Abstract: Electrochemical water splitting is regarded as the most auspicious technology for renewable sources, transport, and storage of hydrogen energy. Currently, noble Pt metal and noble-metal oxides (IrO₂ and RuO₂) are recognized as state-of-the-art electrocatalysts for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively. Searching for earth-abundant electrocatalysts for the HER and OER with remarkable performance and high stability to replace precious metals plays a significant role in the commercial application of electrochemical water splitting. In this review, recent advancements in nanostructured transition metal electrocatalysts are assessed through the selected examples of nitrides, carbides, phosphides, sulfides, borides, layered double hydroxides, and oxides. Recent breakthroughs in nanostructured transition metal electrocatalysts are discussed in terms of their mechanisms, controllable production, structural design, and innovative strategies for boosting their performance. For instance, most nanostructured transition metal electrocatalysts for overall water splitting (OWS) only function well in neutral and alkaline solutions. Finally, current research challenges and future perspectives for increasing the performance of nanostructured transition metals for OWS are proposed.

Key words: Hydrogen evolution reaction (HER), Oxygen evolution reaction (OER), Overall water splitting (OWS), Transition metal electrocatalyst, Innovative strategies, Basic electrochemistry