Electrode structure optimization combined with water feeding modes for Bi-Functional Unitized Regenerative Fuel Cells

Bi-functional Unitized Regenerative Fuel Cells (URFCs) based on proton-exchange membrane (PEM) electrolyte are promising in the field of energy storage. Their performance was investigated with catalyst loadings, carbon paper hydrophobicity and water feeding modes in both fuel cell (FC) and water electrolysis (WE) operations. The optimum membrane electrode assembly (MEA) is with 0.20 mg cm−2 Pt (in 50% Pt/C catalyst) for the hydrogen electrode (HE), and a total catalyst loading of 0.80 mg cm−2 for the oxygen electrode (OE). And its performance can reach 2.18 A cm−2 at 1.80 V in WE test and 0.64 A cm−2 at 0.60 V in FC test with air oxidant. Comparison of different carbon papers reveals that suitable hydrophobicity of OE carbon papers is obtained when the PTFE content accounts for 26.95 wt.%. Choice of water feeding modes, which has an influence on URFC performance in WE mode, is proven to have relations with current density and carbon paper hydrophobicity in a sophisticated way.