MXene-Regulated Metal-Oxide Interfaces with Modified Intermediate Configurations Realizing Nearly 100% CO2 Electrocatalytic Conversion

Electrocatalytic CO₂ reduction via renewable electricity provides a sustainable way to produce valued chemicals, while it suffers from low activity and selectivity. Herein, we constructed a novel catalyst with unique Ti₃C₂T_x MXene-regulated Ag−ZnO interfaces, undercoordinated surface sites, as well as mesoporous nanostructures. The designed Ag−ZnO/Ti₃C₂T_x catalyst achieves an outstanding CO₂ conversion performance of a nearly 100% CO Faraday efficiency with high partial current density of 22.59 mA cm⁻² at −0.87 V versus reversible hydrogen electrode. The electronic donation of Ag and up-shifted d-band center relative to Fermi level within MXene-regulated Ag−ZnO interfaces contributes the high selectivity of CO. The CO₂ conversion is highly correlated with the dominated linear-bonded CO intermediate confirmed by in situ infrared spectroscopy. This work enlightens the rational design of unique metal-oxide interfaces with the regulation of MXene for high-performance electrocatalysis beyond CO₂ reduction.     

Understanding the Synergy between Fe and Mo Sites in the Nitrate Reduction Reaction on a Bio-Inspired Bimetallic MXene Electrocatalyst

Mo- and Fe-containing enzymes catalyze the reduction of nitrate and nitrite ions in nature. Inspired by this activity, we study here the nitrate reduction reaction (NO₃RR) catalyzed by an Fe-substituted two-dimensional molybdenum carbide of the MXene family, viz., Mo₂CT_x : Fe (T_x are oxo, hydroxy and fluoro surface termination groups). Mo₂CT_x : Fe contains isolated Fe sites in Mo positions of the host MXene (Mo₂CT_x) and features a Faradaic efficiency (FE) and an NH₃ yield rate of 41 % and 3.2 μmol h⁻¹ mg⁻¹, respectively, for the reduction of NO₃⁻ to NH₄⁺ in acidic media and 70 % and 12.9 μmol h⁻¹ mg⁻¹ in neutral media. Regardless of the media, Mo₂CT_x : Fe outperforms monometallic Mo₂CT_x owing to a more facile reductive defunctionalization of T_x groups, as evidenced by in situ X-ray absorption spectroscopy (Mo K-edge). After surface reduction, a T_x vacancy site binds a nitrate ion that subsequently fills the vacancy site with O* via oxygen transfer. Density function theory calculations provide further evidence that Fe sites promote the formation of surface O vacancies, which are identified as active sites and that function in NO₃RR in close analogy to the prevailing mechanism of the natural Mo-based nitrate reductase enzymes.     

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.     

Nitrogen-Doped Porous MXene (Ti3C2) for Flexible Supercapacitors with Enhanced Storage Performance

Flexible supercapacitors (FSCs) are limited in flexible electronics applications due to their low energy density. Therefore, developing electrode materials with high energy density, high electrochemical activity, and remarkable flexibility is challenging. Herein, we designed nitrogen-doped porous MXene (N-MXene), using melamine-formaldehyde (MF) microspheres as a template and nitrogen source. We combined it with an electrospinning process to produce a highly flexible nitrogen-doped porous MXene nanofiber (N-MXene-F) as a self-supporting electrode material and assembled it into a symmetrical supercapacitor (SSC). On the one hand, the interconnected mesh structure allows the electrolyte to penetrate the porous network to fully infiltrate the material surface, shortening the ion transport channels; on the other hand, the uniform nitrogen doping enhances the pseudocapacitive performance. As a result, the as-assembled SSC exhibited excellent electrochemical performance and excellent long-term durability, achieving an energy density of 12.78 Wh kg⁻¹ at a power density of 1080 W kg⁻¹, with long-term cycling stability up to 5000 cycles. This work demonstrates the impact of structural design and atomic doping on the electrochemical performance of MXene and opens up an exciting possibility for the fabrication of highly FSCs.     

Hierarchical Porous and Three-Dimensional MXene/SiO2 Hybrid Aerogel through a Sol-Gel Approach for Lithium–Sulfur Batteries

A unique porous material, namely, MXene/SiO₂ hybrid aerogel, with a high surface area, was prepared via sol-gel and freeze-drying methods. The hierarchical porous hybrid aerogel possesses a three-dimensional integrated network structure of SiO₂ cross-link with two-dimensional MXene; it is used not only as a scaffold to prepare sulfur-based cathode material, but also as an efficient functional separator to block the polysulfides shuttle. MXene/SiO₂ hybrid aerogel as sulfur carrier exhibits good electrochemical performance, such as high discharge capacities (1007 mAh g^–1 at 0.1 C) and stable cycling performance (823 mA h g^–1 over 200 cycles at 0.5 C). Furthermore, the battery assembled with hybrid aerogel-modified separator remains at 623 mA h g^–1 over 200 cycles at 0.5 C based on the conductive porous framework and abundant functional groups in hybrid aerogel. This work might provide further impetus to explore other applications of MXene-based composite aerogel.     

Electronic Configuration Regulation by N-Doped MXenes Boosting Electrocatalytic Performance of Cobalt Phthalocyanine

The precise control of electronic configurations of catalytic sites via molecular engineering is significantly desirable for boosting electrocatalytic activity. We reported a new-type composite electrocatalyst with cobalt phthalocyanine supported on N-doped MXene nanosheets (N-MXene/CoPc) through a self-assembly process. Beneficial from the joint action of N sites participation and axial coordination, N-MXene/CoPc exhibits a high ORR activity with positive onset potential (E_onset=0.98 V vs. RHE) and half-wave potential (E_1/2=0.863 V), which is superior over the pristine CoPc (E_1/2=0.72 V) and the composite with undoped MXene as support (MXene/CoPc, E_1/2=0.771 V). Additionally, N-MXene/CoPc exhibits an excellent durability with only 8.5 % attenuation after 25000 s of continuous i-t test, while a more obvious decay 18.6 % for 20 wt.% Pt/C. This work not merely reported a robust ORR catalyst, but more provides a reasonable design strategy for nonnoble-metal catalysts through catalyst-support interactions.     

Multi-ion intercalated Ti3C2Tx MXene and the mutual modulation within interlayer

Intercalation of ions between the adjacent MXene layers can change the interlayer environment and influence the electrochemical ion storage capacity. In order to understand the effect of multi-ions confined by the MXene layers on the performance of electrochemical energy storage, Co²⁺, Mn²⁺ and Ni²⁺ intercalated into Ti₃C₂T_x MXene which already pre-intercalated Al³⁺ are obtained by spontaneous static action. Based on the monitor of (002) crystal orientation, intercalated multi-ions can regulate and control the interlayer environment of MXenes via stress, which induces lattice shrinkage occurring in the c axis. Limited by ion storage mechanism-performance, the multi-ion occupies the interspace of MXene and affects the electrochemical performance. This work would offer guidance to understand the relationship among the multi-ion and MXene by two-dimensional (2D) layered materials.     

Surface-Controlled CdS/Ti3C2 MXene Schottky Junction for Highly Selective and Active Photocatalytic Dehydrogenation-Reductive Amination

Photocatalytic valorization and selective transformation of biomass-derived platform compounds offer great opportunities for efficient utilization of renewable resources under mild conditions. Here, the novel three-dimensional hierarchical flower-like CdS/Ti₃C₂ Schottky junction (MCdS) composed of surface-controlled CdS and pretreated Ti₃C₂ MXene is created for photocatalytic dehydrogenation-reductive amination of biomass-derived amino acid production under ambient temperature with unprecedented activity and selectivity. Schottky junction efficiently promotes photoexcited charge migration and separation and inhibits photogenerated electron-hole recombination, which results in a super-high activity. Meanwhile, CdS with the reduced surface energy supplies sufficient hydrogen sources for imine reduction and induces the preferential orientation of alanine, thus contributing superior selectivity. Moreover, a wide range of hydroxyl acids are successfully converted into corresponding amino acids and even one-pot conversion of glucose to alanine is easily achieved over MCdS. This work illustrates the mechanism of crystal orientation control and heterojunction construction in controlling catalytic behavior of photocatalytic nanoreactor, providing a paradigm for construction of MXene-based heterostructure.     

Portable Electrochemical Sensing of Indole-3-acetic Acid Based on Self-assembled MXene and Multi-walled Carbon Nanotubes Composite Modified Screen-printed Electrode

As a typical plant hormone, indole-3-acetic acid (IAA) can regulate the biological activities including division, growth and differentiation of plant cells. In this paper, a MXene and multi-walled carbon nanotubes composite was prepared by self-assembly procedure, which was modified on screen-printed electrode (SPE) to construct a wireless portable electrochemical sensor. Electrochemical investigations of IAA were studied by cyclic voltammetry and an irreversible oxidation process could be observed. The excellent electroanalytical method of IAA was realized on the modified SPE with the detection range as 0.05–125.0 μmol/L and the detection limit as 16.7 nmol/L. The sensor was used for IAA content analysis in different part of pea seedlings with satisfactory results.