Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH) 2 /NiCo 2 O 4 heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions . The optimized Ni(OH) 2 /NiCo 2 O 4 (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm −2 for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm −2 . The improved catalytic performance of the Ni(OH) 2 /NiCo 2 O 4 heterojunctions is attributed to the chemical synergic combining of Ni(OH) 2 and NiCo 2 O 4 , large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.