Bifunctional CoNi/Fe3O4@GO catalyst for hydrogen generation through NaBH4 in different solvolytic environments: The effect of sequential metal introduction

Abstract

In the present study, an easily-prepared binary metal supported on a magnetic nanocomposite of graphene oxide was synthesized with a particular focus on the sequence of metal introduction. Specifically, the Co/Ni/Fe3O4@GO, Ni/Co/Fe3O4@GO, and CoNi/Fe3O4@GO samples were synthesized, and subjected to a comprehensive characterization. Following the incorporation of nickel into the cobalt-based catalyst, the surface areas of the samples and the dispersion of the particles were notably enhanced. The positive effect of nickel introduction was found to be more pronounced in the CoNi/Fe3O4@GO nanocatalyst, which was synthesized via the simultaneous impregnation-reduction of cobalt and nickel nanoparticles. The prepared catalysts were found to be efficient catalysts in the sodium borohydride hydrolysis/methanolysis/ethanolysis process. Notably, the results revealed that the CoNi/Fe3O4@GO exhibited superior performance in the methanolysis reaction compared to the other catalysts. Impressively, this catalyst yielded a high hydrogen generation rate of 8200 mL/min.gcat. A thorough kinetic analysis of the catalyzed methanolysis reaction revealed a remarkably low activation energy of 21.45 kJ/mol. Furthermore, a thermodynamic study yielded an activation entropy (ΔS) of −97.75 J/K, which is indicative of a Langmuir-Hinshelwood-type mechanism for the methanolysis of sodium borohydride.