Preparation And Investigation On The Structure-Activity Relationship Of Oxygen Reduction Catalyst For High Temperature Proton Exchange Membrane Fuel Cells

Compared with traditional low-temperature proton exchange membrane fuel cell（PEMFC）,high-temperature proton exchange membrane fuel cell（HT-PEMFCS）has a broad application prospect because of its improved electrode reaction rate,fuel efficiency,enhanced CO tolerance and simplified hydrothermal management.Aiming to tackel the issues of phosphoric acid posioning and poor stability for the carbon supported platinum catalyst towards cathodic oxygen reduction（ORR）in HT-PEMFC,this thesis focuses on the design,synthesis and the structure-activity relationship of non-platinum electrocatalyst as well as the design and synthesis of anti-corrosion support by a combined methods of electrochemical,modern spectroscopy techniques and theoretical calculations.The main results are as follows:1.In order to solve the problem of poor activity and stability of non-noble metal ORR electrocatalysts,double metal atomic catalyst Fe,Ni-N-C was designed and synthesized.The catalytic activity,stability and phosphoric acid toxicity resistance of Fe,Ni-N-C catalysts were investigated.The results show that the catalyst has good activity and stability,and its activity in phosphoric acid electrolyte has surpassed that of commercial platinum/carbon catalyst.It was found that Ni plays a dual role in improving the ORR activity and stability of Fe-N-C.On the one hand,the active sites of Ni-N_x and Fe-N_x synergistically catalyzed ORR in the high over-potential region.On the other hand,Ni acted as a catalyst in the carbonization process at high temperature,which improved the graphitization degree of Fe,Ni-N-C catalyst,thus enhancing the stability of Fe,Ni-N-C catalyst.2.To reveal the structure-activity relationship of non-noble metal catalyst towards phosphoric acid poisoning resistance,metal framework compound（MOF）with precise metal-nitrogen coordinated structure was adopted as the precursor for non-noble electrocatalysts.By changing the heat treatment temperature,the central metal coodinated structure was modulated to investigate the effect of coordinated structure of metal on catalytic activity towards ORR and phosphoric acid poisoning resistance.Combined with the DFT calculations,it is shown that the incorporation of Fe to the active sites could weaken the adsorption of phosphate anion to the C sites neighboring N,thereby inhibiting pyridine N to be protonated irreversibly.Specially,an axial OH ligand mitigates the adsorption of phosphate anion to Fe center.3.In order to solve the problem of poor stability of HT-PEMFC carbon-loaded platinum catalyst,we designed and prepared the anti-corrosion three-dimensional flower-like titanium dioxide interinserted with reduced graphene oxide composite support for carrying highly dispersed Pt nanoparticles,and investigated the catalytic ORR activity and stability of the catalyst.The catalytic activity of the Pt/TiO₂@RGO catalyst did not decay after 30 thousand cycles of accelerated aging test,and the morphology and structure of the catalyst kept good.Using Pt/TiO₂@RGO catalyst as cathode catalyst,the highest power density of PEMFC can reach 920 mW cm^-2,which shows a good application prospect.