Preparation And Property Of Platinum/Carbon The Nanofibrous Catalyst Layer For High Temperature Proton Exchange Membrane Fuel Cells

High-temperature proton exchange membrane fuel cells（HT-PEMFC）based on polybenzimidazole（PBI）have the advantages of low fuel purity,simple hydrothermal management,relatively low cost,high system efficiency and are one of the ideal power supplies used as distributed energy systems and mobile systems.However,high-temperature proton exchange membrane fuel cells are still in the preliminary development stage,and the performance and durability cannot meet the requirements of large-scale commercialization.In addition,in order to weaken the poisoning effect of phosphoric acid on the catalyst to obtain better cell performance,the noble metal platinum loading in the catalyst layer is currently relatively high(about 1 mg_Pt/cm² in commercial electrodes),which significantly increases the cost of the cell.The traditional catalyst layer is generally formed by the dense accumulation of catalyst particles and requires the addition of a binder to maintain its structural stability.Therefore,there are problems such as difficult supply of reactants and low utilization of deep catalyst.Different from the particle-deposited catalyst layer,the three-dimensional network structure of the nanofibrous catalyst layer（NFCL）has the following characteristics:（1）It does not need to add an additional binder with no proton conductivity,which provides more reactant transport channels;（2）Three-dimensional network structure can provide efficient electronic channels,and the large holes formed by the fibers are conducive to the rapid transfer of gas;（3）nanofiber framework helps to disperse the catalyst particles and prevent them from forming large aggregates.Therefore,in order to improve the utilization of the catalyst and achieve the goal of reducing the catalyst loading,this paper used ultrasonic spraying and electrospinning technology to prepare a self-supporting catalyst layer based on nanofibers and combined with physical and chemical structure characterization methods,the performance characteristics of the cell based on the NFCL were studied,which provides some guidance for the preparation process and structural design of the catalyst layer in the future.The main research content includes:（1）The self-supporting NFCL with low loading is prepared by ultrasonic spraying technology.The size of the fiber diameter has an important influence on the structure of NFCL and cell performance.When the fiber diameter is small,the fiber stack is dense,and the dispersibility of the catalyst is poor and most of the catalyst particles are dispersed on the surface of the carbon nanofibrous layer,while fibers witn larger diameters are sparsely stacked,and the catalyst easily enters the deep and has good dispersion.The self-supporting catalyst layer prepared with 9%polyacrylonitrile（PAN）solution has better space structure and cell performance.The maximium power density can reach 300.81 mW/cm²(cathode:0.1mgPt/cm²,0.1 mg_Pt/cm²,anode:0.3 mg_Pt/cm²),which is better than the conventional particle deposition catalyst layer at the same loading.（2）The self-supporting NFCL is prepared by electrospinning technology.The three-dimensional network structure is conducive to electron and gas transmission,significantly reducing the internal resistance of the cell.At the same time,the catalyst is evenly dispersed on the surface of the fiber,and the specific surface area is up to 218.75 m²/g,which provides more stable points for the electrochemical reaction.It shows good stability when it is used as the cathode and anode of the HT-PEMFC（cell voltage remains almost unchanged after 20 h operation）.The maximum power density can reach 238 mW/cm² at 0.483 mg_Pt/cm².Although there is still a certain distance compared to the commercial cell performance(1 mg_Pt/cm²,500mW/cm²),considering the low catalyst loading used in this paper,the NFCL still has certain advantages and can be used as a catalyst layer,which can provide some guidance for the preparation and structural optimization of the catalytic layer.