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.
