Ir-based bifunctional electrocatalysts for overall water splitting

High-purity hydrogen production by electrocatalytic overall water splitting plays an important role in energy conversion and storage. The development of high-performance bifunctional electrocatalysts that could simultaneously catalyze the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) can simplify the overall water electrolyser system design and is highly desired but full of great challenges. Due to the sluggish kinetics of the OER, iridium (Ir)-based catalysts with high intrinsic activity, stability and a wide pH window of the OER are ideal materials for bifunctional catalysts. In this review, we summarize the recent progress on Ir-based HER/OER bifunctional electrocatalysts (Ir-BEs) for overall water splitting. We focus on the composition optimization and morphology optimization in enhancing the overall water splitting performance of Ir-BEs, highlighting the fundamental understanding of the key factors that contribute to the performance improvements, including the structure of surface active sites, metal-support interaction, synergistic effect, electronic/geometric effects, etc. Finally, the current challenges faced and outlook are provided for guiding the rational deign of advanced Ir-BEs for overall water splitting.