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Harnessing energy from the environment promotes the rapid development of micro-power generators and relevant power management modules of alternating current (AC) line-filtering to obtain a stabilized direct current (DC) output for storage and use. Micro-supercapacitors (MSCs) with miniaturized volume and high-frequency response are regarded as a critical component in filtering circuits for microscale power conversion. Here, we reported the fabrication of the wafer-sized planar MSCs (M-MSCs) based on 2D Ti3C2Tx MXene using a photolithography technique. The M-MSCs exhibited an areal capacitance of 153 μF cm−2 and a frequency characteristic (f0) of 5.6 kHz in aqueous electrolyte. Moreover, by employing suitable ionic liquid as electrolyte, the voltage window was expanded to 2 V and the f0 could be pushed to 6.6 kHz relying on the electrical double-layer mechanism and lower adsorption energy while maintaining quasi-rectangular cyclic voltammogram curves at 5000 V s−1. Furthermore, the integrated MSCs pack was constructed and exhibited excellent rectifying ability by filtering various high-frequency 5000 Hz AC signals with different waveforms into stable DC outputs. Such ultrahigh-rate and high-voltage M-MSCs module for kHz AC line-filtering would be potentially integrated with customizable electronics to realize on-chip rectifiers in high-density integrated circuit.

A novel N,O symmetric double-coordinated configuration of unsaturated Fe single atoms confirmed within a graphene framework (Fe–N,O/G) is demonstrated experimentally and theoretically for a highly active and durable ORR catalyst in Zn-air batteries.

Phase change materials (PCMs) have garnered intensive attention due to their high energy density and stable energy output in the field of thermal energy storage. However, the low thermal conductivity (TC) and liquid phase leakage of PCMs during phase transition significantly prevent widespread applications. Recently, two-dimensional (2D) materials are being extensively applied in improving the performance of PCMs, relying on their ultrahigh TC and excellent loading capacity. Importantly, their superior optical and electrical properties can offer PCMs with multi-responsive thermal energy conversion ability. This review summarizes the latest developments, emerging trends and challenges of 2D materials for advanced PCMs. We proceed from the importance of thermal energy storage and the key roles of 2D materials in the performance improvement of PCMs. Then, the fundamentals related to energy storage and thermal conduction mechanism of PCMs is systematic discussed. Further, the major preparation strategies and the major applications of 2D materials-based PCMs are emphasized in the thermal management of lithium-ion battery, solar-thermal, solar-thermal-electric and electro-thermal conversion and storage. Finally, the challenges and emerging perspectives are envisaged for deepening the future study and extending the applications of 2D materials for high-performance PCMs.

Monolithic integrated micro-supercapacitors (MIMSCs) with high systemic performance and cell-number density are important for miniaturized electronics to empower the Internet of Things. However, fabrication of customizable MIMSCs in an extremely small space remains a huge challenge considering key factors such as materials selection, electrolyte confinement, microfabrication and device-performance uniformity. Here, we develop a universal and large-throughput microfabrication strategy to address all these issues by combining multistep lithographic patterning, spray printing of MXene microelectrodes and controllable 3D printing of gel electrolytes. We achieve the monolithic integration of electrochemically isolated micro-supercapacitors in close proximity by leveraging high-resolution micropatterning techniques for microelectrode deposition and 3D printing for precise electrolyte deposition. Notably, the MIMSCs obtained demonstrate a high areal-number density of 28 cells cm−2 (340 cells on 3.5 × 3.5 cm2), a record areal output voltage of 75.6 V cm−2, an acceptable systemic volumetric energy density of 9.8 mWh cm−3 and an unprecedentedly high capacitance retention of 92% after 4000 cycles at an extremely high output voltage of 162 V. This work paves the way for monolithic integrated and microscopic energy-storage assemblies for powering future microelectronics.

Phase change materials have a key role for wearable thermal management, but suffer from poor water vapor permeability, low enthalpy value and weak shape stability caused by liquid phase leakage and intrinsic rigidity of solid–liquid phase change materials. Herein, we report for the first time a versatile strategy for designed assembly of high-enthalpy flexible phase change nonwovens (GB-PCN) by wet-spinning hybrid graphene-boron nitride (GB) fiber and subsequent impregnating paraffins (e.g., eicosane, octadecane). As a result, our GB-PCN exhibited an unprecedented enthalpy value of 206.0 J g−1, excellent thermal reliability and anti-leakage capacity, superb thermal cycling ability of 97.6% after 1000 cycles, and ultrahigh water vapor permeability (close to the cotton), outperforming the reported PCM films and fibers to date. Notably, the wearable thermal management systems based on GB-PCN for both clothing and face mask were demonstrated, which can maintain the human body at a comfortable temperature range for a significantly long time. Therefore, our results demonstrate huge potential of GB-PCN for human-wearable passive thermal management in real scenarios.

Microscale electrochemical energy storage devices, e.g., micro-supercapacitors (MSCs), possessing tailored performance and diversified form factors of lightweight, miniaturization, flexibility and exceptional integration are highly necessary for the smart power sources-unitized electronics. Despite the great progress, the fabrication of MSCs combining high integration with high volumetric performance remains largely unsolved. Herein, we develop a simple, fast and scalable strategy to fabricate graphene based highly integrated MSCs by a new effective continuous centrifugal coating technique. Notably, the resulting highly conductive graphene films can act as not only patterned microelectrodes but also metal-free current collectors and interconnects, endowing modular MSCs with high integrity, remarkable flexibility, tailored voltage and capacitance output, and outstanding performance uniformity. More importantly, the strong centrifugal force and shear force generated in continuous centrifugal coating process lead to graphene films with high alignment, compactness and packing density, contributing to excellent volumetric capacitance of ~31.8 F cm−3 and volumetric energy density of ~2.8 mWh cm−3, exceeding most reported integrated MSCs. Therefore, our work paves a novel way for simple and scalable fabrication of integrated MSCs and offers promising opportunities as standalone microscale power sources for new-generation electronics.

Battery-supercapacitor hybrid devices (BSHDs) are promising for certain applications requiring both high energy and power densities, but restricted by the electrolyte-consuming mechanism and imbalance of charge-storage capacity and electrode kinetics between battery-type and capacitor-type electrodes. Herein, a new prototype of rocking-chair lithium-ion BSHD with high energy and power densities is developed by employing pseudocapacitive T-Nb2O5 with a porous nanoflower structure as the anode and battery-type LiNi0.815Co0.15Al0.035O2 complexed in a three-dimensional interconnected conductive network as the cathode. Benefiting from the rational selection and optimization of the active material and electrode architecture, the anode and cathode exhibit exceptionally matched faradaic capacity and kinetics. Consequently, the BSHD delivers superior performance (165 W h kg−1 at 105 W kg−1 and 9.1 kW kg−1 at 83 W h kg−1) to previously reported rocking-chair BSHDs and could surpass the state-of-the-art electrolyte-consuming BSHDs at the device level. Therefore, this work will open a new avenue towards high-performance BSHDs.

The aqueous zinc-ion batteries (ZIBs) are highly competitive, exceptionally safe electrochemical energy storage devices, but suffer from the poor cyclability and unattainable capacity caused by structural instability of cathode materials. In this work, we reported a general 2D template ion-adsorption approach to assemble 2D amorphous V2O5/graphene heterostructures with highly stable layer-by-layer stacked structure and ultrathin thickness of 6 ​nm, for high-safe, rechargeable aqueous ZIBs. Owing to the unique features with strong synergistic effect, the resulting ZIBs show high capacity of 447 ​mAh/g at 0.3 A/g, extraordinary rate capability of 202 ​mAh/g at 30 A/g, and ultra-long lifespan up to 20,000 cycles at 30 A/g, greatly outperforming the vanadium based ZIBs reported. Moreover, the new-concept planar interdigital zinc ion micro-batteries, constructed by mask-assisted filtration strategy, display large volumetric capacity of 63 ​mAh/cm3 at 0.2 ​mA/cm2, high volumetric energy density of 49 ​mWh/cm3, robust flexibility, and impressive modular integration in series and in parallel for boosting the capacity and voltage output, demonstrative of great potential as microscale power sources. Therefore, this approach will offer various opportunities to construct layer-by-layer stacked 2D heterostructures with fast ion-electron conductivity for ZIBs and other batteries.

Graphite is a key cathode material for aluminum-ion batteries (AIBs), but appears poor structural stability and cyclability due to the slow kinetics of intercalation and usage of conductive additives. So far, reasonable design and construction of high-conductive, flexible, binder-free graphitic film cathodes with fast kinetics of anion intercalation mechanism still remains challenging for high-power and high-energy AIBs. Herein, we report the reasonable design for facile construction of high-conductive and mechanically flexible film cathode of high-quality few-layer graphene (FLG) nanosheets for high capacity and fast AIBs, thanks to the strong synergy of ionic surface adsorption/desorption of graphene and ionic intercalation/deintercalation of graphite. The FLG nanosheets prepared by electrochemical cathodic exfoliation from graphite, exhibit predominantly 3–5 layers, extremely low ID/IG ratio of

Pursuing high areal energy density and developing scalable fabrication strategies of micro-batteries are the key for the progressive printed microelectronics. Herein, the scalable fabrication of multi-layer printable lithium ion micro-batteries (LIMBs) with ultrahigh areal energy density and exceptional flexibility is reported, based on highly conductive and mechanically stable inks by fully incorporating the polyurethane binders in dibasic esters with high-conducting additives of graphene and carbon nanotubes into active materials to construct a cross-linked conductive network. Benefiting from relatively higher electrical conductivity (≈7000 mS cm-1 ) and stably connected network of microelectrodes, the as-fabricated LIMBs by multi-layer printing display robust areal capacity of 398 µAh cm-2 , and remarkable areal energy density of 695 μWh cm-2 , which are much higher than most LIMBs reported. Further, the printed LIMBs show notable capacity retention of 88% after 3000 cycles, and outstanding flexibility without any structure degradation under various torsion states and folding angles. Importantly, a wearable smart bracelet, composed of a serially connected LIMBs pack, a temperature sensor, and a light-emitting diode, is realized for the automatic detection of body temperature. Therefore, this strategy of fabricating highly conductive and mechanically stable printable ink will open a new avenue for developing high-performance printable LIMBs for smart microelectronics.

MXenes are one of the key materials for micro-supercapacitors (MSCs), integrating miniaturized energy-storage components with microelectronics. However, the energy densities of MSCs are greatly hampered by MXenes’ narrow working potential window (typically ≤0.6 V) in aqueous electrolytes. Here, we report the fabrication of high-voltage MXene-MSCs through the efficient regulation of reaction kinetics in 2D Ti3C2Tx MXene microelectrodes using a water-in-LiCl (WIL, 20 m LiCl) salt gel electrolyte. Importantly, the intrinsic energy-storage mechanism of MXene microelectrodes in WIL, which is totally different from traditional electrolytes (1 m LiCl), was revealed through insitu and exsitu characterizations. We validated that the suppression of MXene oxidation at high anodic potential occurred due to the high content of WIL regulating anion intercalation in MXene electrodes, which effectively broadened the voltage window of MXene-MSCs. Remarkably, the symmetric planar MXene-MSCs presented a record operating voltage of 1.6 V, resulting in an exceptionally high volumetric energy density of 31.7 mWh cm−3. With the ultra-high ionic conductivity (69.5 mS cm−1) and ultralow freezing point (−57°C) of the WIL gel electrolyte, our MSCs could be operated in a wide temperature range of −40 to 60°C, and worked for a long duration even at −40°C, demonstrative of its practicality in extreme environments.

Two-dimensional (2D) mesoporous nanosheets as electrodes present a critical materials platform for dramatically boosting the performance of planar micro-supercapacitors (MSCs) due to their unique features of interconnected porous network, enriched nanopore arrays, and high specific surface area. However, efficient strategies for constructing such complicated mesoporous architectures are very limited. Here, we developed a supramolecular bottom-up self-assembly strategy for direct synthesis of ultrathin mesoporous manganese dioxide (m-MnO2) nanosheets for high-energy all-solid-state planar asymmetric MSCs (AMSCs). The m-MnO2 nanosheets exhibited ultrathin thickness of 10 nm, uniformly interconnected network of mesopores with size of 5–15 nm, high surface area of 128 m2 g−1, and remarkably enhanced capacitance of 243 F g−1 at 1 mV s−1 in comparison with non-mesoporous MnO2 nanosheets (123 F g−1). Further, all-solid-state AMSCs were assembled based on m-MnO2 nanosheets as positive electrode, porous VN nanosheets as negative electrode, and electrochemically exfoliated graphene as conductive agent and metal-free current collector in “water-in-salt” gel electrolyte. Importantly, our all-solid-state AMSCs operated stably at 2.0 V and offered impressive energy density of 21.6 mWh cm−3, outperforming most reported MnO2 based MSCs, and two times higher than lithium thin-film batteries (≤10 mWh cm−3). Also, they presented long-term cycling stability with 90% capacity retention after 5000 cycles, outstanding flexibility without observable capacitance decay under different bending angles, and facile serial and parallel interconnection for creating high-voltage and high-capacitance integrated bipolar cells. Therefore, our proposed strategy will open many opportunites for patterning novel 2D mesoporous metal oxide nanosheets for high-performance microscale electrochemical energy storage devices.

High-efficiency lithium-sulfur (Li-S) batteries depend on advanced electrode structure that can attain high sulfur utilization at lean-electrolyte and limited lithium. Herein, a twinborn holey Nb4N5-Nb2O5 heterostructure is designed as a dual-functional host for both redox-kinetics-accelerated sulfur cathode and dendrite-inhibited Li anode simultaneously for long-cycling and lean-electrolyte Li-S full batteries. Benefiting from the accelerative polysulfides anchoring-diffusion converting efficiency and electronic-conducting properties of Nb4N5-Nb2O5, polysulfide-shutting is significantly alleviated. Meanwhile, the lithiophilic nature of holey Nb4N5-Nb2O5 is applied as ion-redistributor for homogeneous Li-ion deposition. Taking advantage of these merits, the Li-S full batteries present the excellent electrochemical properties, including a minimum capacity decay of 0.025% per cycle, and a high areal-capacity of 5.0 mAh cm− 2 at sulfur loading of 6.9 mg cm− 2, corresponding to negative to positive capacity ratio (2.4:1) and electrolyte to sulfur ratio (5.1 µl mg− 1). Therefore, this work opens a new avenue for boosting high-performances Li-S batteries towards practical applications.

The prosperity of smart portable microdevices urgently requires an advanced integrated microsystem equipped with cost-effective safe microbatteries and ultra-stable sensitive sensors. However, the practical application of smart microdevices is limited by complex active materials with single function. Here, the two-dimensional (2D) mesoporous nanosheets of polyaniline decorated on graphene with large specific surface area of 141 m

Graphene and other two-dimensional materials (2DMs) have attracted intensive interest for use in energy storage and conversion systems because of their unique structure and remarkable properties. Although significant progress has been made in this field, certain intrinsic limitations obstruct the achievement of desired properties. 2D heterostructures, upon stacking or stitching different 2DMs in well-defined sequences or patterns, could significantly entail drastic changes in their properties, and thereby synergistically combine the merits of individual 2DMs while eliminating their related drawbacks. Herein, we provide a topical review of recent advances in the preparation and characterization of 2D heterostructures for energy-related applications. Firstly, an introduction is given to the definition and importance of 2D heterostructures, followed by their typical categories of vertically stacked heterostructures and horizontal in-plane heterostructures reported so far. Secondly, the state-of-the-art synthesis approaches to fabricate 2D heterostructures, including mechanically aligned transfer, chemical vapor deposition, liquid exfoliation and self-assembly, and layer by layer self-assembly, are introduced in detail. Then, the current status of advanced characterization techniques like scanning probe-, electron-diffraction-, X-ray-, and spectroscopy-based techniques that are critical for the accurate identification of 2D heterostructures and understanding of the performance-enhancing mechanisms of devices is systemically summarized. Furthermore, recent applications of 2D heterostructures in energy storage (e.g., lithium/sodium ion batteries, lithium sulfur batteries, supercapacitors, and micro-supercapacitors) and conversion (e.g., hydrogen/oxygen evolution reactions and photocatalysis) are exemplified to highlight their positive synergistic effect. Finally, future challenges and prospective solutions that may direct the growth of 2D heterostructures and their energy-related applications are proposed.

Aqueous sodium ion micro-batteries (ANIMBs) hold great promise in smart wearable microelectronics due to the abundant reserves, low cost and high safety of sodium. However, their applications are substantially hindered by the narrow electrochemical stability window of aqueous electrolytes within a limited temperature range. Herein, we report a prototype of high-voltage planar ANIMBs based on symmetric interdigital microelectrodes working in water-in-salt (WiS) electrolyte (17 M NaClO4) and displaying exceptional performance at low temperature. This work features nanoflower Na3V2(PO4)3 (NVP)-based electrodes with perfectly matched voltage range as both anode and cathode in the WiS electrolyte operating in a widened electrochemical stability window (2.7 V vs. Na+/Na) under ultralow freezing point of −50 oC. The resulting ANIMBs with interdigital in-plane geometry deliver remarkable volumetric capacity of 45 mAh/cm3 and energy density of 77 mWh/cm3, which are superior to most reported sodium-based micropower sources. Notably, the NVP||NaClO4||NVP micro-batteries exhibit a high coulombic efficiency of > 99% at room temperature down to −40 oC. Furthermore, the NVP||NaClO4||NVP ANIMBs present admirable flexibility and modular integration. We believe that our ANIMBs can potentially enjoy wide market adoption ranging from domestic appliances to safe intelligent wearable microelectronics, especially those applications that need to be operated below freezing temperature.

The future of mankind holds great promise for things like the Internet of Things, personal health monitoring systems, and smart cities. To achieve this ambitious goal, it is imperative for electronics to be wearable, environmentally sustainable, and safe. However, large-scale manufacture of self-sufficient electronic systems by exploiting multifunctional materials still faces significant hurdles. Herein, multitasking aqueous printable MXene inks are reported as an additive-free high-capacitance electrode, sensitive pressure-sensing material, highly conducting current collector, metal-free interconnector, and conductive binder. By directly screen printing MXene inks, MXene-based micro-supercapacitors (MSCs) and lithium-ion microbatteries (LIMBs) are delicately fabricated on various substrates. The as-prepared MSCs exhibit ultrahigh areal capacitance of 1.1 F cm-2 and the serially connected MSCs offer a record voltage of 60 V. The quasi-solid-state LIMBs deliver a robust areal energy density of 154 μWh cm-2 . Furthermore, an all-flexible self-powered integrated system on a single substrate based on the multitasking MXene inks is demonstrated through seamless integration of a tandem solar cell, the LIMB, and an MXene hydrogel pressure sensor. Notably, this integrated system is exceptionally sensitive to body movements with a fast response time of 35 ms. Therefore, this multipurpose MXene ink opens a new avenue for powering future smart appliances.

MXene is rising as a versatile two-dimensional material (2DM) for electrochemical energy storage devices. MXene has boosted the performance of supercapacitors thanks to its pseudocapacitive charge storage mechanism with electric double layer behavior. Further, MXene has helped batteries achieve high capacity while endowing fast charge-discharge by virtue of its suitable interlayer spacing and unique chemistry. Such achievements are a result of MXene’s intrinsic properties like high electrical conductivity, defined layered structure and ability to sustain customizations, tailoring the electrodes towards a specific target. Not only that, MXene has showcased its merits by enabling supercapacitors and batteries to surpass the convention and venture into the territory of micro-supercapacitors (MSCs), hybrid capacitors and batteries beyond Li-ion. Herein, we present a topical review discussing the present status of MXene-based energy storage devices and corresponding challenges. By rational analysis, we also provide some key avenues for further research that may help overcome these shortcomings and enable this family of MXene materials attain its full potential.

The increasing demand for portable, wearable, and miniaturized electronics has substantially promoted the immense development of planar microsupercapacitors (MSCs) built on a single substrate. Atomically thin two-dimensional (2D) nanosheets, by virtue of their intrinsically unique structure and fascinating electrochemical properties, provide a new material platform for the creation of high performance planar MSCs in which the electrolyte ions can completely utilize flat architecture and ultrathin thickness of 2D nanosheets, parallel to the direction of ionic diffusion along the plane of 2D nanosheets. Herein, we present an overview and perspective on diverse 2D materials for planar MSCs. First, an introduction is presented to highlight the advances of MSCs, the uniqueness of 2D materials in the assembly of planar MSCs with three different configurations, i.e., stacked, interdigital, and 3D planar geometries, and the progress of microfabrication techniques for microelectrodes of MSCs. Second, the state-of-the-art 2D materials to manufacture planar MSCs, including graphene, transition metal oxides/hydroxides, transition metal dichalcogenides, metal carbides, metal nitrides, phosphorene, boron nitride, metal-organic frameworks, and covalent-organic frameworks, are systemically discussed in detail. Special emphasis is given to the multiple roles of 2D materials for functional components as active materials, current collectors, additives/binders, and separators for planar MSCs. Finally, the existing challenges and prospective solutions of 2D materials for planar MSCs with high performance and various innovative form factors are proposed.