Synthesis And Catalytic Performance Study Of Non/Low Pt Oxygen Reduction Catalysts Face To Proton Exchange Membrane Fuel Cell Applications

High temperature proton exchange membrane fuel cell（HT-PEMFC）can be combined with methanol reforming device due to its high tolerance of CO in anode hydrogen,which perfectly solves the heavy dependence of hydrogen storage and transportation technology in conventional proton exchange membrane fuel cell（LT-PEMFC）.Therefore,It is a promising clean energy efficient utilization technology.At present,the operating power and stability of HT-PEMFC are still lower than that of LT-PEMFC,which cannot meet the requirements of large-scale commercial applications.The cathodic oxygen reduction reaction（ORR）with slow kinetics and oxidative atmosphere is the shortcoming of HT-PEMFC performance.The best catalyst for catalyzing the cathodic reaction of HT-PEMFC is still carbon-supported platinum-based nanoparticles.Since phosphoric acid composite membranes are commonly used as solid electrolytes in HT-PEMFC,strongly adsorbed species such as phosphate radicals lead to the degradation of Pt-based catalyst performance and the corresponding increase in dosage.Therefore,the high cost,high dosage,and susceptibility to phosphate poisoning have become the main reasons for limiting the application of platinum-based ORR catalysts in HT-PEMFC.In order to reduce the operating cost and improve the operating efficiency of HT-PEMFC,this paper solves the above bottleneck problem by designing and synthesizing cheap and phosphoric acid-resistant high-activity non-Pt and low-Pt ORR electrocatalysts.The research achievements include the following two aspects:（1）In this paper,a series of M-N-C single metal and iron-based bimetal catalysts were synthesized using ZIF-8 nano-polyhedron as the template by host-guest encapsulation and co-adsorption wet chemical methods.The catalytic activities of oxygen reduction at room temperature in the different acidic and alkaline mediums were compared and evaluated.The catalyst with the highest ORR catalytic activity in the phosphoric acid solution medium was the iron-manganese bimetallic catalyst prepared by the co-adsorption experiment method.Its half-wave potential of oxygen reduction is higher than that of commercial Pt/C(E_1/2=0.85 V vs.0.81 V),and it has good stability.At the same time,the peak power density of conventional hydrogen-oxygen fuel cell using the iron-manganese bimetallic catalyst as cathode catalyst can reach1055 m W cm^-2,indicating that this bimetallic nitrogen-carbon porous catalyst has good applicability in battery devices,which overcomes the previous mass transfer problems of Fe-N-C catalyst in devices,and is expected to realize the application of non-Pt cathode oxygen reduction catalyst in HT-PEMFC.（2）Based on the above works,in order to further improve the ORR activities of the catalysts,five M-N-C catalysts were selected as the supports to prepare low Pt catalysts by reducing H₂Pt Cl₆·6H₂O by Na BH₄ and loading different amounts of Pt nanoparticles on them.TEM images showed that Pt nanoparticles were uniformly distributed on Co-N-C,but there was a certain degree of agglomeration on Fe-N-C.The testing technology of RDE was used to analyze the oxygen reduction catalytic activity in different acidic and alkaline mediums at room temperature.Among them,Pt/Co-N-C_（I）has the best catalytic activity with E_1/2=0.84 V in H₃PO₄ medium.The highest output power density of LT-PEMFC using it as cathode catalyst can reach 1893 m W cm^-2.The non-Pt and low-Pt electrocatalysts prepared in this paper have excellent oxygen reduction catalytic activities in phosphoric acid medium,and provide key materials for the subsequent development of HT-PEMFC.All the catalysts assembled into fuel cells have high power output density,indicating that the prepared catalysts have good applicability in battery devices,which have provided beneficial exploration for large-scale commercial applications of PEMFC.