Nickel Cobalt Oxide as an Efficient Electrocatalyst for Overall Water Splitting in Alkaline Media

This study presents nickel cobalt oxide (NiCo 2 O 4 ), with spiky microsphere morphology and spinel structure, as an electrocatalyst for overall water splitting in an alkaline medium. Structural and electrochemical studies of NiCo 2 O 4 , NiO, and Co 3 O 4 prepared using the solvothermal method are presented. The crystallite sizes of the as‐prepared NiCo 2 O 4 , NiO, and Co 3 O 4 were estimated from the X‐ray diffraction data to be 8, 18, and 25 nm, respectively. NiCo 2 O 4 displays an electrochemical surface area of 35.75 cm 2 , higher than NiO (22.5 cm 2 ) and Co 3 O 4 (15.25 cm 2 ). The X‐ray photoelectron spectroscopy spectra indicate the formation of a partially inverse spinel structure in NiCo 2 O 4 , where both Ni and Co ions exhibit mixed valence states. The bimetallic NiCo 2 O 4 displays lower overpotentials and favorable kinetics toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in comparison with the monometallic oxides of Co 3 O 4 and NiO in alkaline media. To achieve a current density of 10 mA cm −2 , the as‐prepared NiCo 2 O 4 requires overpotentials of 339 and −174 mV for OER and HER, respectively, in 1 M KOH. In the two‐electrode setup, a current density of 10 mA cm −2 is achieved at 2.76 V, exhibiting long‐term stability for overall water splitting.