Hydriding characteristics of LaNi4.7Al0.3 alloys with surfaces modified by high-purity anhydrous HF were evaluated after long-term preservation in air. Affected by poisoning species in air, untreated alloy hydriding activity was enormously decreased. HF-treated alloys with a modified surface layer containing metal fluoride NiF2, LaF3 and AlF3 maintained relatively high activity. In high-humidity air, metal fluoride NiF2 reacted with moisture to form hydrous Ni(OH)2, and permeation of poisonous species such as O2, CO and CO2 was markedly inhibited by moisture-condensed hydrate screens.
Hydrogen storage alloys exhibit reversible high-rate hydrogen absorption and desorption reactions. The hydrogen storage density of the alloys is higher than that liquid H2. The exposure of the alloys to impurity gases such as O2, CO, CO2, and H2O readily reduces reactivity with H2 gas. In this study, the surface of LaNi5-xAlx alloy was treated using anhydrous hydrogen fluoride to examine the effect of CO on fluorinated alloy H2 reactivity. This HF treatment effectively reduced alloy surface poisoning by CO. Compared with the initial transfer, the HF-treated alloy still exhibited 80% hydrogen transfer after 100-cycle hydriding-dehydriding reactions in a H2 gas including 1000ppm CO, while the transfer became zero for untreated alloy after five hydriding-dehydriding cycles. AES analysis of HF-treated samples showed that the HF treatment induced the surface segregation of Ni and F atoms where almost no La atoms was detected. The concentration of La atoms was found to increase with depth, in which a mixed region of La, Ni, Al, F, and O atoms was formed. This fluorinated surface layer seems to function both to prevent surface CO poisoning and to act as a catalyst.
Electrodes modified using aggregated cobalt-porphyrin/polymer ligand systems were prepared and electro-catalytic activity for oxygen (O2) reduction was investigated physicochemically. The maximum value of water yield due to O2 four-electron reduction was 56%. The apparent number of electrons involved in O2 reduction was 2.7 to 31. Two reactions due to O2 two- and four-electron reduction occurred on modified electrodes. Modification (adsorption) stability of the electrocatalyst system was over a few hours under hydrodynamic conditions.
A titanium dioxide photocatalyst was electrochemically fixed onto an alumite surface in a (NH4)2 TiO (C2O4)2 solution. The photocatalytic activity of alumite fixed with TiO2 was evaluated from the CH3CHO photodecomposition. It was found that TiO2 has photocatalytic activity. The photocatalytic mechanism is discussed based on the photoresponse of the rest potential. Alumite fixed with TiO2 has potential practical applications.