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.     

A Two‐Dimensional Lamellar Membrane: MXene Nanosheet Stacks

Two‐dimensional (2D) materials are promising candidates for advanced water purification membranes. A new kind of lamellar membrane is based on a stack of 2D MXene nanosheets. Starting from compact Ti₃AlC₂, delaminated nanosheets of the composition Ti₃C₂T_x with the functional groups T (O, OH, and/or F) can be produced by etching and ultrasonication and stapled on a porous support by vacuum filtration. The MXene membrane supported on anodic aluminum oxide (AAO) substrate shows excellent water permeance (more than 1000 L m⁻² h⁻¹ bar⁻¹) and favorable rejection rate (over 90 %) for molecules with sizes larger than 2.5 nm. The water permeance through the MXene membrane is much higher than that of the most membranes with similar rejections. Long‐time operation also reveals the outstanding stability of the MXene membrane for water purification.     

Fluorine‐Free Synthesis of High‐Purity Ti3C2Tx (T=OH,O) via Alkali Treatment

MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy‐related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium‐ion battery and supercapacitor performance. Here an alkali‐assisted hydrothermal method is used to prepare a MXene Ti₃C₂T_x (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti₃C₂T_x with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti₃C₂T_x film electrode (ca. 52 μm in thickness, ca. 1.63 g cm^?3 in density) is 314 F g^?1 via gravimetric capacitance at 2 mV s^?1 in 1 m H₂SO₄. This surpasses (by ca. 214 %) that of the multilayer Ti₃C₂T_x prepared via HF treatments. This fluorine‐free method also provides an alkali‐etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.     

Room‐Temperature Carbide‐Derived Carbon Synthesis by Electrochemical Etching of MAX Phases

Porous carbons are widely used in energy storage and gas separation applications, but their synthesis always involves high temperatures. Herein we electrochemically selectively extract, at ambient temperature, the metal atoms from the ternary layered carbides, Ti₃AlC₂, Ti₂AlC and Ti₃SiC₂ (MAX phases). The result is a predominantly amorphous carbide‐derived carbon, with a narrow distribution of micropores. The latter is produced by placing the carbides in HF, HCl or NaCl solutions and applying anodic potentials. The pores that form when Ti₃AlC₂ is etched in dilute HF are around 0.5 nm in diameter. This approach forgoes energy‐intensive thermal treatments and presents a novel method for developing carbons with finely tuned pores for a variety of applications, such as supercapacitor, battery electrodes or CO₂ capture.     

Synthesis of Carbon/Sulfur Nanolaminates by Electrochemical Extraction of Titanium from Ti2SC

Herein we electrochemically and selectively extract Ti from the MAX phase Ti₂SC to form carbon/sulfur (C/S) nanolaminates at room temperature. The products are composed of multi‐layers of C/S flakes, with predominantly amorphous and some graphene‐like structures. Covalent bonding between C and S is observed in the nanolaminates, which render the latter promising candidates as electrode materials for Li‐S batteries. We also show that it is possible to extract Ti from other MAX phases, such as Ti₃AlC₂ , Ti₃SnC₂ , and Ti₂GeC, suggesting that electrochemical etching can be a powerful method to selectively extract the “M” elements from the MAX phases, to produce “AX” layered structures, that cannot be made otherwise. The latter hold promise for a variety of applications, such as energy storage, catalysis, etc.     

Fluorine‐Free Synthesis of High‐Purity Ti3C2Tx (T=OH,O) via Alkali Treatment

MXenes, 2D compounds generated from layered bulk materials, have attracted significant attention in energy‐related fields. However, most syntheses involve HF, which is highly corrosive and harmful to lithium‐ion battery and supercapacitor performance. Here an alkali‐assisted hydrothermal method is used to prepare a MXene Ti₃C₂T_x (T=OH, O). This route is inspired from a Bayer process used in bauxite refining. The process is free of fluorine and yields multilayer Ti₃C₂T_x with ca. 92 wt % in purity (using 27.5 m NaOH, 270 °C). Without the F terminations, the resulting Ti₃C₂T_x film electrode (ca. 52 μm in thickness, ca. 1.63 g cm⁻³ in density) is 314 F g⁻¹ via gravimetric capacitance at 2 mV s⁻¹ in 1 m H₂SO₄. This surpasses (by ca. 214 %) that of the multilayer Ti₃C₂T_x prepared via HF treatments. This fluorine‐free method also provides an alkali‐etching strategy for exploring new MXenes for which the interlayer amphoteric/acidic atoms from the pristine MAX phase must be removed.     

The Ti3AlC2 MAX Phase as an Efficient Catalyst for Oxidative Dehydrogenation of n‐Butane

Dehydrogenation or oxidative dehydrogenation (ODH) of alkanes to produce alkenes directly from natural gas/shale gas is gaining in importance. Ti₃AlC₂, a MAX phase, which hitherto had not been used in catalysis, efficiently catalyzes the ODH of n‐butane to butenes and butadiene, which are important intermediates for the synthesis of polymers and other compounds. The catalyst, which combines both metallic and ceramic properties, is stable for at least 30 h on stream, even at low O₂:butane ratios, without suffering from coking. This material has neither lattice oxygens nor noble metals, yet a unique combination of numerous defects and a thin surface Ti_1?yAl_yO_2?y/2 layer that is rich in oxygen vacancies makes it an active catalyst. Given the large number of compositions available, MAX phases may find applications in several heterogeneously catalyzed reactions.     

H+−H− Pairs in Partially Oxidized MAX Phases for Bifunctional Catalytic Conversion of Furfurals into Linear Ketones

Currently, less favorable C=O hydrogenation and weak concerted acid catalysis cause unsatisfactory catalytic performance in the upgrading of biomass-derived furfurals (i.e., furfural, 5-methyl furfural, and 5-hydroxymethyl furfural) to ketones (i.e., cyclopentanone, 2,5-hexanedione, and 1-hydroxyl-2,5-hexanedione). A series of partially oxidized MAX phase (i.e., Ti₃AlC₂, Ti₂AlC, Ti₃SiC₂) supporting Pd catalysts were fabricated, which showed high catalytic activity; Pd/Ti₃AlC₂ in particular displayed high performance for conversion of furfurals into targeted ketones. Detailed studies of the catalytic mechanism confirm that in situ hydrogen spillover generates Frustrated Lewis H⁺−H⁻ pairs, which not only act as the hydrogenation sites for selective C=O hydrogenation but also provide acid sites for ring opening. The close intimate hydrogenation and acid sites promote bifunctional catalytic reactions, substantially reducing the reported minimum reaction temperature of various furfurals by at least 30–60 °C.     

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.     

Functional MXene Materials: Progress of Their Applications

Nowadays, two‐dimensional materials have many applications in materials science. As a novel two‐dimensional layered material, MXene possesses distinct structural, electronic, and chemical properties; thus, it has potential applications in many fields, including battery electrodes, energy storage materials, sensors, and catalysts. Up to now, more than 70 MAX phases have been reported. However, in contrast to the variety of MAX phases, the existing MXene family merely includes Ti₂C, Ti₃C₂, (Ti_1/2, Nb_1/2)₂C, (V_1/2, Cr_1/2)₃C₂, Nb₂C, Ti₃CN, Ta₄C₃, V₂C, and Nb₄C₃. Among these materials, the Ti₃C₂T_x MXene exhibits prominently high volumetric capacitance, and the rate at which it transports electron is suitable for electrode materials in batteries and supercapacitors. Hence, Ti₃C₂T_x is commonly utilized as an electrode material in ion batteries such as Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, and Al³⁺ batteries. What is more, Ti₂C has the biggest specific surface area among all of these potential MXene phases, and therefore, Ti₂C has remarkably high gravimetric hydrogen storage capacities. In addition, Ti₂CO₂ materials display extremely high activity for CO oxidation, which makes it possible to design catalysts for CO oxidation at low temperatures. Furthermore, Ti₃C₂T_x with O, OH, and/or F terminations can be used for water purification owing to excellent water permeance, favorable filtration ability, and long‐time operation ability. This review supplies a relatively comprehensive summary of various applications of MXenes over the past few years.     

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.     

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.     

Functional Group Modification and Bonding Characteristics of Ti3C2 MXene-Organic Composites from First-Principles Calculations

The unique physical structure and abundant surface functional groups of MXene make the grafted organic molecules exhibit specific electrical and optical properties. This work reports the results of first-principles calculations to investigate the composite systems formed by different organic molecular monomers, namely acrylic acid (AA), acrylamide (AM), 1-aziridineethanol (1-AD) and glucose, and Ti₃C₂ MXene saturated with different functional groups, namely −OH, −O and −F. The results show that the interaction between organic molecules and the MXene surface depends on the type of functional groups of the organic molecules, while the strength of the interaction is determined by the type of surface functional groups and the number of hydrogen bonds. The bare Ti₃C₂ and Ti₃C₂(OH)₂ can readily form strong chemical and hydrogen bonds with AA and AM molecules, leading to strong adsorption energy and a large amount of charge transfer, while the interaction between organic molecules and MXene saturated by −F or −O groups mainly exhibits physical interactions, accompanied by low adsorption energy and a small amount of charge transfer. This research provides theoretical guidance for the synthesis of high-performance MXene organic composite systems.     

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.     

Acceptorless Photocatalytic Dehydrogenation of Furfuryl Alcohol (FOL) to Furfural (FAL) and Furoic Acid (FA) over Ti3C2Tx/CdS under Visible Light

Acceptorless photocatalytic dehydrogenation is not only a promising alternative to photocatalytic water splitting for hydrogen generation but also provides a green and sustainable strategy for the synthesis of value-added organic compounds. In this work, Ti₃C₂T_x/CdS nanocomposites were obtained by self-assembly of hexagonal CdS in the presence of preformed Ti₃C₂T_x nanosheets, which serves as a photocatalyst for acceptorless dehydrogenation of biomass-derived furfuryl alcohol (FOL) to furfural (FAL) and furoic acid (FA) in neutral and alkaline medium respectively, with simultaneous generation of stoichiometric hydrogen under visible light. Ti₃C₂T_x MXene acts as an efficient cocatalyst for the photocatalytic dehydrogenation of FOL over CdS, with an optimum performance achieved over 0.50 wt% Ti₃C₂T_x/CdS nanocomposite. This study provides an economic and sustainable strategy for the simultaneous valorization of biomass-derived FOL to produce FAL and FA as well as the production of clean energy hydrogen under mild condition based on noble metal-free semiconductor-based photocatalysts.     

Two-dimensional vanadium carbide(V_2CT_x) MXene as supercapacitor electrode in seawater electrolyte

In this study,two-dimensional V_2CT_x MXene has been prepared by selectively etching Al layers from V_2 AlC MAX phase by NaF+HCl etching at 90℃ for 72 h and its performance as supercapacitor(SC)electrode were tested using simulating seawater as electrolyte.V_2CT_x MXene-based electrodes shows a good capacitance of 181.1 F/g,which is in accordance with the volumetric specific capacitance of 317.8 F/cm3,and with 89.1% capacitance retention even after 5000 cycle.Compared with other MXenes,V_2CT_x have better electrochemical performance as SC electrode.This work provides an innovative strategy to apply V_2CT_x MXene as SC electrode in safety and effective seawater electrolyte.     

Co-existence of magnetic phases in two-dimensional MXene

This study reports first synthesis of MXene-derived co-existing magnetic phases. New family of two-dimensional (2D) materials such as Ti₃C₂ namely MXene, having transition metal forming hexagonal structure with carbon atoms have attracted tremendous interest now a days. We have reported structural, optical and magnetic properties of un-doped and La-doped Ti₃C₂T_x MXene, synthesized using co-precipitation method. The lattice parameter (LP) calculated for La-MXene are a = 5.36 Å, c = 18.3 Å which are slightly different from the parent un-doped MXene (a = 5.35 Å, c = 19.2 Å), calculated from X-ray diffraction data. The doping of La⁺³ ions shrinks Ti₃C₂T_x layers perpendicular to the planes. The band gap for MXene is calculated to be 1.06 eV which is increased to 1.44 eV after doping of La⁺³ ion that shows its good semiconducting nature. The experimental results and density functional theory (DFT) calculations for magnetic properties of both the samples have been presented and discussed, indicating the co-existence of ferromagnetic-antiferromagnetic phases. The results presented here are novel and is first report on co-existence of magnetic properties of 2D carbides for potential applications in two-dimensional spintronics.     

零维/二维MXene复合膜的制备及其超级电容器性能

采用水热法制备了0D/2D复合Ti₃C₂T_x MXene,利用X射线衍射、动态光散射和荧光光谱表征了其结构与形貌,结果表明形成了量子点吸附于纳米片的Ti₃C₂T_x复合结构（QDT）。相比未引入量子点的Ti₃C₂T_x,由QDT组装得到的自支撑膜电极的电化学性能有了显著提高：在三电极体系中,扫速为5 mV·s^-1时,比电容为338 F·g^-1,当扫速达到2 000 mV·s^-1,电容保持率达到46%;在两电极体系中,0.5 A·g^-1时的比电容达到216 F·g^-1,10 000次循环后电容保持率为87%。以上性能可归结于：量子点提供了更多的离子吸附位点,且纳米片尺寸减小,缩短了离子传输路径。     

Highly Efficient Adsorption of Bilirubin by Ti3C2Tx MXene

We discovered that the 2D Ti₃C₂T_x MXene sheet displays an ultra-high removal capability for bilirubin (BR). In particular, MXene shows 47.6 times higher removal efficiency over traditional activated carbon absorbents. The effect of MXene on the removal rate of BR in BR solution containing different concentrations of bovine serum albumin (BSA) was studied. The adsorption capacity of BSA for BR at high concentration of 5 g L⁻¹ was about 85% of the best adsorption capacity. The MXene before and after adsorption was characterized by SEM, FT-IR and XPS. Furthermore, MXene beads were prepared, and the hemoperfusion simulation experiment was carried out. The results show that the adsorption capacity of MXene for bilirubin can reach 1192.9 mg g⁻¹. This study suggests that MXene may be promising in the treatment of hyperbilirubinemia.     

MXene/枝状Co/聚偏氟乙烯复合光热膜制备及其界面蒸发性能

使用湿法刻蚀方式将Ti₃AlC₂刻蚀剥离成单/少层Ti₃C₂T_xMXene纳米片,采用电化学还原法制备枝状Co,然后以亲水的聚偏氟乙烯(PVDF)膜为基底通过真空抽滤制备Ti₃C₂T_x/枝状Co/PVDF复合光热膜。对复合材料的结构和形貌进行表征,研究了复合光热膜的光吸收性能和界面蒸发性能。结果表明,在模拟1个太阳光照下(光照强度为1kW·m^-2),Ti₃C₂T_x/枝状Co/PVDF复合光热膜的光吸收率达到95.3%,纯水蒸发速率达到1.78kg·m^-2·h^-1,界面蒸发效率高达97.5%。此外,还测试了在模拟海水中的界面蒸发性能,蒸发冷凝得到的水达到世界卫生组织(WHO)和美国环境保护署(EPA)饮用水标准,蒸发速率达到1.61kg·m^-2·h^-1,循环5次后稳定在1.59kg·m^-2·h^-1。