A review on nickel cobalt sulphide and their hybrids: Earth abundant, pH stable electro-catalyst for hydrogen evolution reaction

The production of hydrogen from electrocatalytic water splitting using a clean energy source has become a sustainable route to overcome the problems related to fossil fuels. Therefore, it is essential to develop a non-precious, stable and highly efficient electrocatalyst. Nickel and cobalt sulphide have gained much attention as hydrogen evolution reaction (HER) catalysts due to their pH stability, low cost and high activity. But the application of these sulphides is limited due to high over-potentials, low surface area and less catalytic active sites available for HER. Furthermore, Nickel and cobalt sulphide can be coupled with different functional components to enhance their catalytic activity. This comprehensive review focuses on the progress made so far to enhance the electrochemical properties of nickel and cobalt sulphides and their composites with various active materials. The comparative survey of their HER activities is made in terms of their electrocatalytic performance parameters.