Preparation Of Ni-Mo-Based Catalyst And Its Electrocatalytic Performance Towards Urea Electrolysis

The electrochemical total hydrolysis reaction consists of two half reactions,respectively the hydrogen evolution reaction（HER）at the cathode and the oxygen evolution reaction（OER）at the anode.In theory,the OER reaction requires a higher potential,which restricts the large-scale application of water electrolysis hydrogen production technology.Urea oxidation reaction（UOR）requires a relatively lower theoretical potential,and only N₂,H₂,and CO₂ are produced during the entire reaction process,which can not cause environmental pollution.The urea electrolysis technology,in which UOR reaction replaces OER reaction to produce hydrogen,is a promising electrochemical hydrogen production method.However,the 6e^-reaction and the unclear reaction mechanism involved in the UOR reaction process are still difficult problems in this technology.The key to improving its performance is to explore an efficient dual-functional catalyst for hydrogen production by urea electrooxidation.In this thesis,by designing and optimizing the catalyst,nickel-molybdenum-based catalysts with good catalytic effects on HER and UOR were prepared.The contents are as follows:1.A nickel-molybdenum alloy catalyst（Mo Ni₄@CC）was deposited on the carbon cloth by electrodeposition.Under other conditions unchanged,by changing the deposition time,deposition current density and the ratio of nickel and molybdenum in the deposition solution,the best catalyst was screened out through related electrochemical experiments.In the UOR and HER processes,the best deposition time was 1 h,the best deposition current density was-80m A cm^-2,the best nickel-molybdenum ratio in the HER process was 1:4,while in UOR the optimal ratio of nickel and molybdenum in the deposition process was 3:2.With the optimized HER catalyst used as the working electrode,the overpotential was only 26 m V when the current density reached-10 m A cm^-2 in a solution system of 1 mol L^-1KOH,the Tafel slope was 82 m V dec^-1.With UOR catalyst used as the working electrode in a mixed solution of 1 mol L^-1KOH and 0.5 mol L^-1urea,when current density reached 10 m A cm^-2,it required a potential of 1.399V,and the Tafel slope was 93 m V dec^-1.The urea electrolytic cell need a potential of 1.48 V to reach a current density of 10 m A cm^-2,which was 0.21 V lower than that during water electrolysis,and it showed a good stability in the stability test for 10 h.2.The self-supporting NiMoO precursor was prepared by a simple hydrothermal method.Under other conditions unchanged,by changing the hydrothermal time and hydrothermal temperature,different catalysts were prepared for optimization.After comparative tests,the best one was selected in the HER and UOR processes.The best hydrothermal time was 4 h,and the best hydrothermal temperature was 150℃.The self-supporting Ni（PO₃）₂-NiMoP₂@NF catalyst was prepared by further low-temperature phosphating in the tube furnace.The best phosphating temperature was 350℃and the best ratio of nickel and molybdenum was 1:1.The process catalyst had the best catalytic performance in HER and UOR.When it was used as a working electrode in a 1 mol L^-1KOH solution system,it required an overpotential of 50 m V with a current density of-10 m A cm^-2,and the Tafel slope was 87 m V dec^-1.In the mixed solution of 1 mol L^-1KOH and 0.5 mol L^-1urea,a potential of 1.384 V was required to reach a current density of 10 m A cm^-2,and the Tafel slope was 22 m V dec^-1.The urea electrolytic cell need a potential of 1.50 V to reach a current density of 10 m A cm^-2,which was 0.8 V lower than that during water electrolysis,and it showed a good stability in the stability test for 10 h.