Performance loss due to gas coverage on catalyst surface in polymer electrolyte membrane electrolysis cell*

In this study, we carry out a fundamental and modeling study to investigate, for the first time, the gas coverage at the catalyst surface and its impacts on performance loss in polymer electrolyte membrane electrolysis cells (PEMECs). Oxygen, produced in the anode catalyst layer (CL) through the oxygen evolution reaction (OER), is removed via the pore network of the anode CL and porous transport layer (PTL) to the flow field. Oxygen gas bubbles can cover the catalyst surface and reduce the area for catalyst OER activity and hence cell performance. To investigate the oxygen bubbles' impact, we consider various degrees of gas coverage and temperatures (25 degrees C, 80 degrees C, and 95 degrees C) in the range of current density from 0 to 7 A/cm2. We also, for the first time, elucidate the impacts of CL's material properties on gas coverage morphology in the nano/micropores of CLs. Analytical solutions are derived for the gas fraction and gas composition at different temperatures and pressures. It was found that the gas fraction can be as high as 85% with water vapor contributing to 71% of the total gas coverage when operating at 95 degrees C and 1 atm. The modeling results indicate the gas coverage can contribute 57% of the total overpotential at 95 degrees C, 7 A/cm2, and a coverage coefficient of 7. The work contributes to a fundamental understanding of the impacts of two-phase phenomena on PEMEC performance and is valuable for catalyst layer design and optimization.