(Invited) Degradation Aspects of Electrocatalysts and Materials in PEM Water Electrolyzers

Abstract

When coupled to renewable but nonetheless intermittent power sources such as wind or solar, polymer electrolyte membrane (PEM) electrolyzers are intended to be in operation for tens of thousands of hours [1]. Hence, the long-term behavior of catalyst coated membranes (CCMs) under some specific operating characteristics is of great importance. Previous durability studies have focused on electrolyzers operating at constant current input, showing little to no significant degradation (<4µVh) after 40.000 h at moderate conditions (25 cell stack, around 50°C and 1,3 A/cm²)[2]. In another study, constant and highly variable operation mode was compared for three used stacks after 7.500 h and indicated that variable operation might result in higher cell decay [3]. To the best of our knowledge, no durability data has been published yet, that fundamentally contrasts the effects of defined dynamic load profiles and constant operation on the cell decay in single cell tests. This is particularly crucial, since coupling PEM electrolysis to renewable power sources involves dealing with fluctuating power inputs, startup, and shutdown incidents that for PEM fuel cells are known to accelerate degradation. In this study we demonstrate for the first time, the different effect of a constant and defined dynamic operation on the cell decay. For this purpose, durability tests were performed using state-of-the-art PEM electrolysis cells. The physicochemical characteristics were comprehensively addressed and the main process constraints (e.g., electrical, reaction, and transport) were analyzed. Exceptional improvements could be demonstrated using new membrane and catalyst materials enhancing performance, gas separation, and overall durability. Our results also show an effect of the operation mode on the degradation rate. Moderate conditions of 1 A/cm² show no significant degradation after 1000h. This is in line with the above mentioned results for commercial electrolyzer units. At higher current densities significant degradation rates were found. This study undeniably suggests coupling PEM electrolyzers to intermittent power sources under long term operation, contributing to transformative knowledge in the field of energy conversion and storage. [1]. M. Carmo, D. Fritz, J. Mergel and D. Stolten, International Journal of Hydrogen Energy, 38, 4901-4934 (2013) [2] Katherine Ayers, presented at the DOE Fuel Cell Technologies Program Webinar, May 23, 2011 [3] 2013 Annual Merit Review Proceedings, II.A.2, Renewable Electrolysis Integrated Systems Development and Testing