Hydrogen Absorption-Desorption Cycle Durability and CO Tolerance of Hydrogen Absorbing Alloys Developed in WE-NET Project

Hydrogen absorbing alloys, “traditional alloys”, have been studied for the applications to nickel-metal hydride batteries and hydrogen storage tanks for portable power generators and fuel cell vehicles, because of their high volumetric hydrogen density over 90 kg-H2/m3 and good kinetics for the reaction with hydrogen. IMURA, Japan Metals & Chemicals, Japan Steel Works, Sumitomo Steel, and OSTEC had promoted development of high-capacity alloys for room-temperature use in the second phase (FY1999-FY2002) of WE-NET Project, the Japanese national project for hydrogen systems, and Ca-Mg-Ni-based Laves-phase alloys, for example Ca0.25Mg0.66Y0.09Ni1.86, and BCC-structured alloys, Ti1.01Cr1.49V0.30, Ti1.10Cr1.39Mo0.30, V74.5Ti10Cr12.5Mn3, and V75.5Ti10Cr11Mn2Ni1.5. We will report hydrogen absorption-desorption cycle durability and influence of CO impurity of the novel alloys in order to give information for development of hydrogen storage systems. Although Ca0.25Mg0.66Y0.09Ni1.86 indicated considerable decrease, ca 40%, in hydrogen capacity within initial 20 cycles, decrease in prolonged cycles from 20th cycle to 400th was only 10% of the first cycle. This alloy indicated considerable influence of CO in hydrogen even at 1 ppm. The BCC alloys showed stable capacity over 1000 cycles in pure hydrogen and hydrogen containing 1 ppm of CO, although the capacities of Ti1.01Cr1.49V0.30 and Ti1.10Cr1.39Mo0.30 deceased ca. 15% within initial 100 cycles. Those alloy indicated appreciable influence by 10 ppm of CO in hydrogen.