2.4 V ultrahigh-voltage aqueous MXene-based asymmetric micro-supercapacitors with high volumetric energy density toward a self-sufficient integrated microsystem.

Two-dimensional MXenes are key high-capacitance electrode materials for micro-supercapacitors (MSCs) catering to integrated microsystems. However, the narrow electrochemical voltage windows of conventional aqueous electrolytes (≤ 1.23 V) and symmetric MXene MSCs (typically ≤ 0.6 V) substantially limit their output voltage and energy density. Highly concentrated aqueous electrolytes exhibit lower water molecule activity, which inhibits water splitting and consequently widens the operating voltage window. Herein, we report ultrahigh-voltage aqueous planar asymmetric MSCs (AMSCs) based on a highly concentrated LiCl-gel quasi-solid-state electrolyte with MXene (Ti3C2T x ) as the negative electrode and MnO2 nanosheets as the positive electrode (MXene//MnO2-AMSCs). The MXene//MnO2-AMSCs exhibit a high voltage of up to 2.4 V, attaining an ultrahigh volumetric energy density of 53 mWh cm-3. Furthermore, the in-plane geometry and the quasi-solid-state electrolyte enabled excellent mechanical flexibility and performance uniformity in the serially/parallel connected packs of our AMSCs. Notably, the MXene//MnO2-AMSC-based integrated microsystem, in conjunction with solar cells and consumer electronics, could efficiently realize simultaneous energy harvesting, storage, and conversion. The findings of this study provide insights for constructing high-voltage aqueous MXene-based AMSCs as safe and self-sufficient micropower sources in smart integrated microsystems.

Redox Promoted Rapid and Deep Reconstruction of Defect-Rich Nickel Precatalysts for Efficient Water Oxidation.

Understanding the reconstruction mechanism to rationally design cost-effective electrocatalysts for oxygen evolution reaction (OER) is still challenging. Herein, a defect-rich NiMoO4 precatalyst is used to explore its OER activity and reconstruction mechanism. In situ generated oxygen vacancies, distorted lattices, and edge dislocations expedite the deep reconstruction of NiMoO4 to form polycrystalline Ni (oxy)hydroxides for alkaline oxygen evolution. It only needs ≈230 and ≈285 mV to reach 10 and 100 mA cm-2, respectively. The reconstruction boosted by the redox of Ni is confirmed experimentally by sectionalized cyclic voltammetry activations at different specified potential ranges combined with ex situ characterization techniques. Subsequently, the reconstruction route is presented based on the acid-base electronic theory. Accordingly, the dominant contribution of the adsorbate evolution mechanism to reconstruction during oxygen evolution is revealed. This work develops a novel route to synthesize defect-rich materials and provides new tactics to investigate the reconstruction.

Hybrid ion/electron interfacial regulation stabilizes the cobalt/oxygen redox of ultrahigh-voltage lithium cobalt oxide for fast-charging cyclability.

High-voltage and fast-charging LiCoO2 (LCO) is key to high-energy/power-density Li-ion batteries. However, unstable surface structure and unfavorable electronic/ionic conductivity severely hinder its high-voltage fast-charging cyclability. Here, we construct a Li/Na-B-Mg-Si-O-F-rich mixed ion/electron interface network on the 4.65 V LCO electrode to enhance its rate capability and long-term cycling stability. Specifically, the resulting artificial hybrid conductive network enhances the reversible conversion of Co3+/4+/O2-/n- redox by the interfacial ion-electron cooperation and suppresses interface side reactions, inducing an ultrathin yet compact cathode electrolyte interphase. Simultaneously, the derived near-surface Na+/Mg2+/Si4+-pillared local intercalation structure greatly promotes the Li+ diffusion around the 4.55 V phase transition and stabilizes the cathode interface. Finally, excellent 3 C (1 C = 274 mA g-1) fast charging performance is demonstrated with 73.8% capacity retention over 1000 cycles. Our findings shed new insights to the fundamental mechanism of interfacial ion/electron synergy in stabilizing and enhancing fast-charging cathode materials.

Metal telluride nanosheets by scalable solid lithiation and exfoliation.

Transition metal tellurides (TMTs) have been ideal materials for exploring exotic properties in condensed-matter physics, chemistry and materials science1-3. Although TMT nanosheets have been produced by top-down exfoliation, their scale is below the gram level and requires a long processing time, restricting their effective application from laboratory to market4-8. We report the fast and scalable synthesis of a wide variety of MTe2 (M = Nb, Mo, W, Ta, Ti) nanosheets by the solid lithiation of bulk MTe2 within 10 min and their subsequent hydrolysis within seconds. Using NbTe2 as a representative, we produced more than a hundred grams (108 g) of NbTe2 nanosheets with 3.2 nm mean thickness, 6.2 µm mean lateral size and a high yield (>80%). Several interesting quantum phenomena, such as quantum oscillations and giant magnetoresistance, were observed that are generally restricted to highly crystalline MTe2 nanosheets. The TMT nanosheets also perform well as electrocatalysts for lithium-oxygen batteries and electrodes for microsupercapacitors (MSCs). Moreover, this synthesis method is efficient for preparing alloyed telluride, selenide and sulfide nanosheets. Our work opens new opportunities for the universal and scalable synthesis of TMT nanosheets for exploring new quantum phenomena, potential applications and commercialization.

The status and challenging perspectives of 3D-printed micro-batteries.

In the era of the Internet of Things and wearable electronics, 3D-printed micro-batteries with miniaturization, aesthetic diversity and high aspect ratio, have emerged as a recent innovation that solves the problems of limited design diversity, poor flexibility and low mass loading of materials associated with traditional power sources restricted by the slurry-casting method. Thus, a comprehensive understanding of the rational design of 3D-printed materials, inks, methods, configurations and systems is critical to optimize the electrochemical performance of customizable 3D-printed micro-batteries. In this review, we offer a key overview and systematic discussion on 3D-printed micro-batteries, emphasizing the close relationship between printable materials and printing technology, as well as the reasonable design of inks. Initially, we compare the distinct characteristics of various printing technologies, and subsequently emphatically expound the printable components of micro-batteries and general approaches to prepare printable inks. After that, we focus on the outstanding role played by 3D printing design in the device architecture, battery configuration, performance improvement, and system integration. Finally, the future challenges and perspectives concerning high-performance 3D-printed micro-batteries are adequately highlighted and discussed. This comprehensive discussion aims at providing a blueprint for the design and construction of next-generation 3D-printed micro-batteries.

Monolithically integrated micro-supercapacitors with high areal number density produced by surface adhesive-directed electrolyte assembly.

Accurately placing very small amounts of electrolyte on tiny micro-supercapacitors (MSCs) arrays in close proximity is a major challenge. This difficulty hinders the development of densely-compact monolithically integrated MSCs (MIMSCs). To overcome this grand challenge, we demonstrate a controllable electrolyte directed assembly strategy for precise isolation of densely-packed MSCs at micron scale, achieving scalable production of MIMSCs with ultrahigh areal number density and output voltage. We fabricate a patterned adhesive surface across MIMSCs, that induce electrolyte directed assembly on 10,000 highly adhesive MSC regions, achieving a 100 µm-scale spatial separation between each electrolyte droplet within seconds. The resultant MIMSCs achieve an areal number density of 210 cells cm-2 and a high areal voltage of 555 V cm-2. Further, cycling the MIMSCs at 190 V over 9000 times manifests no performance degradation. A seamlessly integrated system of ultracompact wirelessly-chargeable MIMSCs is also demonstrated to show its practicality and versatile applicability.

Recent advancement and key opportunities of MXenes for electrocatalysis.

MXenes are promising materials for electrocatalysis due to their excellent metallic conductivity, hydrophilicity, high specific surface area, and excellent electrochemical properties. Herein, we summarize the recent advancement of MXene-based materials for electrocatalysis and highlight their key challenges and opportunities. In particular, this review emphasizes on the major design principles of MXene-based electrocatalysts, including (1) coupling MXene with active materials or heteroatomic doping to create highly active synergistic catalyst sites; (2) construction of 3D MXene structure or introducing interlayer spacers to increase active areas and form fast mass-charge transfer channel; and (3) protecting edge of MXene or in situ transforming the surface of MXene to stable active substance that inhibits the oxidation of MXene and then enhances the stability. Consequently, MXene-based materials exhibit outstanding performance for a variety of electrocatalytic reactions. Finally, the key challenges and promising prospects of the practical applications of MXene-based electrocatalysts are briefly proposed.

Electrochemically Exfoliated Graphene Additive-Free Inks for 3D Printing Customizable Monolithic Integrated Micro-Supercapacitors on a Large Scale.

Three-dimensional (3D) printing technology with enhanced fidelity can achieve multiple functionalities and boost electrochemical performance of customizable planar micro-supercapacitors (MSCs), however, precise structural control of additive-free graphene-based macro-assembly electrode for monolithic integrated MSCs (MIMSCs) remains challenging. Here, the large-scale 3D printing fabrication of customizable planar MIMSCs is reported utilizing additive-free, high-quality electrochemically exfoliated graphene inks, which is not required the conventional cryogenic assistance during the printing process and any post-processing reduction. The resulting MSCs reveal an extremely small engineering footprint of 0.025 cm2, exceptionally high areal capacitance of 4900 mF cm-2, volumetric capacitance of 195.6 F cm-3, areal energy density of 2.1 mWh cm-2, and unprecedented volumetric energy density of 23 mWh cm-3 for a single cell, surpassing most previously reported 3D printed MSCs. The 3D printed MIMSC pack is further demonstrated, with the maximum areal cell count density of 16 cell cm-2, the highest output voltage of 192.5 V and the largest output voltage per unit area of 56 V cm-2 up to date are achieved. This work presents an innovative solution for processing high-performance additive-free graphene ink and realizing the large-scale production of 3D printed MIMSCs for planar energy storage.

Recent Advances in Flexible Wearable Supercapacitors: Properties, Fabrication, and Applications.

A supercapacitor is a potential electrochemical energy storage device with high-power density (PD) for driving flexible, smart, electronic devices. In particular, flexible supercapacitors (FSCs) have reliable mechanical and electrochemical properties and have become an important part of wearable, smart, electronic devices. It is noteworthy that the flexible electrode, electrolyte, separator and current collector all play key roles in overall FSCs. In this review, the unique mechanical properties, structural designs and fabrication methods of each flexible component are systematically classified, summarized and discussed based on the recent progress of FSCs. Further, the practical applications of FSCs are delineated, and the opportunities and challenges of FSCs in wearable technologies are proposed. The development of high-performance FSCs will greatly promote electricity storage toward more practical and widely varying fields. However, with the development of portable equipment, simple FSCs cannot satisfy the needs of integrated and intelligent flexible wearable devices for long durations. It is anticipated that the combining an FSC and a flexible power source such as flexible solar cells is an effective strategy to solve this problem. This review also includes some discussions of flexible self-powered devices.

Breaking the Ru-O-Ru Symmetry of a RuO2 Catalyst for Sustainable Acidic Water Oxidation.

Proton exchange membrane water electrolysis is a highly promising hydrogen production technique for sustainable energy supply, however, achieving a highly active and durable catalyst for acidic water oxidation still remains a formidable challenge. Herein, we propose a local microenvironment regulation strategy for precisely tuning In-RuO2 /graphene (In-RuO2 /G) catalyst with intrinsic electrochemical activity and stability to boost acidic water oxidation. The In-RuO2 /G displays robust acid oxygen evolution reaction performance with a mass activity of 671 A gcat -1 at 1.5 V, an overpotential of 187 mV at 10 mA cm-2 , and long-lasting stability of 350 h at 100 mA cm-2 , which arises from the asymmetric Ru-O-In local structure interactions. Further, it is unraveled theoretically that the asymmetric Ru-O-In structure breaks the thermodynamic activity limit of the traditional adsorption evolution mechanism which significantly weakens the formation energy barrier of OOH*, thus inducing a new rate-determining step of OH* absorption. Therefore, this strategy showcases the immense potential for constructing high-performance acidic catalysts for water electrolyzers.

Protocol for fabrication of Pt/RuO2/graphene bifunctional oxygen catalyst in Li-O2 batteries.

The commercial mass production of bifunctional oxygen catalysts with high activity and stability is critical for constructing high-performance lithium-oxygen (Li-O2) batteries, but remains challenging. Herein, we describe a protocol for the scalable fabrication of a 2D bifunctional electrocatalyst of Pt/RuO2/graphene by spatial confinement strategy and elaborately evaluate its oxygen reduction/evolution reactions for advanced Li-O2 batteries. We then detail the synthesis steps for preparing materials followed by assembly and evaluation of the three-electrode systems and coin-type Li-O2 batteries. For complete details on the use and execution of this protocol, please refer to Li et al. (2023).1.

A Biodegradable High-Performance Microsupercapacitor for Environmentally Friendly and Biocompatible Energy Storage.

Biodegradable and biocompatible microscale energy storage devices are very crucial for environmentally friendly microelectronics and implantable medical applications. Herein, a biodegradable and biocompatible microsupercapacitor (BB-MSC) with satisfying overall performance is realized via the combination of three-dimensional (3D) printing technique and biodegradable materials. Due to the 3D-interconnected structure of electrodes and elaborated design of electrolyte, the as-prepared BB-MSC exhibits superior overall performance than most of biodegradable devices, including a wide operation voltage of 1.8 V, high areal specific capacitance of 251 mF/cm2, good cycle stability, and favorable low-temperature resistance (-20 °C), demonstrative of reliability and practicality of our devices even in frosty environments. Importantly, the smooth degradation has been realized for the BB-MSC after being buried in natural soil for ∼90 days, and its implantation does not affect the healthy status of SD rats. Therefore, this work explores avenues for the design and construction of environmentally friendly and biocompatible microscale energy storage devices.

Natural-Wood-Inspired Ultrastrong Anisotropic Hybrid Hydrogels Targeting Artificial Tendons or Ligaments.

Hydrogels are able to mimic the flexibility of biological tissues or skin, but they still cannot achieve satisfactory strength and toughness, greatly limiting their scope of application. Natural wood can offer inspiration for designing high-strength hydrogels attributed to its anisotropic structure. Herein, we propose an integrated strategy for efficient preparation of ultrastrong hydrogels using a salting-assisted prestretching treatment. The as-prepared poly(vinyl alcohol)/cellulose nanofiber hybrid hydrogels show distinct wood-like anisotropy, including oriented molecular fiber bundles and extended grain size, which endows materials with extraordinarily comprehensive mechanical properties of ultimate breaking strength exceeding 40 MPa, strain approaching 250%, and toughness exceeding 60 MJ·m-3, and outstanding tear resistance. Impressively, the breaking strength and toughness of the reswollen preoriented hydrogels approach 10 MPa and 25 MJ·m-3, respectively. In vitro and in vivo tests demonstrate that the reswollen hydrogels do not affect the growth and viability of the cells, nor do they cause the inflammation or rejection of the mouse tissue, implying extremely low biotoxicity and perfect histocompatibility, showcasing bright prospects for application in artificial ligaments or tendons. The strategy provided in this study can be generalized to a variety of biocompatible polymers for the fabrication of high-performance hydrogels with anisotropic structures.

Aqueous Organic Batteries Using the Proton as a Charge Carrier.

Benefiting from the merits of low cost, nonflammability, and high operational safety, aqueous rechargeable batteries have emerged as promising candidates for large-scale energy-storage applications. Among various metal-ion/non-metallic charge carriers, the proton (H+ ) as a charge carrier possesses numerous unique properties such as fast proton diffusion dynamics, a low molar mass, and a small hydrated ion radius, which endow aqueous proton batteries (APBs) with a salient rate capability, a long-term life span, and an excellent low-temperature electrochemical performance. In addition, redox-active organic molecules, with the advantages of structural diversity, rich proton-storage sites, and abundant resources, are considered attractive electrode materials for APBs. However, the charge-storage and transport mechanisms of organic electrodes in APBs are still in their infancy. Therefore, finding suitable electrode materials and uncovering the H+ -storage mechanisms are significant for the application of organic materials in APBs. Herein, the latest research progress on organic materials, such as small molecules and polymers for APBs, is reviewed. Furthermore, a comprehensive summary and evaluation of APBs employing organic electrodes as anode and/or cathode is provided, especially regarding their low-temperature and high-power performances, along with systematic discussions for guiding the rational design and the construction of APBs based on organic electrodes.

Monolithic integrated micro-supercapacitors with ultra-high systemic volumetric performance and areal output voltage.

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.

Vapor-Liquid-Solid Growth of Site-Controlled Monolayer MoS2 Films Via Pressure-Induc ed Supercritical Phase Nucleation.

In this study, a novel pressure-induced supercritical phase nucleation method is proposed to synthesize monolayer MoS2 films, which is promoter free and can avoid contamination of films derived from these heterogeneous promoters in most of the existing techniques. The low-crystallinity and size-controlled MoO2(acac)2 particles are recrystallized on the substrate via the pressure-sensitive solvent capacity of supercritical CO2 and these particles are used as growth sites. The size of single-crystal MoS2 on the substrate is found to be dependent on the wetting area of the pyrolyzed precursor droplets (MoO2) on the surface, and the formation of continuous films with high coverage is mainly controlled by the coalescence of MoO2 droplets. It is enhanced by the increase of the nucleation site density, which can be adjusted by the supersaturation of the supercritical fluid solution. Our findings pave a new way for the controllable growth of MoS2 and other two-dimensional materials and provide sufficient and valuable evidence for vapor-liquid-solid growth.

Unraveling oxygen vacancy site mechanism of Rh-doped RuO2 catalyst for long-lasting acidic water oxidation.

Exploring durable electrocatalysts with high activity for oxygen evolution reaction (OER) in acidic media is of paramount importance for H2 production via polymer electrolyte membrane electrolyzers, yet it remains urgently challenging. Herein, we report a synergistic strategy of Rh doping and surface oxygen vacancies to precisely regulate unconventional OER reaction path via the Ru-O-Rh active sites of Rh-RuO2, simultaneously boosting intrinsic activity and stability. The stabilized low-valent catalyst exhibits a remarkable performance, with an overpotential of 161 mV at 10 mA cm-2 and activity retention of 99.2% exceeding 700 h at 50 mA cm-2. Quasi in situ/operando characterizations demonstrate the recurrence of reversible oxygen species under working potentials for enhanced activity and durability. It is theoretically revealed that Rh-RuO2 passes through a more optimal reaction path of lattice oxygen mediated mechanism-oxygen vacancy site mechanism induced by the synergistic interaction of defects and Ru-O-Rh active sites with the rate-determining step of *O formation, breaking the barrier limitation (*OOH) of the traditional adsorption evolution mechanism.