Effects of a TiC substrate on the catalytic activity of Pt for NO reduction

Theoretical investigation of synergistically boosting the anchoring and electrochemical performance of lithiophilic/sulfiphilic transition metal carbides for lithium-sulfur batteries

Lithium-sulfur (Li-S) battery is one of the most promising next-generation energy-storage systems with a high energy density and low cost. However, their commercial applications face several challenges, such as the shuttle effect caused by the soluble lithium polysulfide (LiPSs) intermediates and the sluggish sulfur redox reaction. In this article, we systematically investigated the anchoring and electrochemical performance of a series of transition metal carbides (TMCs: TiC, VC, ZrC, NbC, HfC, TaC) as cathode materials for Li-S batteries by theoretical calculations. The lithiophilic/sulfiphilic non-polar (001) surfaces of TMCs can offer moderate binding strength with LiPS intermediates, ensuring good performance of sulfur immobilization. These TMCs can also facilitate lithium diffusion, indicating the good rate performance of Li-S batteries. We also demonstrated that the studied TMCs can be classified into two classes according to their catalytic activity for Li2S decomposition which originated from their different electronic structural features. Furthermore, TiC, ZrC, and HfC exhibited excellent bifunctional electrochemical activity through reducing the Gibbs free energy for sulfur reduction reactions (SRRs) and lowering the barrier for Li2S decomposition which facilitates accelerating electrode kinetics and elevating utilization of sulfur. Our results offer a systematic approach to designing and screening non-polar materials for high-performance Li-S batteries, based on the rational electronic structure and lattice match strategy.

Liquid-Metal-Assisted Synthesis of Single-Crystalline TiC Nanocubes with Exposed {100} Facets for Enhanced Electrocatalytic Activity in the Hydrogen Evolution Reaction

Although TiC nanostructures show promise as non-noble-metal-based electrocatalysts, improved synthesis methods are required. Herein, single-crystalline TiC nanocubes with exposed {100} facets are grown by combusting TiO₂  + kMg + C reactive mixtures (k = 4-6.5 mol) in argon. During the synthesis, the temperature increases to 1200-1550 °C and excess Mg (2-4.5 mol) forms a liquid pool. The obtained TiC nanocubes have edge lengths of 50-300 nm and surface areas of 12.2-30.05 m² g^-1 . Insights into the TiC nanocube formation mechanism are obtained using density functional theory modeling of the surface energies of TiC nanocrystals and shape visualization using the Wulff construction method. During TiC nucleation and growth within the Mg melt, liquid Mg likely acts as a capping agent for {111} facets, thus promoting the formation of {100} facets. The TiC nanocubes show high electrocatalytic activity for the hydrogen evolution reaction, with a lower overpotential (0.298 V at 10 mA cm^-2 ) than other TiC nanostructures (0.400-0.815 V).

Stability and Catalytic Performance of Single-Atom Supported on Ti2 CO2 for Low-Temperature CO Oxidation: A First-Principles Study

Based on first-principles calculations, the potential of Ti₂ CO₂ monolayer (MXene) as a single-atom catalyst (SAC) support for 3d transition metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is studied for CO oxidation. We first screen the support effect according to the stability of a single metal atom and find that Sc and Ti supported on Ti₂ CO₂ have stronger adsorption energy than the cohesive energy of their bulk counterparts and therefore, we selected Sc and Ti supported on Ti₂ CO₂ for further catalytic reactions. The stability and the potential catalytic reactivity are verified by electronic structure and charge transfer analysis. Both Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms are considered in this study, and lower energy barriers of 0.002 and 0.37 eV were found in the ER mechanism compared to the LH mechanism, which are 0.25 and 0.34 eV for Sc and Ti catalysts, respectively. Moreover, kinetic ER and LH mechanisms are favorable for both Sc- and Ti/Ti₂ CO₂ because of the comparable energy barrier to other metals and SAC supported on 2D materials. However, Ti/Ti₂ CO₂ catalyst is thermodynamically unfavorable. Based on these calculations, we propose that Sc supported on Ti₂ CO₂ is the best catalyst for CO-oxidation. The current study not only broadens the scope of the single-atom Sc catalyst but also extends the consideration of MXene support for catalyst optimization.

The Synthesis, Structure, Morphology Characterizations and Evolution Mechanisms of Nanosized Titanium Carbides and Their Further Applications

It is widely known that the special performances and extensive applications of the nanoscale materials are determined by their as-synthesized structures, especially their growth sizes and morphologies. Hereinto, titanium carbides, which show brilliant comprehensive properties, have attracted considerable attention from researchers. How to give full play to their potentials in the light-weight manufacture, microwave absorption, electromagnetic protection, energy conversion and catalyst areas has been widely studied. In this summarized article, the synthesis methods and mechanisms, corresponding growth morphologies of titanium carbides and their further applications were briefly reviewed and analyzed according to their different morphological dimensions, including one-dimensional nanostructures, two-dimensional nanosheets and three-dimensional nanoparticles. It is believed that through the investigation of the crystal structures, synthesis methods, growth mechanisms, and morphology characterizations of those titanium carbides, new lights could be shed on the regulation and control of the ceramic phase specific morphologies to meet with their excellent properties and applications. In addition, the corresponding development prospects and challenges of titanium carbides with various growth morphologies were also summarized.

An electronic perturbation in TiC supported platinum monolayer catalyst for enhancing water-gas shift performance: DFT study

The water-gas shift (WGS) reaction behaviors over the TiC(0 0 1) supported Pt monolayer catalyst (Pt_ML/TiC(0 0 1)) are investigated by using the spin-unrestricted density functional theory calculations. Importantly, we find that the Pt_ML/TiC(0 0 1) system exhibits a much lower density of Pt-5d states nearby the Fermi level compared with that for Pt(1 1 1), and the monolayer Pt atoms undergo an electronic perturbation when in contact with TiC(0 0 1) support that would strongly improve the WGS activity of supported Pt atoms. Our calculations clearly indicate that the dominant reaction path follows a carboxyl mechanism involving a key COOH intermediate, rather than the common redox mechanism. Furthermore, through the detailed comparisons, the results demonstrate that the strong interactions between the monolayer Pt atoms and TiC(0 0 1) support make Pt_ML/TiC(0 0 1) a highly active catalyst for the low-temperature WGS reaction. Following the route presented by Bruix et al (2012 J. Am. Chem. Soc. 134 8968-74), the positive effect derived from strong metal-support interaction in the metal/carbide system is revealed.

Single Pd atomic catalyst on Mo2CO2 monolayer (MXene): unusual activity for CO oxidation by trimolecular Eley–Rideal mechanism

A Pd atom Mo₂CO₂ exhibits excellent stability and high activity to CO oxidation.

First-principles investigation of H2S adsorption and dissociation on titanium carbide surfaces

The adsorption and dissociation reactions of H₂S on TiC(001) are investigated using first-principles density functional theory calculations. The geometric and electronic structures of the adsorbed S-based species (including H₂S, SH and S) on TiC(001) are analyzed in detail. It is found that the H₂S is bound weakly, while SH and atomic S are bound strongly on the TiC(001) surface. The transition state calculations show that the formation of SH from H₂S (H₂S → SH + H) is very easy, while the presence of a co-adsorbed H will inhibit the further dissociation of SH (SH + H → S + H + H). In contrast, the hydrogenation of the adsorbed SH is rather easy (SH + H → H₂S). Therefore, the dissociative SH can be removed via the hydrogenation reaction. It is concluded that it is difficult for H₂S to dissociate completely to form atomic S and poison the TiC surface. The results will further provide understanding of the mechanism of the sulfur tolerance of the TiC anode of proton exchange membrane fuel cells (PEMFCs).

Configurations and characteristics of boron and B36 clusters

Characteristics of the ring and linear structures of the boron cluster B₃₆ and its doped clusters were investigated with DFT/B3LYP/6-31G. The results illustrate that the ring B₃ structure is the most stable configuration compared with other rings. Odd and even linear structures have different bonding; there is one different bond in the center of even linear structures, while the remaining bonds have left and right symmetry. The B₃₆ cluster upholds the configuration rule of pure ring and linear molecules. However, the N-doped B₃₆N cluster exhibits obvious distortion compared with the B₃₆ molecule. The impurity N changes the structure of the energy band of the B₃₆ cluster. The wavelength of absorption spectra and electronic circular dichroism of the N-doped B₃₆N cluster shifts to a longer wavelength compared with that of the B₃₆ cluster.