Dual Co_xS_y-Modified Tungsten Disulfide Double-Heterojunction Electrocatalyst for Efficient Hydrogen Evolution in All-pH Media

Abstract

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 (|ΔG 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.

Overall Spontaneous Water Splitting for Calcium Bismuthate Ca(BiO2)2: Flexible-Electronic-Controlled Band Edge Position and Adsorption-Site-Modulated Bond Strength

“…In contrast to the oxidation reaction, the first step of the hydrogen evolution half reaction is downhill, indicating that the Ca­(BiO 2 ) 2 monolayer undergoes self-exothermic reaction during the process of combining a proton and an electron to form H* without requiring external energy input. This is similar to the free energy curves generated by hydrogen evolution reactions for the SiS/ZnO heterojunction, MXene, and MXene derivatives and at different reaction sites on the WS 2 /Co 9 S 8 heterojunction . However, the reduction of H 2 from the intermediate state H* in the second step is impeded by a high barrier of 1.84 and 2.26 eV in an acidic (pH 0, black lines) and neutral (pH 7, blue lines) dark environment (light off), resulting in photogenerated holes generating only a potential of 0.48 V even when the Ca­(BiO 2 ) 2 monolayer at pH 0 is exposed to light (light on), requiring an additional absorption of 1.85 eV (red lines).…”

“…This is similar to the free energy curves generated by hydrogen evolution reactions for the SiS/ZnO heterojunction, 72 MXene, and MXene derivatives 73 and at different reaction sites on the WS 2 /Co 9 S 8 heterojunction. 74 However, the reduction of H 2 from the intermediate state H* in the second step is impeded by a high barrier of 1.84 and 2.26 eV in an acidic (pH 0, black lines) and neutral (pH 7, blue lines) dark environment (light off), resulting in photogenerated holes generating only a potential of 0.48 V even when the Ca(BiO 2 ) 2 monolayer at pH 0 is exposed to light (light on), requiring an additional absorption of 1.85 eV (red lines). Therefore, we add an additional bias of 1.37 V (U = 0.48 + 1.37 = 1.85 V) in the acidic (pH 0) and illuminated environment to drive the hydrogen evolution half reaction thermodynamically downhill.…”

Regulation of the electronic structure and surface wettability of a Co9S8 electrocatalyst by nitrogen and phosphorous co-doping for efficient overall water splitting

“…S7 †), and comparable to those of cobalt-based HER electrocatalysts reported (Table S1 †). 64,65 Moreover, N-Co 9 S 8 and P-Co 9 S 8 materials display obviously reduced overpotentials at the given current densities of 10 and 100 mA cm −2 in comparison with the pristine Co 9 S 8 (Fig. S8 †), revealing that even N or P single doping can increase the HER activity of Co 9 S 8 .…”

VOC of Inverted Perovskite Solar Cells Based on N‐Doped PCBM Exceeds 1.2 V: Interface Energy Alignment and Synergistic Passivation

“…A PCE of 23.1% was obtained by N-DMBI doping. [8c] Additionally, mixed PCBM with a small content of insulating polymers, such as polystyrene (PS), [9] polyethylenimine (PEI), [10] poly(methyl methacrylate) (PMMA) [11] and poly(amidoamine) (PAMAM) dendrimers, [12] could passivate interface defects, achieved the highest PCE of 18.63% accompanied by the significantly improved stability of the PSCs. [11a] Therefore, the polymer should be superior to a small molecule for doping PCBM taking into account device stability.…”