Polytypic Phase Transition of Nb_1–xV_xSe₂ via Colloidal Synthesis and Their Catalytic Activity toward Hydrogen Evolution Reaction

Abstract

Polytypes of two-dimensional transition metal dichalcogenide can extend the architecture and application of nanostructures. Herein, Nb1–x V x Se2 alloy nanosheets in the full composition range (x) were synthesized by a colloidal reaction. At x = 0.1–0.3, a phase transition occurred from various hexagonal (three 2H and one 4H types) phase NbSe2 to an atomically homogeneous 1T phase VSe2. Density functional theory calculations also revealed a polytypic phase transition at x = 0.3, which was shifted close to 0 in the presence of Se vacancies. Furthermore, the calculations validate favorable formation of Se vacancies at the phase transition. The sample at x = 0.3 exhibited enhanced electrocatalytic activity toward the hydrogen evolution reaction (HER) in 0.5 M H2SO4. The Gibbs free energy indicates that the catalytic HER performance is correlated with the active Se vacancy sites of polytypic structures.

Full Composition Tuning of W1–xNbxSe2 Alloy Nanosheets to Promote the Electrocatalytic Hydrogen Evolution Reaction

“…We suggest that the Se vacancies can also contribute to produce the 2H α phase. 35 At x = 0.75, the stability of 2H β vs 2H α (4.06 meV/atom) is smaller than that at x = 1 (10.83 meV/atom). Therefore, the thin layered morphology and the Se vacancies could stabilize the 2H α phase.…”

“…Interestingly, the WSe 2 -like 2H structure coexists as reported in our previous work on the Nb 1−x V x Se 2 nanosheets. 35 This will be discussed in the following section. The clustering feature was previously observed for Nb (7% or 10%)-doped WS 2 and Nb (12.8%)-doped WSe 2 , which were synthesized using CVD (at 550 or 1000 °C) and CVT (at 1000 °C), respectively.…”

“…Moreover, conversion to the metallic phase can lower the activation energy. The alloy phase would satisfy this criterion, and significantly improved catalytic properties have been reported for (MoW)­S 2 , (MoW)­Se 2 (NbTa)­S 2 , (MoRe)­S 2 , (MoRe)­Se 2 , (MoNb)­Se 2 , (MoV)­Se 2 , (NbV)­Se 2 , and (MoWVNbTa)­S 2 . The Nb doping (2–11%) of WS 2 or WSe 2 usually improves their HER activity, but there have been few reports on the whole-composition tuning of a W–Nb alloy TMD. ,− …”

Pt modulation of NbSe2 for enhanced activity and stability: a new Pt3Nb2Se8 compound for highly-efficient alkaline hydrogen evolution

“…24–28 For example, Salehi-Khojin's group developed a phase modulation method by cation alloying to fabricate metastable 1T-phase Mo 0.5 Nb 0.5 Se 2 for improved electrical properties. 29 Moreover, Kang's group reported composition-tuned Mo 1− x Nb x Se 2 30 and Nb 1− x V x Se 2 31 with various defects or Se vacancies, to expose abundant activated sites for enhanced catalytic activity. However, although the catalytic activity has been improved through these strategies, they generally suffer from degraded structural stability.…”

“…x Se 231 with various defects or Se vacancies, to expose abundant activated sites for enhanced catalytic activity. However, although the catalytic activity has been improved through these strategies, they generally suffer from degraded structural…”