Agglomerate Engineering to Boost PEM Water Electrolyzer Performance

Abstract Densely packed IrO x ‐ionomer agglomerates play a crucial role in the high mass transport resistance inside the anode catalyst layer (ACL), which in turn greatly affects the electrolysis performance at high current density. Therefore, agglomerate engineering for PEMWE is proposed in this work to enhance the oxygen transport process inside ACLs. Using self‐assembling nanotechnology, tightly packed primary aggregates are avoided and introduce the interconnected submicron pores and nanocavities into the catalyst‐ionomer agglomerate, confirmed by synchrotron radiation‐based nano‐CT, TEM, and BET. Such agglomerate engineering results in the enhancement of both dissolved oxygen and oxygen bubble transport inside the ACL confirmed by RDE tests and in‐situ bubble visualization. As a result, the mass transport overpotential is significantly reduced from 330 to 30 mV at 5 A cm −2 in PEMWE, optimized Ohmic resistance and catalyst utilization are also observed. Finally, high operating current density is achieved, i.e., 5 A cm −2 @2.04 V with Nafion 115 membrane and 7 A cm −2 @ 2.07 V with Nafion 212 membrane, under a low catalyst loading of 0.72 mg Ir cm −2 . This study proves the importance and feasibility of agglomerate engineering in further elevating the performance of PEMWE.