Preparation Of Nickel-based Composite Nanomaterials And Their Performance Study For The Electrooxidation Of Urea

Environmental pollution caused by the burning of fossil fuels has caused widespread concern about the development of alternative energy sources.Urea is considered an excellent hydrogen carrier,which is much higher than compressed or liquid hydrogen.Urea electrolysis has been considered as an effective way to produce hydrogen from urea-rich wastewater,but the urea oxidation reaction（UOR）is a slow and complex process,which results in its actual power efficiency being much lower than other fuel cells.Therefore,a rational and efficient electrocatalyst for UOR is necessary.In this thesis,a series of nickel-chromium oxide composite nanomaterials were successfully prepared by simple hydrothermal method and subsequent heat treatment,and supported on different supports.The electrocatalysis activity of UOR was evaluated by electrochemical tests in alkaline electrolyte.First of all,NiO/NiCr₂O₄ composite nano-catalysts with different proportions（denoted as NiO/NiCr₂O₄-m,m=1,2,3）were prepared and supported on glassy carbon electrodes to evaluate their electrocatalytic oxidation of urea of activity.The experimental results showed that the NiO/NiCr₂O₄-2 catalyst has a large electrochemical surface area(155.64 m² g^-1),which provides many active sites and electron transport channels for UOR.Under a low catalyst loading of 50μg cm^-2,the current density provided by the NiO/NiCr₂O₄-2 electrode in a 1.0 mol L^-1 KOH solution containing 0.33 mol L^-1 urea is 994 m A cm^-2 mg^-1（potential is+0.5 V vs.Ag/Ag Cl）,with excellent redox properties and stability.Secendly,NiO-NiCr₂O₄ composite material（NiO-NiCr₂O₄/NF）was successfully grown on the nickel foam substrate,and its activity of electrooxidizing urea in alkaline environment was evaluated.The experimental results show that in 1.0 mol L^-1 KOH and0.33 mol L^-1 urea solutions,the catalytic current density of NiO-NiCr₂O₄/NF is as high as275 m A cm^-2 at 0.7 V vs.Ag/Ag Cl potential.The initial current retention rate of NiO-NiCr₂O₄/NF electrode is about 82%,which proves its excellent stability in the UOR process.In this thesis,with the synergistic effect of NiO and NiCr₂O₄,NiO/NiCr₂O₄ composite nanocatalyst provides more active sites for UOR.Ni³⁺effectively suppresses the catalyst’s surface poisoning and shows excellent electrocatalytic activity.It is a promising candidate for direct urea fuel cells.