Polymer electrolyte electrolysis: A review of the activity and stability of non-precious metal hydrogen evolution reaction and oxygen evolution reaction catalysts.

The potential for generating green hydrogen by electrolysis (water splitting) has resulted in a substantial amount of literature focusing on lowering the current production cost of hydrogen. A significant contributor to this high cost is the requirement for precious metals (namely Pt and Ir/Ru (oxides)) to catalyse the two main reactions involved in electrolysis: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Herein we overview the current literature of non-precious metal HER and OER catalysts capable of efficient water splitting within a polymer electrolyte membrane (PEM) electrolyser, recording the activity and stability of each catalyst and allowing for direct comparison to be made. Additionally, we highlight the inapplicability of catalyst stability testing in many academic studies for commercial electrolyser applications and propose a universal stability-testing regime for HER and OER catalysts that more accurately mimics the conditions within an operating electrolyser. • Stability studies of cathodic catalysts don't translate to commercial electrolysis. • Anodic catalyst stability studies are more comprehensive for electrolysis operation. • Stability of novel catalysts needs to be benchmarked against the optimal catalysts. • Combining active and stable first row transition metals shows promising catalysis. • A stability testing regime for proton exchange membrane electrolysis is proposed. [ABSTRACT FROM AUTHOR]