The Preparation Of ZIF-based Nitrogen-doped Carbon Material And Its Electrocatalytic Performance

Proton exchange membrane fuel cell(PEMFC)which is a kind of low temperature fuel cell has many advantages,such as low operating temperature,fast start,high energy conversion efficiency and friendly environment.It has a wide range of applications.However,the oxidation-reduction reaction in PEMFC generally uses platinum noble metal catalysts which has higher cost and less resources.Therefore,it is the key to find a catalyst with low price,high catalytic efficiency and good stability.As a subclass of metal organic matrix material(MOFs),zeolite imidazole framework(ZIFs)has the advantages of both high specific surface area of MOFs and regular pore structure as well as high stability.It has become a new platform for the synthesis of new carbon nanocomposites.In this paper,single metal and bimetallic ZIF based nitrogen doped carbon materials were prepared and their electrocatalytic properties were studied.First,2-methyl imidazole and nitric acid zinc salt were mixed to get regular polyhedron ZIF-8 precursor by self-assembly reaction.We changed the carbonization temperature to achieve a better performance of catalyst for oxygen reduction.To explore the influence of carbonization temperature on the catalyst,we used scanning electron microscopy,transmittance electron microscopy and X-ray diffraction to analyze surface topography,structure and degree of graphitization.Then we analyzed type,content and chemical state of elements by XPS,and concluded that carbonization temperature was one of the most important factors that affected catalyst activity.In order to evaluate the catalytic performance of carbon material,we used the CV,LSV,K-L equation and the methanol tolerance and stability tests to verify that Carbonated ZIF-8 crystals at 800 ? temperature had the highest peak potential,oxygen reduction initiating potential,half wave potential and limiting current density.Secondly,we designed a kind of bimetallic ZIFs templated nitrogen doped porous carbon catalyst Zn0.5Co0.5.We changed the ratio of nitric acid zinc salt and Cobaltous nitrate to produce Zn0.5Co0.5 crystal which has similar structure to ZIF-8 and ZIF–67.We use Zn0.5Co0.5 crystal as template to get a efficient catalyst with strong stability and rich active site by high temperature carbonization.XPS results further showed that cobalt existed in the form of Co-N,which further increased the active site in the catalyst and promoted the catalytic performance of the catalyst.The results of electrocatalytic test indicated that the peak potential,half wave potential and limiting current density of ZIFs catalyst of Zn0.5Co0.5 were comparable with commercial Pt/C.The K-L curve at different rotational speeds could be found that the number of electron transfer of the catalyst is close to 4.It is an ideal catalyst path,which was helpful to improve the catalytic efficiency of the catalyst.