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High power K+ ion capacitors have great potential in various large-scale applications because of the cost advantages and the low redox potential of K/K+. However, the large ionic radius of potassium brings huge challenges for the development of suitable electrode materials. Here we demonstrate a general strategy for preparing porous MXene electrodes that can significantly enhance K+ storage performance. Using V 2 C MXene as a model system, we show that the K+ ion storage capacity can be greatly boosted by a simple sequential acid/alkali treatment. The resulting product, K–V 2 C, not only delivers a capacity of 195 mAh g−1 (in contrast to 98 mAh g−1 of pristine V 2 C) at 50 mA g−1, but also good rate performance. The charge storage mechanism was carefully studied and is shown to involve a solvent co-intercalation process. In addition, full cells were fabricated by coupling the K–V 2 C anode and Prussian blue analogous (K x MnFe(CN) 6) cathode, which can work at a high average operating voltage of ~3.3 V within a wide range (0.01 V–4.6 V). Moreover, the devices can achieve a high energy density of 145 Wh kg−1 at a power density of 112.6 W kg−1, suggesting that K–V 2 C, and other porous MXenes prepared by our approach, are promising electrodes in mobile ion capacitors. Porous V2C MXene is made by a simple dual acid/alkali treatment, the as-obtained product K–V2C exhibits much enhanced performance for K-ion storage. The reaction mechanisms are carefully investigated via various characterizations. Image 1 • A general and simple sequential acid/alkali treatment is developed to prepare the porous MXenes. • The resulting K–V 2 C, not only delivers a capacity of 195 mAh g−1 at 50 mA g−1, but also good rate performance. • The charge storage mechanism was carefully studied by extensive characterizations such as XRD, XPS, NMR. • Full cells were fabricated successfully, which can work at a high operating voltage and achieve a high energy density. [ABSTRACT FROM AUTHOR]

We demonstrate a novel strategy to enhance sulfur loading and rate performance for Li–S battery by synchronously coupling a nanostructured cathode with an antifouling separator via a facile electrostatic self-assembly approach. The assembly of two dimensional (2D) MXene and positively charged 1D CNT-Polyethyleneimine was observed to controllably address the key issues of sluggish ionic transport, and produce an integrate cathode with dynamic crosslinking network. Moreover, an antifouling separator is proposed by this strategy for the first time, which features well-organized inter-lamellar porosity, dual polarity and high conductivity. The antifouling separator is found to play a pivotal role in: 1) low-order polysulfide activation, 2) high rate cyclability, and 3) Li dendrites inhibition. Our integrated design realizes a long-term capacity of 980 mAh g−1 at 5 mA cm−2 over 500 cycles (sulfur loading: 2.6 mg cm−2). Furthermore, a flexible self-assembled cathode with high loading (5.8 mg cm−2) and superb mechanical strength (13 MPa), demonstrates an appealing areal capacity of 7.1 mAh cm−2 and rate performance at nearly 10 mA cm−2. Image 1 • A self-assembly strategy to prepare interlinked Mxene and PEI for high loading cathode. • A separator with ultrafast ion conductivity and antifouling property. • A dual chemisorption mechanism to boost the low order polysulfide conversion. • The integrated Li–S battery showing reliable capacity (800 mAh g−1) at nearly 10 mAh cm−2. [ABSTRACT FROM AUTHOR]

MXenes, a large family of two-dimensional transition metal carbides and nitrides, have been attracting great interest since the discovery of Ti 3 C 2 T x in 2011. The unique combination of metallic conductivity and hydrophilicity in Ti 3 C 2 T x resulted in outstanding performances in electrochemical applications. The surface of MXene is highly chemically active after selective chemical etching of their precursor phases and always forms surface terminations such as hydroxyl, oxygen, or fluorine. Those surface functional groups not only affect their hydrophilic behavior and electrochemical properties such as ion adsorption and diffusion, but also affect their electronic structure, conductivity, work function, and hence their electronic properties. In this review, the emerging electronic and photonic applications of MXenes (henceforth referred to as MXetronics ) are discussed. This is a fast-emerging field of MXene research with huge potential. Image 1 • 2D Ti 3 C 2 T x MXene has shown promising performance in electrochemical energy storage applications based on its metallic conductivity and hydrophilic surface nature. • The rich surface chemistry, tunable interlayer spacing and work function of MXenes feature them as promising candidate materials in nanoelectronic devices, beyond energy storage applications. • The recent progress in electronic and photonic applications of MXenes (MXetronics) is summarized, and remaining challenges are discussed. [ABSTRACT FROM AUTHOR]

Abstract Pseudocapacitance is generally associated with either surface redox reactions or ion intercalation processes without a phase transition. Typically, these two mechanisms have been independently studied, and most works have focused on optimizing one or the other in different material systems. Here we have developed a strategy based on solubility contrast, in which the contribution from the two capacitive mechanisms is simultaneously optimized. Taking layered birnessite MnO 2 as a model, controllable nanostructures and oxygen vacancies are achieved through a simple coprecipitation process. Simultaneously controlling crystallite size and defect concentration is shown to enhance the charging-discharging kinetics together with both redox and intercalation capacitances. This synergistic effect results from enhanced ionic diffusion, electronic conductivity, and large surface-to-volume ratio. In addition, considerable cycling durability is achieved, resulting from improved framework strength by defect creation and the absence of proton (de)intercalation during discharge/charge. This work underscores the importance of synergistically regulating nanostructure and defects in redox-active materials to improve pseudocapacitive charge storage. Graphical abstract Less means more: Nanostructure and surface chemistry play significant roles in adjusting the capacitive charge storage. A simple yet efficient coprecipitation method based on the solubility difference is developed, creating oxygen vacancies and downscaling the particle size and thereby largely improving pseudocapative performance. fx1 Highlights • Solubility difference of inorganic salts controls the deposition chemistry of birnessite MnO 2. • Surface chemistry and nanostructures can be created simultaneously by the inorganic salts that can be easily removed. • Nanostructures shorten the cation diffusion pathways. • Oxygen deficiency favors high-performance pseudocapacitance due to the enhanced framework stability and electron transfer ability. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The fabrication of 3D laser-derived graphene (LDG) electrodes and their emerging applications are reviewed. • LightScribe using ordinary DVD technologies and CO2 laser-induced graphene routes are emphasized. • Tunable micro-structure, doping and selective growth of functional materials is the key for versatile nature of LDG electrodes. Abstract Printing of binder-free graphene electrodes directly on substrates has the potential to enable a large number of applications. Though conventional processing techniques such as ink-jet, screen-printing, and roll coating methods offer reliable and scalable fabrication, device performance has often been limited by re-stacking of the graphene sheets and by presence of passive binders and or additives. Laser-based, direct-write technologies have shown promise as a reliable, maskless, and template-free patterning method. Thus, laser-derived graphene (LDG) electrode is emerging as a promising three-dimensional graphene electrode that can be simultaneously derived from precursor carbons or polymers and patterned upon laser exposure. The LDG can be obtained through irradiation by a variety of laser sources including CO 2 infrared laser and femtosecond laser pulses, depending on the nature of the starting carbon precursors. Controlling the microstructure, amount and types of doping, and post-deposition methods enable a variety of applications including energy storage, catalysis, sensing and biomedicine. In this review article, we discuss recent progress in using laser-based fabrication of printed 3D graphene electrodes and its wide spectrum of applications. The review also discusses the material aspects of 3D graphene electrodes and provides an outlook for future potential. [ABSTRACT FROM AUTHOR]

Abstract Vanadium diselenide (VSe 2) is a transition metal dichalcogenide with metallic conductivity, which makes it a potentially promising electrode material for electrochemical applications. However, the development of VSe 2 electrodes for such applications has been severely hampered by the difficulty of preparing nanosized products. In this work, a new facile solvothermal synthesis process is developed and optimized to synthesize ultrathin VSe 2 nanosheet assemblies. To obtain the ultrathin nanosheets, N-methyl pyrrolidone, which has similar surface energy to many transition metal dichalcogenides, was used as the solvent to limit the crystal growth along the c -axis direction. The resulting ultrathin VSe 2 nanosheets exhibit good performance toward alkaline ion (Li+ and Na+) storage, which can be significantly enhanced by carbon coating. Specifically, the carbon-coated VSe 2 nanosheets can deliver high capacities of 768 mA h g-1 (Li+ storage) and 571 mA h g-1 (Na+ storage) along with outstanding stability. Graphic abstract Solution synthesis of ultrathin VSe 2 using NMP as the solvent. The simultaneously carbon-coated product exhibits excellent performance for both Li+ and Na+ storage. fx1 Highlights • Ultrathin VSe 2 hierarchical structure were synthesized using a facile solvothermal method. • The synthesis method provides a general idea to the rational growth of ultrathin nanosheets of other TMD materials. • The as-obtained products show good electrochemical performance toward the lithium and sodium ion storage. [ABSTRACT FROM AUTHOR]

We report a phosphine (PH 3 ) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe 2 O 3 as a demonstration, we show that the plasma activation simultaneously improves the conductivity, creates atomic-scale vacancies (defects), as well as increases active surface area, and thus leading to a greatly enhanced performance with a high areal capacitance of 340 mF cm −2 at 1 mA cm −2 , compared to 66 mF cm −2 of pristine Fe 2 O 3 . Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe 2 O 3 anodes and electrodeposited MnO 2 cathodes can achieve a high stack energy density of 0.42 mW h cm −3 at a stack power density of 10.3 mW cm −3 along with good stability (88% capacitance retention after 9000 cycles at 10 mA cm −2 ). Our work provides a simple yet effective strategy to greatly enhance the electrochemical performance of Fe 2 O 3 anodes and to further promote their application in asymmetric supercapacitors. [ABSTRACT FROM AUTHOR]

The development of miniaturized, wearable, and implantable electronics has increased the demand for small stand-alone power modules that have steady output and long life-time. Given the limited capacity of energy storage devices, one promising solution is to integrate energy harvesting and storage materials to efficiently convert ambient mechanical energy to electricity for direct use or to store the harvested energy by electrochemical means. Here, a highly compact self-charging power unit is proposed by integrating triboelectric nanogenerator with MXene-based microsupercapacitors in a wearable and flexible harvester-storage module. The device can utilize and store the random energy from human activities in a standby mode and provide power to electronics when active. As a result, our microsupercapacitor delivers a capacitance of 23 mF/cm 2 with 95% capacitance retention after 10,000 charge-discharge cycles, while the triboelectric nanogenerator exhibits a maximum output power of 7.8 µW/cm 2 . Given the simplicity and compact nature, our device can be integrated with a variety of electronic devices and sensors. [ABSTRACT FROM AUTHOR]

We report a versatile route for the preparation of metal phosphides using PH 3 plasma for supercapacitor applications. The high reactivity of plasma allows rapid and low temperature conversion of hydroxides into monometallic, bimetallic, or even more complex nanostructured phosphides. These same phosphides are much more difficult to synthesize by conventional methods. Further, we present a general strategy for significantly enhancing the electrochemical performance of monometallic phosphides by substituting extrinsic metal atoms. Using NiCoP as a demonstration, we show that the Co substitution into Ni 2 P not only effectively alters the electronic structure and improves the intrinsic reactivity and electrical conductivity, but also stabilizes Ni species when used as supercapacitor electrode materials. As a result, the NiCoP nanosheet electrodes achieve high electrochemical activity and good stability in 1 M KOH electrolyte. More importantly, our assembled NiCoP nanoplates//graphene films asymmetric supercapacitor devices can deliver a high energy density of 32.9 Wh kg −1 at a power density of 1301 W kg −1 , along with outstanding cycling performance (83% capacity retention after 5000 cycles at 20 A g −1 ). This activity outperforms most of the NiCo-based materials and renders the NiCoP nanoplates a promising candidate for capacitive storage devices. [ABSTRACT FROM AUTHOR]

In this report, we show that oxide battery anodes can be grown on two-dimensional titanium carbide sheets (MXenes) by atomic layer deposition. Using this approach, we have fabricated a composite SnO 2 /MXene anode for Li-ion battery applications. The SnO 2 /MXene anode exploits the high Li-ion capacity offered by SnO 2 , while maintaining the structural and mechanical integrity of the conductive MXene platform. The atomic layer deposition (ALD) conditions used to deposit SnO 2 on MXene terminated with oxygen, fluorine, and hydroxyl-groups were found to be critical for preventing MXene degradation during ALD. We demonstrate that SnO 2 /MXene electrodes exhibit excellent electrochemical performance as Li-ion battery anodes, where conductive MXene sheets act to buffer the volume changes associated with lithiation and delithiation of SnO 2 . The cyclic performance of the anodes is further improved by depositing a very thin passivation layer of HfO 2 , in the same ALD reactor, on the SnO 2 /MXene anode. This is shown by high-resolution transmission electron microscopy to also improve the structural integrity of the SnO 2 /MXene anode during cycling. The HfO 2 coated SnO 2 /MXene electrodes demonstrate a stable specific capacity of 843 mAh/g when used as Li-ion battery anodes. [ABSTRACT FROM AUTHOR]

Zinc ion hybrid capacitors hold great potential for future energy storage that requires both high energy density and high power capability. However, the charge storage mechanism of porous carbon cathode is ambiguous in Zn2+ ion-containing aqueous solutions, albeit porous carbon usually stores charge by electric double-layer capacitance. Herein, we developed a supermolecule-mediated direct pyrolysis carbonization strategy to convert sustainable sodium lignosulfonate resources into three-dimensional highly heteroatom-doped porous carbons with large mesopores. Through this strategy, we obtained lignin-derived porous carbons with high heteroatom dopings (14.9 at% nitrogen and 4.7 at% oxygen) and relatively high specific surface areas. Furthermore, the nitrogen doping configurations were mainly edge-nitrogen dopants even under high pyrolysis temperatures (> 900 °C). Lignin-derived nitrogen-doped porous carbon showed a high gravimetric specific capacitance of 266 F g−1 with high rate capability, which is endowed by the increased surface pseudocapacitance. First-principles calculations and molecular dynamics simulations indicate that the edge nitrogen and oxygen dopants contribute to the reversible adsorption/desorption of zinc ions and protons. Pores size less than 6.8 Å can cause a significant diffusion energy barrier for the hydrated zinc ions, thus degrading the capacitance and rate capability. [Display omitted] • A novel supermolecule-mediated defect engineering was developed to prepare high-nitrogen doped porous carbons. • Nitrogen and oxygen dopants contribute to the pseudocapacitance of porous carbon cathodes. • The influence of pore size on the storage of Zn2+ ions are investigated by molecular simulation methods. [ABSTRACT FROM AUTHOR]

Asymmetric supercapacitors provide a promising approach to fabricate capacitive energy storage devices with high energy and power densities. In this work, asymmetric supercapacitors with excellent performance have been fabricated using ternary (Ni, Co) 0.85 Se on carbon fabric as binder-free positive electrode and porous free-standing graphene film as negative electrode. Owing to their metal-like conductivity (~1.67×10 6 S m −1 ), significant electrochemical activity, and superhydrophilic nature, our nanostructured ternary nickel cobalt selenides result in a much higher areal capacitance (2.33 F cm −2 at 4 mA cm −2 ), better rate performance and cycling stability than their binary selenide equivalents, and other ternary oxides and chalcogenides. Those hybrid supercapacitors can afford impressive areal capacitance and stack capacitance of 529.3 mF cm −2 and 6330 mF cm −3 at 1 mA cm −2 , respectively. More impressively, our optimized asymmetric device operating at 1.8 V delivers a very high stack energy density of 2.85 mW h cm −3 at a stack power density of 10.76 mW cm −3 , as well as 85% capacitance retention after 10,000 continuous charge–discharge cycles. Even at a high stack power density of 1173 mW cm −3 , this device still deliveries a stack energy density of 1.19 mW h cm −3 , superior to most of the reported supercapacitors. [ABSTRACT FROM AUTHOR]

Summary Research on electrochemical energy storage devices including Li ion batteries (LIBs), Na ion batteries (NIBs) and supercapacitors (SCs) has accelerated in recent years, in part because developments in nanomaterials are making it possible to achieve high capacities and energy and power densities. These developments can extend battery life in portable devices, and open new markets such as electric vehicles and large-scale grid energy storage. It is well known that surface reactions largely determine the performance and stability of electrochemical energy storage devices. Despite showing impressive capacities and high energy and power densities, many of the new nanostructured electrode materials suffer from limited lifetime due to severe electrode interaction with electrolytes or due to large volume changes. Hence control of the surface of the electrode material is essential for both increasing capacity and improving cyclic stability of the energy storage devices. Atomic layer deposition (ALD) which has become a pervasive synthesis method in the microelectronics industry, has recently emerged as a promising process for electrochemical energy storage. ALD boasts excellent conformality, atomic scale thickness control, and uniformity over large areas. Since ALD is based on self-limiting surface reactions, complex shapes and nanostructures can be coated with excellent uniformity, and most processes can be done below 200 °C. In this article, we review recent studies on the use of ALD coatings to improve the performance of electrochemical energy storage devices, with particular emphasis on the studies that have provided mechanistic insight into the role of ALD in improving device performance. [ABSTRACT FROM AUTHOR]

Aqueous zinc batteries are among the most promising large-scale energy storage technologies but their practical application is hindered by the low redox reversibility of Zn anode in aqueous electrolytes. In this work, an indium-coated carbon-zinc composite (ICZ) anode is demonstrated with outstanding cyclic stability in classic aqueous zinc sulfate electrolytes. Compared with Zn and the carbon-zinc composite (CZ) anodes, the ICZ anode reduces the high overpotential required for Zn nucleation, and prevents high-rate HER and its related parasitic reactions, endowing high redox reversibility of the ICZ anode. Consequently, the ICZ anode enhances the cyclic stability of zinc ion batteries and zinc ion capacitors. The practical potential of the ICZ anode is demonstrated by an ICZ//porous carbon pouch cell delivering a high areal capacity of 4.7 mAh cm−2 at 6 mA cm−2. Our work provides an effective redox-kinetics regulation strategy for Zn anodes in aqueous zinc batteries. [Display omitted] • An indium-carbon composite coating layer is utilized to boost the reversibility of Zn anode. • Poor cycling stability of Zn foil is elucidated by the GCD curves and microscopy images. • High energy barrier for Zn nucleation triggers high-rate parasitic reactions. • The ICZ anode shows superior effects in suppressing parasitic reactions. • The ICZ pouch cell achieves a high areal capacity of 4.7 mAh cm−2 at 6 mA cm−2. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) are potential cost-effective electrochemical energy storage devices for future grid-scale energy storage. However, the limited capacities of carbonaceous anodes hamper their commercial development. Edge-nitrogen doping has been demonstrated as an effective strategy to enhance the reversible capacities of carbonaceous anodes. In this work, we demonstrate a general strategy to synthesize three-dimensional high edge-nitrogen doped turbostratic carbons (3D-ENTC) through catalytic pyrolysis of graphitic carbon nitride, which is enabled by metal cyanamides. The 3D-ENTC exhibits a three-dimensional carbon nanosheet framework with a high edge-nitrogen doping level of 18.9 at% and a total nitrogen doping level of 21.2 at%. Further, 3D-ENTC displays high capacities of 420 and 403 mA h g−1 at a current density of 50 mA g−1, high rate capabilities, and superior cycling stability when used as the anodes of PIBs and SIBs, respectively. The different charge storage mechanisms of 3D-ENTC anodes in PIBs and SIBs are elucidated by in situ electrochemical impedance spectroscopy. We find that 3D-ENTC stores Na+ ions mainly by adsorption, while 3D-ENTC stores K+ ions by adsorption and intercalation. This work opens a new avenue for designing high edge-nitrogen doped carbon anodes for SIBs and PIBs. Catalytic pyrolysis enables high edge-nitrogen doped carbon by annealing g-C 3 N 4 and ZnO. The carbonization mechanism of g-C 3 N 4 was uncovered using multiple techniques. The highly edge-nitrogen doped 3D-ENTC electrode shows remarkable performance towards Na and K ion storage. This work uncovers the different storage behavior of mobile K and Na in amorphous carbon anodes. This work presents a general synthesis strategy for high-edge nitrogen-doped carbon anodes for Na and K ion storage. [Display omitted] • Catalytic pyrolysis is developed for the synthesis of high edge-nitrogen doped carbon anodes. • Zinc cyanamide acts as the catalyst for retarding the complete decomposition of C 3 N 4. • The obtained carbon anode shows a high edge-nitrogen doping level of 18.9 at%. • The obtained carbon anode shows high performance for Na and K storage. • The different behaviors of Na and K storage are elucidated. [ABSTRACT FROM AUTHOR]

Due to the low density of sulfur and the large portion of carbon-based materials used as conducting network and lithium polysulfide (LiPS) host, the practical volumetric energy density of lithium–sulfur (Li–S) batteries barely rivals the Li-ion batteries. Here, MXene (Ti 3 C 2 T x)-based membrane with unique 3D hierarchical structure, high electronic conductivity, abundent active binding sites, fast ion transport, and high affinity for lithium polysulfides has been developed as a new host material to improve the electrochemical performance of Li-S batteries. With a density of 2.2 g cm−3, a MXene-based cathode containing 4.0 mg cm−2 sulfur delivers a high volumetric capacity of 2.7 Ah cm−3 after 200 cycles. Based on operando XRD and ex-situ XPS results, we find that the Ti-OH bonds present on the surface of MXene membrane can effectively trigger the LiPS transformation. Furthermore, α -S 8 , as the stable charge product, is first reported in MXene-based host along with its possible important role in curtailing active mass loss and enhancing cycling capability. Our results reveal that 2D MXene with rationally-designed architecture enable high volumetric capacity Li-S batteries for practical applications. An excellent lithium-sulfur battery with high volumetric capacity is enabled by a 3D hierarchical MXene (Ti 3 C 2 T x) electrode, which can effectively regulate the polysulfides shuttling via a dual-play immobilization mechanism of thiosulphate/polythionate redox conversion and Lewis acid-base interactions. α -S 8 is first reported as the stable charge product and its important role is studied in detail. [Display omitted] • An efficient encapsulation strategy was developed to construct a robust hierarchically structured MXene cathode of Li-S batteries. • Combined in-situ and ex-situ measurements suggest that the thiosulphate/polythionate complex serves as key redox transfer mediator to facilitate the surface-redox reaction. • α-S 8 is firstly reported as the stable charge-stage product and its fast nucleation and stability effectively curtail active mass loss and enhances cycling capability. [ABSTRACT FROM AUTHOR]

Future renewable energy integrated grid systems require rechargeable batteries with low cost, high safety, and long cycle life. The much higher abundance of sodium and potassium compared to lithium in earth crust indicates that rechargeable sodium and potassium batteries are attractive replacements for lithium-ion batteries. Rechargeable potassium batteries have gained tremendous attention during the past decade. However, the development of rechargeable potassium batteries is still in its infancy. This review summarizes the recent technological developments in rechargeable potassium batteries. First, we summarize the latest achievements of active materials design, mechanistic understanding, and exploration of new active materials. We propose new directions in tuning the architecture and enhancing the electrochemical performances of high-performance anodes and cathodes. Second, we also summarize the advances that have been achieved in the new configurations of rechargeable potassium battery systems (potassium-ion capacitors, potassium dual ion batteries, potassium-sulfur batteries, and potassium-oxygen batteries). Finally, we propose future directions and design strategies that could be employed to advance rechargeable potassium batteries toward commercial applications. In this review, a large family of rechargeable batteries based on potassium as charge carrier are summarized. Rechargeable potassium ion batteries include potassium-ion batteries, potassium-ion capacitors, potassium-ion-based dual ion batteries, potassium-sulfur batteries, and potassium-oxygen batteries. Future directions and design strategies that could be employed to advance rechargeable potassium batteries toward commercial applications are proposed. [Display omitted] • Rechargeable potassium ion battery as a promising rechargeable battery system. • Current status and future research trends of rechargeable potassium batteries. • Strategies for developing practical anodes and cathodes for potassium batteries. • Recent advances of different configurations of rechargeable potassium batteries. [ABSTRACT FROM AUTHOR]

Organic dual-ion batteries show high energy densities which are, in principle, suitable for large-scale energy storage, but they suffer from inherent instability and safety issues. Aqueous batteries feature low cost, high ionic conductivity, and much improved safety, showing more enormous potential for grid-scale energy storage. Conventional dual-ion batteries (DIBs) involve the reversible intercalation of electrolyte-born anions and cations into cathodes and anodes, respectively. Here we develop a new full aqueous battery involving the co-intercalation of K+ and H+ in both anode and cathode. This dual-ion battery constitutes a cathode of defective Prussian Blue nanostructures, an anode of atomically thin Ti 3 C 2 T x MXene nanosheets, and an aqueous electrolyte of mildly acidic KNO 3 solution. The open frameworks of both cathode and anode together with the existence of abundant structural water in both electrodes enable fast kinetics for K+ and H+ (de)intercalation. Accordingly, the full battery exhibits improved energy (e.g., 41.5 Wh kg1 based on both cathode and anode) and power (e.g., 5030 W kg1) densities, whereas capacity retention of 74% can be achieved after 3000 cycles. We believe that this new dual-cation battery design presents a promising way to improve aqueous battery performance. Different from the conventional dual-ion batteries, a dual-cation battery is developed using a nanostructured Prussian Blue cathode and a Ti 3 C 2 T x MXene anode. The structural water networks in cathode and anode enable fast co-intercalation of H+ and K+, allowing for improved power and energy densities and stability for this dual-cation battery. ga1 • Abundant structural H 2 O in Prussian Blue cathode and MXene anode. • Sufficient tunnel size of cathode and interlayer space of anode. • Promoted H+ and K+ cointercalation into cathode and anode induced by structural H 2 O and enlarged tunnels/interlayer spacing. • Enhanced energy density, power density and cycling stability. [ABSTRACT FROM AUTHOR]

We report a novel flexible solar tracking system based on a photothermal-thermomechanical (PT-TM) actuator comprised of Ti 3 C 2 T x MXene and polyvinylidene fluoride (PVDF) bilayer. The actuation function of the proposed device originates from photothermal and surface plasmon-assisted effects in MXenes, coupled with thermomechanical deformation of in-plane aligned PVDF polymer. Two types of solar tracking modes are evaluated based on the experimental deformation behavior of the PT-TM actuator. We find that the uniaxial East-West solar tracking option increases the overall energy intensity reaching the solar module by over 30%, in comparison with the optimized tilting-controlled mode. We also demonstrate the thermally driven self-oscillation of the MXene-PVDF device, which may have promising potential for optically and thermally driven soft robotics. The PT-TM actuator devices display robust mechanical strength and durability, with no noticeable degradation in their performance after more than 1000 cycles. A novel flexible photothermal-thermomechanical (PT-TM) actuator comprised of Ti 3 C 2 T x MXene and polyvinylidene fluoride (PVDF) bilayer is developed. The actuation function of the proposed device originates from photothermal and surface plasmon-assisted absorption in MXenes, coupled with thermomechanical deformation of in-plane aligned PVDF polymer. The actuator can greatly enhance solar energy harvesting compared to a tilt-controlled solar tracking system. Image 1 • The actuation mechanism is shown to originate from thermomechanical deformation of the in-plane aligned PVDF polymer chains coupled with optical absorption effects in MXene. • We demonstrate that our autonomous actuator can be used in a solar tracking application and can increase the overall energy intensity reaching the solar module by over 30% compared to the optimized tilting-controlled mode. • We also demonstrate thermally driven self-oscillation of MXene-PVDF device, which may have potential in optically and thermally driven soft robotics. [ABSTRACT FROM AUTHOR]

Rationally constructing an interlayer to suppress the lithium polysulfide (LiPS) shuttling but allow fast transport of Li-ions is of great significance for high-density Li–S batteries. Despite numerous nanomaterials have been explored, an effective approach to fabricate an ideal interlayer is still elusive. Herein, we developed a new electropolymerization strategy to grow in-situ a polycarbazole-type interlayer with a number of merits to boost the reversible capacity. Firstly, the membrane is microporous but compact with uniform 0.82 nm nanochannels that can effectively suppress the diffusion of polysulfide species. Secondly, using the CNT (700 nm) as conductive substrate, the electropolymerized membrane is ultrathin (60 nm), which facilitates fast transport of lithium ions and rate performance. Thirdly, the membrane is electron conductive (23 S m−1) that benefits the charge transfer and redox reaction. Li–S batteries configured with such an UCCM type of interlayer have showed enhanced sulfur utilization by threefold, with a reversible capacity of 920 mA h g−1 after 600 cycles at 0.2 C, and a high areal density of 10 mAh cm−2 at 11.2 mg cm−2 sulfur loading. A safer lithium-ion sulfur full-cell with lithiated graphite anode demonstrated a stable capacity over 4 mAh cm−2 under a low electrolyte/sulfur ratio of ~10 μL mg−1. An ultrathin, continuous, and conductive microporous sieving membrane was grown in-situ on Li–S separator via an electropolymerization technique. This novel technique significantly inhibits the polysulfide shuttling, provides fast pathways for Li+ transport, and enhances charge transfer kinetics. Image 1 • An electropolymerization approach is developed to grow high-performance interlayers for Li–S battery. • Such an interlayer is ultrathin, continuous, microporous with desired conductivity and polysulfides suppression ability. • Li–S full cell shows a reliable capacity (10 mAh cm−2) at 11.2 mg cm−2 sulfur loading. • The electropolymerization mechanism is explored as a universal nanofilms fabrication method. [ABSTRACT FROM AUTHOR]

A critical limitation to conventional electrochemical double-layer capacitors is their low energy densities. This has triggered significant interest in developing new pseudocapacitive materials, which utilize faradaic mechanisms to increase their energy densities. In this work, graphitic carbon nitride (g-C 3 N 4) and Ti 3 C 2 T x MXene are hybridized to form a unique two-dimensional (2D) heterostructure, which delivers remarkable pseudocapacitive characteristics and robust stability towards lithium storage. Interestingly, the improved kinetics is reflected by insignificant influence of (dis)charge rates on the pseudocapacitance even when testing at a 120C rate, and small peak potential offsets at high scan rates, revealing that there are no significant diffusion limitations in the heterostructure. This unexpected fast kinetics is related to the intrinsic chemical and electronic coupling effects between g-C 3 N 4 and MXene, which can synergistically improve both electron transfer and lithium diffusion kinetics compared to MXene itself. Couple makes double: The abundant surface terminations of MXene make it feasible to directly grow a thin layer of g-C 3 N 4 on the surface of MXene, bringing strong coupling effect between these two 2D materials. The resultant charge redistribution not only facilitates the Li+ intercalation kinetics, but also improves the electrochemical cycling stability. Image 1 • The fascinating surface chemistry of MXene allows rational design of two-dimensional heterostructure. • Strong chemical bonding exists between MXene and g-C 3 N 4. • The heterostructure shows excellent Li+ intercalation pseudocapacitance. • Chemical-bonding-induced charge redistribution ensures a fast Li+ intercalation kinetics. [ABSTRACT FROM AUTHOR]

Efficient carrier extraction is essential for high performance optoelectronic devices, such as solar cells and photodetectors. Conventional strategies to separate photogenerated carriers typically involve the fabrication of a p-n junction by doping and the use of carrier selective charge transport layers. However, these techniques often require high temperature processes or costly materials. In this work, we demonstrate an innovative and simple approach of extracting photogenerated carriers from organometallic halide perovskites utilizing triboelectricity. The triboelectric device can be easily fabricated at low temperature using inexpensive materials on plastic substrates, enabling it to be readily integrated into self-powered optoelectronic devices. As a proof-of-concept, we fabricated a triboelectrics-assisted perovskite photodetector, which enabled us to study the surface charges generated using different electrical contacts and bending conditions performed by the device. With the assistance of a triboelectric charge-induced electric field, the photocurrent and transient photoresponses were significantly enhanced. Furthermore, we integrated the plastic triboelectric device with a flexible photodetector to demonstrate this carrier collection approach in flexible/wearable electronics. To the best of our knowledge, this work is the first report of carrier extraction in organometallic halide perovskite photodetector by triboelectric charges, demonstrating a potential use for carrier extraction in other semiconductor-based optoeletronic devices. Image 1 ● We demonstrate a novel approach to extract photo-generated carriers from an organometallic halide perovskite PD by triboelectricity generated by harvesting mechanical energy. ● We study and verify the working principle of photo-carrier extraction by such an approach by a series of electrical characterization. ● We demonstrate the modulation of photoresponse of a perovskite PD by mechanical bending of the triboelectric generator. ● This work not only presents an innovative approach to realize photo-carrier extraction by triboelectricity from mechanical motion, but also demonstrates carrier transport layer-free optoelectronic devices for potentially more simple and stable devices. [ABSTRACT FROM AUTHOR]

In this paper pulsed laser deposition (PLD) methods are used to study p-n CdTe/CdS heterojunctions fabricated in-situ . In-situ film deposition allows higher quality p-n interfaces by minimizing spurious contamination from the atmosphere. Morphologic and structural analyses were carried for CdTe films deposited on various substrates and different deposition conditions. The electrical characteristics and performance of the resulting p-n heterojunctions were studied as function of substrate and post-deposition anneal temperature. In-situ growth results on diodes with a rectification factor of ~ 10 5 , an ideality factor < 2, and a reverse saturation current ~ 10 − 8 A. The carrier concentration in the CdTe film was in the range of ~ 10 15 cm − 3 , as measured by C-V methods. The possible impact of sulfur diffusion from the CdS into the CdTe film is also investigated using High Resolution Rutherford Back-Scattering. [ABSTRACT FROM AUTHOR]

The thermal stability and contact resistance of TaAlN thin films as electrical contacts to SiGe thermoelectric elements are reported. We demonstrate that a sharp interface is maintained after the device annealed at 800 ° C for over 100 h, indicating that no interdiffusion takes place between TaAlN and SiGe. A specific contact resistivity of (2.1 ± 1.3) × 10 −6 Ω-cm 2 for p-type SiGe and (2.8 ± 1.6) × 10 −5 Ω-cm 2 for n-type SiGe is demonstrated after the high temperature annealing. These results show that TaAlN is a promising contact material for high temperature thermoelectrics such as SiGe. [ABSTRACT FROM AUTHOR]

Ternary transition metal oxides such as NiCo 2 O 4 show great potential as supercapacitor electrode materials. However, the unsatisfactory rate performance of NiCo 2 O 4 may prove to be a major hurdle to its commercial usage. Herein, we report the development of NiCo 2 O 4 @TiN core–shell nanostructures for all-solid-state supercapacitors with significantly enhanced rate capability. We demonstrate that a thin layer of TiN conformally grown by atomic layer deposition (ALD) on NiCo 2 O 4 nanofiber arrays plays a key role in improving their electrical conductivity, mechanical stability, and rate performance. Fabricated using the hybrid NiCo 2 O 4 @TiN electrodes, the symmetric all-solid-state supercapacitor exhibited an impressive stack power density of 58.205 mW cm −3 at a stack energy density of 0.061 mWh cm −3 . To the best of our knowledge, these values are the highest of any NiCo 2 O 4 -based all-solid-state supercapacitor reported. Additionally, the resulting NiCo 2 O 4 @TiN all-solid-state device displayed outstanding cycling stability by retaining 70% of its original capacitance after 20,000 cycles at a high current density of 10 mA cm −2 . These results illustrate the promise of ALD-assisted hybrid NiCo 2 O 4 @TiN electrodes within sustainable and integrated energy storage applications. [ABSTRACT FROM AUTHOR]

Organometal trihalide perovskite solar cells have recently attracted lots of attention in the photovoltaic community due to their escalating efficiency and solution processability. The most efficient organometallic mixed-halide sensitized solar cells often employ 2,2′7,7′-tetrakis-( N , N -di- p -methoxyphenyl-amine)-9,9′-spirobifluorene (spiro-MeOTAD) as the hole-transporting material. In this work, we investigated the effect of different atmospheric storage conditions, particularly vacuum, dry nitrogen, and dry air, on the photovoltaic performance of TiO 2 –CH 3 NH 3 PbI 3− x Cl x –spiro-MeOTAD solar cells. We found that spin coating of spiro-MeOTAD in an oxygen atmosphere alone was not adequate to functionalize its hole-transport property completely, and our systematic experiments revealed that the device efficiency depends on the ambient atmospheric conditions during the drying process of spiro-MeOTAD. Complementary incident photon to current conversion efficiency (IPCE), light absorption and photoluminescence quenching measurements allowed us to attribute the atmosphere-dependent efficiency to the improved electronic characteristics of the solar cells. Furthermore, our Fourier transform infrared and electrical impedance measurements unambiguously detected modifications in the spiro-MeOTAD after the drying processes in different gas environments. Our findings demonstrate that proper oxidization and p-doping in functionalizing spiro-MeOTAD play a very critical role in determining device performance. These findings will facilitate the search for alternative hole-transporting materials in high-performance perovskite solar cells with long-term stability. [ABSTRACT FROM AUTHOR]

Abstract: A round robin for the performance of roll-to-roll coated flexible large-area polymer solar-cell modules involving 18 different laboratories in Northern America, Europe and Middle East is presented. The study involved the performance measurement of the devices at one location (Risø DTU) followed by transportation to a participating laboratory for performance measurement and return to the starting location (Risø DTU) for re-measurement of the performance. It was found possible to package polymer solar-cell modules using a flexible plastic barrier material in such a manner that degradation of the devices played a relatively small role in the experiment that has taken place over 4 months. The method of transportation followed both air-mail and surface-mail paths. [Copyright &y& Elsevier]

Laser-derived graphene (LDG) technology is gaining attention as a promising material for the development of novel electrochemical sensors and biosensors. Compared to established methods for graphene synthesis, LDG provides many advantages such as cost-effectiveness, fast electron mobility, mask-free, green synthesis, good electrical conductivity, porosity, mechanical stability, and large surface area. This review discusses, in a critical way, recent advancements in this field. First, we focused on the fabrication and doping of LDG platforms using different strategies. Next, the techniques for the modification of LDG sensors using nanomaterials, conducting polymers, biological and artificial receptors are presented. We then discussed the advances achieved for various LDG sensing and biosensing schemes and their applications in the fields of environmental monitoring, food safety, and clinical diagnosis. Finally, the drawbacks and limitations of LDG based electrochemical biosensors are addressed, and future trends are also highlighted. • Laser-derived graphene (LDG) is a new material for the development of electrochemical sensors and biosensors. • Methods for fabrication of LDG are discussed. • Strategies for the modification of LDG for electrochemical sensors and biosensors are outlined. • These sensing strategies have found applications in environmental monitoring, food safety, and clinical diagnosis. • Current challenges and future perspectives in the field of LDG based electrochemical sensors and biosensors. [ABSTRACT FROM AUTHOR]

Laser-scribed graphene electrodes (LSGEs) have recently shown a potential for the development of electrochemical biosensors thanks to their electronic properties, porous structures, and large surface area that can support the charge transfer. In this paper, the authors present a comparative study of the electrochemical performances of LSGEs with the conventional screen-printed carbon electrodes (SPCEs) toward the detection of most commonly used phenolic compounds and biomolecules. Cyclic voltammetry measurements showed a significant enhancement in the electron transfer rate of all tested electroactive species at LSGEs compared to conventional SPCE. We have suggested, for the first time, a mechanistic study for catecholamine redox reactions at LSGE as the electron transfer–chemical reaction–electron transfer mechanism. Moreover, the excellent performances of LSGE were observed in terms of the electrocatalytic detection of paracetamol (PCM). Therefore, the second part of this study compared the analytical performances of LSGE and SPCE with respect to the detection of PCM. The LSGE allows a fast and reversible system for PCM with a low ΔE p of 88 mV while the SPCE exhibits a quasi-reversible system with a higher ΔE p of 384 mV. The LSGE demonstrated a PCM linear range of concentration between 0.1 μM and 10 μM, with a detection limit of 31 nM. In addition, the LSGE showed a successful applicability with good selectivity and sensitivity for PCM determination in real samples of pharmaceutical tablets. Hence, LSGEs could be an excellent platform for simple and low-cost electrochemical biosensor applications. • Production of mask-free, porous LSGE and their first ever electrochemical application for biomolecules detection. • LSGE enhances the electrocatalytic activity as well as the electron transfer rate of all tested biomolecules. • A mechanism for the oxidation-reduction reaction of catecholamines and their precursor LDopa was proposed. • The LSGE allows a fast and reversible system for PCM, while the SPCE exhibits a quasi-reversible system. • The LSGE demonstrated a LOD of 31 nM for PCM with high selectivity in pharmaceutical formulation samples. [ABSTRACT FROM AUTHOR]