Hydrogen gas-rechargeable metal hydride electrode for Ni-MH battery 

[[abstract]]Some nonbreakable pellets made of an AB(5) alloy and metallic powder Ag or Ni were used as the anode in a Ni-MH battery such that the anode could be charged in hydrogen gas and discharged in electrolyte. The performance is influenced by the alloy properties, electrode porosity, hydrogen pressure, discharge current, electrolyte polarization, and contamination in the system. For the pellet Ag/AB(5) = 10, continuous discharge can proceed but only for a limited time. The lower porosity of the pellet may be the main problem. For the pellet Ni/AB(5) = 25, it can be discharged unlimitedly at a constant hydrogen pressure of 20 atm. When discharged with a fixed amount of hydrogen gas, the adsorbed hydrogen is immediately discharged on the surface rather than being absorbed into the bulk, and the discharge capacity comes mostly from the gaseous hydrogen rather than from the hydrogen already dissolved in the bulk of alloy. Therefore, the pellet acts more like a catalyst for hydrogen dissociation than as an absorbent. Furthermore, a minimum of similar to 7 atm of hydrogen pressure is required for the system to operate properly. It is suggested that, in order for such a system to operate better under the wet condition, a higher hydrogen gas pressure be maintained to accelerate the hydrogenation rate and more porous pellets be used for faster reaction kinetics. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1938087] All rights reserved.[[note]]SC