Phase-Transition Mo_1–xV_xSe₂ Alloy Nanosheets with Rich V–Se Vacancies and Their Enhanced Catalytic Performance of Hydrogen Evolution Reaction

Abstract

Alloys of transition-metal dichalcogenide can display distinctive phase evolution because of their two-dimensional structures. Herein, we report the colloidal synthesis of Mo1–x V x Se2 alloy nanosheets with full composition tuning. Alloying led to a phase transition at x = 0.7 from the semiconducting 2H phase MoSe2 to the metallic 1T phase VSe2. It also produced significant V and Se vacancies, which became the richest in the 2H phase at x = 0.3–0.5. Extensive spin-polarized density functional theory calculations consistently predicted the 2H–1T phase transition at x = 0.7, in agreement with the experimental results. The vacancy formation energy also supports the formation of V and Se vacancies. Alloying in the 2H phase enhanced the electrocatalytic performance toward hydrogen evolution reaction (HER) at x = 0.3 (in 0.5 M H2SO4) or 0.4 (in 1 M KOH). The Gibbs free energy along the HER pathway indicates that this maximum performance is due to the highest concentration of active V and Se vacancy sites.

PEM water electrolysis for hydrogen production: fundamentals, advances, and prospects

“…The 1T phase of TMDs possesses high electrical conductivity and a larger number of active sites compared to the 2H phase [42][43][44], which could result in a higher charger transfer rate in the electrochemical process. Recently, Kang and co-workers [45] successfully synthesized Mo 1-x V x Se 2 alloy nanosheets through a colloidal reaction, which could lead to the phase transition from a semiconducting 2H phase MoSe 2 to the metallic 1T phase VSe 2 (Fig. 3).…”

“…Morozan et al [24] adopted microwave irradiation or heat treatment in a furnace under inert and reductive atmospheres to prepare the bimetallic FeMoS catalyst, which presented a low overpotential of 140 mV at the current density of 10 mA cm −2 . Combining with [45] carbon nanotubes (CNTs), the composite catalyst could operate at 500 mA cm −2 using a voltage of less than 300 mV compared to using Pt as the cathode catalyst in PEM electrolyser. Zhao et al [48] prepared an ultrastable Pd-doped MoS 2 material and supported on a vertical graphene network (VGN@Pd-MoS 2 ), which exhibited a stable operation over 1000 h at 10 mA cm −2 and provide a prospect to replace Pt for PEM electrolysis.…”

“…c Ball-and-stick model of Mo 1-x V x Se 2 with different vacancies. d OER polarization curves and (e) Turnover frequency curves of Mo 1-x V x Se 2 and Pt/C catalysts[45]…”

Phase-transition engineering induced lattice contraction of the molybdenum carbide surface for highly efficient hydrogen evolution reaction

“…26 Despite this considerable research, phasetransition engineering is considered to be an effective approach to tune a catalyst's intrinsic electronic structure, on which the HER performance strongly depends. [27][28][29][30] For instance, Lau and co-workers observed in situ phase transformation from cubic NiSe 2 to hexagonal NiSe during the HER process, where some of the Se À ions lost electrons and rearranged while the other Se À ions gained electrons and bonded with Ni atoms with lattice distortion. The charge transfer from the Se atom to the Ni atom led to enhanced conductivity and a shi of the d-band center, which contributed to improving the HER performance.…”

Highly stable and uniformly dispersed 1T-MoS2 nanosheets co-induced by chemical pressure and 2D template method with high supercapacitor performance

“…19,20 The atomic size mismatch inevitably can lead to the formation of mircostrain, which has been conrmed an effective method to achieve 1T-MoS 2 . [21][22][23][24][25] Considering the different atomic sizes of Mo and W, the partial substitution of W for Mo can cause microstrain, which possibly promotes the 1T phase transformation of MoS 2 . [26][27][28] On the other hand, the external microstrain created by 1T-MoS 2 anchoring on other materials can also stabilize the 1T phase.…”