Amorphous/Crystalline Heterostructure Transition-Metal-based Catalysts for High-Performance Water Splitting

The rational phase engineering on transition-metal-based (TM-based) catalysts is an efficient strategy to improve the catalytic performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in water splitting. Combining high conductivity from crystalline phase with orderly atomic arrangement and high activity from amorphous phase with abundant unsaturated sites, more amorphous/crystalline (a/c) heterostructure TM-based catalysts with optimized electronic structures have been confirmed to exhibit superior OER and HER properties with well-balanced activity and stability. However, the rational design of the a/c TM-based catalysts for water splitting is often ignored. In this review, we firstly summarized the amorphization/crystallization strategies for constructing a/c TM-based catalysts including pyrolysis method, composition-tuned approach, electrochemical method, chemical etching and other strategies. Then, we introduced various kinds of a/c TM-based catalysts such as a/c TM-based alloys, oxides and hydroxides, nitrides/phosphides/sulfides, and composites. In addition, the roles of a/c interfaces on the performance promotion for OER and HER have been analyzed, which involved the active sites increasement with optimized d-band center, catalytic kinetics acceleration with fast electron transfer, and stability enhancement with electron density redistribution. Finally, we proposed the existing challenges and further perspectives referring to the precise synthesis, in-depth activity investigation and performance promotion.