Full Composition Tuning of W_1–xNb_xSe₂ Alloy Nanosheets to Promote the Electrocatalytic Hydrogen Evolution Reaction

Abstract

Composition modulation of transition metal dichalcogenides is an effective way to engineer their crystal/electronic structures for expanded applications. Here, fully composition-tuned W1–x Nb x Se2 alloy nanosheets were produced via colloidal synthesis. These nanosheets ultimately exhibited a notable transition between WSe2 and NbSe2 hexagonal phases at x = 0.6. As x approaches 0.6, point doping is converted into cluster doping and eventually separated domains of WSe2 and NbSe2. Extensive density functional theory calculations predicted the composition-dependent crystal structures and phase transitions, consistently with the experiments. The electrocatalytic activity for the hydrogen evolution reaction (HER) in acidic electrolyte was significantly enhanced at x = 0.2, which was linked with the d-band center. The Gibbs free energy for the H adsorption at various basal and edge sites supported the enhanced HER performance of the metallic alloy nanosheets. We suggested that the dispersed doping structures of Nb atoms resulted in the best HER performance. Our findings highlight the significance of composition tuning in enhancing the catalytic activity of alloys.

Composition-Tuned (MoWV)Se2 Ternary Alloy Nanosheets as Excellent Hydrogen Evolution Reaction Electrocatalysts

“…The HER can be described using a cathodic reaction (2H + + 2 e – → H 2 ), and therefore the reaction performance is maximized when the Gibbs free energy for H adsorption (|Δ G H* |) is close to 0. Based on our previous study, Se sites (no vacancies) on the basal plane are not favorable for HER because Δ G H* = 1.89, 2.05, and −2.55 eV for MoSe 2 , WSe 2 , and VSe 2 , respectively. − Significantly, Δ G H* is close to 0 for the Se and V sites of (MoWV)­Se 2 ( C6 ). Figure d shows that Δ G H* = −0.05 eV for the Se coordinated with 3 V. Additionally, Δ G H* = 0.15, 0.16, and 0.33 eV for the Se coordinated with (2V, W), (2V, Mo), and (Mo, W, V), respectively, as shown in Figure S23.…”

“…MoSe 2 , WSe 2 , and VSe 2 exhibit E f = 20.14, 27.08, and 0.093 meV/atom, respectively. 12, 13,16 It suggests that E f decreases with increasing x V , thereby explaining the higher concentration of Se vacancies at higher x V values.…”

“…Therefore, sample 6 with an intermediate ε d (−3.45 eV) shows the optimal catalytic activity for HER. Previous studies on (WV)­Se 2 , (WNb)­Se 2 , and (MoVNb)­Se 2 nanosheets have showed a volcano-type trend in HER performance, obtaining the optimal results at ε d = −3.5 eV. − Because the ε d of MoSe 2 is within the plot range, the corresponding HER performance is included on the right side. The good correlation proves that ε d is the dominant descriptor for the composition-dependent HER performance of group V–VI TMD alloy materials.…”

“…7−16 The binary alloy catalysts studied thus far include (MoW)S 2 , 7 (MoW)Se 2 , 8 (MoRe)S 2 , 9 (MoRe)Se 2 , 10 (NbTa)S 2 , 11 (MoNb)Se 2 , 12 (MoV)Se 2 , 13 (NbV)Se 2 , 14 (WV)-Se 2 , 15 and (WNb)Se 2 . 16 However, their composition control remains challenging, and therefore, the alloying of multiple TMDs has been rarely investigated. Recently, colloidal synthesis was used to prepare ternary alloy nanosheets of (MoVNb)Se with enhanced HER performance.…”

“…Recently, two-dimensional transition metal dichalcogenides (TMDs) have been considered promising HER catalysts owing to their large surface-to-volume ratio, earth abundance, low price, and excellent stability in harsh environments. − However, despite significant research efforts, TMD catalysts suffer from higher overpotentials than the Pt-based ones. Alloying is an effective method to enhance the electrocatalytic activity because the combination of different TMs can tune the electronic structures. − The binary alloy catalysts studied thus far include (MoW)­S 2 , (MoW)­Se 2 , (MoRe)­S 2 , (MoRe)­Se 2 , (NbTa)­S 2 , (MoNb)­Se 2 , (MoV)­Se 2 , (NbV)­Se 2 , (WV)­Se 2 , and (WNb)­Se 2 . However, their composition control remains challenging, and therefore, the alloying of multiple TMDs has been rarely investigated.…”