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Developing highly conductive, stable, and active hydrogen evolution reaction (HER) catalysts is a critical step towards establishing the hydrogen economy. However, there are few catalysts, except for noble metals, that can meet all the requirements. Recently, two-dimensional (2D) transition metal carbon/nitride (MXene) materials have shown excellent performance in catalysis, and have attracted wide attention from researchers. In this study, the effectiveness of non-metal element (B, C, N, P, and S)-doped Ti3C2O2 MXene in the electrocatalytic hydrogen evolution reaction was investigated using density functional theory (DFT) calculations. Non-metal atoms as electron donors can provide additional electrons to the O functional group on the catalyst surface, thereby reducing charge transfer from H to O and the interaction between H and O. The Gibbs free energy (∆GH) of non-metal element-doped Ti3C2O2 is closer to 0 than that of pristine Ti3C2O2, demonstrating better hydrogen evolution performance. Furthermore, in the hydrogen evolution path, the desorption process is more inclined to the Heyrovsky mechanism, and doping greatly reduces the energy barrier of the reaction, thereby improving the catalytic efficiency. The present results prove that doping with non-metallic elements is an effective means of improving the catalytic activity of Ti3C2O2 for hydrogen evolution.

• V Ti -Ti 3 C 2 O 2 and TM-doped (TM=Ti, Pt, Au) α-type Ti 3 C 2 O 2 have the potential to become sensor for SF 6 characteristic decomposition components. • Compared with Ti 3 C 2 (OH) 2 , V Ti -Ti 3 C 2 O 2 shows better adsorption properties to SO 2 , SOF 2 by chemisorption. • TM-doped (TM=Ti, Pt, Au) Ti 3 C 2 O 2 show good adsorption properties to SO 2 , SOF 2 , SO 2 F 2 by physisorption. • The theoretical calculation results are important to guide the experiments on preparing V Ti -Ti 3 C 2 O 2 and TM-doped (TM=Ti, Pt, Au) α-type Ti 3 C 2 O 2 based adsorbent. Detecting the partial discharge in gas-insulated switchgear (GIS) equipment by detecting the type and concentration of SF 6 characteristic decomposition products is very important and effective in ensuring the regular operation of GIS equipment. In this study, V Ti -Ti 3 C 2 O 2 (Ti-deficient Ti 3 C 2 O 2) and TM-doped (TM = Ti, Pt, Au) α-type Ti 3 C 2 O 2 were carried out as the gas-sensing materials. The gas adsorption structures of SO 2 , SOF 2 , and SO 2 F 2 on the surfaces of TM-modified Ti 3 C 2 O 2 were established. Different adsorption systems' adsorption energies, electron densities, state densities, and times for gas desorption were examined using DFT calculations. Following the analysis, physical adsorption of SO 2 , SOF 2 , and SO 2 F 2 occurs on the surface of Pt-Ti 3 C 2 O 2 and Au-Ti 3 C 2 O 2 , while chemical adsorption occurs on the surface of V Ti -Ti 3 C 2 O 2. As a result, it is challenging to remove the gas molecules from the surface of V Ti -Ti 3 C 2 O 2 , while it is simple to remove them from Pt-Ti 3 C 2 O 2 and Au-Ti 3 C 2 O 2 surfaces. At the same time, compared with gas adsorption on the surface of pristine Ti 3 C 2 O 2 , TM-modified Ti 3 C 2 O 2 can improve the adsorption performance of pristine Ti 3 C 2 O 2 on the characteristic decomposition products of SF 6 to a certain extent. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • TM-Ti 3 C 2 O 2 has thermal and chemical stability. • TM-Ti 3 C 2 O 2 is selective to the products produced by CO 2 reduction hydrogenation reaction. • Co-Ti 3 C 2 O 2 has the best catalytic performance for CH 4 production. • Linear relationship between the dependence of U L affinity on *CO, *HCOOH and *OH in the basic steps of CO 2 RR mechanism. Electrocatalytic CO 2 reduction reaction (CO 2 RR) can transform CO 2 into high-value-added chemicals, which is a key step toward alleviating greenhouse gas emissions and achieving carbon neutrality. Therefore, we constructed a transition metal single-atom catalyst anchored on Ti 3 C 2 O 2 (TM-Ti 3 C 2 O 2) through theoretical calculation. The results show that TMs are stable and capable of activating CO 2. The embedding of TM breaks the symmetry of Ti 3 C 2 O 2 , causing different degrees of charge distribution of TM and distinct selectivity to CH 4 products. Co-Ti 3 C 2 O 2 is the optimum candidate for producing CH 4 with limiting potential of −0.21 V. We established a linear relationship between the activity descriptor and the limiting potential of the product, which provided a method for screening efficient TMs. With applied potential, Co, Sc, and V-Ti 3 C 2 O 2 exhibited great advantages in the CO 2 RR to CH 4. This research serves as a point of reference for industrial production and helps to achieve the objective of carbon peaking more efficiently. [ABSTRACT FROM AUTHOR]

[Display omitted] • Schottky junction formation inhibits photogenerated electron-hole complexation. • Regulation of different O vacancy (Vo) concentrations to enhance CO 2 adsorption activity. • The introduction of Vo improves the selectivity of C 2 reduction products. The selectivity of photocatalytic CO 2 reduction has not received deserved attention up to date. As one type of notable product, the C 2 selectivity is much less than those of the predominant C 1 products. However, conversing CO 2 to higher value added C 2 organics would be more attractive and challengeable in coupling active intermediate *CO, which is thought as a key step leading to formation of C 2 products. This paper designs a defective ZnTi-LDHs/Ti 3 C 2 O 2 photocatalyst through density functional theory (DFT) calculation to improve selectivity of the C 2 products by enhancing adsorption activation of CO 2 and C C coupling reaction. The formation of Schottky junction greatly inhibit recombination of the photogenerated electron-hole pairs and increase the density of photogenerated electrons on the defective ZnTi-LDHs/Ti 3 C 2 O 2 surface. Furthermore, the presence of surficial oxygen vacancies changes the adsorption state of CO 2 molecule and make more enriched electrons boost CO 2 adsorption and activation, especially lower the Gibbs free energy barrier for forming the *CO intermediate favored for reducing CO 2 to multi-electron products. Finally, the photocatalytic mechanism and reaction pathway of CO 2 reduction to C 2 products on O-defect-rich ZnTi-LDHs/Ti 3 C 2 O 2 are proposed. Our work provides a new strategy for designing photocatalyst to produce the high value-added C 2 products. [ABSTRACT FROM AUTHOR]

As a typical two-dimensional (2D) MXene, Ti3C2O2 has been considered as a potential material for high-performance hydrogen evolution reaction (HER) catalyst, due to its anticorrosion and hydrophilic surface. However, it is still a challenge to improve the Ti3C2O2 surficial HER catalytic activity. In this work, we investigated the HER activity of Ti3C2O2 after the surface was doped with S, Se, and Te by the first principles method. The results indicated that the HER activity of Ti3C2O2 is improved after being doped with S, Se, Te because the Gibbs free energy of hydrogen adsorption (ΔGH) is increased from −2.19 eV to 0.08 eV. Furthermore, we also found that the ΔGH of Ti3C2O2 increased from 0.182 eV to 0.08 eV with the doping concentration varied from 5.5% to 16.7%. The HER catalytic activity improvement of Ti3C2O2 is attributed to the local crystal structure distortion in catalytic active sites and Fermi level shift leads to the p-d orbital hybridization. Our results pave a new avenue for preparing a low-cost and high performance HER catalyst. [ABSTRACT FROM AUTHOR]