Compared with the traditional Haber Bosch process, green and pollution-free electrocatalytic nitrogen reduction (NRR) has received considerable attention in the electrocatalysis field in the last decade. To address the issue of its low reactivity as well as the existence of competitive reactions, efficient electrocatalysts are particularly important. In this paper, NiO nanomaterials were synthesized by a simple water bath reaction. The effect of different calcination temperatures on the structure of NiO catalyst and its catalytic activity was studied. Uniform NiO-600 nanoparticles (56 ± 9.3 nm) obtained at 600 ℃ showed the best electrocatalytic NRR activity with an NH3 yield of 12 μg h− 1 mg− 1 and a Faraday efficiency of 5.5% at -0.5V (vs.RHE). The small particle size of the nanoparticles provided more active sites and the oxygen-rich vacancies facilitated the adsorption and activation of N2, which improved the catalytic activity of NiO-600. This study highlights the need for calcination temperature regulation and the huge impact on catalyst structure.

Facile synthesis of Ni-based oxides nanocatalyst: effect of calcination temperature on NRR properties of NiO
    Abstract
    1 Introduction
    2 Experimental section
        2.1 Source of materials
        2.2 Synthesis of NiO catalyst
        2.3 Preparation work before electrode preparation
        2.4 Preparation of the electrode
        2.5 Material characterization and electrocatalytic tests
            2.5.1 Electrocatalytic NRR test
            2.5.2 Standard curve for determining the NH3 formation
            2.5.3 Calculation of NH3 formation
            2.5.4 Detection of N2H4
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Xiaoyan Huang(Key Laboratory of Novel Biomass‑Based Environmental and Energy Materials in Petroleum and Chemical Industry, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor &Green Chemical Technology, School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430205, China)
• Xiujing Xing(Chemistry Department, University of California, Davis 95616, USA)
• Wei Xiong(Key Laboratory of Novel Biomass‑Based Environmental and Energy Materials in Petroleum and Chemical Industry, Key Laboratory of Green Chemical Engineering Process of Ministry of Education, Hubei Key Laboratory of Novel Reactor &Green Chemical Technology, School of Chemistry and Environmental Engineering, Wuhan Institute of Technology, Wuhan 430205, China) Corresponding author
• Hao Li(Advanced Institute for Materials Research (WPI‑AIMR), Tohoku University, Sendai 980‑8577, Japan)