Mechanism and kinetics of sodium borohydride hydrolysis over crystalline nickel and nickel boride and amorphous nickel–boron nanoparticles

Abstract

The initial hydrogen generation turnover rates during the hydrolysis of sodium borohydride over nickel catalysts (crystalline nickel (Ni), crystalline nickel boride (Ni3B), and amorphous nickel–boron (Ni–B) nanoparticles) were measured to investigate the reaction kinetics and mechanisms by varying the reactant concentrations and reaction temperatures. Nickel catalysts with and without boron follow different hydrolysis pathways; hydroxide ions are involved in the activation of reactant molecules over Ni3B and Ni–B catalysts. This study explicitly reports the zero-order and first-order reaction kinetics with respect to the reactant concentration over Ni, Ni3B and Ni–B catalysts. The initial hydrogen generation turnover rates and activation energies determined from the experimental data indicate that the amorphous Ni–B nanoparticles exhibit the highest turnover rate and lowest activation energy for the hydrolysis of borohydride among the investigated catalysts. This study provides a general strategy for the development of borohydride hydrolysis catalysts via the modification of a metal catalyst using boron, which causes the crystalline structure to become amorphous and leads to electron-rich, highly undercoordinated metal atoms at the surface.