The Synthesis Of MOFs-derived Catalysts And The Research On Their Performance For Borohydride Oxidation Reaction

Direct borohydride fuel cell（DBFC）is a proton exchangd membrane fuel cell with high electromotive force and energy density.However,the high cost of noble metal catalysts required for DBFC anodes and borohydride oxidation reaction（BOR）in the anode of DBFC is simultaneously accompanied by side reactions,which reduces the utilization rate of fules and and makes the marketization process slow.In order to solve this problem,it is urgent to develop a high efficienct electrocatalysts with high selectivity for BOR,thus inhibitting the occurrence of side reactions.When Au is used as the DBFC anode catalysts,BH₄^–is oxidized at the anode close to the theoretical 8 e^–,which can achieve high fuel utilization.The existing graphite materials show an ideal electrocatalytic effect due to the combination of the two-dimensional layered structure of SP² hybrid atoms and the metal-N_x（M-N_x）structure,which is because there esists a large amount of charges transfer between N-C and M-N_x,and N atoms play a key role in stabilizing the graphite defect sites.Based on the above considerations,in this thesis,the noble metal Au combining with the transition metal with M-N_x structure were loaded on carbon black.Because Au and M-N_x provide active sites for catalyzing BOR,and the materials with N-C structure play a role as carriers,which not only reduces the cost but also greatly improves the catalytic activity for BOR.The specific research contents are as follows:（1）Ni@NC nanoparticles were obtained by a high temperature heat treatment of Ni-ZIF8 in an inert atmosphere,and then Ni@NC and Au nanoparticles were loaded on XC-72R carbon black with good electrical conductivity by chemical reduction method.The morphologies and crystal structures of Au/Ni@NC/C catalysts were studied by XRD and TEM,indicating Ni existed in the Au/Ni@NC/C electrocatalysts which evenly distributed on the carbon black.Further electrochemical test studies showed that the electrocatalytic activity of Au/Ni@NC/C-50 for BOR was 41.5 m A cm^-2 higher than that of 20 wt.%Au/C and exhibited good stability.（2）Co and Ni transition metals were introduced into ZIF8 by an ultrasonic-assisted method to form M-N_x structures,and then Au/Co Ni@NC/C electrocatalysts with different metal molar ratios were prepared by a high temperature pyrolysis and chemical reduction method.The morphologies and crystal structures of Au/Co Ni@NC/C catalysts were studied by XRD and TEM,and the catalytic activity of Au/Co Ni@NC/C for BOR was evaluated by CV,CA,CP and LSV test techniques.Due to the incorporation of Co and Ni metals,their synergy with Au along with the formation of M-N-C active sites enhanced the catalytic activity of BOR on Au/Co Ni@NC/C electrodes.The results demonstrated that the number of transferred electrons of Au/Co Ni@NC/C-50 was 6.3 close to the ideal 8-electron BOR.What’s more,it owned the highest peak current density and the best stability.（3）Au/Fe@NC/C materials were prepared by a co-precipitation and a chemical reduction method.Physical characterizations such as TEM and XPS were used to analyse the sizes and surface compositions of the Fe@NC and Au/Fe@NC/C prepared at different temperatures.A series of electrochemical tests were performed on the prepared catalysts,and it was found that the Fe@NC material had a certain effect on the BOR,and synergized with Au nanoparticles to improve the catalytic activity of BOR.