Vertically-stacked W/W 2 C heterojunctions with high electrocatalytic capability for the hydrogen evolution reaction in a wide pH range.

The hydrogen evolution reaction (HER) in water splitting is among the foremost methods to produce clean and green hydrogen from renewable sources. The practical use of the HER technology is however hindered by the high price and/or the relatively low efficiency of the currently used catalysts. Herein, we report a heterostructured W/W 2 C electrocatalyst featuring vertically stacked interfaces and embedded in N-doped porous graphitic carbon (denoted as W/W 2 C@N-PGC) as a high-performance electrocatalyst for the HER in a wide pH range. The catalyst synthesis, accomplished through a straightforward one-pot method, is both facile and highly efficient, involving freeze-drying a suspension of the starting materials followed by pyrolyzing the obtained dry gel. Density functional theory calculations revealed the crucial role of the W/W 2 C heterojunction in promoting the two key steps of the HER, viz. HOH bond scission and H 2 emission. Electrochemical data confirmed the excellent electrocatalytic capability of W/W 2 C@N-PGC toward the HER process in a wide pH range including alkaline, acidic, and neutral electrolytes. In 1.0 M KOH, we measured a low overpotential of 102 mV to drive a current density of 10 mA cm -2 ; a long-term stability (up to 24 h) was also realized. The data presented in this work highlight the importance of electrocatalysts with heterojunctions for the HER and the methodology presented in this work may be extended to other contemporary energy-related technologies such as CO 2 reduction, oxygen evolution, and oxygen reduction reactions.