Electrochemical evaluation of the de-/re-activation of oxygen evolving Ir oxide

Abstract

Understanding the influence of dynamic and stationary polarization on the deactivation of state-of-the-art IrO_x catalysts is imperative for the design and operation of robust and efficient proton exchange membrane water electrolyzers. In this work, the deactivation and activity regeneration of a commercial IrO_x catalyst were investigated under potentiodynamic and potentiostatic conditions in acidic media using rotating disk electrode and electrogravimetry methods. Systematic electrochemical protocols were designed to decouple reversible from irreversible activity losses. Cyclic voltammetry provided a metric of the active surface area and traced the charge growth under different oxygen evolution reaction conditions. A direct log t dependent charge growth is observed, accompanied by the same fractional kinetic activity decay under potentiodynamic conditions. The loss is essentially recoverable after electrochemical reductive treatment, however at the expense of mild material dissolution. In contrast, an extended potentiostatic operation induced irreversible intrinsic degradation after a critical time (0.5–1 h), accompanied by stability enhancement. This irreversible deactivation is attributed to a gradual transformation of the hydrated IrO_x to a dehydrated condensed oxide. Our results suggest that Ir dissolution during the regenerative treatment is not prohibitive, as long as the low potential modulations are not frequent.