Applications of MXene‐Based Single‐Atom Catalysts

Abstract

Catalytic science, including heterogeneous catalysis, homogeneous catalysis, and enzyme catalysis, is involved in various fields of production and life, including energy, pharmaceuticals, environmental protection and so on. Thereinto, heterogeneous catalysis, which is usually driven by metal-based catalysts, effectively reduces production costs due to its easy recovery nature and thus plays a dominant role in industrial production. However, the distribution of active sites in heterogeneous catalysts is uncontrollable, and it is difficult to utilize the structure-activity relationship to adjust the catalyst performance. Through reducing the size of the nonmetallic catalyst and increasing the exposure of the active site, the catalytic performance can be significantly improved. Thus, design and synthesis of catalysts on atomic scale is an efficient strategy to improve catalytic activity.In 2011, Zhang et al. prepared atomically dispersed Pt species and proposed the concept of single-atom (SA) catalyst for the first time, defining single-atom catalysts (SACs) as a supported catalyst in which metal species are dispersed in the form of isolated atoms. [1] Compared with traditional catalysts, SACs have an atomic utilization efficiency of 100%, and can achieve high catalytic performance under low metal load, which greatly reduces the production cost. [2] Shi et al. loaded only 4.1 wt% Pt SAs on the surface of MoSe 2 , showing excellent alkaline electrocatalytic hydrogen evolution performance. [3] In addition, SACs have the properties of reusability and controllable structure, which combine the advantages of homogeneous and heterogeneous catalysis. [4,5] Usually, single-metal sites have uniform and adjustable coordination structures, showing the superiority of catalyzing specified reactions and improving product selectivity. By changing the activation temperature, Ren et al. synthesized Pt SAs with different electronic environment and oxidation state on Fe 2 O 3 in a controllable manner. [6] Moreover, Pd SAs with different coordination are synthesized by replacing different organic ligands, and the Pd@POL-1 coordinated with organic phosphine showed high catalytic selectivity for the hydrosilylation reaction of internal alkyne. [7] Due to the high cohesive energy, individual metal atoms tend to aggregate to form nanoclusters. [8] To obtain stable and highly dispersed metal atoms, it is usually necessary to anchor the isolated metal atoms onto a substrate, where strong charge transfer would occur through the bonding of the metal atoms to the reactive sites on the substrate. Metal oxide, metal-organic framework, molybdenum disulfide, graphene, and so on are common carriers that can be used to fix metal atoms. [9][10][11][12][13] Among them, 2D materials show good application prospects due to large specific surface area. [14,15] As a new type of 2D materials, metallic carbides, nitrides, or carbonic nitrides (MXenes), with the general structure of M n þ 1 X n T x , where M is transition metal (TM), X is carbon/nitrogen elemen...

Regulating the Local Electronic Structure of Copper Single Atoms with Unsaturated B,O-Coordination for Selective 1O2 Generation

“…Heteroatom doping is regarded as an effective strategy to modulate the electronic structure of SACs by altering the coordinated atoms of the metal center. − Ti 3 C 2 T x MXene was proved to be a promising support for the dispersion and immobilization of single-atom sites through surface negatively charged O terminals, exhibiting excellent catalytic activity for PMS activation. − Moreover, the tunable functional groups and interlayer structure on the surface of Ti 3 C 2 T x MXene are more favorable for coordination modulation and dispersion of metal sites. − Therefore, on the one hand, the introduction of Ti 3 C 2 T x MXene can provide a diverse coordination environment different from M-N x sites; on the other hand, the electronic structure of the metal sites can be further modulated by doping Ti 3 C 2 T x MXene with heteroatoms of different electronegativities, which can reveal the catalytic activity and structure–activity relationship of SACs in Fenton-like reactions. , …”

Anchoring 0D Cd0.5Zn0.5S nanoparticles on a 3D porous N-doped Ti3C2Tx MXene matrix for efficient photocatalytic hydrogen evolution

“…S11, ESI †) further confirms the existence of lattice defects in the TCT MXene nanoflakes, which can be generated by decreasing the thickness of 2D MXene nanoflakes, thus facilitating the escape of some of the original atoms from the lattice to create intrinsic defects. 55,56 Therefore, based on the comprehensive XPS and HRTEM results, it is rational to deduce that the N-TCT MXene matrix is tightly coupled with the CZS nanoparticles by Cd-N bonds, which could act as a directional interfacial electron transfer channel, as schematically shown in Fig. 4f.…”

Rational design of MXene-based single atom catalysts for Na–Se batteries from sabatier principle

“…Various strategies can be employed to create MXene-based SACs, including anchoring into vacancy site, substituting surface atoms, or bonding with surface termination. 23,40 Based on the previous research, 32 a terminated O atom was removed to form a vacancy site on the MXene surface, in which a single zinc atom was embedded to form Zn–M 2 CO 2 . 41 The optimized structures of Zn–M 2 CO 2 are shown in Fig.…”