Catalyst Dissolution in Pem Water Electrolysis: Influence of Time, Current Density and Iridium Ion Transport in Single-Pass and Recirculation Water Flow Modes

Abstract

The current study targets three major aspects central to the phenomenon of Iridium (Ir) catalyst dissolution in polymer electrolyte membrane water electrolyzers; the stabilization over time, the influence of current density and the mechanisms of transport and deposition of dissolved Ir species. Quasi-online measurements of Ir dissolution at the anode side of single-cells using single-pass water flow reveal that oxygen molecules produced per Ir dissolved increases by up to two orders of magnitude with current density and then level off. Experiments under water recirculation show that Ir ions are back-transported into the catalyst coated membrane. Model-aided analysis suggests that Ir species re-deposited into the catalyst layer are stabilized at elevated concentrations of dissolved Ir ions. Application of single-pass flow is recommended for stability testing. An observed stabilization of over two orders of magnitude with time provides promising insight into the applicability of low Ir loadings under steady-state conditions.

Keywords: Water electrolysis, OER, Iridium dissolution, re-deposition, ion transport