MXene: a promising photocatalyst for water splitting

Abstract

Identifying suitable photocatalysts for photocatalytic water splitting to produce hydrogen fuel via sunlight is an arduous task by the traditional try-and-error method.Thanks to the progress of density functional theory one can nowadays accelerate the process of finding candidate photocatalysts. In this work, by ab initio calculations we investigated on 48 two-dimensional (2D) transition metal carbides also referred to as MXenes to understand their photocatalytic property. Our results highlight 2D Zr 2 CO 2 and Hf 2 CO 2 as the candidate single photocatalysts for possible high efficient photocatalytic water splitting. The significantly property of 2D Zr 2 CO 2 and Hf 2 CO 2 is that they exhibit unexpectedly high and directionally anisotropic carrier mobility, which may effectively facilitate the migration and separation of photogenerated electron-hole pairs. Meanwhile, these two MXenes also exhibit very good optical absorption performance in the wavelength ranging approximately from 300 to 500 nm.The stability of 2D Zr 2 CO 2 and Hf 2 CO 2 in liquid water is expected to be good based on ab initio molecular dynamics simulations. Finally, the absorption and decomposition of water molecule on the 2D Zr 2 CO 2 surface and the subsequently followed formation process of hydrogen were studied, which contributes to the unraveling of the micro-mechanism of photocatalytic hydrogen production on MXene.Our findings will open a new way to facilitate the discovery and application of MXenes for photocatalytic water splitting. Fig. 3. The electronic band edge positions with respect to the water reduction and oxidation potential levels.Fig. 4. Imaginary part of the dielectric function of 2D Zr 2 CO 2 and Hf 2 CO 2 .

Electronic properties and applications of MXenes: a theoretical review

“…More recent theoretical studies have shown that M 2 CO 2 (M= Ti, Zr, and Hf) exhibits the band gap in the range of 0.92-1.75 eV (calculated using the HSE06 method) [63] with very good light absorbance in the wavelength from 300 to 500 nm [62]. Moreover, it is found that Zr 2 CO 2 and Hf 2 CO 2 exhibit high and directionally anisotropic carrier mobility [62].…”

“…Moreover, it is found that Zr 2 CO 2 and Hf 2 CO 2 exhibit high and directionally anisotropic carrier mobility [62]. The large and anisotropic carrier (electron and hole) mobility in these systems facilitate the migration and separation of photogenerated electron-hole pairs [62].…”

“…The large and anisotropic carrier (electron and hole) mobility in these systems facilitate the migration and separation of photogenerated electron-hole pairs [62]. Therefore, Zr 2 CO 2 and Hf 2 CO 2 can be used as photocatalyst for hydrogen generation from water [62].…”

“…Theoretically, many applications have been proposed for MXenes in electronic [39][40][41][42][43], magnetic [44][45][46][47][48], optical [49,50], thermoelectric [51][52][53][54][55][56], and sensing devices [57], as well as being new potential materials for catalytic and photocatalytic reactions [58][59][60][61][62][63], hydrogen storage media [64,65], and nanoscale superconductivity [66]. Some of MXenes are predicted to be topological insulators with large band gaps involving only d orbitals [67][68][69][70][71].…”

Fabrication of tunable hierarchical MXene@AuNPs nanocomposites constructed by self-reduction reactions with enhanced catalytic performances

“…Presently, research on MXene is mainly focused on lithium ion batteries [28,29], supercapacitors and fuel cells [30][31][32]. Additionally, some special aspects regarding the catalytic performances of MXene materials, such as high-performance oxygen evolution, efficient electrocatalyst for hydrogen evolution and single-atom catalyst for CO oxidation, have been investigated [33][34][35][36][37]. Moreover, in recent years, our group has prepared some novel MXene/Ag composites, MXene-based nanoflower-shaped TiO 2 /C composites, and MXene/magnetic iron oxide nanocomposites, which demonstrate unusual electrocatalytic activity, extraordinary long cycle lifetime lithium storage and catalytic activity for the dehydrogenation of sodium alanates, respectively [38][39][40][41].…”