Investigation of hydrogen evolution using Na3M2SbO6 (M = Co2+, Ni2+, Cu2+, Zn2+) as photocatalyst

Abstract

Four honeycomb structured oxides of the type Na3M2SbO6 (M = Co, Ni, C, Zn) were prepared and characterized using a combination of powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The XPS measurements show that in each case the transition metal cation is divalent, and the Sb is pentavalent. The activity of these as photocatalysts for the direct production of hydrogen from water has been determined. Of these four oxides, Na3Co2SbO6 displayed the highest activity as a Hydrogen Evolution Catalyst (HEC), with an observed H2 evolution rate of 1.323 μmol·hr−1. The rate of hydrogen evolution does not correlate with the measured bandgap, that varied from 2.090(16) eV in Na3Co2SbO6, which allows it to absorb sunlight, to 4.66 eV in Na3Zn2SbO6 that falls outside the visible spectrum. Na3Ni2SbO6 was found to be inefficient as a hydrogen evolution catalyst.