PEMFC Catalyst Layers: The Role of Micropores and Mesopores on Water Sorption and Fuel Cell Activity
- 16 May 2011
- journal article
- Published by American Chemical Society (ACS) in ACS Applied Materials & Interfaces
- Vol. 3 (6), 1827-1837
- https://doi.org/10.1021/am200590w
Abstract
The effects of carbon microstructure and ionomer loading on water vapor sorption and retention in catalyst layers (CLs) of PEM fuel cells are investigated using dynamic vapor sorption. Catalyst layers based on Ketjen Black and Vulcan XC-72 carbon blacks, which possess distinctly different surface areas, pore volumes, and microporosities, are studied. It is found that pores <20 nm diameter facilitate water uptake by capillary condensation in the intermediate range of relative humidities. A broad pore size distribution (PSD) is found to enhance water retention in Ketjen Black-based CLs whereas the narrower mesoporous PSD of Vulcan CLs is shown to have an enhanced water repelling action. Water vapor sorption and retention properties of CLs are correlated to electrochemical properties and fuel cell performance. Water sorption enhances electrochemical properties such as the electrochemically active surface area (ESA), double layer capacitance and proton conductivity, particularly when the ionomer content is very low. The hydrophilic properties of a CL on the anode and the cathode are adjusted by choosing the PSD of carbon and the ionomer content. It is shown that a reduction of ionomer content on either cathode or anode of an MEA does not necessarily have a significant detrimental effect on the MEA performance compared to the standard 30 wt % ionomer MEA. Under operation in air and high relative humidity, a cathode with a narrow pore size distribution and low ionomer content is shown to be beneficial due to its low water retention properties. In dry operating conditions, adequate ionomer content on the cathode is crucial, whereas it can be reduced on the anode without a significant impact on fuel cell performance.Keywords
This publication has 30 references indexed in Scilit:
- On the Micro-, Meso-, and Macroporous Structures of Polymer Electrolyte Membrane Fuel Cell Catalyst LayersACS Applied Materials & Interfaces, 2010
- Review in Applied Electrochemistry. Number 54 Recent Developments in Polymer Electrolyte Fuel Cell ElectrodesJournal of Applied Electrochemistry, 2004
- PEM fuel cell electrodesJournal of Power Sources, 2004
- Influence of the composition on the structure and electrochemical characteristics of the PEFC cathodeElectrochimica Acta, 2003
- Ionic Conductivity of PEMFC ElectrodesJournal of the Electrochemical Society, 2003
- Nafion content in the catalyst layer of polymer electrolyte fuel cells: effects on structure and performanceElectrochimica Acta, 2001
- Electrical impedance studies of acid form NAFION® membranesSolid State Ionics, 1993
- High Performance Catalyzed Membranes of Ultra‐low Pt Loadings for Polymer Electrolyte Fuel CellsJournal of the Electrochemical Society, 1992
- Thin-film catalyst layers for polymer electrolyte fuel cell electrodesJournal of Applied Electrochemistry, 1992
- Methods to Advance Technology of Proton Exchange Membrane Fuel CellsJournal of the Electrochemical Society, 1988