Solid-state naBH4 composites as hydrogen generation material: Effect of thermal treatment of a catalyst precursor on the hydrogen generation rate

Abstract

Solid-state composites based on sodium borohydride (NaBH4) were studied for applications as hydrogen generation materials. Hydrates of cobalt and nickel chlorides subjected to a thermal treatment were added to the composites as catalyst precursors. Using thermal analysis and FTIR spectroscopy, it was shown that the amount of water removed increases with the increasing temperature. Herewith, the water molecules that remained in the samples were strongly bound to the metal and isolated from each other. According to the ultraviolet–visible (UV-vis) spectroscopy data, with the increasing temperature of the thermal pretreatment there took place a substitution of a portion of water molecules by chloride ions in the nearest environment of the metal. It appeared that it was the resulting weakening of the electrostatic field on metal that was mainly responsible for the formation of a more finely dispersed catalytic phase of amorphous cobalt boride in the reaction medium under the action of sodium borohydride. The smaller particles of the active components led to a faster rate of gas generation when water was added to the solid-state NaBH4 composites. This trend remained for both the cobalt and the nickel catalytic systems even when the activity was calculated per gram of the metal. Thus, for the preparation of solid-state NaBH4 composites, hydrates of cobalt and nickel chlorides with a low content of water should be used.