| 研究実績の概要 |
Development of cost-effective electrocatalyst for oxygen reduction reaction (ORR) for low-temperature fuel cells (Solid proton/alkaline conducting membrane fuel cells) is one of the major priority research worldwide. In the present case, we have synthesized trimetallic zeolitic imidazole framework (t-ZIF) and used it as a single precursor for the preparation of the precious metal-free catalyst. t-ZIF contain Co, Fe, and Zn as metal centres and 2-methylimidazole as a ligand. During carbonization, t-ZIF produces nitrogen and Fe/Co-Nx doped carbon/ carbon nanotubes alloyed with metal/metal oxide particles encased inside the carbon structures (FeCo-NCZ). Since the electrocatalyst developed from a single precursor, a uniform distribution of active reaction centres (Fe-Nx, Co-Nx, pyridinic/graphitic coordinated nitrogen, etc.) on the surface of the electrocatalyst is obtained. Highly porous nature of the carbon achieved by the leaching-out of Zn at high temperature. The peculiar morphology and reasonably good surface area assist better mass transport and fast electron transport. ORR performance of FeCo-NCZ in alkaline (0.1 M KOH) condition shows the onset potential and half-wave potential of 1.04 V and 0.91 V vs. RHE respectively, which is more positive to commercial Pt/C catalyst. FeCo-NCZ reduces oxygen molecule through direct 4 e- pathways and shows reaction kinetic similar to Pt/C. More importantly, FeCo-NCZ displays high fuel tolerance and electrochemical stability in alkaline condition even at 60 oC. Our study shows FeCo-NCZ is a suitable alternative to Pt/C.
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