FeBO3 as a low cost and high-performance anode material for sodium-ion batteries

The research of borate materials as sodium-ion batteries (SIBs) anode is still in the early stages, but the boron polyoxoanions are attracting intense interest due to their low atomic weight and high electronegative features. In this work, FeBO₃ was prepared with low-cost raw materials and evaluated as SIBs anode. The FeBO₃ shows a high reversible capacity of 328 mAh/g at the current density of 0.4 A/g. In addition, the electrochemical performance of FeBO₃ can be improved by carbon coating. The prepared carbon-coated FeBO₃ composite has a reversible capacity of 426 mAh/g (at 0.4 A/g) and an outstanding rate capability of 272 mAh/g (at 1.6 A/g). Furthermore, the sodium storage mechanism of FeBO₃ was studied by in-situ XRD and ex-situ XPS.     

Ternary BiOBr/TiO2/Ti3C2Tx MXene nanocomposites with heterojunction structure and improved photocatalysis performance

The rational design and construction of heterojunction structure is an effective strategy to improve the photocatalytic performance. Herein, a series of BiOBr nanosheets-immobilized TiO₂/Ti₃C₂T_x MXene hybrid materials with heterojunction structure were synthesized by a facial one-step hydrothermal method. The ternary composites show outstanding performance as photocatalysts for the degradation of rhodamine B due to the optimized synergetic effects of BiOBr, TiO₂ and Ti₃C₂T_x. The improved photocatalytic performance is remarkably attributed to the construction of a heterojunction between TiO₂ and BiOBr due to their well-matching of energy band position, which can enhance the absorption for visible light and promote the transfer of photo-generated charge carriers. Moreover, Ti₃C₂T_x acts as an electron trap to further accelerate the separation of photo-generated electrons and holes.     

Robust and easily retrievable Pd/Ti_3C_2T_x■graphene hydrogels for efficient catalytic hydrogenation of nitroaromatic compounds

Ti_3C_2T_x has been emerging as an attractive platform to prepare composite catalysts,and their assembly into integrated catalytic mate rials repre sents a key step forward toward practical applications.Howeve r,the swelling behavior of Ti_3C_2T_x leads to significant structure change,which challenges the stability of Ti_3C_2T_x-based integrated functional materials for catalytic applications.Here we report a facile synthesis of Pd/Ti_3C_2T_x■graphene hydrogels in which Pd/Ti_3C_2T_x are spatially encapsulated in the 3 D porous graphene framework.The porous interconnected structure not only affords efficient mass transfer and desirable functional accessibility to catalytic active sites,but also effectively buffers the swelling behavior of Ti_3C_2T_x.When applied for catalytic hydrogenation of nitroaromatic compounds,the mechanically robust Pd/Ti_3C_2T_x■graphene hydrogels exhibit efficient activities,easy separability,and good cyclability.This work is expected to promote the application of Ti_3C_2T_x-based functional materials for practical applications involving interactions with salt solutions,such as supercapacitors,catalysis,and water purification.     

Plasmon-enabled N2 photofixation on partially reduced Ti3C2 MXene

Benefiting from the superior conductivity, rich surface chemistry and tunable bandgap, Ti₃C₂ MXene has become a frontier cocatalyst material for boosting the efficiency of semiconductor photocatalysts. It has been theoretically predicted to be an ideal material for N₂ fixation. However, the realization of N₂ photofixation with Ti₃C₂ as a host photocatalyst has so far remained experimentally challenging. Herein, we report on a sandwich-like plasmon- and an MXene-based photocatalyst made of Au nanospheres and layered Ti₃C₂, and demonstrate its efficient N₂ photofixation in pure water under ambient conditions. The abundant low-valence Ti (Ti^(4−x)+) sites in partially reduced Ti₃C₂ (r-Ti₃C₂) produced by surface engineering through H₂ thermal reduction effectively capture and activate N₂, while Au nanospheres offer plasmonic hot electrons to reduce the activated N₂ into NH₃. The Ti^(4−x)+ active sites and plasmon-generated hot electrons work in tandem to endow r-Ti₃C₂/Au with remarkably enhanced N₂ photofixation activity. Importantly, r-Ti₃C₂/Au exhibits ultrahigh selectivity without the occurrence of competing H₂ evolution. This work opens up a promising route for the rational design of efficient MXene-based photocatalysts.

N₂ photofixation in water is realized under ambient conditions using partially reduced Ti₃C₂ MXene that is interlaminated with Au nanospheres.     

Lithium storage properties of Ti3C2Tx (Tx = F,Cl, Br) MXenes

In this work, Ti₃C₂T_x MXene with -F, -Cl and -Br surface terminations are synthesized and the effect of these halogen terminations on the lithium storage properties is investigated. A maximum Li⁺ storage capacity of 189 mAh/g is achieved with Ti₃C₂Br_x MXene much higher than Ti₃C₂Cl_x and Ti₃C₂F_x with 138 mAh/g and 123 mAh/g, respectively. Density functional theory (DFT) calculation shows that the adsorption formation energy of halogen atoms on Ti atoms follows the trend of Ti-F > Ti-Cl > Ti-Br, leading to the same trend in the content of terminations on corresponding MXenes. In addition, inevitable exposure of MXene to oxygen causes competition between halogen and oxygen. Theoretical results show Ti₃C₂Br_x MXene has the highest Ti to O ratio and the lowest Ti to Br ratio, the high lithium affinity of O explains the maximum Li-ion storage capacity with Ti₃C₂Br_x MXene. This work shed light on the opportunity for achieving improved lithium storage properties of MXene electrodes by regulating the surface chemistry.     

A Hybrid Assembly of MXene with NH2−Si Nanoparticles Boosting Lithium Storage Performance

A facile hybrid assembly between Ti₃C₂T_x MXene nanosheets and (3‐aminopropyl) triethoxylsilane‐modified Si nanoparticles (NH₂?Si NPs) was developed to construct multilayer stacking of Ti₃C₂T_x nanosheets with NH₂?Si NPs assembling together (NH₂?Si/Ti₃C₂T_x). NH₂?Si/Ti₃C₂T_x exhibits a significantly enhanced lithium storage performance compared to pristine Si, which is attributed to the robust crosslinking architecture and considerably improved electrical conductivity as well as shorter Li⁺ diffusion pathways. The optimized NH₂?Si/Ti₃C₂T_x anode with Ti₃C₂T_x: NH₂?Si mass ratio of 4 : 1 displays an enhanced capacity (864 mAh g^?1 at 0.1 C) with robust capacity retention, which is significantly higher than those of NH₂?Si NPs and Ti₃C₂T_x anodes. Furthermore, this work demonstrates the important effect of the MXene‐based electrode architecture on the electrochemical performance and can guide future work on designing high‐performance Si/MXene hybrids for energy storage applications.     

In situ decoration of CoP/Ti3C2Tx composite as efficient electrocatalyst for Li-oxygen battery

Application of Li-oxygen (Li-O₂) battery is in urgent need of bifunctional ORR/OER electrocatalyst. A surface-functionalization CoP/Ti₃C₂T_x composite was fabricated theoretically, with the optimized electronic structure and more active electron, which is beneficial to the electrochemical reaction. The accordion shaped Ti₃C₂T_x is featured with large specific surface area and outstanding electronic conductivity, which is beneficial for the adequate exposure of active sites and the deposition of Li₂O₂. Transition metal phosphides provide more electrocatalytic active sites and present good electrocatalytic effect. The CoP/Ti₃C₂T_x composite served as the electrocatalyst of Li-O₂ battery reaches a high specific discharge capacity of 17,413 mAh/g at 100 mA/g and the lower overpotential of 1.25 V, superior to those of the CoP and Ti₃C₂T_x individually. The composite of transition metal phosphides and MXene are applied in Li-O₂ battery, not only demonstrating higher cycling stability of the prepared CoP/Ti₃C₂T_x composite, but pointing out the direction for their electrochemical performance improvement.     

3D crumbled MXene for high-performance supercapacitors

MXene materials have recently attracted considerable attention in energy storage application owing to their metallic conductivity, 2D structure and tunable surface terminations. However, the restacking of 2D MXene nanosheets hinders the ion transport and accessibility to the surface, resulting in adverse effect on their electrochemical performances. Here, with the assistance of hexamethylenetetramine (C₆H₁₂N₄), 2D Ti₃C₂T_x MXene nanosheets were fabricated into a 3D architecture with crumbled and porous structure through an electrostatic self-assembly followed by annealing. The resultant 3D structure can expose massive active sites and facilitates the ion transport, which is beneficial for sufficient utilization of the outstanding superiorities of the MXene. Therefore, as a pseudocapacitive material, the 3D crumpled and porous Ti₃C₂T_x MXene shows a gravimetric capacitance of 333 F/g at 1 A/g, and maintains 261 F/g and 132 F/g at ultrahigh current densities of 100 A/g and 1000 A/g, respectively, revealing promising potential for application in supercapacitors.     

Surface Engineering Strategy Using Urea To Improve the Rate Performance of Na2Ti3O7 in Na-Ion Batteries

Na₂Ti₃O₇ (NTO) is considered a promising anode material for Na-ion batteries due to its layered structure with an open framework and low and safe average operating voltage of 0.3 V vs. Na⁺/Na. However, its poor electronic conductivity needs to be addressed to make this material attractive for practical applications among other anode choices. Here, we report a safe, controllable and affordable method using urea that significantly improves the rate performance of NTO by producing surface defects such as oxygen vacancies and hydroxyl groups, and the secondary phase Na₂Ti₆O₁₃. The enhanced electrochemical performance agrees with the higher Na⁺ ion diffusion coefficient, higher charge carrier density and reduced bandgap observed in these samples, without the need of nanosizing and/or complex synthetic strategies. A comprehensive study using a combination of diffraction, microscopic, spectroscopic and electrochemical techniques supported by computational studies based on DFT calculations, was carried out to understand the effects of this treatment on the surface, chemistry and electronic and charge storage properties of NTO. This study underscores the benefits of using urea as a strategy for enhancing the charge storage properties of NTO and thus, unfolding the potential of this material in practical energy storage applications.     

Pt immobilized spontaneously on porous MXene/MAX hybrid monolith for hydrogen evolution reaction

Designing efficient electrocatalysts with low Pt loadings for hydrogen evolution reaction(HER) is urgently required for renewable and sustainable energy conversion.Here,we report a strategy that Pt nanoparticulates are spontaneously immobilized on porous MXene/MAX monolith as HER catalysts by utilizing the redox reaction between Ti_3C_2T_x MXene and [PtCl_4]~2 in H_2 PtCl_6 aqueous solution.By taking advantage of homogeneously distributed Pt nanoparticulates on highly electrically conductive porous Ti_3C_2T_x/Ti_3AlC_2 monolith,the as-prepared electrocatalysts show high catalytic performance for hydrogen evolution.Specifically,the binder-free electrocatalysts have Pt loadings as low as 8.9 μg/cm~2,with low overpotential of 43 mV at a curre nt density of 10 mA/cm~2 and low Tafel slope that three times lower than porous Ti_3C_2T_x/Ti_3AlC_2 without Pt loading.This strategy offers a new approach to constructing ultra-low Pt-loading HER catalysts on the basis of in situ redox reaction between noble metal ions and MXenes.     

Improving Na+ transport kinetics and Na+ storage of hierarchical rhenium-nickel sulfide (ReS2@NiS2) hollow architecture by assembling layered 2D-3D heterostructures

Mixed metal sulfides have been widely used as anode material of sodium-ion batteries (SIBs) because of their excellent conductivity and sodium ion storage performance. Herein, ReS₂@NiS₂ heterostructures have been triumphantly designed and prepared through anchoring ReS₂ nanosheet arrays on the surface of NiS₂ hollow nanosphere. Specifically, the carbon nanospheres was used as hard template to synthesize NiS₂ hollow spheres as the substrate and then the ultrathin two-dimensional ReS₂ nanosheet arrays were uniformly grown on the surface of NiS₂. The internal hollow property provides sufficient space to relieve the volume expansion, and the outer two-dimensional nanosheet realizes the rapid electron transport and insertion/extraction of Na⁺. Owing to the great improvement of the transport kinetics of Na⁺, NiS₂@ReS₂ heterostructure electrode can achieve a high specific capacity of 400 mAh/g at the high current density of 1 A/g and still maintain a stable cycle stability even after 220 cycles. This hard template method not only paves a new way for the design and construct binary metal sulfide heterostructure electrode materials with outstanding electrochemical performance for Na⁺ batteries but also open up the potential applications of anode materials of SIBs.     

X-ray crystal structures and solution dynamics of sodium organofluorotitanates [Na{Ti2(C5Me5)2F7}] and [NaTi6(C5Me5)5F20(H2O)]·(THF)

[Na{Ti₂(C₅Me₅)₂F₇}] (1) was prepared from sodium fluoride and [{Ti(C₅Me₅)F₃}₂] [H.W. Roesky, et al., Angew. Chem. Int. Ed. Engl. 31 (1992) 864-866]. The solid-state 1 consists of a polymeric chain of two rows of dititanate anions [Ti₂(C₅Me₅)₂F₇]⁻ connected by sodium ions in the middle of the chain. Each sodium ion is coordinated by five fluorine atoms from three [Ti₂(C₅Me₅)₂F₇]⁻ anions. The variable-temperature ¹⁹F NMR of CD₃CN solution of 1 revealed interconversions of monomeric species [Na(CD₃CN)_n{Ti₂(C₅Me₅)₂F₇}] (1solv) with different number of CD₃CN ligands on the sodium ion. The addition of HMPA to the CD₃CN solution of 1 allows ¹⁹F NMR observation of 1·HMPA (1a) and 1·HMPA·CD₃CN (1b) in the slow exchange. The solid-state structure of [NaTi₆(C₅Me₅)₅F₂₀(H₂O)]·(THF) (2·THF) reveals the sodium ion coordinated by four fluorine atoms from the anion [Ti₂(C₅Me₅)₂F₇]⁻ and by three fluorine atoms from the cluster [Ti₄(C₅Me₅)₃F₁₃(H₂O)].     

Achieving high yield of Ti3C2Tx MXene few-layer flakes with enhanced pseudocapacior performance by decreasing precursor size

Ti₃C₂T_x, a most studied member of MXene family, shows promise as a candidate electrode for pseudocapacitor due to its electronic conductivity and hydrophilic surface. However, the unsatisfactory yield of Ti₃C₂T_x few-layer flakes significantly restricted it in real applications. Here, we proposed a simple solution to boost the yield of Ti₃C₂T_x few-layer flakes by decreasing precursor size. When using the small 500 mesh Ti₃AlC₂ powders as raw material, high yield of 65% was successfully achieved. Moreover, the as-received small flakes also exhibit an enhanced pseudocapacior performance owing to their excellent electrical conductivity, expanded interlayer space and more O content on the surface. This work not only sheds light on the cost effective mass production of Ti₃C₂T_x few-layer flakes, but also provides an efficient solution for the design of MXene electrodes with high pseudocapacior performance.     

Synthesis, structure, and ionic conductivity of Na5Li3Ti2S8

The compound Na₅Li₃Ti₂S₈ has been synthesized by the reaction of Ti with a Na/Li/S flux at 723 K. Na₅Li₃Ti₂S₈ crystallizes in a new structure type with four formula units in space group C2/c of the monoclinic system. The structure contains three crystallographically independent Na⁺ cations and two crystallographically independent Li⁺ cations. Na₅Li₃Ti₂S₈ possesses a channel structure that features two-dimensional layers built from Li(1)S₄ and TiS₄ tetrahedra. The layers, which are stacked along c, comprise eight-membered rings and sixteen-membered rings. Na(3)⁺ cations are located between the eight-membered rings and Na(1)⁺, Na(2)⁺, and Li(2)⁺ cations are located between the sixteen-membered rings. These cations are each octahedrally coordinated by six S²⁻ anions. The ionic conductivity σ_T of Na₅Li₃Ti₂S₈ ranges from 8.8×10⁻⁶ S/cm at 303 K to 3.8×10⁻⁴ S/cm at 483 K. The activation energy E_a is 0.40 eV.     

二维层状Ti3C2Tx-MXene@VS2用于高性能锂离子电池负极

为探索一种高性能的锂离子电池负极材料,采用酸刻蚀法制备了高导电性、高稳定性的二维层状Ti₃C₂T_x,通过溶剂热法制备了具有高理论比容量的花瓣状VS₂纳米片,再经过简单的液相混合得到了二维层状Ti₃C₂T_x-MXene@VS₂复合物。通过扫描电子显微镜、透射电子显微镜、X射线光电子能谱、X射线衍射和能谱分析对复合材料的形貌和结构进行了表征,采用循环伏安、恒流充放电、长循环和交流阻抗谱对复合材料的电化学性能进行了研究。结果表明：VS₂纳米片均匀地分布在Ti₃C₂T_x的层间及表面,该复合物具有高的可逆容量(电流密度为0.1A·g^-1时,比容量为610.5mAh·g^-1)、良好的倍率性能(电流密度为2A·g^-1时,比容量为197.1mAh·g^-1)和良好的循环稳定性(电流密度为0.2 A·g^-1时,循环600圈后比容量为874.9 mAh·g^-1;电流密度为2 A·g^-1时,循环1 500圈后比容量为115.9mAh·g^-1)。     

Titanium Carbide (Ti3C2Tx) MXene Ornamented with Palladium Nanoparticles for Electrochemical CO Oxidation

Titanium carbide (Ti₃C₂T_x) MXene possesses various unique physicochemical and catalytic properties. However, the electrochemical CO oxidation performance is not yet addressed experimentally. Herein, Ti₃C₂T_x (T_X=OH, O, and F) ordered and exfoliated two-dimensional nanosheets ornamented with semi-spherical palladium nanoparticles (2.5 Wt. %) with an average diameter of (10±1 nm) (denoted as Pd/Ti₃C₂T_x) is rationally designed for the electrochemical CO oxidation. The fabrication process is based on the selective chemical etching of Ti₃AlC₂ and delamination under sonication to form Ti₃C₂Tx nanosheets that are used as a substrate and reducing agent for supporting in situ growth of Pd nanoparticles via impregnation with Pd salt. Interestingly, Pd-free Ti₃C₂T_x displayed inferior CO oxidation activity, while Pd/Ti₃C₂T_x enhanced the CO oxidation activity substantially. This is attributed to the combination of outstanding physicochemical properties of Ti₃C₂T_x and the catalytic merits of Pd nanoparticles.     

Ti3C2: An Ideal Co-catalyst?

How 2D Ti₃C₂ enhances photocatalytic efficiency remains unclear. Now, it is shown that it is graphene quantum dots (GQDs) derived from Ti₃C₂, rather than 2D Ti₃C₂ itself, that play the role of co-catalyst for La₂Ti₂O₇/Ti₃C₂ (LTC) composites during the photocatalytic reaction. After modification of Ti₃C₂ derivatives, the photocatalytic efficiency of La₂Ti₂O₇ is enhanced 16 times over pure La₂Ti₂O₇. Solid-state NMR, Raman, and HRTEM results confirm the existence of GQDs in Ti₃C₂ and LTC composites. The GQDs are formed during the chemical change from Ti₃AlC₂ to Ti₃C₂ via HF etching, as Ti atoms are removed and unsaturated carbon bonds are left, which react with each other to form sp² π-conjugation GQDs. 2D Ti₃C₂ is completely oxidized to CO_x modified TiO_x species, causing Ti₃C₂ to lose its electrical conductivity and the role as co-catalyst. GQDs largely suppress the photogenerated charge recombination of La₂Ti₂O₇, as revealed by the photoluminescence (PL) and transient photocurrent.     

Electrochemical and in-situ X-ray diffraction studies of Ti3C2Tx MXene in ionic liquid electrolyte

2D titanium carbide (Ti₃C₂T_x MXene) showed good capacitance in both organic and neat ionic liquid electrolytes, but its charge storage mechanism is still not fully understood. Here, electrochemical characteristics of Ti₃C₂T_x electrode were studied in neat EMI-TFSI electrolyte. A capacitive behavior was observed within a large electrochemical potential range (from − 1.5 to 1.5 V vs. Ag). Intercalation and de-intercalation of EMI⁺ cations and/or TFSI⁻ anions were investigated by in-situ X-ray diffraction. Interlayer spacing of Ti₃C₂T_x flakes decreases during positive polarization, which can be ascribed to either electrostatic attraction effect between intercalated TFSI⁻ anions and positively charged Ti₃C₂T_x nanosheets or steric effect caused by de-intercalation of EMI⁺ cations. The expansion of interlayer spacing when polarized to negative potentials is explained by steric effect of cation intercalation.     

Ultrathin Ti3C2 nanowires derived from multi-layered bulks for high-performance hydrogen evolution reaction

One-dimensional ultrathin nanowires（NWs） offer a great deal of promising properties for electrochemical energy storage and conversion due to their nanoscale confinement effect and high surface-to-volume ratios. It is highly desirable to precisely design and synthesize ultrathin Ti₃C₂ NWs in the aspect of size,crystalline structure and composition. Here, we report a simple alkalization strategy to design the ultrathin Ti₃C₂ NWs for hydrogen evolution re...     

Memristive Effect in Ti3C2Tx (MXene) Polyelectrolyte Multilayers

The emerging novel class of two-dimensional materials – MХenes – have attracted significant research attention. However, there are only few reports on using the most prominent member of the MXene family, Ti₃C₂T_x, as an active material for memristive devices within a polyelectrolyte matrix and its deposition on inert electrodes like ITO and Pt. In this study, we systematically investigate Ti₃C₂T_x MXenes synthesized with two classical delamination agents, such as lithium chloride and tetramethylammonium hydroxide, to identify the most suitable candidate for memristive device applications. The characteristics of memristors based on the hybrid structures consisting of MXene−polyelectrolyte multilayers, specifically polyethyleneimine (PEI) and poly(sodium 4-styrenesulfonate) (PSS) are explored. The PEI(MXene)/PSS memristor exhibits a voltage threshold (V_SET/RESET) range of 1.5–2.0 V, enabling the transition from a high-resistive state (HRS) to a low-resistive state (LRS), along with a significant current switching ratio of approximately two orders of magnitude. The observed V_SET/RESET difference of approximately 4 V is further supported by density functional theory (DFT) calculated redox potential. These findings underscore the potential of polyelectrolyte-based memristors, such as the in PEI−Ti₃C₂T_x−PSS system, in facilitating the development of highly functional, self-assembled memristive devices with diverse applications.