Preparation Of NiO@TiO₂ Nanorods And Their Electrochemical Nitrogen Fixation Performance

As an environmentally-benign and sustainable option for NH₃ synthesis,the electrochemical nitrogen reduction reaction（NRR）is expected to replace the traditional Haber–Bosch process.Transition metals with empty d-orbitals achieve NRR activity via a“πback-donation”process.However,the problem in overcoming hydrogen evolution reaction（HER）competition makes the exploration of transition metal-based catalysts with relatively inferior HER activity worthwhile.The challenges lie in designing a rational structure for efficient NRR.In this dissertation,Ni O thin film is attached to Ti O₂ nanorods by magnetron sputtering to obtain Ni O@Ti O₂ nanorods.In this process,Ni³⁺and oxygen vacancy are simultaneously integrated on Ni O@Ti O₂ nanorods,and the electrochemical nitrogen fixation performance of the materials is greatly improved through“πback-donation”process.This dissertation mainly focuses on the design,preparation,characterization and electrochemical nitrogen fixation performance of Ni O@Ti O₂ nanorods.The main research contents of this paper are as follows:（1）The original Ti O₂ nanorods were grown on carbon cloth after plasma treatment by hydrothermal reaction.Ni O film is attached to the Ti O₂ nanorods by magnetron sputtering at different sputtering temperatures（100-400℃）,and Ni O@Ti O₂ nanorods are obtained at different sputtering temperatures（100℃:NT-100,200℃:NT-200,300℃:NT-300,400℃:NT-400）.Scanning electron microscope（SEM）images show that the morphology of the nanorods does not change significantly before and after magnetron sputtering.Transmission electron microscope（TEM）images show that both Ti O₂ and Ni O are crystal structures.X-ray photoelectron spectroscopy（XPS）spectrum shows the surface chemical composition and bonding structure of Ni O@Ti O₂ nanorods at different magnetron sputtering temperatures,which verifies the existence of Ni³⁺and oxygen vacancy on Ni O@Ti O₂ nanorods.Electron paramagnetic resonance spectrum（EPR）spectrum reconfirms the presence of Ni³⁺and oxygen vacancy on Ni O@Ti O₂ nanorods,and the concentration of oxygen vacancy increased with increasing temperature.（2）The theoretical analysis of the nitrogen fixation performance of Ni O@Ti O₂ nanorods is carried out by using density functional theory（DFT）.The theoretical calculation results show that the binding of Ni³⁺with oxygen vacancy could provide active sites,promote“πback-donation”and improve NRR activity.The performance,reliability and stability of Ni O@Ti O₂nanorods electrochemical nitrogen fixation are studied.Electrochemical nitrogen fixation performance test results show that Ni O@Ti O₂ nanorods can achieve the highest NH₃ yield(10.75μg h^-1 cm^-2_cat.)and Faraday efficiency（9.83%）when the magnetron sputtering temperature is 300℃.It is nearly 10 times higher than that of initial Ti O₂ nanorods.The results of N¹⁵ isotope labeling experiment shows that the raw gas is the only nitrogen source for NH₃production.The stability test results show that the electrochemical performance and the structure of Ni O@Ti O₂ do not change significantly after 10 consecutive electrolysis cycles.