2015 Fiscal Year Annual Research Report
ＭＯＦを基盤としたカーボンアロイ触媒および高性能非白金燃料電池の設計・開発
| Project/Area Number |
15F15377
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| Research Institution | Tokyo Institute of Technology |
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Principal Investigator |
山口 猛央 東京工業大学, 資源化学研究所, 教授 (30272363)
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| Co-Investigator(Kenkyū-buntansha) |
UNNI SREEKUTTAN 東京工業大学, 資源化学研究所, 外国人特別研究員
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| Project Period (FY) |
2015-11-09 – 2018-03-31
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| Keywords | Fuel Cell / Oxygen Reduction / Metal Organic Framework / Electrocatalyst / Pt-Free Catalysts / Imidazolate Framework |
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| Outline of Annual Research Achievements |
Pt-free electrocatalyst for oxygen reduction reaction (ORR) with improved activity and stability is a daunting task for the development of efficient alternative for Pt/C in low temperature fuel cells. A core-shell type nanostructure with metal oxide nanoparticle encased inside the heteroatom-doped carbon shell is an efficient strategy for efficient Pt-free electrocatalysts development. ZIF was chosen as a precursor for such core-shell type catalyst where metal ion turns to metal oxide and ligand will act as nitrogen and carbon source during high-temperature annealing. In a typical synthesis, cobalt nitrate solution was directly mixing with imidazole triethylamine (TEA) solution to produce ZIF-67 with size less than 60 nm with 100% yield. XRD pattern of ZIF-67 reveals that prepared MOF has sodalite morphology. Prepared ZIF-67 annealed at the different temperature in an inert atmosphere followed by acid washing produce Co3O4 covered with the carbon shell enriched with Co-N coordination (Co3O4@Co-N-C). In Co3O4@Co-N-C, Co3O4 nanoparticles have cubic spinel structure and possess an average particle size of 50 nm. The electrochemical analysis in oxygen saturated 0.1 M NaOH shows that 800 oC annealed ZIF-67 shows lower over potential towards ORR with an optimum catalyst loading of 0.16 mg cm-2 . Even though Co3O4@Co-N-C displays core-shell structure, the electrocatalytic activity is lag behind the Pt/C for an overpotential of 50 mV. A further modification is necessary to reducing the gap between Pt/C and non-precious catalyst.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The non-noble electrocatalysts based on the heteroatom-doped carbon nanotube, graphene and carbon nano horn, etc. show ORR activity in alkaline medium but the issues like improved ORR performance, electrochemical stability, etc. persist. The improved activity and stability of a non-Pt electrocatalyst based on carbon morphologies can be achieved by modifying the density of active reaction centres through amending the composition of respective active materials in the catalysts. The effective modulation of active reaction centres can be attained by in-situ doping of heteroatoms or its metal coordination and high density of microporosity without compromising its electrical conductivity. However, during long-term cell operation, corrosion of carbon will occur and it leads to the leaching of active centres, hence, reduce the catalytic performance. The remedy to this issue is directly coating a metal/metal oxide with metal and heteroatom-doped carbon. Such core-shell based catalyst design prevent the corrosion effect through in-situ regeneration of metal-nitrogen interaction on carbon during high potential operation fuel cell. However, currently available typical carbon coating techniques on metal/metal oxide are not capable of developing an electrocatalyst as mentioned above. The uniform carbon coating and controlling the nano size morphologies are practically difficult. Hence, the primary focus of the research activities devoted to design a core-shell type carbon electrocatalyst which possesses uniform morphology, high electrochemical performance and durability.
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| Strategy for Future Research Activity |
1. Effect of graphitization of carbon shell in Co3O4@Co-N-C to improve the electrocatalytic activities to overcome the current overpotential limitations.
2. Detailed physicochemical and electrochemical characterization followed by durability analysis of Co3O4@Co-N-C.
3. Development of Fe3O4 encased Fe-N in doped carbon shell (Fe3O4@Fe-N-C) based electrocatalysts and its detailed physicochemical and electrochemical characterizations.
4. Development of cobalt ferrite encased Fe & Co-N doped carbon shell (CoFe2O4@Fe, Co-N-C) and its detailed physicochemical and electrochemical characterization.
5. Electrochemical durability analysis of Co3O4@Co-N-C, Fe3O4@Fe-N-C and CoFe2O4@Fe, Co-N-C.
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