Bottom-up Electrosynthesis of Highly Active Tungsten Sulfide (WS_3–x) Films for Hydrogen Evolution

Abstract

Transition metal dichalcogenides have been extensively studied as promising earth-abundant electrocatalysts for hydrogen evolution reaction (HER). However, despite the intention to achieve sustainable energy generation, conventional syntheses typically use environmentally damaging reagents and energy-demanding preparation conditions. Hence, we present electrochemical synthesis as a green and versatile alternative to traditional methods. In this fundamental study, we demonstrated the bottom-up synthesis of a mixed WS2/WS3 film-like material via cyclic voltammetry (CV). The film-like material can be directly electrosynthesized on any conductive substrates and renders the catalyst immobilization step redundant. Through stepwise analysis of deposition voltammograms facilitated by straightforward modification of CV conditions, and characterization using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), a two-step mechanism involving the initial WS3 deposition and subsequent partial reduction to WS2 was proposed. The WS2/WS3 material was determined to possess composition of WS2.64. Compared to non-electrosynthesized WSx materials, its predominantly basal orientation limited the heterogeneous electron transfer rate toward surface-sensitive redox couples. However, WS2.64 demonstrated excellent HER activity, with the lowest Tafel slope of 43.7 mV dec(-1) to date; this was attributed to different metal-chalcogen binding strengths within WS2.64. Fundamental understanding of the electrosynthesis process is crucial for green syntheses of inexpensive and highly electrocatalytically active materials for sustainable energy production. Albeit, the process may be different for a myriad of nanomaterials, this study can be exploited for its analyses from which the conclusions were made, to empower electrochemical synthesis as the prime fabrication approach for HER electrocatalyst development.

Aromatic-Exfoliated Transition Metal Dichalcogenides: Implications for Inherent Electrochemistry and Hydrogen Evolution

“…MoS 2 , MoSe 2 , and WS 2 , is the increase in HER overpotential of the exfoliated materials in the order PhLi < Anth < Naph, with the bulk materials exhibiting the highest overpotentials. We previously proposed that catalysts with large exposed HERactive sites impart significantly lower HER overpotentials, 35 through a simple study of electrocatalysts with different surface area. This implies that PhLi-exfoliated TMDs possessed the highest density of active sites, followed by Anth-and Naphexfoliated equivalents.…”

“…22,23 To exploit these promising attributes for hydrogen generation, considerable amounts of exfoliated TMDs are needed. However, mass production is presently limited; preparation methods such as colloidal syntheses 24,25 and liquid-phase exfoliation 26−28 are currently at the forefront in this aspect, though pristine nanosheets of high crystallinity could be achieved with mechanical 29,30 and shear 31,32 exfoliation, whereas chemical vapor deposition 33,34 and electrodeposition syntheses 35,36 impart greater autonomy in size and thickness of the deposited layer. Despite its prevalence, the liquid-phase exfoliation method is lacking in the latter aspects mentioned above, necessitating more in-depth comprehension of the implications of exfoliation conditions on the electrocatalytic properties of TMDs to address these inadequacies.…”

Co9S8@N,P-doped porous carbon electrocatalyst using biomass-derived carbon nanodots as a precursor for overall water splitting in alkaline media

“…[1][2][3] To drive electrocatalytic water splitting to generate H 2 , an active electrocatalyst for the hydrogen evolution reaction (HER) is critically important, which would reduce the overpotential for the HER, thereby making the whole water splitting process more energy efficient. To date, the most efficient HER electrocatalysts are almost exclusively applied in acidic media owing to the rapid reaction rate of H + to H 2 on the catalyst surface, [4][5][6][7][8] however, studies on HER catalysts in alkaline media are relatively rare due to the more complex reaction mechanism of OH À on the catalyst surface and the sluggish kinetics of the counterpart electrode reaction for the oxygen evolution reaction (OER) during electrocatalytic water splitting. [9][10][11] So far, Pt-based and Ru/Ir-based catalysts have been extensively considered as the most active electrocatalysts for the HER and OER respectively in alkaline media, however, their high costs and source scarcity have limited large-scale production applications.…”

Earth‐Abundant Transition‐Metal‐Based Electrocatalysts for Water Electrolysis to Produce Renewable Hydrogen

“…[19] There are also some different viewpoints of MoS 2 active sites. [29] The WS 2 /WS 3 material was synthesized through an electrochemical method.T he obtained product possessed ac ompositiono f WS 2.64 and ac hain-likes tructure consisting of S 2À and S 2 2À li- [30] Layered WSe 2 films were also reported to be active for water reduction.T he Ta fel slope (77.4 mV dec À1 )o fW Se 2 on carbon fiber paper was al ittle larger than that of the MoSe 2 counterparts (59.8 mV dec À1 ), suggesting ar elativelys low HER kinetics on WSe 2 surface. [20] Other researchers have mentioned that thermodynamically stable defects existed in the metallic twin boundaries of slightly Mo-enriched MoTe 2 and some other chalcogenides, endowing the basal plane of the 2H phase with ah igh HER activity.…”