無水フッ化水素で表面改質したLaNi_<5-x>Al_x(x=0, 0.3)の水素化・脱水素化特性に及ぼすCOの影響 [in Japanese] Effect of CO on the Cyclic Hydriding-Dehydriding Characteristics of the LaNi_<5-x>Al_x(x=0, 0.3)Alloys Treated by Anhydrous Hydrogen Fluoride [in Japanese]
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Hydrogen storage alloys exhibit reversible high-rate hydrogen absorption and desorption reactions. The hydrogen storage density of the alloys is higher than that liquid H<sub>2</sub>. The exposure of the alloys to impurity gases such as O<sub>2</sub>, CO, CO<sub>2</sub>, and H<sub>2</sub>O readily reduces reactivity with H<sub>2</sub> gas. In this study, the surface of LaNi<sub>5-x</sub>Al<sub>x</sub> alloy was treated using anhydrous hydrogen fluoride to examine the effect of CO on fluorinated alloy H<sub>2</sub> 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 H<sub>2</sub> 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.
- Jitsumu Hyomen Gijutsu
Jitsumu Hyomen Gijutsu 48(12), 1212-1217, 1997-12-01
The Surface Finishing Society of Japan