The development of aqueous ammonium-ion batteries (AAIBs) requires electrode materials that combine high NH4 + storage capacity with rapid and reversible ion transport. Herein, a metal-vacancy MXene/polyaniline (Mo4/3CTz/PANI) composite is reported, in which the pseudocapacitive response is synergistically activated by introducing 0.1 m H2SO4 into 1 m (NH4)2SO4 electrolyte. This proton-assisted modulation enables rapid and reversible NH4 +/H3O+ co-intercalation, in contrast to the negligible ion insertion observed in the absence of H2SO4. Combined experimental and density-functional theory (DFT) analyses reveal that proton doping significantly improves the electronic conductivity of PANI and induces a reversible Mo6+/Mo5+ redox transition during cycling, which dynamically modulates the NH4 + adsorption energy (from -4.155 to -4.567 eV), thus facilitating both intercalation and deintercalation of NH4 +. As a result, the composite achieves a high specific capacity of 245 mAh g-1 at 0.1 A g-1, with excellent capacity retention of 84.2% after 11,000 cycles at 1.0 A g-1. Furthermore, the MnO2/CNTs||M:P = 5:1 full cell delivers a high energy density of 81.6 Wh kg-1 and a power density of 16 000 W kg-1. This work highlights a promising strategy for advancing MXene-based electrodes via proton-enhanced ion storage mechanisms, paving the way for high-performance AAIBs.

Molecular weight (M-n) and conjugation of polymers can profoundly influence the performance of all-polymer solar cells (all-PSCs) via nanostructures of bulk heterojunctions (BHJs). To study the correlation between M-n and the performance of all-PSCs based on an acceptor with a flexible conjugation-break spacer (FCBS), three batches of acceptors, named PYTS, were synthesized with different number-average M-n from 9, 13 to 19 kDa. Blends with a polymer donor PBDB-T, the all-PSCs based on PYTS with M-n of 9 kDa and 19 kDa, exhibit power conversion efficiencies (PCEs) of 5.99% and 9.43%, respectively, primarily due to the increased short-circuit current density (J(sc)) from 13.02 to 18.73 mA cm(-2). To disclose the impact of M-n on device performance, dynamics of mixed PBDB-T:PYTS solutions to solid BHJs is studied by monitoring the drying process with home-made in situ multifunctional spectroscopy, which demonstrates that PYTS with M-n of 19 kDa has a longer drying time than the PYTS with M-n of 9 kDa. Prolonged drying of the BHJs with higher M-n PYTS facilitates more tightly packed structures with higher crystallinity. A systematic investigation on the nanostructures of BHJs, charge generation, transport and recombination is carried out with grazing-incidence wide-angle X-ray scattering (GIWAXS), transient absorption spectroscopy (TAS) and characterization of all-PSCs. The results indicate that increased crystallinity in the BHJs benefits exciton dissociation, electron transport, prolonged carrier lifetimes, and decreased non-geminate recombination rate constants in the corresponding devices. Combining the in situ study of drying and the investigation on films and devices provides us a comprehensive understanding of the interplay between M-n, the drying process, the nanostructures of BHJs and device performance. This work not only emphasizes the essential role of M-n in governing the device performance, but also exhibits recorded film formation through the in situ spectroscopy, enabling us to manipulate the nanostructure of BHJs by optimizing M-n of polymers and processing parameters.

Aqueous zinc-ion batteries (AZIBs) based on vanadium oxides or sulfides are promising candidates for large-scale rechargeable energy storage due to their ease of fabrication, low cost, and high safety. However, the commercial application of vanadium-based electrode materials has been hindered by challenging problems such as poor cyclability and low-rate performance. To this regard, sophisticated nanostructure engineering technology is used to adeptly incorporate VS2 nanosheets into the MXene interlayers to create a stable 2D heterogeneous layered structure. The MXene nanosheets exhibit stable interactions with VS2 nanosheets, while intercalation between nanosheets effectively increases the interlayer spacing, further enhancing their stability in AZIBs. Benefiting from the heterogeneous layered structure with high conductivity, excellent electron/ion transport, and abundant reactive sites, the free-standing VS2/Ti(3)C(2)Tz composite film can be used as both the cathode and the anode of AZIBs. Specifically, the VS2/Ti3C2Tz cathode presents a high specific capacity of 285 mAh g(-1) at 0.2 A g(-1). Furthermore, the flexible Zn-metal free in-plane VS2/Ti3C2Tz//MnO2/CNT AZIBs deliver high operation voltage (2.0 V) and impressive long-term cycling stability (with a capacity retention of 97% after 5000 cycles) which outperforms almost all reported Vanadium-based electrodes for AZIBs. The effective modulation of the material structure through nanocomposite engineering effectively enhances the stability of VS2, which shows great potential in Zn2+ storage. This work will hasten and stimulate further development of such composite material in the direction of energy storage.

Supercapacitors based on two-dimensional MXene (Ti3C2Tz) have shown extraordinary performance in ultrathin electrodes with low mass loading, but usually there is a significant reduction in high-rate performance as the thickness increases, caused by increasing ion diffusion limitation. Further limitations include restacking of the nanosheets, which makes it challenging to realize the full potential of these electrode materials. Herein, we demonstrate the design of a vertically aligned MXene hydrogel composite, achieved by thermal-assisted self-assembled gelation, for high-rate energy storage. The highly interconnected MXene network in the hydrogel architecture provides very good electron transport properties, and its vertical ion channel structure facilitates rapid ion transport. The resulting hydrogel electrode show excellent performance in both aqueous and organic electrolytes with respect to high capacitance, stability, and high-rate capability for up to 300 mu m thick electrodes, which represents a significant step toward practical applications.

Fiber type devices are promising for applications in wearable and portable electronics. However, scalable fabrication of fiber electrodes with multifunctional performance for use in distinct fields remains challenging. Herein, high performance smart fibers based on Mo1.33C i-MXene nanosheets and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate hybrid paste are fabricated with an easily scalable spinning approach. The hybrid fibers produced by this method can be applied in both high-performance supercapacitors and electrochemical transistors (ECTs). When assembled into a fiber type asymmetric supercapacitor with reduced graphene oxide (rGO) fiber, a capacitance of 105 F g(-1) and an energy density of 37 mW h g(-1) were reached for a potential window of 1.6 V. The hybrid fiber based ECT shows high transconductance and fast response time. This work demonstrates the potential of i-MXene-based fiber electrodes for multifunctional applications, to aid in the development of the next-generation, high-performance wearable electronic devices.

Solar energy, although it has the highest power density available in terms of renewable energy, has the drawback of being erratic. Integrating an energy harvesting and storage device into photovoltaic energy storage modules is a viable route for obtaining self-powered energy systems. Herein, an MXene-based all-solution processed semitransparent flexible photovoltaic supercapacitor (PSC) was fabricated by integrating a flexible organic photovoltaic (OPV) with Ti3C2Tx MXene as the electrode and transparent MXene supercapacitors with an organic ionogel as the electrolyte in the vertical direction, using Ti3C2Tx thin film as a common electrode. In the quest for a semitransparent flexible PSC, Ti3C2Tx MXene was first used as a transparent electrode for OPV with a high power conversion efficiency of 13.6%. The ionogel electrolyte-based transparent MXene supercapacitor shows a high volumetric capacitance of 502 F cm(-3) and excellent stability. Finally, a flexible PSC with a high average transmittance of over 33.5% was successfully constructed by all-solution processing and a remarkable storage efficiency of 88% was achieved. This strategy enables a simple route for fabricating MXene based high-performance all-solution-processed flexible PSCs, which is important for realizing flexible and printable electronics for future technologies.

Two-dimensional (2D) transition metal carbides and carbonitrides, called MXenes, with metallic conductivity and hydrophilic surfaces, show great promise as electrode materials for supercapacitors. A major drawback of 2D nanomaterials is the re-stacking of the nanosheets, which prevents full utilization of surface area and blocks the access of the electrolyte. In this study, a free-standing nanocomposite paper electrode is realized by combining Mo1.33C MXene and positively charged biopolymer lignin (the second most abundant biopolymer in nature, L-DEA). The self-assembled layered architecture with alternating polymer and MXene flakes increases the interlayer space to promote ion transport, and with combining charge storage capability of the lignin derivative and MXene in an interpenetrating MXene/L-DEA nanocomposite, which offers an impressive capacitance of 503.7 F g(-1). Moreover, we demonstrate flexible solid-state asymmetric supercapacitors (ASCs) using Mo1.33C@L-DEA as the negative electrode and electrochemically exfoliated graphene with ruthenium oxide (EG@RuOx) as the positive electrode. This asymmetric device operates at a voltage window of 1.35 V, which is about two times wider than that of a symmetric Mo1.33C@L-DEA based supercapacitor. Finally, the ASCs can deliver an energy density of 51.9 Wh kg(-1) at a power density of 338.5 W kg(-1), with 86 % capacitance retention after 10000 charge-discharge cycles.

Low-cost, non-toxic, abundant organic thermoelectric materials are currently under investigation for use as potential alternatives for the production of electricity from waste heat. While organic conductors reach electrical conductivities as high as their inorganic counterparts, they suffer from an overall low thermoelectric figure of merit (ZT) due to their small Seebeck coefficient. Moreover, the lack of efficient n-type organic materials still represents a major challenge when trying to fabricate efficient organic thermoelectric modules. Here, a novel strategy is proposed both to increase the Seebeck coefficient and achieve the highest thermoelectric efficiency for n-type organic thermoelectrics to date. An organic mixed ion-electron n-type conductor based on highly crystalline and reduced perylene bisimide is developed. Quasi-frozen ionic carriers yield a large ionic Seebeck coefficient of -3021 mu V K-1, while the electronic carriers dominate the electrical conductivity which is as high as 0.18 S cm(-1)at 60% relative humidity. The overall power factor is remarkably high (165 mu W m(-1)K(-2)), with aZT= 0.23 at room temperature. The resulting single leg thermoelectric generators display a high quasi-constant power output. This work paves the way for the design and development of efficient organic thermoelectrics by the rational control of the mobility of the electronic and ionic carriers.

Materials with tailored properties are crucial for high performance electronics applications. Hybrid materials composed of inorganic and organic components can possess unique merits for broad application by synergy between the advantages the respective material type offers. Here we demonstrate a novel electrochemical polymerization (EP) enabled by a 2D transition metal carbide MXene for obtaining conjugated polymer-MXene composite films deposited on conducting substrates without using traditional electrolytes, indispensable compounds for commonly electrochemical polymerization. The universality of the process provides a novel approach for EP allowing fast facile process for obtaining different new polymer/MXene composites with controlled thickness and micro-pattern. Furthermore, high performance microsupercapacitors and asymmetric microsupercapacitors are realized based on the excellent composites benefiting from higher areal capacitance, better rate capabilities and lower contact resistance than conventional electropolymerized polymers. The AMSCs exhibit a maximum areal capacitance of 69.5 mF cm(-2), an ultrahigh volumetric energy density (250.1 mWh cm(-3)) at 1.6 V, and excellent cycling stability up to 10000 cycles. The excellent electrochemical properties of the composite polymerized with MXene suggest a great potential of the method for various energy storage applications.

MXenes, a young family of 2D transition metal carbides/nitrides, show great potential in electrochemical energy storage applications. Herein, a high performance ultrathin flexible solid-state supercapacitor is demonstrated based on a Mo_1.33C MXene with vacancy ordering in an aligned layer structure MXene/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) composite film posttreated with concentrated H₂SO₄. The flexible solid-state supercapacitor delivers a maximum capacitance of 568 F cm^-3, an ultrahigh energy density of 33.2 mWh cm^-3 and a power density of 19 470 mW cm^-3. The Mo_1.33C MXene/PEDOT:PSS composite film shows a reduction in resistance upon H₂SO₄ treatment, a higher capacitance (1310 F cm^-3) and improved rate capabilities than both pristine Mo_1.33C MXene and the nontreated Mo_1.33C/PEDOT:PSS composite films. The enhanced capacitance and stability are attributed to the synergistic effect of increased interlayer spacing between Mo_1.33C MXene layers due to insertion of conductive PEDOT, and surface redox processes of the PEDOT and the MXene.