This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyt...This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells（PEFCs）. Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 2000 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.展开更多
An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a follow...An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive deposition and diffusion （TRD） chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that the chromizing speed at 500℃ was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1/~m in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500℃ for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.展开更多
During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of ...During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of active domains ρ decreases as the height h increases.A simple scaling argument leads to a scaling law of ρ~ h^（-γ） with a coarsening exponent γ=d/z,where d is the dimension of the substrate surface and z the dynamic exponent of a growth front.This scaling relation is confirmed by performing kinetic Monte Carlo simulations of the ballistic deposition model on a two-dimensional（d=2） surface,even when an isolated deposited particle diffuses on a crystal surface.展开更多
Aerosol deposition from the plug laminar flow regime in a circular tube due to diffusion and thermophoresis is studied theoretically, and the aerosol concentration, mean concentration or deposition efficiency, and She...Aerosol deposition from the plug laminar flow regime in a circular tube due to diffusion and thermophoresis is studied theoretically, and the aerosol concentration, mean concentration or deposition efficiency, and Sherwood number are calculated and analyzed by using the analytical solutions based on the detailed comparison with the previous studies. The results show that aerosol concentration distributions for both mechanisms of individual diffusion and combined consideration of diffusion and thermophoresis are symmetrical. However, the axial concentration for the case of diffusion alone is maximal, the maximal values for deposition parameter larger than zero, which appears in the region of non-dimensional radial coordinate from 0 to 1. The large influence of thermophoresis on aerosol mean concentration is found from the detailed comparison, and the bigger of the transport distance and the deposition parameter, the smaller of the aerosol mean concentration. The Sherwood number decreases with the increase of axial coordinate for deposition parameter equal and larger than zero, and the bigger of the deposition parameter, the larger of the deposition velocity.展开更多
基金supported by the Ministry of Knowledge Economy (MKE, Korea) under the Global Collaborative R&D program supervised by the KIAT (N0000698)
文摘This study shows the preparation of a TiO2 coated Pt/C（TiO2/Pt/C） by atomic layer deposition（ALD）,and the examination of the possibility for TiO2/Pt/C to be used as a durable cathode catalyst in polymer electrolyte fuel cells（PEFCs）. Cyclic voltammetry results revealed that TiO2/Pt/C catalyst which has 2 nm protective layer showed similar activity for the oxygen reduction reaction compared to Pt/C catalysts and they also had good durability. TiO2/Pt/C prepared by 10 ALD cycles degraded 70% after 2000 Accelerated degradation test, while Pt/C corroded 92% in the same conditions. TiO2 ultrathin layer by ALD is able to achieve a good balance between the durability and activity, leading to TiO2/Pt/C as a promising cathode catalyst for PEFCs. The mechanism of the TiO2 protective layer used to prevent the degradation of Pt/C is discussed.
基金This work was financially supported by the National Natural Science Foundation of China(Granted No.50671038).
文摘An optimized low-temperature chromizing process at 500℃ was realized on a plain medium-carbon steel with 0.45 wt pct carbon via a duplex chromizing process which consists of a precursor plasma nitriding, and a followed salt bath thermoreactive deposition and diffusion （TRD） chromizing process. CrN layer with a thin diffusion layer underneath was formed. The duplex chromizing process was studied by optical microscopy （OM）, scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）. It was found that the chromizing speed at 500℃ was successfully enhanced by adding more Cr-Fe powders into the salt bath, and the CrN layer formed at the cost of the prior nitride compound layer. A CrN layer with average 8.1/~m in thickness and 1382 HV0.01 in microhardness was formed on the substrate by duplex chromizing at 500℃ for 24 h. Further more, the CrN layer consisted of nanocrystalline CrN grains.
文摘During heteroepitaxial overlayer growth multiple crystal domains nucleated on a substrate surface compete with each other in such a manner that a domain covered by neighboring ones stops growing.The number density of active domains ρ decreases as the height h increases.A simple scaling argument leads to a scaling law of ρ~ h^（-γ） with a coarsening exponent γ=d/z,where d is the dimension of the substrate surface and z the dynamic exponent of a growth front.This scaling relation is confirmed by performing kinetic Monte Carlo simulations of the ballistic deposition model on a two-dimensional（d=2） surface,even when an isolated deposited particle diffuses on a crystal surface.
基金supported by the Scientific Research Program of Ningxia High Education Institution(grant No.NYG2024200)Natural Science Foundation of Ningxia,China(grant Nos.2021AAC03241,2023AAC03045)First-Class Discipline(Pedagogy)Construction Program of Ningxia High Education Institution(grant No.NXYLXK2021B10).
文摘Aerosol deposition from the plug laminar flow regime in a circular tube due to diffusion and thermophoresis is studied theoretically, and the aerosol concentration, mean concentration or deposition efficiency, and Sherwood number are calculated and analyzed by using the analytical solutions based on the detailed comparison with the previous studies. The results show that aerosol concentration distributions for both mechanisms of individual diffusion and combined consideration of diffusion and thermophoresis are symmetrical. However, the axial concentration for the case of diffusion alone is maximal, the maximal values for deposition parameter larger than zero, which appears in the region of non-dimensional radial coordinate from 0 to 1. The large influence of thermophoresis on aerosol mean concentration is found from the detailed comparison, and the bigger of the transport distance and the deposition parameter, the smaller of the aerosol mean concentration. The Sherwood number decreases with the increase of axial coordinate for deposition parameter equal and larger than zero, and the bigger of the deposition parameter, the larger of the deposition velocity.
