Studies on catalytic behavior of Co–Ni–B in hydrogen production by hydrolysis of NaBH 4

Abstract

Catalyst powders of Co–B, Ni–B, and Co–Ni–B, with different molar ratios of Co/Ni, were synthesized by chemical reduction of cobalt and nickel salts with sodium borohydride at room temperature. Surface morphology and structural properties of the catalyst powders were studied using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. Surface electronic states and composition of the catalysts were studied by X-ray photoelectron spectroscopy (XPS). The catalytic activity of the powders has been tested by measuring the H 2 generation rate and yield by the hydrolysis of NaBH 4 in basic medium. Co–Ni–B with the Co/(Co + Ni) molar ratio ( χ Co) of 0.85 exhibited much superior activity with highest H 2 generation rate as compared to the other powder catalysts. The enhanced activity obtained with Co–Ni–B ( χ Co = 0.85) powder catalyst could be attributed to: large active surface area and electron transfer by alloying large quantity of B to active Co and Ni sites on the surface of the catalyst. The electron enrichment, detected in the XPS spectra on active Co and Ni sites in Co–Ni–B, higher than that of Co–B and Ni–B seems to be able to facilitate the catalysis reaction by providing the negative charge electron required by the reaction. Synergetic effect of the Co and Ni atoms in Co–Ni–B catalyst is able to lower the activation energy up to 34 kJ mol −1 as compared to 45 kJ mol −1 obtained with Co–B powder. Structural modification, caused by the heat-treatment at 773 K for 2 h in Ar atmosphere, was not able to change the activity of the Co–Ni–B powder.