Water Oxidation on Spinel NiCo₂O₄ Nanoneedles Anode: Microstructures, Specific Surface Character, and the Enhanced Electrocatalytic Performance

Abstract

Aiming to improve the electrochemical catalytic performance of the spinel NiCo 2 O 4 as water oxidation catalyst, solvothermal method was employed in this work to fabricate NiCo 2 O 4 directly on conductive substrate FTO as integrated anode. By simply altering the solvent in the precursor solution, NiCo 2 O 4 with different morphology was obtained. The electrocatalytic water oxidation behavior of both NiCo 2 O 4 nanoneedles (NNs) and NiCo 2 O 4 nanosheets (NSs) were investigated in analytical scale, and the results showed that NiCo 2 O 4 NNs exhibited enhanced catalytic performance with lower onset potential, larger current density, and faster kinetics in water oxidation process compared with NiCo 2 O 4 NSs. Meanwhile, both the anodes presented excellent stability in the basic conditions which favored oxygen evolution. The reasons for the superior catalytic activity of NiCo 2 O 4 NNs were also discussed in depth by investigating the surface elements composition and distribution, as well as the different chemical state of the surface adsorbed oxygen. It suggested that the NiCo 2 O 4 NNs anode surface which was better hydroxylated and had more physic- and chemisorbed water was beneficial for enhanced water oxidation performance. It was believed that the present work may provide valuable experimental foundation and an exemplary method for improving the activity of water oxidation catalyst.