Dual Co x S y -Modified Tungsten Disulfide Double-Heterojunction Electrocatalyst for Efficient Hydrogen Evolution in All-pH Media.

The rational design and preparation of a heterogeneous electrocatalyst for hydrogen evolution reaction (HER) has become a research hotspot, while applicable and pH-universal tungsten disulfide (WS 2 )-based hybrid composites are rarely reported. Herein, we propose a novel hybrid catalyst (WS 2 /Co 9 S 8 /Co 4 S 3 ) comprising two heterojunctions of WS 2 /Co 4 S 3 and WS 2 /Co 9 S 8 , which grow on the porous skeleton of Co, N-codoped carbon (Co/NC) flexibly applicable to all-pH electrolytes. The effect of double heterogeneous coupling on HER activity is explored as the highly flexible heterojunction is conducive to tune the activity of the catalyst, and the synergistic interaction of the double heterojunctions is maximized by adjusting the proportion of heterojunction components. Theoretical calculations show that both WS 2 /Co 9 S 8 and WS 2 /Co 4 S 3 heterojunctions have a Gibbs free energy of H reaction (|Δ G H* |) close to 0.0 eV and a facile decomposition water barrier. As collective synergy of dual Co x S y -modified WS 2 double heterojunction, WS 2 /Co 9 S 8 /Co 4 S 3 greatly enhances HER activity compared to bare Co 9 S 8 /Co 4 S 3 or single heterojunction (WS 2 /Co 9 S 8 ) in all-pH media. Besides, we have elucidated the unique HER mechanism of the double heterojunction to decompose H 2 O and confirm its excellent activity under alkaline and neutral conditions. Thus, this work provides new insights into WS 2 -based hybrid materials potentially applied to sustainable energy.