Boosting the efficiency of electrocatalytic water splitting via in situ grown transition metal sulfides: a review

The growing needs for sustainable and efficient energy sources have heightened interest in electrocatalytic water splitting (EWS), a promising method for hydrogen production as a clean and renewable energy carrier. EWS, which splits water molecules into hydrogen and oxygen, faces efficiency challenges due to the slow kinetics of the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode. Developing effective electrocatalysts is essential to overcome these limitations. Among the various electrocatalysts studied, transition metal sulfides (TMSs) have garnered significant attention due to their low cost and abundant active sites. Despite the superior electrochemical performance of TMSs compared to other materials, their inherent low conductivity and sluggish reaction kinetics remain major challenges. Recent advancements have focused on the in situ growth of TMSs on conductive substrates to enhance electron transfer and overall catalytic performance, eliminating the need for polymer binders and improving electrode stability. This review provides an in-depth analysis of the key aspects involved in the synthesis of in situ grown TMS electrodes, including the selection of TMS active materials, various substrates, and preparation strategies. The review then offers a comprehensive overview of different types of in situ grown TMS electrodes, with a focus on the most extensively researched materials: molybdenum sulfides, cobalt sulfides, nickel sulfides, and their composites. Finally, the limitations and future perspectives are discussed, highlighting potential directions for advancing the development of in situ grown TMS catalysts.