Hydrogen is a clean, efficient, renewable energy resource and the most promising alternative to fossil fuels for future carbon-neutral energy supply. Therefore, sustainable hydrogen production is highly attractive and urgently demanded, especially via water electrolysis that has clean, abundant precursors and zero emission. However, current water electrolysis is hindered by the sluggish kinetics and low cost/energy efficiency of both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this regard, electrochemical synthesis offers prospects to raise the efficiency and benefit of water electrolysis by fabricating advanced electrocatalysts and providing more efficient/value-adding co-electrolysis alternatives. It is an eco-friendly and facile fabrication method for materials ranging from molecular to nano scales via electrolysis or other electrochemical operations. In this review, we firstly introduce the basic concepts, design protocols, and typical methods of electrochemical synthesis. Then, we summarize the applications and advances of electrochemical synthesis in the field of electrocatalytic water splitting. We focus on the synthesis of nanostructured electrocatalysts towards more efficient HER, as well as electrochemical oxidation of small molecules to replace OER for more efficient and/or value-adding co-electrolysis with HER. We systematically discuss the relationship between electrochemical synthetic conditions and the product morphology, selectivity to enlighten future explorations. Finally, challenges and perspectives for electrochemical synthesis towards advanced water electrolysis, as well as other energy conversion and storage applications are featured.
