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

Aiming to improve the electrochemical catalytic performance of the spinel NiCo2O4 as water oxidation catalyst, solvothermal method was employed in this work to fabricate NiCo2O4 directly on conductive substrate FTO as integrated anode. By simply altering the solvent in the precursor solution, NiCo2O4 with different morphology was obtained. The electrocatalytic water oxidation behavior of both NiCo2O4 nanoneedles (NNs) and NiCo2O4 nanosheets (NSs) were investigated in analytical scale, and the results showed that NiCo2O4 NNs exhibited enhanced catalytic performance with lower onset potential, larger current density, and faster kinetics in water oxidation process compared with NiCo2O4 NSs. Meanwhile, both the anodes presented excellent stability in the basic conditions which favored oxygen evolution. The reasons for the superior catalytic activity of NiCo2O4 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 NiCo2O4 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.