New insights into the mechanism of H2 generation through NaBH4 hydrolysis on Co-based nanocatalysts studied by differential reaction calorimetry

To our knowledge, the present study is the first investigation by liquid-phase calorimetry of the mechanism of hydrogen generation by hydrolysis of sodium borohydride catalyzed by Co2B nanoparticles generated in situ. The differential reaction calorimeter was coupled with a volumetric hydrogen measurement, allowing a simultaneous thermodynamic and kinetic study of the reaction. At the end of the reaction, the catalyst was characterized ex situ by TEM, XRD, magnetism, N2 adsorption, TGA–DTA, and the liquid hydrolysis products were analyzed by Wet-STEM and 11B-NMR. The in situ preparation method made it possible to form nanoparticles (<12 nm) of Co2B which are the active phase for the hydrolysis reaction. In semi-batch conditions, the Co2B catalyst formed in situ is subsequently reduced by each borohydride addition and oxidized at the end of the hydrolysis reaction by OH− in the presence of metaborate. A coating of the nanoparticles has been observed by calorimetry and physico-chemical characterization, corresponding to the formation of a 2–3 nm layer of cobalt oxide or hydroxide species.