Preparation And Electrochemical Performances Of Ni-based Non-noble Metal Catalysts For Methanol Fuel Cell Anode

Compared with the traditional energy,fuel cells have the obvious superiority in environmental protection and efficiency.However,problems such as the high cost and low catalytic efficiency of catalyst seriously hinder its commercialization.In this thesis,three kinds of Ni-based catalysts were prepared for the purpose of preparing high performance non-noble metal catalysts.It shows excellent performance in the catalysis of methanol fuel cell.The main contents are as follows:(1)Mn doped Ni(OH)2/C nanosheet catalysts were prepared by co-precipitation method.The activity and stability of the catalyst were significantly improved with the addition of Mn element.The oxidation peak current density can be obtained to be 188mA/cm2 in 1 M NaOH solution with 0.5 M methanol,which is about one time higher than that of the pure Ni(OH)2.Furthermore,activity can remain about 70%after testing 30,000s at 0.7 V.The electrochemical active area,surface redox species coverage and proton transfer coefficient of the catalyst were investigated.The results show that the electrochemical active area,surface redox species coverage and proton transfer coefficient of the Ni(OH)2/C catalyst with 5%Mn are 76.75cm2,7.31×10-6 mol/cm2 and 6.57×10-8 cm2/s,respectively,much higher than those of other prepared catalysts.The density functional theory was used to calculate the adsorption energy of the catalyst.The mechanism of Ni(OH)2/C modified by Mn was explained,in which,Mn can adsorb the intermediate product CO at first,so that Ni element can exposed to more active centers,thus avoiding the phenomenon of "catalyst poisoning".(2)The composite support was obtained by mixing the MXene phase with carbon nanotubes.MXene phase was obtained by HF etching.This composite support have the unique construction with the layered structure of MXene and the high conductivity of carbon nanotubes.When the mass ratio of MXene to carbon nanotubes was 3:7,the oxidation peak current density of the prepared catalyst was 141mA/cm2,and it was about 2.5 times that of CNT support catalyst and 3 times that of MXene support catalyst.In addition,the catalytic reaction was analyzed from the dynamic perspective.The electrochemical active area,surface redox species coverage and proton transfer coefficient for all samples were studied.The highest values of the sample with the mass ratio of MXene to carbon nanotubes for 3:7 were 70.25cm2,3.84×10-6 mol/cm2 and 1.88×10-5 cm/s,respectively.(3)The LaNiO3 perovskite oxide catalyst was studied.The catalysts with perovskite position for A site deficient and A site excess were prepared.It was found that La0.95NiO3 for A site deficient catalysts has the best electrochemical performances.The current density was about 50mA/cm2 in 1MNaOH solution with 0.5M methanol.The activity was almost not decreased after 57,000s cycling in the electrolyte.The energy band structure,d-band center,methanol adsorption energy and Ni-O bond length were calculated by density functional theory,and the results were used to explain the high performance of perovskite oxide catalyst with A site deficient.The reasons of perovskite oxide catalyst with A site deficient with high performances are considered as the high adsorption energy of methanol,leading to promote its catalytic oxidation of methanol.