福室 直樹

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.

The thermal stability of electroless nickel-phosphorus (Ni-P) film and cobalt-tungsten–phosphorus (Co-W-P) film deposited on GaAs substrate was investigated. X-ray photoelectron spectroscopy and x-ray diffraction measurements indicated that the Ni-P film changed from amorphous to crystalline by annealing at 240°C for 1 h due to the diffusion of Ni into the GaAs substrate and the increase in P concentration in the Ni-P film. On the other hand, the crystallinity of the Co-W-P film did not change by annealing at 240°C for 1 h. Cross-sectional observation showed that the thickness of the crystallized Ni-P film did not change from 3 to 1000 h of high-temperature storage at 270°C, and no void was observed in the Ni-P film. Migration of Ni atoms could be suppressed by the crystallization of the Ni-P film. On the other hand, voids were formed in the Co-W-P film after high-temperature storage at 270°C for 100 h. Since the Co-W-P film consists of nanoscale crystalline and amorphous phases, atoms diffuse from the amorphous portion to the GaAs substrate. Graphical Abstract: [Figure not available: see fulltext.].