福室 直樹

Hydrogen polymer electrolyte fuel cells (PEFCs) are key technologies for achieving a low-carbon society, but conventional oxygen reduction reaction (ORR) catalysts sucg as Pt/C suffer from degradadation of carbon supports during operation. To overcome this limitation, we developed a nanostructured catalyst support by coating tin oxide (SnO2) nanoparticles with cobalt-manganese oxide (CMO), enabling nanoscale interface engineering. The CMO layer was formed via electroless deposition of cobalt-manganese oxyhydroxide (CMOH) followed by thermal conversion at 300 °C. Platinum (Pt) and carbon black (Ketjenblack®, KB) were then incorporated to obtain Pt-CMO-SnO2/KB. The resulting catalyst exhibited a 1.97-fold higher mass activity (119.9 A gPt-1 at 0.9 V) than conventional Pt/C and showed significantly enhanced durability, retaining 33% more mass activity after voltage cycliying. Scanning transmission electron microscopy (STEM) combined with energy-dispersive X-ray spectroscopy (EDX) revealed selective Pt deposition on the CMO surface rather than on carbon. X-ray photoelectron spectroscopy (XPS) further confirmed strong metal-support interactions that suppressed Pt agglomeration and detachment. This nanointerface-guided design provides as effective and scalable strategy for improving ORR activity and durability in next-generation PEFC catalysts.

Proton-exchange-membrane hydrogen fuel cells (PEMFCs) are an important energy device for achieving a sustainable hydrogen society. Carbon-based catalysts used in PEMFCs’ cathode can degrade significantly during operation-voltage shifts due to the carbon deterioration. The longer lifetime of the system is necessary for the further wide commercialization of PEMFCs. Therefore, carbon-free catalysts are required for PEMFCs. In this study, highly crystallized conducting Sb-doped SnO2 (Sb-SnO2) nanoparticles (smaller than 7 nm in size) were synthesized using an ozone-assisted hydrothermal synthesis. Pt nanoparticles were loaded on Sb-SnO2 supporting particles by polyol method to be “Pt/Sb-SnO2 catalyst”. The Pt/Sb-SnO2 catalyst showed a high oxygen reduction reaction (ORR) mass activity (178.3 A g−1-Pt @ 0.9 V), compared to Pt/C (149.3 A g−1-Pt @ 0.9 V). In addition, the retention ratio from the initial value of electrochemical surface area (ECSA) during 100,000-voltage cycles tests between 1.0 V and 1.5 V, Pt/SnO2 and Pt/Sb-SnO2 catalyst exhibited higher stability (90% and 80%), respectively, than that of Pt/C catalyst (47%). Therefore, the SnO2 and Sb-SnO2 nanoparticles synthesized using this new ozone-assisted hydrothermal method are promising as carbon-free catalyst supports for PEMFCs.