The role of conductivity and phase structure in enhancing catalytic activity of CoSe for hydrogen evolution reaction

We report for the first time that CoSe with tetragonal metallic phase exhibits high electrocatalytic activity for hydrogen evolution reaction (HER) in acid solution. The prepared tetragonal CoSe exhibits an overpotential of 175 mV versus reversible hydrogen electrode at j = −10 mA cm−2 and a notably low Tafel slope of 36.3 mV dec−1, which are considerably superior to that of CoSe with a hexagonal metallic phase (352 mV and 104.6 mV dec−1). Furthermore, by comparing the catalytic activity of both tetragonal and hexagonal phases of CoSe, our study reveals that the electrical conductivity still dominates on the basis that both phases are metallic. The catalytic activity of hexagonal CoSe can be improved by compounding single walled carbon nanotubes and achieve comparable performance with tetragonal CoSe. Combined with previous works that compare a semiconducting phase and a metallic phase, this work in addition deepens our understanding of the role of conductivity and phase structure in enhancing catalytic activity for HER electrocatalysts.