The investigation of Co6−xFexW6N (x = 0, 3, 6) as electrocatalysts for the hydrogen evolution reaction

Abstract

Proton exchange membrane (PEM) water electrolysers are considered the most promising devices for hydrogen production when operated in tandem with renewable energy sources. However, their efficiency depends on catalysts used on the anode and cathode, but the acidic conditions at the membrane restrict the catalysts to noble metals. Hence, the search for non-noble metal catalysts that are active and stable under acidic conditions is important. In this work we demonstrate that phase pure Co₆W₆N (prepared by the nitridation of an oxide precursor) remains stable in 0.5 M H₂SO₄, suggesting that it is a suitable electrocatalyst for the hydrogen evolution reaction (HER) in acidic media. Moreover, it shows a comparatively low overpotential of −150 ± 8 mV at a benchmark current density of 10 mA cm⁻². Furthermore, two isostructural catalysts with the compositions Co₃Fe₃W₆N and Fe₆W₆N showed overpotentials of −225 ± 8 mV and −414 ± 18 mV at 10 mA cm⁻², respectively, suggesting that Co-sites are responsible for the catalytic performance. This was further confirmed by X-ray photoelectron spectroscopy (XPS) which showed that W-oxidation states in Co₆W₆N and Fe₆W₆N are practically identical and hence, cannot be the cause for the overpotential's increase upon the substitution. In this context, Co₆W₆N appears an optimal target for future tests in full-scale electrolysis systems.