Two-Dimensional Transition Metal MXene-Based Photocatalysts for Solar Fuel Generation

Abstract

The exploration of advanced and novel photocatalytic materials has been widely investigated in recent years. MXene, a new two-dimensional (2D) transition metal material, is gaining attention as a suitable alternative for promoting photocatalytic performance because of its flexible adjustability of elemental composition, regular layered structure, and excellent electrical conductivity. This Perspective summarizes the recent significant advancements in 2D MXene-based photocatalysts for solar fuel conversion. The rational design and specific effects of MXene-based photocatalysts for photocatalytic solar fuel generation are described. Moreover, the different roles of MXene in MXene-based photocatalysts, such as functional group provider, photocatalytic electronic acceptor, substrate, and cocatalyst, for improving photocatalytic performance are discussed. Further discussion about the challenges and optimizations for improvements of 2D MXene and MXene-based photocatalysts in the context of promising solar fuel generation is also presented.

Positioning MXenes in the Photocatalysis Landscape: Competitiveness, Challenges, and Future Perspectives

“…The 2D structure and high electronic conductivity of MXenes make people naturally recall the star 2D material, graphene. [64] Thus far, the progress on applying MXenes for photocatalysis is mainly concentrated on using MXenes as electron acceptors to promote the separation of charge carriers in semiconductors, [16,24,25,[45][46][47][48] as graphene has done over the past decade. [65][66][67] As such, we spontaneously encounter the questions: what are the unique properties of MXenes and what can MXenes bring to us for photocatalytic applications?…”

“…Thus far, various semiconductors/ MXenes composites have been constructed and utilized for a broad spectrum of photocatalytic applications, such as environmental remediation, water splitting for hydrogen evolution, CO 2 reduction, and nitrogen photofixation ( Figure 2). [16,[24][25][45][46][47][48] There have been some reviews recapping recent advances in using MXenes-based composites for photocatalytic applications. [16,20,24,25,[45][46][47][48][49] From these previous reviews, we can acknowledge that MXenes have been quickly becoming a research hotspot for constructing composites for photocatalysis.…”

“…[16,[24][25][45][46][47][48] There have been some reviews recapping recent advances in using MXenes-based composites for photocatalytic applications. [16,20,24,25,[45][46][47][48][49] From these previous reviews, we can acknowledge that MXenes have been quickly becoming a research hotspot for constructing composites for photocatalysis. In addition to the valuable information provided in these reviews, it is highly desirable that some key issues of MXenes-based photocatalysis should be reasonably justified, especially the competitiveness and challenges of MXenes as a functional component for photocatalysis, which is the essential goal of the present review.…”

Apparent Potential Difference Boosting Directional Electron Transfer for Full Solar Spectrum‐Irradiated Catalytic H2 Evolution

“…[5][6][7][8][9] Among numerous semiconductor photocatalysts, 2D layered carbon nitride (g-C 3 N 4 ) is a typical reductive visible-light photocatalytic material with a narrow band gap and a low conduction band potential of −1.23 V versus normal hydrogen electrode (NHE) at pH = 7. [9][10][11][12][13][14][15][16][17] g-C 3 N 4 thus has been widely applied to photocatalytically splitting H 2 O into H 2 . [18,19] However, the photo catalytic activity of g-C 3 N 4 is still much low up to now mainly because of the poor charge transfer among layers, which originates from the interlayer electrostatic potential barrier.…”

“…It is known that the electronic structure of g-C 3 N 4 is comprised of sp 2 -hybridized π delocalization electrons with lone electrons on N p z orbitals. [14,[29][30][31][32] If g-C 3 N 4 sheet is curved from planar to tubular structure, the delocalized π electrons will migrate from concave to convex due to the deformation compression in a hybridized intermediate state between sp 2 and sp 3 , [33,34] and finally this uneven distribution of electrons will result in an apparent potential difference between inner and outer surface of the formed g-C 3 N 4 tube (C 3 N 4 T). Thus, the apparent potential difference of C 3 N 4 T as a driving force will promote electrons to overcome the interlayer electrostatic potential barrier, and transfer to outer layers of C 3 N 4 Ts.…”