Polypyrrole-assisted Mo-based Alloys Preparation And Their Electrocatalytic Performance For Oxygen Reduction

Fuel cells have received widespread attention as a clean energy conversion device.The cathode reaction（oxygen reduction reaction）requires a highly active catalyst to improve the reaction kinetics.Although Pt has high catalytic activity,but its anti-toxicity and durability need to be improved,and Pt is not cost-competitive.Therefore,it is very important to reduce the cost of Pt catalysts while improving its activity,anti-toxicity and stability.In view of this,this thesis uses Mo element to form alloys with precious metals（Pt,Pd）.On the one hand,it reduce the utilization of Pt and then decrease the cost of the catalyst.On the other hand,it uses Mo to adjust the electronic structure of the precious metals（Pd,Pt）to improve their catalytic activity,stability and anti-toxicity ability.The detailed research work is as follows:（1）Using propionic acid as the solvent and oxygen in the air as the oxidant,polypyrrole was synthesized by a chemical oxidation method.polypyrrole Nanospheres with uniform size were achieved by adjusting the polymerization reaction rate.The rich pore structure and heteroatoms can effectively combine metal element species,lying the foundation for the subsequent preparation of alloys.（2）Using polypyrrole nanospheres to hold and combine ammonium molybdate and chloropalladic acid,Mo-Pd/N-C alloy composite material was formed by calcination and reduction.In an alkaline electrolyte,it shows quite high activity for ORR(half-wave potential of 0.940 V;mass specific activity of 0.15 A mg _Pd-1 at 0.9 V,which is 3.2 times as high as that of Pt/C（20%）).At the same time,it has very good continuous use stability,with almost no degradation of performance after 30,000 cycles.However,the half-wave potential of Pt/C（20%）decline by 36 m V after only 20,000 cycles.In addition,the catalyst also has excellent resistance to methanol poisoning.After adding 10 m L of 1 M methanol,the current only decreased by 5.5%.（3）Using the same method,Mo-Pt alloy/N-C catalyst was obtained,which also showed excellent electrocatalytic activity for ORR(half-wave potential of 0.970 V,which is higher by 103 m V than that of Pt/C（20%）;mass specific activity of 0.41 A mg_Pt-1 at 0.9 V,which is 9.5 times as high as that of Pt/C（20%）).After 5000 cycles,there is almost no decrease in activity,and the ability to resist methanol poisoning is particularly outstanding.After adding 10 m L of 1 M methanol,the current only declines by 3.9%.