6%, respectively. After this concentration (0.6%), the semicircle radius starts to decrease. Afterward, the present proposed impedance model shows some important physical parameters such as electron diffusion time (τdiff), the recombination time (τrec), the diffusion constant (Dn), the diffusion length (Ln), and the electron mobility (μn). From the dielectric measurements, all devices have a unique relaxation process, which is the property of the Debye relaxation mechanism. Moreover, the dielectric constant (ε′) showed a strong dependence on f and the type of architecture. In addition, the dielectric loss (ε″) decreased significantly with f, and as a result, it has sparked a lot of interest in these materials’ possible uses in electrical energy storage. The dielectric loss tangent (tan(δ))) peaks shifted a little bit toward higher f from the standard to the inverted structures, indicating reduction of relaxation time. Furthermore, we found an MC memory effect in the inverted cells. Then the mechanism responsible for the MC was determined with the current density versus the applied voltage in the log–log scale for the different elaborated cells at VOC. The results suggested that the applied voltage (VOC) corresponds to the trapped charge limited current (TCLC) regime, with traps acting as recombination centers for electron–hole (e–h) pairs, preventing the formation of double carriers MC. For this reason, the MC in the device may be described using a stochastic Liouville equation in the context of the e–h pair model.
, Okkyun Seo, Jaemyung Kim, , ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05929

Abstract:
The local structure and thermal stability of newly synthesized PdRuIr and PdRu alloy nanoparticles (NPs) were studied using X-ray absorption fine structure spectroscopy (XAFS) and compared with those of Ru NPs. Pd K-edge XAFS reveals that a significant fraction of Pd segregates, forming metal NP clusters. In the PdRuIr NPs, a small fraction of Pd forms an alloy with Ir, whereas a majority phase is Ru–Ir alloy having the novel face-centered cubic structure. Apart from the distinct local surroundings, XAFS analysis revealed the presence of an anharmonic disorder in the PdRu and PdRuIr NPs. The previously observed enhanced thermal stability with Pd and Ir doping was investigated using temperature-dependent in situ XAFS. In the Ru NPs, an abrupt change in the near-edge features was observed at 673 K, which was gradually suppressed for PdRu and PdRuIr NPs. At this temperature, the dynamical fluctuations were more pronounced in the pure Ru NPs, helping to convert surface-adsorbed O2 into the volatile RuO4 phase, thereby leading to earlier evaporation of Ru. Dynamical fluctuation suppresses with alloying elements or gets extended to a higher temperature, helping to delay the RuO4 formation process and enhancing the thermal stability of the PdRu and PdRuIr NPs in increasing order.
Katarina Stanciakova, Jaap N. Louwen, , Rosa E. Bulo, Florian Göltl
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04270

Abstract:
Water is ubiquitous in zeolite catalysis, and electronic structure calculations play a crucial role in arriving at an atomistic understanding of water–zeolite interactions. However, a critical evaluation of the performance of different electronic structure methods in describing the interactions between water and zeolites is still missing. Here, we model the adsorption of one water molecule in all-silica chabazite (CHA) and of one and two water molecules in the acidic zeolite SSZ-13 using different electronic structure methods, which include 11 density functional theory (DFT)-based methods and two post Hartree–Fock (HF) methods, namely, the random phase approximation (RPA) and second-order Møller–Plesset (MP2) perturbation theory. We find that all DFT functionals lead to similar structures as long as water is strongly coordinated to the adsorption site, but adsorption energies vary in a range of 50 kJ/mol between the used methods. Subsequently, we use ab initio molecular dynamics calculations to show that all methods reproduce the experimentally observed hydrophobicity of purely siliceous zeolites. Comparing DFT energetics with RPA and MP2 calculations shows that PBE and revPBE-D3 adsorption energies show the best agreement with RPA, while BEEF–vdW agrees the best with MP2 results. At the same time, the performance of PBE functional without any dispersion correction is less consistent with respect to different adsorption sites (BAS, LAS, or the zeolite wall of all-silica CHA) and the BEEF–vdW functional fails to reproduce relative stabilities of the protonation sites. For the adsorption of two water molecules, most methods agree on the formation of a protonated water dimer, and only vdW-DF, vdW-DF2, and BEEF–vdW prefer the formation of a neutral complex. Based on these results, we suggest using the revPBE-D3 functional model water adsorption in purely siliceous or protonated zeolites since it can correctly capture covalent and dispersion interactions, is computationally efficient, correctly predicts the formation of a positively charged water dimer, and is able to closely reproduce adsorption energies calculated at the RPA or MP2 level of theory.
Robert H. Wells, Suming An, , ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04759

Abstract:
A theoretical approach for the study of supported atom catalysis is developed based on recent advances in the study of single-molecule kinetics. This view is particularly useful in exhibiting the role of disorder in single-atom and single-site catalysts on amorphous supports. The distribution of passage times (or waiting times) through a complex catalytic network originating from a set of coupled active sites is described by a probability distribution function (PDF), f(t), that reflects the local environment of the reaction center. An efficient algorithm is developed based on the linear algebra of the Markov transition matrix that produces f(t) or its moments. The kinetics of the hydrogenation reaction of styrene on an organovanadium(III) catalyst supported on amorphous silica is studied. A kinetic model consisting of three intertwined catalytic cycles emanating from three chemically distinct active sites is proposed to describe the chemistry. Density functional theory (DFT) calculations are employed to determine the free energy barriers of the reactions, which are used to construct the rate coefficient matrix. The disorder induced by the amorphous support material is divided into a low-dimensional short-range component reflecting the covalent structures near the reaction center and a weaker long-range component modeling the bulk randomness. The results are computed and analyzed for a wide range of concentration values and disorder scenarios. The unusual structure in the f(t) PDF is found to occur for certain cases that reveal the contribution of multiple catalytic pathways acting in concert.
Kalpani Hirunika Wijesinghe, Naga Arjun Sakthivel, Luca Sementa, Bokwon Yoon, , ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04228

Abstract:
Transformation brought about by ligand exchange is one of the effective methods for the synthesis of gold-thiolate nanomolecules (AuNMs). In this method, the AuNMs are treated with an excess exogenous thiol at an elevated temperature. It has been found that the ligand exchange is often accompanied by conversion of the metal core from a larger size to a smaller size, depending on the type of exogenous capping ligand employed. In this work, we present the transformation of a smaller-size AuNM (133 Au atoms) to a larger-size AuNM (279 Au atoms). Here, we observe that the Au144(SCH2CH2Ph)60 AuNM in the presence of 4-tert-butylbenzenethiol under refluxing conditions first transforms to Au133(SPh-tBu)52, and then with the transformation reaction proceeding to form larger-sized AuNMs, Au191(SPh-tBu)66 and Au279(SPh-tBu)84. The reaction progress was monitored with matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS) and UV–vis spectroscopy, and the intermediates and AuNMs were identified with electrospray ionization (ESI) MS. In conjunction with the above experiments, theoretical explorations using density functional theory calculations have been carried out, probing the energetics and thermodynamic stabilities underlying the observed size-changing transformations. It also elucidates the systematic size-dependent trends in the electronic structure of the original 144-gold-atoms-capped AuNM and the transformation products, including analysis of formation of superatom shells through the use of the core-cluster-shell model.
, Vikash Kumar, Alessandro Romeo, Claudia Wiemer,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05047

Abstract:
Sb2Se3 thin films have received increasing interest for their applications in optoelectronics. However, technological intervention demands a material-specific understanding of the reactivity to different environments. Both thermal annealing and laser irradiation carried out in an ambient atmosphere are expected to induce changes in the pristine crystallographic phase of Sb2Se3, causing the creation of additional secondary phases. Here, we investigate by means of Raman spectroscopy the effect of thermal annealing and laser irradiation at different fluencies on the structural and vibrational properties of Sb2Se3 thin films. The vacuum-annealed Sb2Se3 thin films at 290 °C and subjected to laser excitation power above 2 mW exhibit a secondary phase, revealing the occurrence of selenization. Further, in situ X-ray diffraction over a broad range of annealing temperatures in N2 and ambient atmospheres was employed to study the structural properties of the Sb2Se3 thin films. In situ XRD performed in a N2 atmosphere does not show the formation of the Sb2O3 cubic phase upon annealing until 500 °C. Conversely, a thermally activated systematic crystallization was observed upon annealing in an ambient atmosphere with the formation of the Sb2O3 phase in the temperature range between 280 and 420 °C, until the complete decomposition of the material at 500 °C. Further, the orientation of vertically stacked (hk1) planes remains unchanged under a N2 atmosphere, while horizontally stacked (hk0) planes dominate the (hk1) planes under ambient atmospheres.
Nicholas S. Georgescu, ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05020

Abstract:
Understanding nanoscopic bubble nucleation and growth is critical to reducing significant losses in efficiency during water electrolysis or photoelectrochemical hydrogen production. Herein, we demonstrate the controlled nucleation and growth of H2 nanobubbles at individual Pt nanoparticles (NPs) via the hydrogen evolution reaction (HER) using the dual-barrel mode of scanning electrochemical cell microscopy (SECCM). The NPs, with an average radius of 35 nm, were dispersed on highly oriented pyrolytic graphite (HOPG), an otherwise inert surface, with a spacing much greater than the radius of the probe, allowing for the voltammetric recordings of HER at individual Pt NPs. Finite-element simulations indicate that the concentration of electrogenerated H2 is highly nonuniform at the NP/solution interface, reaching a maximum at the three-phase HOPG/NP/solution boundary. Using finite-element modeling, we establish a correction factor to estimate the H2 surface concentration required for nucleation, as determined from the maximum current measured just prior to bubble formation. Furthermore, a drop in ionic current is measured between the two barrels of the SECCM nanopipette upon bubble formation, in agreement with simulations of local conductance when a nanobubble blocks the current path.
Madhulika Mazumder,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04411

Abstract:
Sodium-ion batteries are gradually leveling up with lithium-ion battery benchmarks in terms of voltage deliverance and electrochemical cyclic stability. The versatility in sodium chemistry makes it possible to investigate diverse polyanionic frameworks as cathodes, by regulating both the cationic and anionic components for enhanced performance. Fluorophosphates are known to be efficient owing to their high energy densities as well as preservation of structural stability in charge–discharge cycles. However, limitations in Na extraction and large diffusion barriers still need to be overcome. In this work, we probe into a transition-metal fluorophosphate framework Na5M(PO4)2F2 (M = V, Cr) and provide a theoretical model for its electrochemistry based on its crystallography and electronic structure. The ability to extract a high content of Na leads to a high voltage. These systems also show superionic Na conduction with very low hopping barriers.
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05570

Abstract:
The study by numerical methods of ionic distributions in charged solid–liquid interfaces allows the interpretation of many concepts and phenomena such as the ζ potential or ion adsorption. Molecular dynamics (MD) can reveal detailed information about electric double layer (EDL), especially the Stern layer, by including electrostatic, van der Waals, and molecular forces. Here, we aim at analyzing the chemical species and the correlations between the ions and the surface including three-body effects, one particle belonging to the surface and two to the solution. Correlations are specified on the basis of interionic distance screening. An extensive description is provided from simulations of three alkaline earth metal chlorides (Mg2+, Ca2+, and Ba2+) aqueous solutions at 0.6 mol·L–1 in the centers of negatively charged silica nanochannels. The resulting McMillan–Mayer potentials of mean force (PMF) exhibit a decreasing affinity of deprotonated silanol along with the series Mg2+ > Ca2+ > Ba2+, while the formation of bulk M2+–Cl– pairs is in reverse order. A similar trend is obtained for the association constants and the residence times. Over 40% of surface-bound Ba2+ ions are correlated with surface-bound Cl–, while the other two cations do not show such trend. When the surface-bound and surface-correlated ions are taken apart, the remaining free ion distributions fit the Poisson–Boltzmann equation well, i.e., the Gouy–Chapman model. This work demonstrates the necessity to account for three-body associations on oxide surface at least for divalent ions.
Shurraya Denning, Jolie M. Lucero, Ahmad A. A. Majid, , ,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04657

Abstract:
Herein, the synergistic effect of combining gas hydrates with a novel prototypical porous organic cage, denoted as CC3 (microporous crystalline structure with diamondoid pores), for methane storage is demonstrated using a high-pressure differential scanning calorimeter. Adding CC3 improved the extent of methane hydrate formation significantly, increasing the water-to-hydrate conversion from 4.5 to 87.5%, thus increasing the amount of methane stored relative to the water in the system from 0.42 to 8.1 mmol/g. The presence of CC3 also decreased the induction time consistently to 0.8 ± 0.1 h, whereas without CC3, hydrates only formed 30% of the time at 5.9 ± 3.9 h of induction time. This increase in conversion and decrease in induction time is attributed to CC3’s large surface area, high methane adsorption, and reversible water uptake. A depression in the hydrate dissociation temperature by as much as 1.6 °C suggests hydrate formation occurred in the confined space in CC3, most likely in its void and interstitial spacing. CC3 displayed remarkable stability, recyclability, and enhanced performance in promoting methane hydrate formation to achieve a high capacity for methane storage.
Zining Zhang, Song Li, Bin Zhao, Xiaole Zhang, , Zhongsheng Wen, Shijun Ji,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05417

Abstract:
Increasing active sites and defect control are both effective ways to enhance electrochemical performance. We introduce N doping and oxygen vacancy into electrolytic MnO2 simultaneously by a simple wet ball milling for the first time. The nanocomposites (named NEG) exhibit a high capacity of 360 mA h g–1 under 0.1 A g–1 current density which is much higher than the capacity in the theory of MnO2 (308 mA h g–1). By comparing the density functional theory calculations with the experimental data, we verify the adsorption between H+/Zn2+ and oxygen vacancies and identify that the oxygen vacancy-containing N-doped MnO2 has a much stronger adsorption effect on H+, which makes a major impact on the capacity storage. The study on the introduction of N dopants and oxygen vacancies might provide a novel idea in the development of manganese-based oxide electrode materials.
Sohyun Park, Jiung Jang,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c05623

Abstract:
Understanding how the Seebeck effect of organic thermoelectric devices is associated with the chemical structure of active molecules within the devices is a key goal in organic and molecular thermoelectrics. This paper describes a series of physical–organic studies that investigate structure–thermopower relationships in self-assembled monolayers (SAMs) through measurements of the Seebeck coefficient (S, μV/K) using the eutectic gallium–indium (EGaIn)-based junction technique. Several hypotheses were derived from a transmission function-based simple toy model, the Lorentzian transmission function-based Mott formula. These hypotheses were tested by comparing values of S for simple alkyl and aryl molecules with different structures in terms of backbone, length, spacer, anchor, and substituent, and for different electrodes (Au vs Ag), and by monitoring responses of S to the structural modifications. Experimentally obtained S values were further reconciled with values simulated by the Mott formula and with interfacial electronic structure and molecule-electrode coupling strength, independently measured by ultraviolet photoelectron spectroscopy and transition voltage spectroscopy.
Ethan P. Kamphaus,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c04559

Abstract:
Lithium–sulfur batteries (LiSB) are a promising next-generation lithium energy storage technology that offers a multifold improvement over the traditional lithium-ion battery. However, the LiSB still faces the unresolved issue of the polysulfide shuttle effect. This phenomenon arises from the dissolution of sulfur intermediate reduction products into the electrolyte, which then causes a cascade of issues throughout the battery. Many mitigation strategies have been proposed to counteract this effect including the use of novel electrolyte compositions. Recently, there has been increased focus on the use of hydrofluorinated ethers as a major constituent of an electrolyte for lithium batteries. Previous studies have reported that the presence of these species create localized high concentration electrolytes (LHCE) which can have many advantages resulting in improved battery performance. Here, we report on how the inclusion of a hydrofluorinated ether BTFE (bis(2,2,2-trifluoroethyl) ether) modifies the general properties of a LiSB electrolyte and the structure of dissolved polysulfide species in the electrolyte. We found that the inclusion of BTFE does not modify the primary solvation structure of Li+ directly but actively participates in secondary solvation shells. With a high concentration of BTFE, the LHCE formation is observed by the presence of clusters of non-BTFE molecules. The structure of polysulfide species in solution was modified by the BTFE in the same way. Much of the primary solvation structure was kept, but the presence of BTFE increased polysulfide–polysulfide clustering. These results indicate that the polysulfide solubility will be limited due to the promotion of clustering.
Can Wang, Dongmei Niu, Yao-Zhuang Nie, Lin Li, Baoxing Liu, Shitan Wang, Haipeng Xie,
The Journal of Physical Chemistry C; https://doi.org/10.1021/acs.jpcc.1c07056

Abstract:
The formation of hybrid interface states plays a crucial role in spin injection from a ferromagnetic metal into organic semiconductors. Here, we investigate the energy-level alignment and spin-polarized hybrid interface states between cobalt and rubrene using photoemission spectroscopy. We reveal that the presence of charge injection from cobalt to the rubrene molecular layer is determined by XPS and UPS measurements. We also find a spin-polarized interface state between cobalt and rubrene at 0.5 eV below the Fermi level, which can be attributed to chemical interaction between rubrene and Co(001). This hybridization state can induce spin polarization inversion at the rubrene/Co(001) interface as measured by spin-polarized UPS. The spin polarization inversion at the rubrene/Co(001) interface can be interpreted by a Zener exchange-type mechanism. On the basis of these observations, we obtain a deeper understanding of the electronic structure of the rubrene/Co(001) spinterface and show the importance for the quantitative description of rubrene/Co(001)-based organic spintronic devices.
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