Editors' Choice—Growth of Layered WS₂Electrocatalysts for Highly Efficient Hydrogen Production Reaction

Abstract

Seeking more economical alternative electrocatalysts without sacrificing much in performance to replace precious metal Pt is one of the major research topics in hydrogen evolution reactions (HER). Tungsten disulfide (WS 2 ) has been recognized as a promising substitute for Pt owing to its high efficiency and low-cost. Since most existing works adopt solution-synthesized WS 2 crystallites for HER, direct growth of WS 2 layered materials on conducting substrates should offer new opportunities. The future economy requires the production of clean energy to replace fossil fuels. Hydrogen is considered as one of the promising future options as a pollution-free energy carrier. Practically, electrocatalytic water splitting has gained attention for sustainable hydrogen production.1 Accordingly, scientists are eagerly seeking for an electrocatalyst that could act as an alternative to the most electrochemically active but expensive platinum metal.2-4 Tungsten disulfide, WS 2 , a member of the semiconducting transition metal dichalcogenide family, has drawn considerable attention due to its semiconducting nature and electrocatalytic activities. [5][6][7][8] Nevertheless, very few studies have been conducted on WS 2 regarding to HER up to date. 5,9-11 The systematic studies of layered WS 2 materials for HER are still not available. 1 Herein, we report our preparation of layered WS 2 electrocatalysts for highly efficient hydrogen production reaction.We have performed the growth of WS 2 by the thermolysis of ammonium tetrathiotungstate (NH 4 ) 2 WS 4 on conducting carbon cloth (CC) substrates under different gaseous environments. As CC is conducting with a high surface area, it is an ideal substrate for loading the WS 2 materials.1 The influence of environmental gas on the electrochemical activity of the obtained WS 2 catalysts were studied. H 2 S was found to give the WS 2 electrocatalysts with superior performance for the hydrogen production with a current density of 10 mA cm −2 at a low overpotential of 184 mV. Materials and MethodsMaterials.-All chemicals including sulfuric acid (H 2 SO 4 ) and ammonium tetrathiotungstate (NH 4 ) 2 WS 4 were purchased from commercial sources and used without further purification. Water used was purified through a Millipore system. Preparation of WS 2 .-The precursor, ammonium tetrathiotungstate solution ((NH 4 ) 2 WS 4 (Alfa Aesa 99.9%) in 5.0 wt% in DMF (dimethylformamide)), was casted on CC substrates (W0S1002 * Electrochemical Society Member.z E-mail: hkw@kaust.edu.sa from CeTech) with a loading amount of 1 mg/cm 2 (Scheme 1). The drop-casted conducting carbon cloth substrate was then baked on a hot plate at 160• C for 20 min. Subsequently, it was fed into the tube furnace for thermolysis process under atmospheric pressure (AP) at varied temperatures and in different gaseous environments, including H 2 S and Ar (10 and 90 sccm respectively), H 2 and Ar (10 and 90 sccm respectively), and pure Ar (100 sccm). In order to exclude oxygen species from the system, tube furnace was pumped and p...

Crystalline tungsten sulfide thin films by atomic layer deposition and mild annealing

“…4a). [67][68][69] The binding energies of the WS2 doublet are in agreement with the semiconducting 2H or 3R phases of WS2, whereas the metallic 1T phase would result in lower binding energies. 3,[67][68][69] The WO3 content relative to the total W content, which likely originates from the oxidation of the films in air, was the lowest at 17% in the sample annealed at 400 °C, compared with 51% in the as-deposited film and 32 and 23%…”

“…The S 2p region expectedly contained a doublet corresponding to S 2in WS2 with binding energies of 162.1 (S 2p3/2) and 163.3 eV (S 2p1/2) as shown in Figure 4b. [67][68][69][70] The broadening of the S 2p peak was attributed to the presence of substoichiometric WSz (z < 2) at binding energies of 161.2 and 162.4 eV and sulfur in oxysulfide or organic environment at 163.3 and 164.4 eV for the S 2p3/2 and S 2p1/2 levels, respectively. [68][69][70] The relative content of the WS2-bound sulfur to the total sulfur content increased with increasing annealing temperature from 47% in the as-deposited film to 68, 71, and 78 % in the films annealed at 300, 400, and 500 °C, respectively.…”

Solution-Based Synthesis of Few-Layer WS2 Large Area Continuous Films for Electronic Applications

“…This doublet corresponds to S 2− sulphur bonded in 2 H phase of WS 2 36 . Fortunately, the absence of S 2 2ligands peaks, which corresponds to the presence of WS 3 and oxidized sulphur species, is a good indicator that the film is stoichiometric for both substrates 37,38 . The peaks obtained from the WS 2 films on the sapphire are almost identical to films grown on SiO 2 /Si.…”

Synthesis, Characterization, and Hydrotreating Activity of NiW Presulfurized Catalysts Prepared via a Tetrathiotungstate-Intercalated NiAl LDH

“…The band at 511 cm –1 is assigned to terminal S–S stretching of S 2 2– in WS 3 . 29 As the temperature increases to 400 °C, the band of WS 3 weakens, whereas two bands at 411 and 350 cm –1 , respectively, attributed to the A 1g vibration of S and the E 2g 1 vibration of W–S in WS 2 41 are observed. A weak band around 175 cm –1 can also be assigned to NiS.…”

“… 48 Martin et al 47 indicated that the S 2p XPS spectrum of WS 3 showed two overlapping doublets attributed to S 2 2– and S 2– in a 1:2 proportion. Alsabban et al 41 suggested that both WS 2 and WS 3 contained S 2– , but only WS 3 possessed S 2 2– . The percentage of S 2 2– in WLDS-300 is 3 times higher than that in WLDS-500, suggesting more WS 3 in the former, which is consistent with the Raman results.…”