Carbide-directed enhancement of electrochemical hydrogen evolution reaction on tungsten carbide-oxide heterostructure

Abstract

Carbide-oxide heterointerfaces have been known to be responsible for electrochemical activity, however, it is rarely investigated in tungsten carbide-oxide heterostructure for the hydrogen evolution reaction (HER). Furthermore, typical carbide preparation includes carbonization of oxide under gaseous carbon sources at a high temperature, resulting in sintering and collapse of the heterostructures. In this work, nano-sized carbon dots (CDs, ∼2 nm in diameter) were adopted as carbon sources and dispersed on tungsten oxide nanorods allowing abundant nucleation sites for oxide-to-carbide conversion, resulting in high density of carbide-oxide heterointerfaces. The resulting tungsten carbide-oxide heterostructure decorated with carbon dots (WO(3-x) - WCy/CDs) exhibited superior electrocatalytic activity toward the HER with a low overpotential of 65 mV at a current density of - 10 mA cm-2 in acidic media. This performance is among the best electrocatalytic activities compared to the state-of-the-art tungsten carbide-based electrocatalysts. Importantly, the single-cell test using WO(3-x) - WCy/CDs as the cathode showed a current density of 10 mA cm-2 with a cell voltage of only 1.47 V, which is very close to that for Pt/C (1.41 V). In addition, a combined analysis of the X-ray spectroscopic and electrochemical results suggested an optimal W-C ratio in the tungsten carbide-oxide composite to guarantee the high HER activity. Theoretical calculations provided more insight into the carbide-directed enhancement of the electrocatalytic activity of WO(3-x) - WCy/CDs.