Electrocatalytic In Fuel Cells:Study Of Non-pt Catalysts

In face of energy shortage and environmental pollution during the 21 st century, all of the world people are committed to developing safe and clean new energy technology. Under the influence of this environment,the fuel cells with the advantages of environment friendly, efficient,practise arise at the historic moment. Fuel cells can completely replace the internal combustion engine, and effectively drive the car. At present,the cathode catalysts of Low Temperature Fuel Cell completely rely on Pt to achieve certain power requirements, but the cost and storage of Pt limit the commercial scale. Therefore, it is important for widely promoting fuel cell technology to develop low cost, highly active and high stability non-noble metal catalytic materials.In this paper, aming at developing and recognising the activity centers low cost, highly active and high stability non-noble metal catalytic materials, then combining the key scientific problems during the research processing, we put forward the preparation of high density of active sites of non-Pt (especially non-noble metal) catalytic materials to enhance the catalytic activey sites of per unit volume, decrease the thickness of the catalytic layer, and reduce the mass transfer resistance.1. Under the premise that M/N/C catalyst can be practical, and combining the advantages of polybenzimidazole, we design a new type of efficient non-precious-metal catalysts for ORR via direct pyrolysis of Poly[2,2'-(1,1'-Mocenium)-5,5'-dibenzimidazole]. The obtained catalysts exhibit higher electrocatalytic activity and stability for ORR under both alkaline and acidic conditions. The Cp2-Fe-PBI-800 catalyst had an excellent ORR activity with onset potential of 1.0 V (vs. RHE) in alkaline media. The Cp2-Co+-PBI-900 catalyst showed the highest ORR activity with onset potential of 998 mV (vs. RHE), which was only 22 mV higher than that of Pt/C under identical conditions in alkaline media. Besides, in acidic media, Cp2-Co+-PBI-800 had an excellent ORR activity with onset potential of 847 mV (vs. RHE) after leaching in 6 M HC1 solution for 12 h. Both the optimal catalysts displayed high durability especially in acidic media. The half-wave potential was also improved by 11 mV after 5k CV scanning cycles in N2. Through the structural characterizations (XRD,XPS,Raman) and electrochemical performance tests, we establish the structure-activity relationship of Cp2-M-PBI catalysts. The polybenzimidazole (PBI) has long-chain and ?-conjugated system,indicating that PBI precursor can be used as a non-precious metal catalyst.2. To prepare high density of active sites catalysts, we used porous design idea. Precursors of tungsten carbide/Melamine/carbon aerogels(WC@C/N/CA) porous catalysts were designed and prepared by using the porous carbon aerogelswith Si02 as the hard template and very large specific surface areas were obtained. By adding tungsten carbide,melamine and Si02 into the early-stage phenolic resin ageing, we prepared the integrated porous catalyst precursors. The chemical state and interaction of key elements in non-Pt catalysts were regulated by high-temperature carbonization, template removal and secondary calcination. Finally, excellent non-Pt oxygen reduction reaction (ORR)catalysts were prepared. The catalyst prepared at 850 ? formed a core-shell (WC@C) structure, and had good catalyst performance after 4 h of secondary calcination. The ORR activity reached 1.027 V under alkaline media, which is higher than that of commercial Pt/C catalysts.And it reached 0.761 V under acidic media. The high ORR activity and stability of the WC@C/N/CA catalysts were explained via X-ray diffraction, X-ray photoelectron spectroscopy, Raman, and Brunauer-Emmett-Teller measurement. Then we establish the structure-activity relationship, activity center and reaction mechanism.The specific surface area was improved because of the porous structures,resulting in the enhancement on the density of active sites.3. Based on the design thought of porous and large specific surface area, and combining the structure characteristics of metal organic framework materials, we prepared Fe-bpdc catalysts with high N contant as ORR catalysts. The ligand named 2, 2'- bipyridine -3,3' dicarboxylic acid were picked out and generated with FeS04 to form Fe-bpdc@MOF.Then pyrolyzed by medium-high temperature toget a serise of Fe-bpdc catalysts. The Fe-bpdc-700 catclyst showed the highest ORR activity with onset potential of 1.092 V (vs. RHE), and had a better stability in alkaline media. The ORR activity reached 0.887 V, and had a better stability under acidic media. Through the structural characterizations (XRD,XPS,Raman) and electrochemical performance tests (LSV, CV), we recognized the activity center, establish the structure-activity relationship, and calculated it entirely meet 4-electron ORR process no matter in alkaline media and acidic media. The structure of MOF materials with porous and large specific surface area, can greatly reduce the thickness of the catalyst used for MEA layer, thus greatly reduce the mass transfer resistance, and enhances the practicability of this kind of catalyst.