Nickel Oxide Particles Catalyze Photochemical Hydrogen Evolution from Water—Nanoscaling Promotes P-Type Character and Minority Carrier Extraction
- 20 April 2015
- journal article
- Published by American Chemical Society (ACS) in ACS Nano
- Vol. 9 (5), 5135-5142
- https://doi.org/10.1021/acsnano.5b00435
Abstract
Nickel(II) oxide (NiO) is an important wide gap p-type semiconductor used as a hole transport material for dye sensitized solar cells and as a water oxidation electrocatalyst. Here we demonstrate that nanocrystals of the material have increased p-type character and improved photocatalytic activity for hydrogen evolution from water in the presence of methanol as sacrificial electron donor. NiO nanocrystals were synthesized by hydrolysis of Ni(II) nitrate under hydrothermal conditions followed by calcination in air. The crystals have the rock salt structure type and adopt a plate-like morphology (50-90 nm × 10-15 nm). Diffuse reflectance absorbance spectra indicate a band gap of 3.45 eV, similar to bulk NiO. Photoelectrochemical measurements were performed at neutral pH with methylviologen as electron acceptor, revealing photo-onset potentials (Fermi energies) of 0.2 and 0.05 eV (NHE) for nanoscale and bulk NiO, respectively. Nano-NiO and NiO-Pt composites obtained by photodepositon of H2PtCl6 catalyze hydrogen evolution from aqueous methanol at rates of 0.8 and 4.5 μmol H2 h(-1), respectively, compared to 0.5 and 2.1 μmol H2 h(-1) for bulk-NiO and NiO-Pt (20 mg of catalyst, 300 W Xe lamp). Surface photovoltage spectroscopy of NiO and NiO-Pt films on Au substrates indicate a metal Pt-NiO junction with 30 mV photovoltage that promotes carrier separation. The increased photocatalytic and photoelectrochemical performance of nano-NiO is due to improved minority carrier extraction and increased p-type character, as deduced from Mott-Schottky plots, optical absorbance, and X-ray photoelectron spectroscopy data.Funding Information
- National Science Foundation
- Research Corporation for Science Advancement
This publication has 70 references indexed in Scilit:
- Inorganic nanostructures for photoelectrochemical and photocatalytic water splittingChemical Society Reviews, 2012
- Rh-Doped SrTiO3 Photocatalyst Electrode Showing Cathodic Photocurrent for Water Splitting under Visible-Light IrradiationJournal of the American Chemical Society, 2011
- Z-scheme photocatalyst systems for water splitting under visible light irradiationMRS Bulletin, 2011
- Recent progress on photocatalytic and photoelectrochemical water splitting under visible light irradiationJournal of Photochemistry and Photobiology C: Photochemistry Reviews, 2010
- Fabrication and photoelectrochemical properties of La5Ti2MS5O7 (M=Ag, Cu) electrodesMaterials Science and Engineering B, 2010
- Efficient Nonsacrificial Water Splitting through Two-Step Photoexcitation by Visible Light using a Modified Oxynitride as a Hydrogen Evolution PhotocatalystJournal of the American Chemical Society, 2010
- Heterogeneous photocatalyst materials for water splittingChemical Society Reviews, 2008
- Inorganic Materials as Catalysts for Photochemical Splitting of WaterChemistry of Materials, 2007
- Powering the planet: Chemical challenges in solar energy utilizationProceedings of the National Academy of Sciences of the United States of America, 2006
- A new type of water splitting system composed of two different TiO2 photocatalysts (anatase, rutile) and a IO3−/I− shuttle redox mediatorChemical Physics Letters, 2001