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 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 the 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 the 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.