Improved electrocatalytic methanol oxidation of NiO nanosheet arrays with synergistic high surface oxygen vacancy and Ni³⁺/Ni²⁺ ratio

The combination of anodic biomass electrooxidation and cathodic hydrogen evolution reaction is an effective strategy to realize energy saving hydrogen production and high value chemical products. Herein, we synthesized dense NiO nanosheet arrays on Ni foam using different heat-treatment temperature, including 400, 450 and 500 °C. The NiO prepared under 500 °C owns the highest oxygen defect concentration (58.1%) and Ni³⁺/Ni²⁺ ratio (3.13), giving the highest intrinsic activity for methanol electrocatalytic oxidation reaction. However, the NiO prepared at 400 °C (named as NiO-400) owns highest catalyst surface area and electrochemical surface area, giving the highest practical activity. Based on the above results, a facile method of surface modification by ultraviolet oxidation is proposed to improve the oxygen defect concentration (from 34.7% to 36.8%) and Ni³⁺/Ni²⁺ ratio (from 2.94 to 3.19) of NiO-400, and the catalytic current was increased by about 48.9%. This work provides some theoretical basis for improving the activity of biomass electrocatalytic oxidation of Ni-based materials.