Adding a New Member to the MXene Family: Synthesis, Structure, and Electrocatalytic Activity for the Hydrogen Evolution Reaction of V₄C₃T_x

Abstract

Two-dimensional transition-metal-based carbides (or nitrides), so-called MXenes, that can be derived from the three-dimensional MAX phases, have attracted considerable attention throughout the past couple of years. The particular structure together with their hydrophilic and metallic nature make them promising candidates for a plethora of applications, such as sensors, electrodes, and catalysts. Obviously, the respective chemical and physical properties are highly dependent on the chemical composition, stoichiometry, and surface structure of the MXene. Here, we introduce a new member of the MXene family, V 4 C 3 T x (T representing the surface groups), based on the chemical exfoliation of the 413 MAX phase V 4 AlC 3 by treatment with aqueous hydrofluoric acid. X-ray powder diffraction data together with scale-bridging electron microscopy studies prove the successful removal of aluminum from the MAX phase structure. The electrocatalytic activity for the hydrogen evolution reaction of this new MXene is tested in acidic solution over the course of 100 cycles. Interestingly, we find a significant improvement of the catalytic performance over time (i.e., the overpotential required to achieve a current density of 10 mA cm −2 decreases by almost 200 mV) that we assign to the removal of an oxide species from the surface of the MXene, as shown by XPS measurements. Our study provides crucial experimental data of the electrocatalytic activity of MXenes together with the evolution of its surface structure that is also relevant for other transition-metal-based MXenes in the context of further potential applications. KEYWORDS: MAX phase, MXene, V 4 AlC 3 , V 4 C 3 T x , hydrogen evolution reaction, electrocatalysis, carbides

Precious‐Metal‐Free Electrocatalysts for Activation of Hydrogen Evolution with Nonmetallic Electron Donor: Chemical Composition Controllable Phosphorous Doped Vanadium Carbide MXene

“…This result corresponds to the highest performance ever reported for MXene phase catalysts in acidic media and it can also be compared with previously reported MoS 2 based materials in the literature (Table S1, Supporting Information). As shown in the summary of recent reports in Figure f, very high overvoltage (>−600 mV) is required in case of Ti‐ (Ti 2 CT x and/or Ti 3 C 2 T x ), V‐based MXene catalysts which are not chemically modified, and Mo‐based (Mo 2 CT x and Mo 2 TiC 2 T x ) or its composite material (MoS 2 /Ti 2 CT x ) . However, previous results mentioned so far show that electrocatalytical activation of the most frequently used Ti‐based MXene can easily induce electrochemical activation via chemical modification, likely simple doping or complexing with heteroatoms such as nitrogen (N) …”

“…These suggest that the surface terminal groups (T x = O, OH, and F) play as the major electrocatalytic active sites for the hydrogen evolution. However, only a limited number of MXenes has been experimentally studied (Ti 2 CT x , Ti 3 C 2 T x , Ti 4 N 3 T x , Mo 2 CT x , Mo 2 Ti 2 CT x , and V 4 C 3 T x ) as electrocatalysts for HER, and unlike theoretical calculations, it was shown that the electrocatalytic performances of Ti‐based MXenes (Ti 2 CT x and Ti 3 C 2 T x ) and V 4 C 3 T x are poor (overpotential ( ƞ ) > 600 mV), with a notable exception for Mo‐based MXene (Mo 2 CT x ) . Therefore, many research groups have attempted to improve electrocatalytic properties through modification of the terminal functional groups on the basal plane of MXenes, and as a representative study, the HER performance of Mo 2 CT x is improved through controlling the terminal functional group coverages on the basal planes by using various etchants .…”

“…In addition to Mo‐ Ti‐based MXene, there have been many other types of MXenes synthesized so far, such as Nb‐ and V‐based MXenes . However, the high H‐binding strength (high Gibbs free energy) causes the poor performance of fully oxygen (O) covered V 2 CT x in HER process, so that research on V 2 CT x based electrocatalysts is still sluggish and no studies on chemical functionalization proceeded. Therefore, the ways to enhance the electrocatalytic activity of V 2 CT x catalysts remains as a challenge.…”

Recent advances in MXenes: From fundamentals to applications

“…Inherited from the MAX phases, the 2D M n+1 X n layers also have hexagonal symmetry and in analogy to graphene, which has hexagonal symmetry, they have been named MXenes. Over [3,27,28,29,30,31,32,33].…”

Environmental Stability of MXenes as Energy Storage Materials

“…Subsequently, a series of different MXenes materials, which possesses various M or/and C or/and n, are synthesized and reported using similar wet chemical etching method, and the naming rules follow the convention described above. For example, Zr 3 C 2 T X , Ti 4 N 3 T X , V 4 C 3 T X , Ta 4 C 3 T X , Ti 2 CT X , V 2 CT X , Nb 4 C 3 T X , Cr 2 CT X (Naguib et al, 2013;Ghidiu et al, 2014b;Urbankowski et al, 2016;Yang et al, 2016;Zhou et al, 2016;Tran et al, 2018;Wu et al, 2018;Xu et al, 2019). In the early stage, MXenes family were roughly classified into the following three categories according to the variable n: M 4 X 3 , M 3 X 2 , and M 2 X (Khazaei et al, 2018).…”