Current progressions in transition metal based hydroxides as bi-functional catalysts towards electrocatalytic total water splitting

To meet the ever-increasing energy demands with only source of fossil fuels will no longer be sufficient for sustainable energy developments. Thus, the choice of water electrolysis is the finest way of producing clean and greener hydrogen energy as an alternative fuel source for future. Hence, it is necessary to develop electrocatalyst which will have high activity, stability and cost effectivity for overall water splitting. Besides, to replace the high-cost noble metals with various transition metals based nanomaterials (NMs) for total water splitting (TWS) is the eventual objective to make the H2 production towards the industrial level. In this line, the recent literature examination gives the clear notion that the transition metal hydroxides (TMOHs) are superior activity towards TWS reactions with low overpotential. But the effects of metal combinations with simple metal hydroxides on their catalytic performance are stagnant towards bi-functional system in the alkaline water electrolysis. This review details the significance of such combinations (mono, bi-, tri-, tetra-metal hydroxides) and their synergistic effect for the first time. The nature of TM hydroxides and their influence in TWS is not explored as a review before and we strongly believed which is extremely important at the current energy scenario in the globe. So in this review we addressed the potentiality of these TM hydroxides and their analogues for real scale studies for the first time. In-addition, this review also highlights how the overpotential values can be reduced with chalcogenides and phosphides substituted TMOHs as a bi-functional catalyst for TWS. Overall, the investigation on these systems can pave a way for researchers to examine further with TM hydroxides in terms of structure, activity and stability in TWS study in future.