Strong Interface Enhanced Hydrogen Evolution over Molybdenum-Based Catalysts

By tuning interfacial structures, we have achieved an extremely small Tafel slope of 34.4 mV dec(-1) for the hydrogen evolution reaction (HER) over a molybdenum oxide catalyst in an acidic electrolyte. Such a small Tafel slope indicates the presence of active sites following the Volmer-Tafel mechanism, which is almost exclusively observed on platinum group metals. We attribute this excellent kinetic property to the enhancement effect from the metal/metal oxide Mo/MoOx) interface in the catalysts. This Mo/MoOx interface was obtained by tuning the hydrogen annealing method. Density functional theory calculations suggest that the hydrogen spillover from the Mo surface to the MoOx surface through an optimized interface will increase the hydrogen coverage on the MoOx surface. Thus, the hydrogen adsorption energy on MoOx can be reduced, making the recombination of the surface hydrogen feasible. Hydrogen temperature-programmed reduction provides clear evidence of hydrogen spillover from Mo to MoO2 at the Mo/MoO2 interfaces. Hence, the above Mo/MoOx interface will also lead to a high HER activity, as demonstrated by the high turnover frequency per active site (at 100, 150, and 200 mV vs the reversible hydrogen electrode, the values are approximately 0.004, 0.249, and 1.398 H-2 respectively). Our study demonstrates a new route to design low-cost-efficient HER catalysts of nonprecious metals by tuning transition metal/oxide interfaces.