Naoki Fukumuro

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.].

In the present study, the effect of electro zinc plating on environmental hydrogen embrittlement of 7075–T6 aluminum alloys was investigated by using a slow strain rate testing device which can detect quantitively the amount of hydrogen generated during deformation and fracture. The testing device can also detect traces of hydrogen gas as low as 5 ppb by using a semiconductor gas sensor at ambient pressure. It was revealed that the environmental hydrogen embrittlement of 7075–T6 aluminum alloys was highly suppressed by zinc–based electroplating, while not fully by anodization. The suppression of the hydrogen embrittlement by zinc plating was caused by the protection of original aluminum surfaces during plastic deformation.