Iridium-based nanomaterials for electrochemical water splitting

Electrochemical water splitting is an appealing technology to produce high-purity hydrogen as a clean and sustainable energy carrier. The efficiency of water splitting largely depends on the intrinsic activity, selectivity, and stability of the electrocatalysts. Hence, soaring scientific endeavors have been made to develop high-performance electrocatalysts and uncover the underling reaction mechanisms. Iridium (Ir)-based nanomaterials are most promising for water splitting due to their favorable intrinsic activity, wide pH window, and high stability. In this review, we first discussed the mechanisms of various Ir-based catalysts in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), including metal, alloys, and oxides. Important criteria and methods for precise evaluation of water splitting catalysts are discussed. Then, the applications of Ir-based nanomaterials in the HER, OER and the overall water splitting are comprehensively reviewed, with an emphasis on correlating the structure-function relationships and the advanced strategies for rational design of reaction-oriented Ir catalysts. Lastly, the current challenges in fundamental studies and future directions in this field are presented.