Polymer electrolyte membrane unitized regenerative fuel cells: Operational considerations for achieving high round trip efficiency at low catalyst loading

Abstract

Unitized regenerative fuel cells (URFCs) are electrochemical devices operating as both fuel cells (FCs) or water electrolysis (WE). For practical efficiency in both FC and WE operations, a substantial amount of platinum and iridium, up to 3 mg cm(-2), is often employed in URFCs. The main obstacle in catalysis of the URFC is oxygen reduction or water oxidation reactions for FC or WE operation, respectively. The electrode also requires different affinities for water, that is, hydrophobicity and hydrophilicity for gas and water transport, respectively. In this study, the water flux of the anode and cathode electrodes is systematically controlled by manipulating the relative humidity of the supplied gas and altering the selection of the electrode in amphiphilic membrane electrode assembly. By investigating the operation factors of URFC, 51 % of high round trip efficiency (@ 0.4 A cm(-2)) was achieved with only 0.65 mg((Pt+Ir)) cm(-2) of the noble catalyst.