Clarification of Degradation Mechanisms of the OER Activity of Ir-Based Electrocatalyst with Potentiodynamic Accelerated Stress Test

Abstract

It is vital to understand the degradation mechanisms for the oxygen evolution reaction (OER) activity under acidic electrolyser operating conditions. To this end, we have studied a commercial benchmark Ir-Oxide electrocatalyst during an accelerated stress test (AST) of potential cycling (2000 cycles at 100 mV s−1) between 1.0 and 1.7 V in 0.1 M HClO4. The OER activity degradation (>60%) has been investigated due to (i) bulk structure changes from metal dissolution, (ii) particle growth and, (iii) surface chemical state changes. Microscopic images of the Ir-Oxide catalyst before and after the AST show no significant change in the particle size or agglomeration; moreover, negligible mass loss of the element. Therefore, the OER activity degradation is found to be dominantly (99%) associated with changes of the surface chemical state of Ir, i.e., increase in the Ir4+/Ir3+ ratio at the surface of Ir-Oxide during the AST.