Hierarchical Nanoflower Arrays of Co 9 S 8 -Ni 3 S 2 on Nickel Foam: A Highly Efficient Binder-Free Electrocatalyst for Overall Water Splitting

Hydrogen production is vital for meeting future energy demands and managing environmental sustainability. Electrolysis of water is considered as the suitable method for H generation in a carbon-free pathway. Herein, the synthesis of highly efficient Co S -Ni S based hierarchical nanoflower arrays on nickel foam (NF) is explored through the one-pot hydrothermal method (Co S -Ni S /NF) for overall water splitting applications. The nanoflower arrays are self-supported on the NF without any binder, possessing the required porosity and structural characteristics. The obtained Co S -Ni S /NF displays high hydrogen evolution reaction (HER), as well as oxygen evolution reaction (OER), activities in 1 m KOH solution. The overpotentials exhibited by this system at 25 mA cm are nearly 277 and 102 mV for HER and OER, respectively, in 1 m KOH solution. Subsequently, the overall water splitting was performed in 1 m KOH solution by employing Co S -Ni S /NF as both the anode and cathode, where the system required only 1.49, 1.60, and 1.69 V to deliver the current densities of 10, 25, and 50 mA cm , respectively. Comparison of the activity of Co S -Ni S /NF with the state-of-the-art Pt/C and RuO coated on NF displays an enhanced performance for Co S -Ni S /NF both in the half-cell as well as in the full cell, emphasizing the significance of the present work. The post analysis of the material after water electrolysis confirms that the surface Co(OH) formed during the course of the reaction serves as the favorable active sites. Overall, the activity modulation achieved in the present case is attributed to the presence of the open-pore morphology of the as formed nanoflowers of Co S -Ni S on NF and the simultaneous presence of the surface Co(OH) along with the highly conducting Co S -Ni S core, which facilitates the adsorption of the reactants and subsequently its conversion into the gaseous products during water electrolysis.