Comparison of liquid exfoliated transition metal dichalcogenides reveals MoSe2 to be the most effective hydrogen evolution catalyst

Abstract

While 2D transition metal dichalcogenides are known to be promising materials for electrocatalysis of hydrogen production, it is not clear which member of this family of materials is the most effective catalyst. Here we perform a comprehensive study, comparing the catalytic performance of electrodes consisting of porous arrays of liquid exfoliated MX₂ nanosheets (M = Mo, W; X = S, Se, Te). We find a clear hierarchy with selenides > sulphides > tellurides with MoSe₂ clearly out-performing the other materials. In all cases the performance, as characterised by current density at a given potential, can be improved by increasing the number of active sites (via control of the electrode thickness) and/or by adding carbon nanotubes to the electrode (i.e. increasing the electrode conductivity). While all materials formed reasonably stable electrodes, addition of nanotubes tended to improve mechanical cohesion. In an attempt to maximise performance, we prepared thick (∼15 μm), free standing MoSe₂/SWNT composite electrodes which displayed Tafel slopes of ∼77 mV per decade and exchange current densities of ∼0.1 mA cm⁻². These electrodes had low onset potentials, reaching −2 mA cm⁻² at −41 mV (vs. RHE) and generated high current densities of −35 mA cm⁻² at −200 mV (vs. RHE).