Tuning the hydrogen evolution activity of beta phase Mo2Cnanoparticles via control of their growthconditions

The use of water electrocatalysis for hydrogen production is a promising, sustainable, and greenhouse-gas-free process to develop disruptive renewable energy technologies. Transition metal carbides, the β-phase Mo2C, are garnering increased attention as hydrogen evolution reaction (HER) catalysts due to their favourable synthesis conditions, stability, and high catalytic efficiency. We use a thermodynamic approach in conjunction with density functional theory and a kinetic model of exchange current density to systematically study the HER activity of β-Mo2C under different experimental conditions. We show that the (011) surface has the highest HER activity, which is rationalized by its lack of strong Mo-based hydrogen adsorption sites. Thus, the HER efficiency of β-Mo2C can be tuned using nanoparticles (NPs) that expose larger fractions of this termination. We give definite maps between NP morphologies and experimental synthesis conditions, and show that the control of carbon chemical potential during synthesis can expose up to 90% of (011) surface, while as H2 ambient has little effect on NPs morphology. The volcano plot shows that under these optimum conditions, the NP exchange current density is ~10-5 A/cm2, that is only slightly smaller than that of Pt (111).