Influence of Carbon on Molybdenum Carbide Catalysts for the Hydrogen Evolution Reaction

The influence of carbon on molybdenum carbide catalysts for the hydrogen evolution reaction (HER) is discussed. The carbon content is adjusted by varying the molar ratio of molybdenum and glucose sources and the holding time in the carbonization process. The carbon plays a crucial role in the determination of phase formation, surface area, and electrical resistance, which are associated with the final HER activity. There is a contradiction between the reduced active sites and improved electrical resistance that results from the reduced content of carbon, and a balance can be achieved with a holding time of 9 h to provide the best HER activity with a low Tafel slope of 55 mV dec(-1) and a high exchange current density of 0.047 mA cm(-2). Importantly, the transformation of the order of the free carbon improves the electrical conductivity remarkably to result in a great improvement in the final HER activity.