Dynamic response analysis of anion exchange membrane water electrolyzers during dry cathode operation

Abstract

Anion exchange membrane water electrolyzers (AEMWEs) offer a promising route for converting intermittent renewable energy into hydrogen for long-term energy storage. However, there is a lack of research on the behavior of AEMWE under dynamic operation, which hinders the assessment of its potential for consuming fluctuating renewable electricity. To address this gap, this study investigates both the steady-state and dynamic behaviors of AEMWEs under wet (continuous electrolyte supply) and dry (no electrolyte feed) cathode feeding modes. The dry cathode mode demonstrates an 80 mV lower cell voltage at 5 A cm-2, attributed to eliminated two-phase flow and enhanced hydrogen bubble removal, reducing mass transport overpotentials. However, its dynamic response is poor, characterized by a response time of 45 s and a voltage overshoot of 135 mV during current steps, caused by transient water starvation at the cathode. We address this issue by enhancing cathode water management through the following strategies: reducing membrane thickness to accelerate water back-diffusion, and utilizing high–ion-exchange-capacity (IEC) binders to improve water retention in the cathode catalyst layer (CCL). As a result, the voltage overshoot is reduced by 120 mV. However, after 200 hours of dynamic operation, the voltage overshoot of the AEMWE increases fivefold, owing to CCL degradation and a drop in water retention capacity. This result highlights the need for developing durable cathodes to improve the dynamic performance of AEMWEs.