Preparation Of Pt-free Oxygen Reduction Catalysts And Their Application In Fuel Cell

At present,great progress has been made in the research on catalysts for oxygen reduction reaction at the cathode of fuel cells,mainly focusing on finding new catalysts that are cheaper and more efficient,in order to further reduce the overall cost of fuel cells.Non-precious metal M-N-C single-atom catalysts have shown great potential to replace Pt-based oxygen reduction reaction（ORR）catalysts in recent reports,but they suffer from poor stability in fuel cells.In addition to the catalyst activity being critical to fuel cells,the structure of the catalyst in actual operation also affects the performance of the fuel cell.At present,there have been many studies on the effect of the pore structure of the catalyst layer on the performance of proton exchange membrane fuel cell（PEMFC）,but the effect of the pore structure of the catalyst layer in the anion exchange membrane fuel cell（AEMFC）is rarely involved.In this paper,a high-performance composite catalyst was developed and applied to AEMFC,and the effect of the pore structure of the catalytic layer on the performance of AEMFC was explored.The main contents are:A novel composite structure ORR catalyst of Ag nanoparticles surrounded by Fe single atoms by exploiting the synergistic effect between nanoparticles and single atoms for ORR was successfully constructed.Through analytical characterization and simulation calculations,it was successfully demonstrated that Ag nanoparticles and the surrounding Fe single atom active sites can synergistically modulate the electronic structure of Ag _NPs@Fe-N-C.The Ag _NPs@Fe-N-C catalyst achieves a half-wave potential of0.885 V in alkaline medium,which is significantly higher than that of comparative samples such as Ag _NPs-N-C and Fe-N-C,with good methanol resistance and stability as well as faster reaction kinetics.This synergistic effect also enables its half-wave potential in acidic medium to reach 0.772 V,which exceeds the Ag _NPs-N-C and Fe-N-C samples with a single active site.Although the half-wave potential in acidic medium is still far from that of commercial Pt/C,it is comparable to it in methanol resistance and stability.Further in the actual fuel cell period test,the peak power density of the AEMFC with Ag _NPs@Fe-N-C as ORR catalyst reaches 0.848 W cm^-2,which is1.37 times that of Fe-N-C based H₂/O₂ cells(0.62 W cm^-2)and 2.16 times(0.393 W cm^-2)of Ag _NPs-N-C-based H₂/O₂ cells.More importantly,the Ag _NPs@Fe-N-C-based AEMFC can be stably discharged for 210 h at a constant current density in H₂/air（CO₂-free）condition,far exceeding the stability of the Fe-N-C-based AEMFC in the same condition（36 h）,demonstrating the introduction of Ag particles in the composite structure not only improves the power density of AEMFC,but also greatly improves the stability.This work provides useful guidance and reference for the further development of Pt-free ORR catalysts for AEMFC.In order to explore the influence of the pore structure of the catalyst layer of the AEMFC membrane electrode assembly on the performance,we took advantage of the controllability of the size of the Si O₂ template to synthesize Co-doped porous catalysts with different pore structures using Zn Co-MOFs as the precursor.Through a series of characterization tests,we found that mesopores always play a more important role than micropores in AEMFC catalytic layer,and further analyzed the internal reasons and laws of the influence of pore structure on it.