The role of nitrogen in transition-metal nitrides in electrochemical water splitting

Summary H2 as a storable fuel can be sustainably generated from direct cleavage of water with a catalytic approach. However, H2 generation is severely affected by poor catalytic activities and the instability of catalyst materials. Recently, transition-metal-based nitrides (TMNs) have been widely explored because of their intrinsic abilities to catalyze water splitting, wide pH stability, high corrosion resistance, and potential for structural modulations. Most investigations have focused on the design of advanced heterostructures for improving catalytic activity. However, identification of the active sites and decoding the inherent mechanisms are often neglected. Here, we investigate the fundamental aspects of H2 production to elucidate the cutting-edge progress of TMNs. First, we explore the engineering of the active sites of ordered and disordered structures and the relation with hydrogen evolution reaction activity. Second, we explain the development of advanced oxygen evolution reaction catalysts by focusing on minimizing autoxidation. Third and finally, we discuss complementary strategies for converting unifunctional TMNs to bifunctional catalysts for overall water splitting.