Performance Study On Electrocatalytic Oxidation Of Urea And Methanol On Nickel Phosphate Materials

Fuel cell has attracted more and more attention and extensive research from the public due to its high energy conversion efficiency,environmental friendliness and wide sources of fuel.Methanol and urea are abundant sources and are easy to store and transport compared with hydrogen.Direct methanol fuel cells?DMFCs?and direct urea fuel cells?DUFCs?are more attractive than conventional hydrogen fuel cells and become one of the new-energy technologies in the world.Anode catalyst is one of the key materials which determine the performance of fuel cell and commercial application.However,the anode catalytic material is mainly composed of expensive platinum,which is susceptible to storage and CO poisoning.Therefore,the development of a new type of the anode catalyst which has high efficiency,low cost and good stability is an important research direction.Nickel-based materials have received extensive attention because of their low cost and high activity.Among them,nickel phosphate is a promising transition metal material and is widely used in electrochemical devices such as supercapacitors and electrochemical sensors.With different reagents as phosphorus source and nickel source,mesoporous nickel phosphate nanotubes,mesoporous nickel phosphate nanosheets,mesoporous nickel phosphate nanocrystals,microporous VSB-5 were synthesized by different methods.Nickel-cobalt phosphate composites were synthesized using nickel chloride as the nickel source,cobalt chloride as the cobalt source,and sodium dihydrogen phosphate as the phosphorus source.The morphologies of the samples were observed by transmission electron microscopy.The phase structures of the Ni-based materials were measured by X-ray powder diffractometry.The coordination structures of nickel ion,PO₄ structures and Ni-O structures were analyzed by UV-Vis,IR and Raman spectroscopy.The chemical composition of the surface of the nickel-based material and the chemical bonding state of each element were analyzed by X-ray photoelectron spectroscopy.The specific surface area and pore size distribution of samples were analyzed by nitrogen adsorption-desorption isotherm.The electrochemical catalytic activity and stability of the electro-oxidation of urea and methanol with different nickel phosphates and commercial nickel oxide are studied by cyclic voltammetry?CV?,linear sweep voltammetry?LSV?,impedance spectroscopy and amperometric i-t curve.The effect of cobalt doping on the onset potential of urea and methanol electro-oxidation was also investigated.Mesoporous nickel phosphate nanosheets possess obvious catalytic activity and excellent stability of urea electrochemical oxidation,which are promising as electrode catalysts for direct urea fuel cell.The oxidation current density of mesoporous nickel phosphate nanosheets in 1 M KOH solution containing 0.1M urea was 30.0 mA cm^-2(600 mA cm^-2 mg^-1).During the test of continuously cycling 300 cycles of voltammetry,the oxidation current at 0.6 V of mesoporous nickel phosphate nanosheets modified fluorine-doped tin dioxide transparent conductive glass?FTO?decreased by 3.33%.During a 96-hour amperometric i-t test,the electrochemical activity still retained 97.47%compared with the maximum value.After 134 days of storage at ambient conditions,the amperometric i-t curve for 96 h was tested again and the oxidation current remained above 85%.Mesoporous nickel phosphate nanotubes possess excellent catalytic activity of methanol electrochemical oxidation and good resistance to CO poisoning,which are promising as electrode catalysts for direct methanol fuel cells.The anode current density of mesoporous nickel phosphate nanotubes in 0.5M KOH solution containing 0.5 M methanol was 40.83 mA cm^-2(577 mA mg^-1).During the cyclic voltammetry 1000-cycle stability test,the anode current at 0.65 V of mesoporous nickel phosphate nanotubes modified FTO glass retained 86.1%.During amperometric i-t test for 24 h,the current still retained 91.3%compared with the maximum value.The catalytic performance of nickel-cobalt phosphate composites in the electrochemical oxidation of urea and methanol was investigated,the doping of cobalt can effectively decrease onset oxidation potential and increase the oxidation current.Nickel-cobalt phosphate composites are promising as electrode catalysts for the fuel cells.Compared with NiPO,the onset potential for urea oxidation of NiCoPO composite?Ni:Co=4:6?in 1 M KOH solution containing 0.1 M urea was reduced by 135 mV,and the onset potential for methanol oxidation of NiCoPO composite?Ni:Co=6:4?in 0.5 M KOH solution containing 0.5 M methanol was reduced by 132 mV.In the Amperometric i-t curve test,the current of the nickel-cobalt phosphate composite was always higher than that of the nickel phosphate and cobalt phosphate.Among them,the urea oxidation current of NiCoPO?Ni:Co=4:6?was the highest,and the methanol oxidation current of NiCoPO?Ni:Co=5:5?was the highest.This paper promotes theoretical and applied research on nickel phosphate catalyst which has superior performance and costs less in the future.It is of great significance to solve the key scientific problems in current energy research such as the realization of the cheapness of fuel cell and substitution of precious metal.