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Abstract

Understanding degradation phenomena of polymer electrolyte water electrolyzers operating under dynamic conditions is imperative for developing and implementing efficient and reliable means of energy storage from fluctuating and intermittent renewable energy sources. Herein, a commercial membrane electrode assembly with an amorphous IrO_x anode is subjected to potential sweeping (1.4–1.8 V) with short and long holds and few steady-state interims for overall 830 h at 60 °C and ambient pressure to simulate frequent alternating idle and nominal operation regimes. Systematic electrochemical diagnostics and physicochemical methods are applied to identify degradation sources. Mild kinetic deactivation (2.6 μV/h) is observed independent on the dynamic protocol, due to loss of electrochemical surface area via crystallization. The amount of Ir dissolved and redeposited in the ionomer anode phase and in the membrane is negligible in comparison to the current state-of-the-art Ir loadings. As compared to kinetic losses, the irreversible resistive losses are one order of magnitude higher and are thought to be caused by the degradation of the membrane close to the anode catalyst layer. These resistive losses are associated specifically with dynamic operation. The two orders of magnitude higher, but recoverable, degradation during steady-state interims is attributed to the growth of inhibiting or long-lived species.