(Invited) Comparison of Catalyst-Coated Electrodes vs. Catalyst-Coated Membranes in PEM Water Electrolysis Cells

Abstract

The PEM (Proton-Exchange Membrane or Polymer Electrolyte Membrane) cell concept [1] is used in fuel cells and water electrolysis cells. PEM water electrolysis is a compact, efficient and flexible technology for the production of “green-hydrogen” from renewable (intermittent) energy sources. The unit cell (Figure 1) is made of several adjacent functional layers: (i) the proton-conducting polymer membrane (1); (ii) two catalysts layers (CLs) for hydrogen/oxygen evolution containing platinum group metals or PGMs (2;2’); (iii) a porous transport layer used for mass transport of reactants/products and electricity distribution (3;3’); (iv) water flow fields for water circulation (4;4’); bipolar plates (5;5’). From a practical viewpoint, the CLs can be deposited on either side of the interfaces formed between the polymer membrane and the porous transport layer: (i) on the supporting porous transport layers to form catalyst-coated electrodes which are then hot pressed against the bare membrane to form membrane – electrode assemblies; (ii) directly onto the membrane to form catalyst-coated membranes (CCM).The aim of this paper is to evaluate the efficiency and durability of both concepts, drawing on recent advances in manufacturing techniques to reduce the loading of PGM catalysts.[1] W.T. Grubb Jr., Batteries with Solid Ion-Exchange Electrolytes. Journal of the Electrochemical Society. 106 (1959) 275-279.[2] C. Rozain, P. Millet, Electrochemical characterization of Polymer Electrolyte Membrane Water Electrolysis Cells, Electrochimica Acta, 131 (2014) 160-167. Figure 1. Schematic diagram showing the cross-section of a PEM water electrolysis cell [2]. Figure 1