Study on the Poisoning and Fine-Powdering Resistance Mechanism of SiO2-Coating on La-Ni Hydrogen Storage Alloy

Hydrogen storage alloys can be poisoned by impurity gases such as H2O, O2, N2, CO, etc., and be fine-powdered by hydride formation. In order to improve the durability of hydrogen storage alloys against surface poisoning by impurity gases and fine-powdering during hydriding process, effectiveness of SiO2-coating layer prepared by fumed silica method was examined for La-Ni based alloy particles as a model system. It was found that, the La-Ni alloy particles were embedded in a porous SiO2 matrix. SiO2-coating effectively improved the durability of La-Ni alloy surface to impurity gases containing oxygen and nitrogen atoms. The anti-poisoning mechanism of the SiO2-coating was investigated. It was found that, the cubic structured phase regions with short-range order arrangement of atoms were formed in the amorphous SiO2-coating layer during the heat treatment process, which were the hydrogen permeation regions with, effectively restricting the passage of larger molecules of oxygen and other harmful impurities. Therefore, the SiO2-coating provided protection to the metal hydride particles from these impurities. Furthermore, the porous SiO2 matrix embedded La-Ni alloy particles were fracture resistant and could withstand more than 1000 hydrogen absorption/desorption cycles without generating fines.