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Potassium-ion batteries (PIBs) are appealing alternatives to conventional lithium-ion batteries (LIBs) because of their wide potential window, fast ionic conductivity in the electrolyte, and reduced cost. However, PIBs suffer from sluggish K+ reaction kinetics in electrode materials, large volume expansion of electroactive materials, and the unstable solid electrolyte interphase. Various strategies, especially in terms of electrode design, have been proposed to address these issues. In this review, the recent progress on advanced anode materials of PIBs is systematically discussed, ranging from the design principles, and nanoscale fabrication and engineering to the structure-performance relationship. Finally, the remaining limitations, potential solutions, and possible research directions for the development of PIBs towards practical applications are presented. This review will provide new insights into the lab development and real-world applications of PIBs.

The rapid development of miniaturized and wearable electronics has stimulated growing needs for compatible miniaturized energy storage components. Owing to their unlimited lifetime and high-power density, miniaturized electrochemical capacitors (microsupercapacitors) are considered to be an attractive solution for the development of these microelectronics, but they often depend on the choice of electrode materials and fabrication protocols for scalable production. Recently, a new family of two-dimensional transition metal carbides, carbonitride and nitrides (referred to as MXenes) has shown great promise in advanced microsupercapacitors with high energy and power densities. This was achieved thanks to the high pseudocapacitance, metallic conductivity and ease of solution processing of MXene. In this review, recent progress on MXene synthesis, microstructure design, and fabrication strategies of MXene microsupercapacitors are discussed, and their electrochemical performance is summarized. Further, we briefly discuss the technical challenges and future directions.

International audience; In this work, a pre-designed Zr-based-MOF encompassing an organic linker with a redox active core is synthesized and its structureproperty relationship as a supercapacitor electrode is investigated. An enhanced performance is revealed by the combination of this MOF's high porosity and redox core incorporation, which alters its double-layer and pseudocapacitance, respectively. An increase in the capacitance performance by a factor of two is achieved via post-synthetic structure rigidification using organic pillars.

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 V2C 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–V2C, not only delivers a capacity of 195 mAh g−1 (in contrast to 98 mAh g−1 of pristine V2C) 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–V2C anode and Prussian blue analogous (KxMnFe(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–V2C, and other porous MXenes prepared by our approach, are promising electrodes in mobile ion capacitors.

In this work, we systematically investigate and compare the activity of MnCo-based electrocatalysts (i.e. selenide, oxide, and hydroxide) for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline solutions. The result indicates that the selenides are oxidized upon OER and the surface generated oxides are the real OER active species. The MnCo selenides exhibit a significantly enhanced performance as compared to the oxide and hydroxide though the real active OER species of these three catalysts are essentially the same. The superior activity of MnCo selenides could be attributed to the high intrinsic conductivity and the high surface active area. Further, the synergy between Mn and Co lowers the energy barrier for catalysis and helps to stabilize the material. The bimetallic MnCo selenides with yolk shell structures possess the optimal electrochemical performance with a low cell voltage of 1.66 V at the current density of 50 mA cm−2, outperforming most of the earth-abundant electrocatalysts. Our work provides a better understanding of the active species of metal selenides and the origin of the performance disparity between selenides (-derived oxides) and oxides electrocatalysts.

Vanadium diselenide (VSe2) is a transition metal dichalcogenide with metallic conductivity, which makes it a potentially promising electrode material for electrochemical applications. However, the development of VSe2 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 VSe2 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 VSe2 nanosheets exhibit good performance toward alkaline ion (Li+ and Na+) storage, which can be significantly enhanced by carbon coating. Specifically, the carbon-coated VSe2 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.

The performance of chemically intercalated V2O5 was found to strongly depend on the interlayer spacing, which is related to the radius of hydrated metal ion, which can be readily tuned by using different intercalated metals. We report a layered Mg2+-intercalated V2O5 as the cathode material for aqueous ZIBs. The large radius of hydrated Mg2+ (∼4.3 A, compared with 3.8 A of commonly used Li+) results in an interlayer spacing as large as 13.4 A (against 11.07 A for Li+-intercalated V2O5), which allows efficient Zn2+ (de)insertion. As a result, the obtained porous Mg0.34V2O5·0.84H2O cathodes work in a wide potential window of 0.1 to 1.8 V versus Zn2+/Zn, and can deliver high capacities of 353 and 264 mA h g–1 at current densities of 100 and 1000 mA g–1, respectively, along with long-term durability. Furthermore, the reversible Zn2+ (de)intercalation reaction mechanism is confirmed by multiple characterizations methods.

Developing advanced materials with high catalytic activity for electrocatalytic applications is of vital importance to mitigate the energy crisis. In this work, we for the first time report a novel method to prepare bimetallic vanadium‑molybdenum nitride (MoVN) thin films by magnetron co-sputtering and further demonstrate their applications for hydrogen evolution reaction (HER). When used as HER catalysts, the resulting MoVN thin film electrodes show superior electrocatalytic activity especially in alkaline electrolyte in contrast to bare VN and Mo2N, delivering a low overpotential of 108 mV to afford a current density of 10 mA cm−2, a Tafel slope of 60 mV dec−1, as well as excellent long-term durability. Most importantly, our study opens opportunities to explore new HER catalyst materials in the family of bimetallic transition metal nitrides. Keywords: Electrocatalytic activity, Bimetallic nitrides, Magnetron co-sputtering, Hydrogen evolution reaction

We report a phosphine (PH3) plasma activation strategy for significantly boosting the electrochemical performance of supercapacitor electrodes. Using Fe2O3 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 Fe2O3. Moreover, the asymmetric supercapacitor devices based on plasma-activated Fe2O3 anodes and electrodeposited MnO2 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 Fe2O3 anodes and to further promote their application in asymmetric supercapacitors.

Metal-layered double hydroxides (LDHs), a family of versatile layered materials recently popular as earth-abundant oxygen evolution reaction (OER) catalysts, allow for both metal substitution and interlayer anion exchange without disrupting the two-dimensional (2D) crystal structure, although the ubiquity of carbonate anions is challenging to avoid. Here, we use hydrothermal synthesis in modified solvents with triethanolamine to directly synthesize bulk NiFe LDHs with carbonate, chloride, and sulfate interlayer anions without inert atmosphere protection. Structural characterizations by X-ray diffraction, infrared spectroscopy, and energy-dispersive X-ray spectroscopy confirm the anion composition. Electrochemical characterization shows that LDHs with these three anions display similar OER catalytic performance after surface area normalization, consistent with observed anion exchange to carbonate in alkaline electrolyte under ambient conditions. However, dodecyl sulfate-intercalated NiFe LDHs prepared by a...

Transition metal nitrides are regarded as a new class of excellent electrode materials for high-performance supercapacitors due to their superior chemical stability and excellent electrical conductivity. We synthesize successfully the porous CrN thin films for binder-free supercapacitor electrodes by reactive magnetron co-sputtering and selective chemical etching. The porous CrN thin film electrodes exhibit high-capacitance performance (31.3 mF cm−2 at 1.0 mA cm−2) and reasonable cycling stability (94% retention after 20000 cycles). Moreover, the specific capacitance is more than two-fold higher than that of the CrN thin film electrodes in previous work. In addition, a symmetric supercapacitor device with a maximum energy density of 14.4 mWh cm−3 and a maximum power density of 6.6 W cm−3 is achieved. These findings demonstrate that the porous CrN thin films will have potential applications in supercapacitors.

A series of graphitic-C3N4/ZnS (g-C3N4/ZnS) supercapacitor electrode materials have been prepared via a one-step calcination process of zinc acetate/thiourea with different mass ratios under nitrogen atmosphere. The optimized g-C3N4/ZnS composite shows a highest specific capacitance of 497.7 F/g at 1 A/g and good cycling stability with capacitance retention of 80.4% at 5 A/g after 1000 cycles. Moreover, g-C3N4/ZnS composites display an improved supercapacitor performance in terms of specific capacitance compared to the pure g-C3N4 and ZnS. In addition, our designed symmetric supercapacitor device based on g-C3N4/ZnS composite electrodes can exhibit an energy density of 10.4 Wh/kg at a power density of 187.3 W/kg. As a result, g-C3N4/ZnS composites are expected to be a prospective material for supercapacitors and other energy storage applications.

NiFe oxyhydroxide (NiFe−OH) has shown promising electrocatalytic oxygen evolution reaction (OER) activity. Here we suggest that the performance of NiFe−OH can be further enhanced by constructing pn junction. Using MnCo carbonate hydroxide (MnCo−CH)@NiFe−OH pn junction as a demonstration, we show that upon the construction of pn junction, the electrons flow from n-type NiFe−OH to MnCo−CH, which consequently generates a positively charged region on NiFe−OH. The density function theory calculation reveals that such an electronic property change results in an improved OER energetics. As a result, the MnCo−CH@NiFe−OH pn junction shows significantly enhanced OER performance that is ∼10 and ∼500 times that of NiFe−OH and MnCo−CH (in terms of the OER currents at the overpotential of 270 mV), respectively. Moreover, the pn junction also shows a greatly boosted hydrogen evolution reaction (HER) and therefore the overall water electrolysis activity that outperforms the Pt/C||RuO2 catalysts.

In this work, we demonstrate that the electrocatalytic activity of transition metal chalcogenides can be greatly enhanced by simultaneously engineering the active sites, surface area, and conductivity. Using metal-organic frameworks-derived (Ni,Co)Se 2 /C hollow rhombic dodecahedra (HRD) as a demonstration, we show that the incorporation of Ni into CoSe 2 could generates additional active sites, the hierarchical hollow structure promotes the electrolyte diffusion, the in-situ hybridization with C improves the conductivity. As a result, the (Ni,Co)Se 2 /C HRD exhibit superior performance toward the overall water-splitting electrocatalysis in 1 M KOH with a cell voltage as low as 1.58 V at the current density of 10 mA cm −2 , making the (Ni,Co)Se 2 /C HRD as a promising alternative to noble metal catalysts for water splitting.

Efficient water splitting demands highly active, low cost, and robust electrocatalysts. In this study, we report the synthesis of penroseite (Ni,Co)Se2 nanocages anchored on 3D graphene aerogel using Prussian blue analogues as a precursor and further their applications in overall water splitting electrolysis. The synergy between the high activity of (Ni,Co)Se2 and the good conductivity of graphene leads to superior performance of the hybrid toward the water splitting in basic solutions. The (Ni,Co)Se2-GA only requires a low cell voltage of 1.60 V to reach the current density of 10 mA cm–2, making the (Ni,Co)Se2-GA hybrid a competitive alternative to noble metal based catalysts for water splitting.

The solution synthesis of ternary metal oxides is difficult due to the competing hydrolysis of metal ions. There are reports of hydro-/solvothermal growth of nanoparticles, but one-dimensional (1D) nanoarrays are less common. Here, we report an alternative and general strategy to circumvent this challenge by converting the 1D binary metal oxide/hydroxide nanostructures initially grown driven by screw dislocations into ternary oxides. Using the α-GaOOH/α-Ga2O3/ZnGa2O4 wide bandgap transparent conductor materials as a demonstration, we synthesize vertical arrays of high aspect ratio α-GaOOH nanorods (NRs) on conducting substrates with controllable length for the first time using a continuous flow reactor and confirm their growth mechanism to be dislocation-driven. Then the α-GaOOH NR arrays can be converted into porous α-Ga2O3 NR arrays, which can be further converted via a solution method into porous ZnGa2O4 nanotube (NT) arrays due to the Kirkendall effect. This work presents a new and general strategy to...

In this report, we demonstrate a simple chemical bath deposition approach for the synthesis of layered SnS nanosheets (typically 6 nm or ∼10 layers thick) at very low temperature (40 °C). We successfully synthesized SnS/C hybrid electrodes using a solution-based carbon precursor coating with subsequent carbonization strategy. Our data showed that the ultrathin carbon shell was critical to the cycling stability of the SnS electrodes. As a result, the as-prepared binder-free SnS/C electrodes showed excellent performance as sodium ion battery anodes. Specifically, the SnS/C anodes delivered a reversible capacity as high as 792 mAh·g−1 after 100 cycles at a current density of 100 mA·g−1. They also had superior rate capability (431 mAh·g−1 at 3,000 mA·g−1) and stable long-term cycling performance under a high current density (345 mAh·g−1 after 500 cycles at 3 A·g−1). Our approach opens up a new route to synthesize SnS-based hybrid materials at low temperatures for energy storage and other applications. Our process will be particularly useful for chalcogenide matrix materials that are sensitive to high temperatures during solution synthesis.

We report a versatile route for the preparation of metal phosphides using PH3 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 Ni2P 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.

Water splitting driven by electricity or sunlight is one of the most promising ways to address the global terawatt energy needs of future societies; however, its large-scale application is limited by the sluggish kinetics of the oxygen evolution reaction (OER). NiFe-based compounds, mainly oxides and hydroxides, are well-known OER catalysts and have been intensively studied; however, the utilization of the synergistic effect between two different NiFe-based materials to further boost the OER performance has not been achieved to date. Here, we report the rapid conversion of NiFe double hydroxide into metallic NiFeP using PH3 plasma treatment and further construction of amorphous NiFe hydroxide/NiFeP/Ni foam as efficient and stable oxygen-evolving anodes. The strong electronic interactions between NiFe hydroxide and NiFeP significantly lower the adsorption energy of H2O on the hybrid and thus lead to enhanced OER performance. As a result, the hybrid catalyst can deliver a geometrical current density of 300 ...

Supercapacitors have been becoming indispensable energy storage devices in micro-electromechanical systems and have been widely studied over the past few decades. Transition metal nitrides with excellent electrical conductivity and superior cycling stability are promising candidates as supercapacitor electrode materials. In this work, we report the fabrication of CrN thin films using reactive DC magnetron sputtering and further their applications for symmetric supercapacitors for the first time. The CrN thin film electrodes fabricated under the deposition pressure of 3.5 Pa show an areal specific capacitance of 12.8 mF cm−2 at 1.0 mA cm−2 and high cycling stability with 92.1% capacitance retention after 20 000 cycles in a 0.5 M H2SO4 electrolyte. Furthermore, our developed CrN//CrN symmetric supercapacitor can deliver a high energy density of 8.2 mW h cm−3 at the power density of 0.7 W cm−3 along with outstanding cycling stability. Thus, the CrN thin films have great potential for application in supercapacitors and other energy storage systems.

Nickel molybdate (NiMoO4) has been regarded as a promising battery-type electrode material for hybrid supercapacitors (HSCs) because of its low cost, high theoretical capacity and richer redox reactions. However, its large-scale application is limited by the poor rate performance and low stability. In this work, we suggest that the electronic structure tuning can effectively improve the capacity but also enhance the stability. Such tuning can be readily realized by coupling NiMoO4 with SnO2. The introduction of SnO2 promotes the electron transfer from NiMoO4 to SnO2 and therefore reduces the electron density of NiMoO4, which leads to an enhanced adsorption of OH− ions and thus boosts the capacity. As a result, the SnO2@NiMoO4/CP core-shell electrode exhibits a high capacity of 0.65 mA h cm−2 (257.8 mAh g−1) at a current density of 5 mA cm−2 (2 mA g−1) along with greatly enhanced stability. Besides, the assembled HSC device using SnO2@NiMoO4/CP as cathode and active carbon/CP as anode shows a superior specific capacity of 109.5 mAh g−1 at 5 mA cm−2 and excellent cycling performance with a capacity retention of 92.2% at 50 mA cm−2, as well as a high specific energy of 78.4 Wh kg−1 at a power density of 895 W kg−1, outperforming many other reported hybrid supercapacitors.

Metal nitrides are potential electrode materials for supercapacitors because of their high conductivity, high capacitance and good corrosion resistance. Herein, we present a general strategy to prepare self-standing bimetallic nitride thin film nanostructures using magnetron co-sputtering and further to boost their electrochemical performance for supercapacitors. Using niobium titanium nitride (TiNbN) as an example, we show that the synergy of Ti and Nb greatly boosts the capacitive performance to a high specific capacitance of up to 59.3 mF cm−2 at 1.0 mA cm−2, along with outstanding cycling stability for at least 20000 cycles. We further demonstrate an all metal nitride based asymmetric device by combing TiNbN with a vanadium nitride (VN) negative electrode. The asymmetric device operates at a voltage window of 1.6 V and achieves a maximum energy density 74.9 mWh cm−3 at a power density of 8.8 W cm−3. Our work not only presents a first demonstration of employing TiNbN as supercapacitor electrode material, but also opens up new possibility for the rational construction of all nitride based high performance asymmetric supercapacitors.

A big challenge in practical water splitting is the sluggish reaction kinetics at high current densities that essentially requires efficient electrocatalysts to lower the overpotentials. While exciting progress has been made in noble metal-based catalysts, earth-abundant materials that can actively catalyze the water splitting at high current densities (e.g. ≥500 mA cm−2) are rare. In this work, we show that a rational design of the catalysts could promote the charge transfer, facilitate the gas release, as well as boost the surface active sites, and therefore significantly enhance the electrocatalytic activity toward both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Using NiCo/NiCo−OH and NiFe/NiFe−OH as examples, we achieved ultralow overpotentials of 184 and 296 mV at 500 mA cm−2 in 1M KOH for HER and OER, respectively. More importantly, the alkaline electrolyzer based on these two materials is able to actively drive the overall water splitting at 1000 mA cm−2 for at least 300 h at a low cell voltage without significant performance decay, which is much superior to the state-of-the-art 20 % Pt/C||RuO2 combination. Our work points out a promising pathway to achieve inexpensive electrocatalysts for practical water splitting at high currents.

Herein we report the control synthesis of lepidocrocite VOOH hollow nanospheres and further their applications in electrocatalytic water splitting for the first time. By tuning the surface area of the nanospheres, the optimal performance can be achieved with low overpotentials of 270 mV for the oxygen evolution reaction (OER) and 164 mV for the hydrogen evolution reaction (HER) at 10 mA cm−2 in 1 m KOH, respectively. Furthermore, when used as both the anode and cathode for overall water splitting, a low cell voltage of 1.62 V is required to reach the current density of 10 mA cm−2, making the VOOH hollow nanospheres an efficient alternative to water splitting.

A series of coral-like Co-doped ZnS were synthesized by hydrothermal method and used for efficient photodegradation of methylene blue. The chemical composition and microstructure of the Co-doped ZnS were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, UV–vis diffuse reflectance spectra, scanning electron microscope, and transmission electron microscopy. The results showed that the Co atoms were incorporated into the Zn-S lattice, forming solid solution-type phase. As the Co dopant concentration increases from 0 to 22.49 at.%, the calculated band gap energy of the doped ZnS decreases from 3.32 to 2.65 eV, which enables stronger absorption of visible light. Furthermore, the Co dopant could act as electron trapping center, which inhibits the recombination of the photoinduced electrons and holes. As such, the Co-doped ZnS micro-corals showed higher photodegradation efficiency for methylene blue compared with pristine ZnS. The optimized photocatalytic activity was achieved on 5.49 at.% Co-doped ZnS.

In this article, Cu 2+ and Mn 2+ are chosen as divalent metal cations to dope and synthesize Li 2 MTi 3 O 8 (M = Cu, Mn, Cu 0.5 Mn 0.5 ) by a simple solid state reaction route. The structures of Li 2 MTi 3 O 8 (M = Cu, Mn, Cu 0.5 Mn 0.5 ) are proved by Rietveld refinement method for the first time. Due to different divalent metal cations M 2+ in the structure, Li 2 MTi 3 O 8 exhibits different electrochemical performances. Li 2 CuTi 3 O 8 shows the highest initial charge capacity of 242 mAh g −1 and Li 2 MnTi 3 O 8 displays the lowest initial charge capacity of 139.5 mAh g −1 among all the three samples. Although Li 2 Cu 0.5 Mn 0.5 Ti 3 O 8 reveals a lower initial charge capacity of 174.5 mAh g −1 , it exhibits better cycle performance than Li 2 CuTi 3 O 8 and Li 2 MnTi 3 O 8 . Li 2 Cu 0.5 Mn 0.5 Ti 3 O 8 keeps the reversible capacity of 143 mAh g −1 after 50 cycles at 100 mA g −1 with capacity retention of 82.2%. Besides, the results of electrochemical impedance spectra indicate that lithium ion can move easily in the tunnels of three-dimensional network formed by the (Li 0.7 Cu 0.15 Mn 0.25 ) tet , which is in agreement with the result that Li 2 Cu 0.5 Mn 0.5 Ti 3 O 8 performs better electrochemical properties than Li 2 CuTi 3 O 8 and Li 2 MnTi 3 O 8 . It provides a possibility and theoretical support to synthesize Ti-based materials Li 2 MTi 3 O 8 with good electrochemical performances.

It is of prime importance to develop dual-functional electrocatalysts with good activity for overall water splitting, which remains a great challenge. Herein, we report the synthesis of a Co-doped nickel selenide (a mixture of NiSe2 and Ni3Se4)/C hybrid nanostructure supported on Ni foam using a metal–organic framework as the precursor. The resulting catalyst exhibits excellent catalytic activity toward the oxygen evolution reaction (OER), which only requires an overpotential of 275 mV to drive a current density of 30 mA cm−2. This overpotential is much lower than those reported for precious metal free OER catalysts. The hybrid is also capable of catalyzing the hydrogen evolution reaction (HER) efficiently. A current density of −10 mA cm−2 can be achieved at 90 mV. In addition, such a hybrid nanostructure can achieve 10 and 30 mA cm−2 at potentials of 1.6 and 1.71 V, respectively, along with good durability when functioning as both the cathode and the anode for overall water splitting in basic media.

Research on next-generation battery technologies (beyond Li-ion batteries, or LIBs) has been accelerating over the past few years. A key challenge for these emerging batteries has been the lack of suitable electrode materials, which severely limits their further developments. MXenes, a new class of 2D transition metal carbides, carbonitrides, and nitrides, are proposed as electrode materials for these emerging batteries due to several desirable attributes. These attributes include large and tunable interlayer spaces, excellent hydrophilicity, extraordinary conductivity, compositional diversity, and abundant surface chemistries, making MXenes promising not only as electrode materials but also as other components in the cells of emerging batteries. Herein, an overview and assessment of the utilization of MXenes in rechargeable batteries beyond LIBs, including alkali-ion (e.g., Na+ , K+ ) storage, multivalent-ion (e.g., Mg2+ , Zn2+ , and Al3+ ) storage, and metal batteries are presented. In particular, the synthetic strategies and properties of MXenes that enable MXenes to play various roles as electrodes, metal anode protective layers, sulfur hosts, separator modification layers, and conductive additives in these emerging batteries are discussed. Moreover, a perspective on promising future research directions on MXenes and MXene-based materials, ranging from material design and processing, fundamental understanding of the reaction mechanisms, to device performance optimization strategies is provided.

We report a novel flexible solar tracking system based on a photothermal-thermomechanical (PT-TM) actuator comprised of Ti3C2Tx 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.

In this work, a microwave approach is developed to rapidly synthesize ultralong zinc pyrovanadate (Zn3 V2 O7 (OH)2 ·2H2 O, ZVO) nanowires with a porous crystal framework. It is shown that our synthesis strategy can easily be extended to fabricate other metal pyrovanadate compounds. The zinc pyrovanadate nanowires show significantly improved electrochemical performance when used as intercalation cathode for aqueous zinc-ion battery. Specifically, the ZVO cathode delivers high capacities of 213 and 76 mA h g-1 at current densities of 50 and 3000 mA g-1 , respectively. Furthermore, the Zn//ZVO cells show good cycling stability up to 300 cycles. The estimated energy density of this Zn cell is ≈214Wh kg-1 , which is much higher than commercial lead-acid batteries. Significant insight into the Zn-storage mechanism in the pyrovanadate cathodes is presented using multiple analytical methods. In addition, it is shown that our prototype device can power a 1.5 V temperature sensor for at least 24 h.

International audience; VO2 (B) features two lithiation/delithiation processes, one of which is kinetically facile and has been commonly observed at 2.5 V versus Li/Li+ in various VO2 (B) structures. In contrast, the other process, which occurs at 2.1 V versus Li/Li+, has only been observed at elevated temperatures due to large interaction energy barrier and extremely sluggish kinetics. Here, it is demonstrated that a rational design of atomically thin, 2D nanostructures of VO2 (B) greatly lowers the interaction energy and Li+‐diffusion barrier. Consequently, the kinetically sluggish step is successfully enabled to proceed at room temperature for the first time ever. The atomically thin 2D VO2 (B) exhibits fast charge storage kinetics and enables fully reversible uptake and removal of Li ions from VO2 (B) lattice without a phase change, resulting in exceptionally high performance. This work presents an effective strategy to speed up intrinsically sluggish processes in non‐van der Waals layered materials.

Supercapacitors as a new type of energy storage devices bridging the gap between conventional capacitors and batteries have aroused widespread concern. Herein, binder-free titanium nitride (TiN) thin film electrodes for supercapacitors prepared by reactive magnetron sputtering technology are reported. The effect of N2 content on the supercapacitor performance is evaluated. A highest specific capacitance of 27.3 mF cm−2 at a current density of 1.0 mA cm−2, together with excellent cycling performance (98.2% capacitance retention after 20,000 cycles at 2.0 mA cm−2) is achieved in a 0.5 M H2SO4 aqueous electrolyte. More importantly, a symmetric supercapacitor device assembled on the basis of TiN thin films can deliver a maximum energy density of 17.6 mWh cm−3 at a current density of 0.2 mA cm−2 and a maximum power density of 10.8 W cm−3 at a current density of 2 mA cm−2 with remarkable cycling stability. As a consequence, TiN thin films demonstrate great potential as promising supercapacitor electrode materials.

This research is financially supported by the National Nature Science Foundation of China (No. 51372212, 51601163).

Transition-metal phosphides (TMPs) are important materials that have been widely used in catalysis, supercapacitors, batteries, sensors, light-emitting diodes, and magnets. The physical and chemical structure of a metal phosphide varies with the method of preparation as the electronic, catalytic, and magnetic properties of the metal phosphides strongly depend on their synthesis routes. Commonly practiced processes such as solid-state synthesis and ball milling have proven to be reliable routes to prepare TMPs but they generally require high temperature and long reaction time. Here, a recently developed plasma-assisted conversion route for the preparation of TMPs is reviewed, along with their applications in energy conversion and storage, including water oxidation electrocatalysis, sodium-ion batteries, and supercapacitors. The plasma-assisted synthetic route should open up a new avenue to prepare TMPs with tailored structure and morphology for various applications. In fact, the process may be further extended to the synthesis of a wide range of transition-metal compounds such as borides and fluorides at low temperature and in a rapid manner.

Research reported in this manuscript was supported by King Abdullah University of Science and Technology (KAUST), Kingdom of Saudi Arabia. F.Z. acknowledges supports from the KAUST Graduate Fellowship. F.Z. also thanks Mr. Qiu Jiang, Dr. Manuel Roldan-Gutierrez, and Dr. Ali Behzad at KAUST core laboratories for several useful discussions.