High‐Efficiency Thermoelectric Power Generation Enabled by Homogeneous Incorporation of MXene in (Bi,Sb)2Te3 Matrix

The (Bi,Sb)₂Te₃ (BST) compounds have long been considered as the benchmark of thermoelectric (TE) materials near room temperature especially for refrigeration. However, their unsatisfactory TE performances in wide‐temperature range severely restrict the large‐scale applications for power generation. Here, using a self‐assembly protocol to deliver a homogeneous dispersion of 2D inclusion in matrix, the first evidence is shown that incorporation of MXene (Ti₃C₂T_x) into BST can simultaneously achieve the improved power factor and greatly reduced thermal conductivity. The oxygen‐terminated Ti₃C₂T_x with proper work function leads to highly increased electrical conductivity via hole injection and retained Seebeck coefficient due to the energy barrier scattering. Meanwhile, the alignment of Ti₃C₂T_x with the layered structure significantly suppresses the phonon transport, resulting in higher interfacial thermal resistance. Accordingly, a peak ZT of up to 1.3 and an average ZT value of 1.23 from 300 to 475 K are realized for the 1 vol% Ti₃C₂T_x/BST composite. Combined with the high‐performance composite and rational device design, a record‐high thermoelectric conversion efficiency of up to 7.8% is obtained under a temperature gradient of 237 K. These findings provide a robust and scalable protocol to incorporate MXene as a versatile 2D inclusion for improving the overall performance of TE materials toward high energy‐conversion efficiency.     

Low‐Temperature Reduction Strategy Synthesized Si/Ti3C2 MXene Composite Anodes for High‐Performance Li‐Ion Batteries

Silicon is attracting enormous attention due to its theoretical capacity of 4200 mAh g^?1 as an anode for Li‐ion batteries (LIBs). It is of fundamental importance and challenge to develop low‐temperature reaction route to controllably synthesize Si/Ti₃C₂ MXene LIBs anodes. Herein, a novel and efficient strategy integrating in situ orthosilicate hydrolysis and a low‐temperature reduction process to synthesize Si/Ti₃C₂ MXene composites is reported. The hydrolysis of tetraethyl orthosilicate leads to homogenous nucleation and growth of SiO₂ nanoparticles on the surface of Ti₃C₂ MXene. Subsequently, SiO₂ nanoparticles are reduced to Si via a low‐temperature (200 °C) reduction route. Importantly, Ti₃C₂ MXene not only provides fast transfer channels for Li⁺ and electrons, but also relieves volume expansion of Si during cycling. Moreover, the characteristics of excellent pseudocapacitive performance and high conductivity of Ti₃C₂ MXene can synergistically contribute to the enhancement of energy storage performance. As expected, Ti₃C₂/Si anode exhibits an outstanding specific capacity of 1849 mAh g^?1 at 100 mA g^?1, even retaining 956 mAh g^?1 at 1 A g^?1. The low‐temperature synthetic route to Si/Ti₃C₂ MXene electrodes and involved battery‐capacitive dual‐model energy storage mechanism has potential in the design of novel high‐performance electrodes for energy storage devices.     

High‐Performance Electrocatalytic Conversion of N2 to NH3 Using Oxygen‐Vacancy‐Rich TiO2 In Situ Grown on Ti3C2Tx MXene

To achieve the energy‐effective ammonia (NH₃) production via the ambient‐condition electrochemical N₂ reduction reaction (NRR), it is vital to ingeniously design an efficient electrocatalyst assembling the features of abundant surface deficiency, good dispersibility, high conductivity, and large surface specific area (SSA) via a simple way. Inspired by the fact that the MXene contains thermodynamically metastable marginal transition metal atoms, the oxygen‐vacancy‐rich TiO₂ nanoparticles (NPs) in situ grown on the Ti₃C₂T_x nanosheets (TiO₂/Ti₃C₂T_x) are prepared via a one‐step ethanol‐thermal treatment of the Ti₃C₂T_x MXene. The oxygen vacancies act as the main active sites for the NH₃ synthesis. The highly conductive interior untreated Ti₃C₂T_x nanosheets could not only facilitate the electron transport but also avoid the self‐aggregation of the TiO₂ NPs. Meanwhile, the TiO₂ NPs generation could enhance the SSA of the Ti₃C₂T_x in return. Accordingly, the as‐prepared electrocatalyst exhibits an NH₃ yield of 32.17 µg h^?1 mg^?1_cat. at ?0.55 V versus reversible hydrogen electrode (RHE) and a remarkable Faradaic efficiency of 16.07% at ?0.45 V versus RHE in 0.1 m HCl, placing it as one of the most promising NRR electrocatalysts. Moreover, the density functional theory calculations confirm the lowest NRR energy barrier (0.40 eV) of TiO₂ (101)/Ti₃C₂T_x compared with Ti₃C₂T_x or TiO₂ (101) alone.     

Achieving High Pseudocapacitance of 2D Titanium Carbide (MXene) by Cation Intercalation and Surface Modification

Supercapacitors attract great interest because of the increasing and urgent demand for environment‐friendly high‐power energy sources. Ti₃C₂, a member of MXene family, is a promising electrode material for supercapacitors owing to its excellent chemical and physical properties. However, the highest gravimetric capacitance of the MXene‐based electrodes is still relatively low (245 F g^?1) and the key challenge to improve this is to exploit more pseudocapacitance by increasing the active site concentration. Here, a method to significantly improve the gravimetric capacitance of Ti₃C₂T_x MXenes by cation intercalation and surface modification is reported. After K⁺ intercalation and terminal groups (OH^?/F^?) removing , the intercalation pseudocapacitance is three times higher than the pristine MXene, and MXene sheets exhibit a significant enhancement (about 211% of the origin) in the gravimetric capacitance (517 F g^?1 at a discharge rate of 1 A g^?1). Moreover, the as‐prepared electrodes show above 99% retention over 10 000 cycles. This improved electrochemical performance is attributed to the large interlayer voids of Ti₃C₂ and lowest terminated surface group concentration. This study demonstrates a new strategy applicable to other MXenes (Ti₂CT_x , Nb₂CT_x , etc.) in maximizing their potential applications in energy storage.     

Enhanced Li‐Ion Accessibility in MXene Titanium Carbide by Steric Chloride Termination

Pseudocapacitance is a key charge storage mechanism to advanced electrochemical energy storage devices distinguished by the simultaneous achievement of high capacitance and a high charge/discharge rate by using surface redox chemistries. MXene, a family of layered compounds, is a pseudocapacitor‐like electrode material which exhibits charge storage through exceptionally fast ion accessibility to redox sites. Here, the authors demonstrate steric chloride termination in MXene Ti₂CT_x (T_x : surface termination groups) to open the interlayer space between the individual 2D Ti₂CT_x units. The open interlayer space significantly enhances Li‐ion accessibility, leading to high gravimetric and volumetric capacitances (300 F g^?1 and 130 F cm^?3) with less diffusion limitation. A Li‐ion hybrid capacitor consisting of the Ti₂CT_x negative electrode and the LiNi_1/3Co_1/3Mn_1/3O₂ positive electrode displays an unprecedented specific energy density of 160 W h kg^?1 at 220 W kg^?1 based on the total weight of positive and negative active materials.     

Rational Design of Hydroxyl‐Rich Ti3C2Tx MXene Quantum Dots for High‐Performance Electrochemical N2 Reduction

To enable an efficient and cost‐effective electrocatalytic N₂ reduction reaction (NRR) the development of an electrocatalyst with a high NH₃ yield and good selectivity is required. In this work, Ti₃C₂T_x MXene‐derived quantum dots (Ti₃C₂T_x QDs) with abundant active sites enable the development of efficient NRR electrocatalysts. Given surface functional groups play a key role on the electrocatalytic performance, density functional theory calculations are first conducted, clarifying that hydroxyl groups on Ti₃C₂T_x offer excellent NRR activity. Accordingly, hydroxyl‐rich Ti₃C₂T_x QDs (Ti₃C₂OH QDs) are synthesized as NRR catalysts by alkalization and intercalation. This material offers an NH₃ yield and Faradaic efficiency of 62.94 µg h^?1 mg^?1_cat. and 13.30% at ?0.50 V, respectively, remarkably higher than reported MXene catalysts. This work demonstrates that MXene catalysts can be mediated through the optimization of both QDs sizes and functional groups for efficient ammonia production at room temperature.     

Biomimetic MXene Textures with Enhanced Light‐to‐Heat Conversion for Solar Steam Generation and Wearable Thermal Management

2D materials are of particular interest in light‐to‐heat conversion, yet challenges remain in developing a facile method to suppress their light reflection. Herein, inspired by the black scales of Bitis rhinoceros, a generalized approach via sequential thermal actuations to construct biomimetic 2D‐material nanocoatings, including Ti₃C₂T_x MXene, reduced graphene oxide (rGO), and molybdenum disulfide (MoS₂) is designed. The hierarchical MXene nanocoatings result in broadband light absorption (up to 93.2%), theoretically validated by optical modeling and simulations, and realize improved light‐to‐heat performance (equilibrium temperature of 65.4 °C under one‐sun illumination). With efficient light‐to‐heat conversion, the bioinspired MXene nanocoatings are next incorporated into solar steam‐generation devices and stretchable solar/electric dual‐heaters. The MXene steam‐generation devices require much lower solar‐thermal material loading (0.32 mg cm^?2) and still guarantee high steam‐generation performance (1.33 kg m^?2 h^?1) compared with other state‐of‐the‐art devices. Additionally, the mechanically deformed MXene structures enable the fabrication of stretchable and wearable heaters dual‐powered by sunlight and electricity, which are reversibly stretched and heated above 100 °C. This simple fabrication process with effective utilization of active materials promises its practical application value for multiple solar–thermal technologies.     

All Pseudocapacitive MXene‐RuO2 Asymmetric Supercapacitors

2D transition metal carbides and nitrides, known as MXenes, are an emerging class of 2D materials with a wide spectrum of potential applications, in particular in electrochemical energy storage. The hydrophilicity of MXenes combined with their metallic conductivity and surface redox reactions is the key for high‐rate pseudocapacitive energy storage in MXene electrodes. However, symmetric MXene supercapacitors have a limited voltage window of around 0.6 V due to possible oxidation at high anodic potentials. In this study, the fact that titanium carbide MXene (Ti₃C₂T_x) can operate at negative potentials in acidic electrolyte is exploited, to design an all‐pseudocapacitive asymmetric device by combining it with a ruthenium oxide (RuO₂) positive electrode. This asymmetric device operates at a voltage window of 1.5 V, which is about two times wider than the operating voltage window of symmetric MXene supercapacitors, and is the widest voltage window reported to date for MXene‐based supercapacitors. The complementary working potential windows of MXene and RuO₂, along with proton‐induced pseudocapacitance, significantly enhance the device performance. As a result, the asymmetric devices can deliver an energy density of 37 µW h cm^?2 at a power density of 40 mW cm^?2, with 86% capacitance retention after 20 000 charge–discharge cycles. These results show that pseudocapacitive negative MXene electrodes can potentially replace carbon‐based materials in asymmetric electrochemical capacitors, leading to an increased energy density.     

Tantalum Nitride Electron‐Selective Contact for Crystalline Silicon Solar Cells

Minimizing carrier recombination at contact regions by using carrier‐selective contact materials, instead of heavily doping the silicon, has attracted considerable attention for high‐efficiency, low‐cost crystalline silicon (c‐Si) solar cells. A novel electron‐selective, passivating contact for c‐Si solar cells is presented. Tantalum nitride (TaN _x ) thin films deposited by atomic layer deposition are demonstrated to provide excellent electron‐transporting and hole‐blocking properties to the silicon surface, due to their small conduction band offset and large valence band offset. Thin TaN_x interlayers provide moderate passivation of the silicon surfaces while simultaneously allowing a low contact resistivity to n‐type silicon. A power conversion efficiency (PCE) of over 20% is demonstrated with c‐Si solar cells featuring a simple full‐area electron‐selective TaN_x contact, which significantly improves the fill factor and the open circuit voltage (V_oc) and hence provides the higher PCE. The work opens up the possibility of using metal nitrides, instead of metal oxides, as carrier‐selective contacts or electron transport layers for photovoltaic devices.     

Capture and Catalytic Conversion of Polysulfides by In Situ Built TiO2‐MXene Heterostructures for Lithium–Sulfur Batteries

The detrimental shuttle effect in lithium–sulfur batteries mainly results from the mobility of soluble polysulfide intermediates and their sluggish conversion kinetics. Herein, presented is a multifunctional catalyst with the merits of strong polysulfides adsorption ability, superior polysulfides conversion activity, high specific surface area, and electron conductivity by in situ crafting of the TiO₂‐MXene (Ti₃C₂T_x) heterostructures. The uniformly distributed TiO₂ on MXene sheets act as capturing centers to immobilize polysulfides, the hetero‐interface ensures rapid diffusion of anchored polysulfides from TiO₂ to MXene, and the oxygen‐terminated MXene surface is endowed with high catalytic activity toward polysulfide conversion. The improved lithium–sulfur batteries deliver 800 mAh g^?1 at 2 C and an ultralow capacity decay of 0.028% per cycle over 1000 cycles at 2 C. Even with a high sulfur loading of 5.1 mg cm^?2, the capacity retention of 93% after 200 cycles is still maintained. This work sheds new insights into the design of high‐performance catalysts with manipulated chemical components and tailored surface chemistry to regulate polysulfides in Li–S batteries.     

Enhanced Rate Capability of Ion‐Accessible Ti3C2Tx‐NbN Hybrid Electrodes

Although 2D Ti₃C₂T_x is a good candidate for supercapacitors, the restacking of nanosheets hinders the ion transport significantly at high scan rates, especially under practical mass loading (>10 mg cm^?2) and thickness (tens of microns). Here, Ti₃C₂T_x‐NbN hybrid film is designed by self‐assembling Ti₃C₂T_x with 2D arrays of NbN nanocrystals. Working as an interlayer spacer of Ti₃C₂T_x, NbN facilitates the ion penetration through its 2D porous structure; even at extremely high scan rates. The hybrid film shows a thickness‐independent rate performance (almost the same rate capabilities from 2 to 20 000 mV s^?1) for 3 and 50 µm thick electrodes. Even a 109 µm thick Ti₃C₂T_x‐NbN electrode shows a better rate performance than 25 µm thick pure Ti₃C₂T_x electrodes. This method may pave a way to controlling ion transport in electrodes composed of 2D conductive materials, which have potential applications in high‐rate energy storage and beyond.     

Interface Engineering of MXene Composite Separator for High‐Performance Li–Se and Na–Se Batteries

Selenium (Se), due to its high electronic conductivity and high energy density, has recently attracted considerable interest as a cathode material for rechargeable Li/Na batteries. However, the poor cycling stability originating from the severe shuttle effect of polyselenides hinders their practical applications. Herein, highly stable Li/Na–Se batteries are developed using ultrathin (≈270 nm, loading of 0.09 mg cm^?2) cetrimonium bromide (CTAB)/carbon nanotube (CNT)/Ti₃C₂T_x MXene hybrid modified polypropylene (PP) (CCNT/MXene/PP) separators. The hybrid separator can immobilize the polyselenides via enhanced Lewis acid–base interactions between CTAB/MXene and polyselenides, which is demonstrated by theoretical calculations and X‐ray photoelectron spectroscopy. The incorporation of CNT helps to improve the electrolyte infiltration and facilitate the ionic transport. In situ permeation experiments are conducted for the first time to visually study the behavior of polyselenides, revealing the prohibited shuttle effect and protected Li anode from corrosion with CCNT/MXene/PP separators. As a result, the Li–Se batteries with CCNT/MXene/PP separators deliver an outstanding cycling performance over 500 cycles at 1C with an extremely low capacity decay of 0.05% per cycle. Moreover, the hybrid separators also perform well in Na–Se batteries. This study develops a preferable separator–electrolyte interface and the concept can be applied in other conversion‐type battery systems.     

MXene‐on‐Paper Coplanar Microsupercapacitors

A simple and scalable direct laser machining process to fabricate MXene‐on‐paper coplanar microsupercapacitors is reported. Commercially available printing paper is employed as a platform in order to coat either hydrofluoric acid‐etched or clay‐like 2D Ti₃C₂ MXene sheets, followed by laser machining to fabricate thick‐film MXene coplanar electrodes over a large area. The size, morphology, and conductivity of the 2D MXene sheets are found to strongly affect the electrochemical performance due to the efficiency of the ion‐electron kinetics within the layered MXene sheets. The areal performance metrics of Ti₃C₂ MXene‐on‐paper microsupercapacitors show very competitive power‐energy densities, comparable to the reported state‐of‐the‐art paper‐based microsupercapacitors. Various device architectures are fabricated using the MXene‐on‐paper electrodes and successfully demonstrated as a micropower source for light emitting diodes. The MXene‐on‐paper electrodes show promise for flexible on‐paper energy storage devices.     

Solving the Capacitive Paradox of 2D MXene using Electrochemical Quartz‐Crystal Admittance and In Situ Electronic Conductance Measurements

Fast ion adsorption processes in supercapacitors enable quick storage/delivery of significant amounts of energy, while ion intercalation in battery materials leads to even larger amounts of energy stored, but at substantially lower rates due to diffusional limitations. Intercalation of ions into the recently discovered 2D Ti₃C₂T_x (MXene) occurs with a very high rate and leads to high capacitance, posing a paradox. Herein, by characterizing the mechanical deformations of MXene electrode materials at various states‐of‐charge with a variety of cations (Li, Na, K, Cs, Mg, Ca, Ba, and three tetra­alkylammonium cations) during cycling by electrochemical quartz‐crystal admittance (EQCA, quartz‐crystal microbalance with dissipation monitoring) combined with in situ electronic conductance and electrochemical impedance, light is shone on this paradox. Based on this work, it appears that the capacitive paradox stems from cationic insertion, accompanied by significant deformation of the MXene particles, that occurs so rapidly so as to resemble 2D ion adsorption at solid‐liquid interfaces. The latter is greatly facilitated by the presence of water molecules between the MXene sheets.     

A Strategy for Synthesis of Carbon Nitride Induced Chemically Doped 2D MXene for High‐Performance Supercapacitor Electrodes

A step‐by‐step strategy is reported for improving capacitance of supercapacitor electrodes by synthesizing nitrogen‐doped 2D Ti₂CT_x induced by polymeric carbon nitride (p‐C₃N₄), which simultaneously acts as a nitrogen source and intercalant. The NH₂CN (cyanamide) can form p‐C₃N₄ on the surface of Ti₂CT_x nanosheets by a condensation reaction at 500–700 °C. The p‐C₃N₄ and Ti₂CT_x complexes are then heat‐treated to obtain nitrogen‐doped Ti₂CT_x nanosheets. The triazine‐based p‐C₃N₄ decomposes above 700 °C; thus, the nitrogen species can be surely doped into the internal carbon layer and/or defect site of Ti₂CT_x nanosheets at 900 °C. The extended interlayer distance and c‐lattice parameters (c‐LPs of 28.66 Å) of Ti₂CT_x prove that the p‐C₃N₄ grown between layers delaminate the nanosheets of Ti₂CT_x during the doping process. Moreover, 15.48% nitrogen doping in Ti₂CT_x improves the electrochemical performance and energy storage ability. Due to the synergetic effect of delaminated structures and heteroatom compositions, N‐doped Ti₂CT_x shows excellent characteristics as an electrochemical capacitor electrode, such as perfectly rectangular cyclic voltammetry results (CVs, R² = 0.9999), high capacitance (327 F g^?1 at 1 A g^?1, increased by ≈140% over pristine‐Ti₂CT_x), and stable long cyclic performance (96.2% capacitance retention after 5000 cycles) at high current density (5 A g^?1).     

Hydrous RuO2‐Decorated MXene Coordinating with Silver Nanowire Inks Enabling Fully Printed Micro‐Supercapacitors with Extraordinary Volumetric Performance

The fabrication of fully printable, flexible micro‐supercapacitors (MSCs) with high energy and power density remains a significant technological hurdle. To overcome this grand challenge, the 2D material MXene has garnered significant attention for its application, among others, as a printable electrode material for high performing electrochemical energy storage devices. Herein, a facile and in situ process is proposed to homogeneously anchor hydrous ruthenium oxide (RuO₂) nanoparticles on Ti₃C₂T_x MXene nanosheets. The resulting RuO₂@MXene nanosheets can associate with silver nanowires (AgNWs) to serve as a printable electrode with micrometer‐scale resolution for high performing, fully printed MSCs. In this printed nanocomposite electrode, the RuO₂ nanoparticles contribute high pseudocapacitance while preventing the MXene nanosheets from restacking, ensuring an effective ion highway for electrolyte ions. The AgNWs coordinate with the RuO₂@MXene to guarantee the rheological property of the electrode ink, and provide a highly conductive network architecture for rapid charge transport. As a result, MSCs printed from the nanocomposite inks demonstrate volumetric capacitances of 864.2 F cm^?3 at 1 mV s^?1, long‐term cycling performance (90% retention after 10 000 cycles), good rate capability (304.0 F cm^?3 at 2000 mV s^?1), outstanding flexibility, remarkable energy (13.5 mWh cm^?3) and power density (48.5 W cm^?3).     

MXene‐Based Mesoporous Nanosheets Toward Superior Lithium Ion Conductors

Although solid polymer electrolytes have some intrinsic advantages in synthesis and film processing compared with inorganic solid electrolytes, low ionic conductivities and mechanical moduli hamper their practical applications in lithium‐based batteries. Here, an efficient strategy is developed to produce a unique solid polymer electrolyte containing MXene‐based mesoporous silica nanosheets with a sandwich structure, which are fabricated via controllable hydrolysis of tetraethyl orthosilicate around the surface of MXene‐Ti₃C₂ under the direction of cationic surfactants. Such unique nanosheets not only exhibit individual, thin, and insulated features, but also possess abundant functional groups in mesopores and on the surface, which are favorable for the formation of Lewis acid–base interactions with anions in polymer electrolytes such as poly(propylene oxide) elastomer, enabling the fast Li⁺ transportation at the mesoporous nanosheets/polymer interfaces. As a consequence, a solid polymer electrolyte with high ionic conductivity of 4.6 × 10^?4 S cm^?1, high Young's modulus of 10.5 MPa, and long‐term electrochemical stability is achieved.     

Lithium Fluoride Based Electron Contacts for High Efficiency n‐Type Crystalline Silicon Solar Cells

Low‐resistance contact to lightly doped n‐type crystalline silicon (c‐Si) has long been recognized as technologically challenging due to the pervasive Fermi‐level pinning effect. This has hindered the development of certain devices such as n‐type c‐Si solar cells made with partial rear contacts (PRC) directly to the lowly doped c‐Si wafer. Here, a simple and robust process is demonstrated for achieving mΩ cm² scale contact resistivities on lightly doped n‐type c‐Si via a lithium fluoride/aluminum contact. The realization of this low‐resistance contact enables the fabrication of a first‐of‐its‐kind high‐efficiency n‐type PRC solar cell. The electron contact of this cell is made to less than 1% of the rear surface area, reducing the impact of contact recombination and optical losses, permitting a power conversion efficiency of greater than 20% in the initial proof‐of‐concept stage. The implementation of the LiF_x/Al contact mitigates the need for the costly high‐temperature phosphorus diffusion, typically implemented in such a cell design to nullify the issue of Fermi level pinning at the electron contact. The timing of this demonstration is significant, given the ongoing transition from p‐type to n‐type c‐Si solar cell architectures, together with the increased adoption of advanced PRC device structures within the c‐Si photovoltaic industry.     

Conductive and Stable Magnesium Oxide Electron‐Selective Contacts for Efficient Silicon Solar Cells

A high Schottky barrier (>0.65 eV) for electrons is typically found on lightly doped n‐type crystalline (c‐Si) wafers for a variety of contact metals. This behavior is commonly attributed to the Fermi‐level pinning effect and has hindered the development of n‐type c‐Si solar cells, while its p‐type counterparts have been commercialized for several decades, typically utilizing aluminium alloys in full‐area, and more recently, partial‐area rear contact configurations. Here the authors demonstrate a highly conductive and thermally stable electrode composed of a magnesium oxide/aluminium (MgO_x/Al) contact, achieving moderately low resistivity Ohmic contacts on lightly doped n‐type c‐Si. The electrode, functionalized with nanoscale MgO_x films, significantly enhances the performance of n‐type c‐Si solar cells to a power conversion efficiency of 20%, advancing n‐type c‐Si solar cells with full‐area dopant‐free rear contacts to a point of competitiveness with the standard p‐type architecture. The low thermal budget of the cathode formation, its dopant‐free nature, and the simplicity of the device structure enabled by the MgO_x/Al contact open up new possibilities in designing and fabricating low‐cost optoelectronic devices, including solar cells, thin film transistors, or light emitting diodes.     

Highly Flexible,Freestanding Supercapacitor Electrode with Enhanced Performance Obtained by Hybridizing Polypyrrole Chains with MXene

Though polypyrrole (PPy) is widely used in flexible supercapacitors owing to its high electrochemical activity and intrinsic flexibility, limited capacitance and cycling stability of freestanding PPy films greatly reduce their practicality in real‐world applications. Herein, we report a new approach to enhance PPy's capacitance and cycling stability by forming a freestanding and conductive hybrid film through intercalating PPy into layered Ti₃C₂ (l‐Ti₃C₂, a MXene material). The capacitance increases from 150 (300) to 203 mF cm^?2 (406 F cm^?3). Moreover, almost 100% capacitance retention is achieved, even after 20 000 charging/discharging cycles. The analyses reveal that l‐Ti₃C₂ effectively prevents dense PPy stacking, benefiting the electrolyte infiltration. Furthermore, strong bonds, formed between the PPy backbones and surfaces of l‐Ti₃C₂, not only ensure good conductivity and provide precise pathways for charge‐carrier transport but also improve the structural stability of PPy backbones. The freestanding PPy/l‐Ti₃C₂ film is further used to fabricate an ultra‐thin all‐solid‐state supercapacitor, which shows an excellent capacitance (35 mF cm^?2), stable performance at any bending state and during 10 000 charging/discharging cycles. This novel strategy provides a new way to design conductive polymer‐based freestanding flexible electrodes with greatly improved electrochemical performances.