Understanding the role of boron and stoichiometric ratio in the catalytic performance of amorphous Co-B catalyst.

• Comparative study of catalytic activity of amorphous Co-B catalyst. • The bonding region between Co and B atoms is most favorable for catalytic activity. • Threefold site with two Co and one B atom is most active site. • Stoichiometry of catalyst affects the number of active sites. • Amorphous Co2B shows perfect balance of all studied catalytic properties. The structural, electronic and hydrogen adsorption properties of amorphous CoB, Co 2 B and Co 3 B structures were investigated using first principle calculations to evaluate their catalytic activity for HER. A total of eight different sites were considered for hydrogen adsorption, of which the threefold site with two Co and single B atom (TF-2Co-B) was found to be most active site for all the three amorphous Co-B structures. The B atom donates electronic charge to the Co-B bond, while, the presence of Co atom is responsible for achieving the optimal charge density necessary for favorable hydrogen adsorption. This interaction between the Co and B atoms makes bonding region between the Co and B atoms most favorable for hydrogen adsorption and not lone Co atom nor the B atom, thus, determining the active sites of Co-B catalyst. The best catalytic behavior of Co 2 B stoichiometry was credited to the perfect balance of magnetic properties, optimum hydrogen adsorption energies and considerable number of active sites it displayed. [ABSTRACT FROM AUTHOR]