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Quasi-two-dimensional (q2D) conducting polymer thin film synergizes the advantageous features of long-range molecular ordering and high intrinsic conductivity, which are promising for flexible thin film-based micro-supercapacitors (MSCs). Herein, we present the high-performance flexible MSCs based on highly ordered quasi-two-dimensional polyaniline (q2D-PANI) thin film using surfactant monolayer assisted interfacial synthesis (SMAIS). Owing to high electrical conductivity, rich redox chemistry, and thin-film morphology, the q2D-PANI MSCs show high volumetric specific capacitance (ca. 360 F/cm3) and energy density (17.9 mWh/cm3), which outperform the state-of-art PANI thin-film based MSCs and promise for future flexible electronics.

The aim of this study was to investigate the relationship between typhoon, climate change, and acute Stanford type A aortic dissection (TAAD) in southern of Zhejiang Province in China.371 patients with TAAD were admitted to three hospitals (the aortic dissection center) in southern of Zhejiang Province, China from January 2015 to December 2020, and data were retrospectively collected, the data included (1) the number of patients admitted in different months and seasons, (2) daily meteorological data in southern of Zhejiang Province, and (3) typhoon information were retrospectively analyzed.The number of TAAD occurred in winter was the highest and in summer was the lowest. The incidence of TAAD was correlated with minimum temperature, maximum wind speed, mean wind speed, and water vapor pressure (P 0.05). Maximum wind speed (RR 0.37; 95% CI 0.17 to 0.80, P = 0.01) and water vapor pressure (RR 0.96; 95% CI 0.92 to 1, P = 0.03) were the protective factor. The occurrence incidence of TAAD under the influence of typhoon climate was less than that during the period not affected by typhoon (P 0.05).There was a correlation between typhoon, climate change, and the occurrence of TAAD in southern Zhejiang Province. Wind speed, vapor pressure, and typhoon may be protective factors.

The rapid development of miniaturized electronic devices has greatly stimulated the endless pursuit of high-performance on-chip micro-supercapacitors (MSCs) delivering both high energy and power densities. To this end, an advanced three-dimensional (3D) microelectrode architecture design offers enormous opportunities due to high mass loading of active materials, large specific surface areas, fast ion diffusion kinetics, and short electron transport pathways. In this review, we summarize the recent advances in the rational design of 3D architectured microelectrodes including 3D dense microelectrodes, 3D nanoporous microelectrodes, and 3D macroporous microelectrodes. Furthermore, the emergent microfabrication strategies are discussed in detail in terms of charge storage mechanisms and structure-performance correlation for on-chip MSCs. Finally, we conclude with a perspective on future opportunities and challenges in this thriving field.

Rechargeable hydrogen gas batteries (RHGBs) have been attracting much attention as promising all-climate large-scale energy storage devices, which calls for low-cost and high-activity hydrogen evolution/oxidation reaction (HER/HOR) bifunctional electrocatalysts to replace the costly platinum-based catalysts. Based on density functional theory (DFT) computations, herein we report an effective descriptor-driven design principle to govern the HER/HOR electrocatalytic activity of double-atom catalysts (DACs) for RHGBs. We systematically investigate the

Bicontinuous porous materials, which possess 3D interconnected pore channels facilitating a smooth mass transport, have attracted much interest in the fields of energy and catalysis. However, their synthesis remains very challenging. We report a general approach, using polymer cubosomes as the template, for the controllable synthesis of bicontinuous porous polymers with an ordered single primitive (SP) cubic structure, including polypyrrole (SP-PPy), poly

Sodium (Na)-ion capacitors possess higher energy density than supercapacitors and higher power density than Na-ion batteries. However, kinetic mismatches between fast capacitive charge storage on the cathode and sluggish battery-type reactions on the anode lead to a poor charge/discharge rate capability and insufficient power output of Na-ion capacitors. Thus, developing suitable anode materials for Na-ion capacitors is urgently desirable. This work demonstrates an electrochemically exfoliated graphite (EEG) anode with enhanced capacitive charge storage, greatly boosting the Na-ion reaction kinetics of co-intercalation. The EEG anode shows a high reversible capacity of 109 mAh g-1 and maintains a good capacity retention of 90% after 1000 cycles. The assembled Na-ion capacitor using the EEG anode can finish the charge/discharge process in less than 10 s, which achieves an ultrahigh power density of 17,500 W kg-1 with an energy density of 17 Wh kg-1. The high capacitive contributions at both the anode and cathode contribute to the fast rate capability and high power output of the fabricated Na-ion capacitors. This work will promote the development of ultrafast charging sodium-ion storage devices.

The great popularity of portable, wearable, and implantable smart electronics has intensively boosted the development of flexible miniaturized power supplies. Owing to the fast charge/discharge capability, high power delivery, long cycling lifetime, easy fabrication and integration, flexible in-plane micro-supercapacitors (FPMSCs) are of significance as the micropower sources for the next-generation flexible on-chip electronics. In this review, we provide a comprehensive overview about FPMSCs and discuss the recent advances in their fabrication and applications. Particular emphasis is put on the emergent device fabrication technologies of FPMSCs, including deposition techniques, coating strategies, etching methods, and printing technologies. Moreover, we highlight the unique applications of FPMSCs in constructing smart responses and self-powered integrated systems in terms of multifunctional operation modes. Finally, the remaining challenges regarding flexibility, performance improvement, smart response, and microdevice integration of FPMSCs are discussed, which will stimulate further research in this thriving field.

Enzymes are ideal receptors for biosensors since they offer excellent selectivity and high catalytic activity. However, once removed from their native environment, enzymes present a short lifespan determining a huge drawback for their application in bio-analytical systems. The use of appropriate immobilization matrices is an effective strategy to preserve enzymatic activity. In this work, an enzymatic amperometric biosensor is designed by entrapping lactate oxidase into a protein-based immobilization matrix, formed by the self-assembly of engineered repeat proteins. Electrochemically exfoliated graphene, functionalized with cobalt phthalocyanine, is employed as electroactive material and transducer of the sensor. Due to the extraordinary enzymatic stabilization provided by the engineered protein film, the device sensitivity is preserved for more than 6 months at room temperature. Furthermore, the presented biosensor can detect lactate with outstanding performance in terms of sensitivity, repeatability, and reproducibility.

Rechargeable aluminium (Al) batteries (RABs) have long-been pursued due to the high sustainability and three-electron-transfer properties of Al metal. However, limited redox chemistry is available for rechargeable Al batteries, which restricts the exploration of cathode materials. Herein, we demonstrate an efficient Al-amine battery based on a quaternization reaction, in which nitrogen (radical) cations (R

The electrocatalytic nitrogen (N2) reduction reaction is recognized as a green and sustainable approach for ammonia (NH3) synthesis alternative to the traditional industrial method – the Haber–Bosch process, while an efficient electrocatalysis of such a process is a prerequisite for N2 reduction. Developing a cost-effective electrocatalyst for the electrocatalytic nitrogen reduction reaction (NRR) under ambient conditions with an excellent catalytic performance remains a great challenge. Here, we report a facile hydrothermal reaction to synthesize Fe-doped manganese oxide (MnO2) with a nanoneedle morphology as a cost-effective electrocatalyst for the NRR. It is verified that Fe plays a critical role in the NRR. This catalyst shows an excellent catalytic performance with a high faradaic efficiency of 16.8% and a high NH3 formation rate of 39.2 μg h−1 mgcat.−1 at −0.29 V vs. the reversible hydrogen electrode in 0.1 M Na2SO4, which are much higher than those of all reported Mn-based NRR catalysts and many other previously reported catalysts. This catalyst also shows excellent durability during electrolysis and recycling tests. In addition, the electrocatalyst mechanism is also assessed in combination with density functional theory.

Advanced electrochemical energy storage devices are in high demand to meet the need for both short-term high power pulse and long-term durable energy outputs. To achieve this goal, a majority of studies have focused on optimization of solid electrode materials. However, the issue of slow diffusion of ions in electrode materials causes unsatisfactory power density in the energy storage devices. In this work, soluble dual-redox additives in an aqueous electrolyte were employed to combine with a S/P co-doped carbon based cathode and a carbon cloth (CC) based anode to construct an aqueous zinc bromine (Zn-Br2) "supercapattery". The as-fabricated supercapattery possessed electrical-double-layer type, pseudocapacitive, and battery-type charge storage in both cathode and anode and successfully united capacitive character and battery-like character in one device. The benefits of the triple functions of charge storage resulted in an extremely high energy density of 270 W h kg-1 and a maximum power density of 9300 W kg-1. The capacitive and pseudocapacitive charge storage processes in the Zn-Br2 supercapattery are able to provide peak power output. Meanwhile, the diffusion-controlled battery-type redox reactions can meet the requirement for high energy. This work provides a new pathway towards development of electrochemical energy storage devices with both battery-level energy density and capacitor-level power density.

Electrochemical intercalation/conversion/alloying reactions, as one of the most important solid-state redox reactions, play essential roles in electrochemical energy storage systems. First-principles calculations hold great potential to fundamental understandings of reversible intercalation/conversion/alloying reactions, which may provide insights into designing high-performance electrode materials. Recently, electrode materials with both battery-type and capacitive charge storage are significantly promising in achieving high energy and high power densities, perfectly fulfilling the rigorous requirements of metal-ion batteries and electrochemical capacitors as the next generation of energy storage devices. Different from traditional electrode materials, the electrode materials with both battery-type and capacitive charge storage enable the charging and discharging processes within the order of minutes or even seconds because of the enhanced surface-controlled charge storage. By combining experimental characterizations and computational simulations, this review summaries the state-of-the-art of design strategies for electrode materials with both battery-type and capacitive charge storage. Moreover, the research opportunities and key technical challenges are suggested regarding further research in this thriving field.

Li-ion conductive polycrystalline Li4B7O12Cl to be used as a solid-state electrolyte was successfully synthesized by an ionothermal route at a low temperature. The reaction of lithium acetate dihyd...

In-plane micro-supercapacitors (MSCs), as promising power candidates for micro-devices, typically exhibit high power densities, large charge/discharge rates, and long cycling lifetimes. The high areal/volumetric capacitances, high energy/power densities, high rate capability, as well as flexibility are the main scientific pursue in recent years. Among diverse electrode materials for MSCs, coordination polymer frameworks are emerging due to the designable porous structure and tunable functionality. However, the unsatisfied electrochemical performance still hinders their practical applications. In this work, we demonstrate the first time an efficient in-situ growth approach to precisely modify the vacancy of Prussian-blue nano-thin films with pyridine by coordination reaction for high energy-density MSCs. Confirmed by the experimental results and density functional theory calculation, the vacancy modification within Prussian-blue network improved the film-forming property, hydrophilicity, and electrochemical activity of the thin films. The resultant MSCs based on pyridine-modified Prussian-blue exhibited an ultrahigh energy density of up to 12.1 mWh cm−3 and an ultra-low time constant (τ0) of 0.038 ms, which are the best values among the state-of-the-art in-plane MSCs. This work provides an attractive solution for structural engineering of promising active materials on molecule level toward high-performance micro-energy devices.

The emergence of phosphorene in 2014 augments the family of two-dimensional (2D) materials, which soon triggered tremendous interest in the field of physics, chemistry, biomedicine, and materials science. Considering the tunable band gap, large interlayer spacing (0.53 nm), high charge carrier mobility and strong in-plane anisotropy, tremendous research efforts have been dedicated to the exploration of phosphorene's applications in electrochemical energy storage systems. This review, both theoretically and experimentally, introduces the state-of-the-art development of few-layer phosphorene as the electrode material for electrochemical energy storage systems. The discussed electrochemical energy storage systems involve Li-ion batteries, Na-ion batteries, K-ion batteries, Li-S batteries and supercapacitors. More importantly, perspectives on future possibilities and opportunities of electrochemical energy storage devices based on few-layer phosphorene are also suggested, including dual-ion batteries and metal-ion hybrid capacitors. Finally, the key challenges of phosphorene electrodes are provided for the further research in this thriving field.

Considerable efforts have been devoted to the development of zinc (Zn) batteries with new battery chemistries (eg. Zn-ion battery, Zn-halogen battery, Zn-alkaline battery, Zn-air battery) that are alternatives to Li-ion technology. Unfortunately, the progress of Zn batteries is hindered by their limited operating voltages (

Lithium ion batteries (LIBs) are widely known for their high energy density, large output voltage, long lifespan, lightweight, and environmentally benign operation. However, owing to the ever-increasing demand for flexible and wearable electronics, there is a growing need to develop bendable LIBs without sacrificing their power density or cycle life. To this end, 3D graphene-based macrostructures (GBMs) are being actively pursued as next-generation, high-performance flexible electrode materials due to their exceptional structural flexibility and superior mechanical properties. This chapter, therefore, aims at summarizing the recent advances in the design and fabrication of 3D GBMs-based high-performance foldable and stretchable electrodes for applications in LIBs.

Advanced supercapacitor electrodes require the development of materials with dense redox sites embedded into conductive and porous skeletons. Two-dimensional (2D) conjugated metal-organic frameworks (c-MOFs) are attractive supercapacitor electrode materials due to their high intrinsic electrical conductivities, large specific surface areas, and quasi-one-dimensional aligned pore arrays. However, the reported 2D c-MOFs still suffer from unsatisfying specific capacitances and narrow potential windows because large and redox-inactive building blocks lead to low redox-site densities of 2D c-MOFs. Herein, we demonstrate the dual-redox-site 2D c-MOFs with copper phthalocyanine building blocks linked by metal-bis(iminobenzosemiquinoid) (M2[CuPc(NH)8], M = Ni or Cu), which depict both large specific capacitances and wide potential windows. Experimental results accompanied by theoretical calculations verify that phthalocyanine monomers and metal-bis(iminobenzosemiquinoid) linkages serve as respective redox sites for pseudocapacitive cation (Na+) and anion (SO42-) storage, enabling the continuous Faradaic reactions of M2[CuPc(NH)8] occurring in a large potential window of -0.8 to 0.8 V vs Ag/AgCl (3 M KCl). The decent conductivity (0.8 S m-1) and high active-site density further endow the Ni2[CuPc(NH)8] with a remarkable specific capacitance (400 F g-1 at 0.5 A g-1) and excellent rate capability (183 F g-1 at 20 A g-1). Quasi-solid-state symmetric supercapacitors are further assembled to demonstrate the practical application of Ni2[CuPc(NH)8] electrode, which deliver a state-of-the-art energy density of 51.6 Wh kg-1 and a peak power density of 32.1 kW kg-1.

The past decade has witnessed substantial advances in the synthesis of various electrode materials with three-dimensional (3D) ordered macroporous or mesoporous structures (the so-called “inverse opals”) for applications in electrochemical energy storage devices. This review summarizes recent advancements in 3D ordered porous (3DOP) electrode materials and their unusual electrochemical properties endowed by their intrinsic and geometric structures. The 3DOP electrode materials discussed here mainly include carbon materials, transition metal oxides (such as TiO2, SnO2, Co3O4, NiO, Fe2O3, V2O5, Cu2O, MnO2, and GeO2), transition metal dichalcogenides (such as MoS2 and WS2), elementary substances (such as Si, Ge, and Au), intercalation compounds (such as Li4Ti5O12, LiCoO2, LiMn2O4, LiFePO4), and conductive polymers (polypyrrole and polyaniline). Representative applications of these materials in Li ion batteries, aqueous rechargeable lithium batteries, Li-S batteries, Li-O2 batteries, and supercapacitors are presented. Particular focus is placed on how ordered porous structures influence the electrochemical performance of electrode materials. Additionally, we discuss research opportunities as well as the current challenges to facilitate further contributions to this emerging research frontier. Three-dimensional ordered porous materials can improve the electrochemical storage of energy. Jing Wang and Yuping Wu from Nanjing Tech University, China and co-workers review the development of these materials for use as electrodes in devices such as batteries and supercapacitors. Three-dimensional ordered porous materials are created by inserting the desired raw material into a template made from an array of spheres. The spheres are removed to leave a hole-filled material ideal for storage. The authors describe how this ordered porous structure influences the electrochemical performance of electrodes made from elementary materials, transition metal oxides, conductive polymers, or carbon-based materials, among others. The challenges for the future are discussed, including developing a better fundamental understanding of charge transport, improving efficiency, scaling-up production, and lowering production costs. The past decade has witnessed substantial advances in the synthesis of various electrode materials with three-dimensional (3D) ordered macroporous or mesoporous structures (the so-called “inverse opals”) for applications in electrochemical energy storage devices. Yuping Wu from Nanjing Tech University anchored recent advancements in 3D ordered porous (3DOP) electrode materials and their unusual electrochemical properties bound by their intrinsic and geometric structures. The team introduces various 3DOP electrode materials and their representative applications as electrode materials. Additionally, the team also provides research opportunities as well as the challenges to facilitate further contributions to this emerging research frontier.

High capacity transition metal oxides have attracted much attention as potential sodium-ion batteries (SIBs) anodes. However, the fast capacity fading greatly limits their practical applications. In this study, highly crystallized mesoporous Fe3O4 nanoparticles encapsulated in the hollow nitrogen-doped carbon nanospheres (denoted as HCM-Fe3O4@void@N-C) have been synthesized and then explored as anode materials for SIBs. The resultant HCM-Fe3O4@void@N-C nanospheres possess a uniform particle size of ~ 180 nm with highly crystallized mesoporous Fe3O4 cores (~ 100 nm in diameter), a large surface area of ~ 250 m2 g−1 and a nitrogen-doped carbon shell (~ 7.6 wt%). Notably, a high discharge capacity of 372 mA h g−1 is obtained after the first five cycles at 160 mA g−1, which can gradually increase and be maintained at an ultrahigh specific capacity of 522 mA h g−1 even after 800 cycles. Besides, remarkable rate performance with a capacity of 196 mA h g−1 at a current density of 1200 mA g–1 and a high Coulombic efficiency (~ 100%) are obtained. Such good performance can be attributed to the unique yolk-shell nanostructure with a high crystallized mesoporous Fe3O4 core, a high conductive N-doped carbon shell, and a suitable void space, paving a new way to design and synthesize high-performance anode materials for SIBs.

In-plane micro-supercapacitors (MSCs) with high power density, remarkable rate capability, and long cycling stability, exhibit promising application potential in modern electronic devices. To satisfy the fast-growing energy demands for the next-generation advanced micro-devices, increasing the energy density of MSCs is urgently desirable but still remains a great challenge. In this work, a series of in-plane asymmetric MSCs (AMSCs) are rationally constructed using a family of nano-sandwiched metal hexacyanoferrate/graphene hybrid thin films with interdigital patterns. The voltage output window of the resultant AMSCs is able to reach up to 1.8 V, delivering superior areal capacitances of up to 19.84 mF cm−2, and ultrahigh energy density of 44.6 mW h cm−3 which is among the best performances of the state-of-the-art MSCs. Moreover, the achieved AMSCs show outstanding mechanical flexibility and integration capability. Thus, this work will promote the development of novel high-performance AMSCs.

In recent years, the design and morphological control of crystals with tailored facets have become hot spots in the field of electrochemical energy storage devices. For electrode materials, morphologies play important roles in their activities because their shapes determine how many facets of specific orientation are exposed and therefore available for surface reactions. This review focuses on the strategies for crystal facet control and the unusual electrochemical properties of electrode materials bound by tailored facets. Here, electrode materials with tailored facets include transition metal oxides such as SnO2, Co3O4, NiO, Cu2O, and MnO2, elementary substances such as Si and Au, and intercalation compounds such as Li4Ti5O12, LiCoO2, LiMn2O4, LiFePO4, and Na0.7MnO2 for various applications of Li-ion batteries, aqueous rechargeable lithium batteries, Na-ion batteries, Li–O2 batteries and supercapacitors. How these electrode materials with tailored facets affect their electrochemical properties is discussed. Finally, research opportunities as well as the challenges in this emerging research frontier are highlighted.

The aqueous rechargeable lithium battery (ARLB) is one of the most promising devices for large-scale grid applications. Currently, a key issue for ARLBs is to develop promising anode materials with favorable electrochemical performances. Here, for the first time, we demonstrate an aqueous battery that utilizes the reversible redox reaction with hydroxide ions (OH- ) in the hematite (Fe2 O3 ) anode and a commercial Li ion intercalation compound in neutral solution as the cathode. The fabricated aqueous battery displays a reversible capacity of 92 mAh g-1 . The morphology of the used Fe2 O3 anode with exposed {1 0 4} facets for this aqueous battery is unique and attractive. Importantly, with the dual-pH neutral-alkaline hybrid electrolyte, many excellent anode materials that previously could only work in alkaline electrolytes can now be successfully combined with commercial cathodes in neutral solutions, which may significantly enrich the range of anode materials for ARLBs. In addition, the reported battery configuration can be extended to other aqueous batteries beyond Li-ion ones with lower cost.

A novel WS2–graphite dual-ion battery (DIB) is developed by combining a conventional graphite cathode and a high-capacity few-layer WS2-flake anode. The WS2 flakes are produced by exploiting wet-jet milling (WJM) exfoliation, which allows large-scale and free-material loss production (i.e., volume up to 8 L h−1 at concentration of 10 g L−1 and exfoliation yield of 100%) of few-layer WS2 flakes in dispersion. The WS2 anodes enable DIBs, based on hexafluorophosphate (PF6–) and lithium (Li+) ions, to achieve charge-specific capacities of 457, 438, 421, 403, 295, and 169 mAh g–1 at current rates of 0.1, 0.2, 0.3, 0.4, 0.8, and 1.0 A g–1, respectively, outperforming conventional DIBs. The WS2-based DIBs operate in the 0 to 4 V cell voltage range, thus extending the operating voltage window of conventional WS2-based Li-ion batteries (LIBs). These results demonstrate a new route toward the exploitation of WS2, and possibly other transition-metal dichalcogenides, for the development of next-generation energy-stor...

Electrochemical reduction has emerged as an environmentally-benign and sustainable approach alternative to the Haber–Bosch process for artificial N2 fixation at ambient conditions, while the challenge associated with N2 activation underlines the demand of efficient electrocatalysts for the N2 reduction reaction (NRR). In this work, Nb2O5 nanofiber is experimentally proved to act as a non-noble-metal NRR electrocatalyst for N2 conversion to NH3 with high activity and selectivity. When tested in 0.1 M HCl, such Nb2O5 nanofiber achieves a high average NH3 yield (43.6 µg h−1 mg−1cat.) and a high Faradaic efficiency (9.26%) at − 0.55 V vs. reversible hydrogen electrode, rivaling the performances of most reported aqueous-based NRR electrocatalysts under ambient conditions and even comparable with those under high temperature and pressure. Notably, it also shows high stability during electrolysis and recycling test. The catalytic mechanism of NRR on Nb2O5 (181) surface is further discussed by density functional theory calculations.

A β-galactoside α2,6-sialyltransferase from Photobacterium damselae (Pd2,6ST) that is capable of sialylating both terminal and internal galactose and N-acetylgalactosamine was herein redesigned for regioselectively producing terminal α2,6-sialosides. Guided by a recently developed bump-hole strategy, a series of mutations at Ala200 and Ser232 sites were created for reshaping the acceptor binding pocket. Finally, a Pd2,6ST double mutant A200Y/S232Y with an altered L-shaped acceptor binding pocket was identified to be a superior α2,6-sialyltransferase which can efficiently catalyze the regioselective α2,6-sialylation of galactose or N-acetylgalactosamine at the nonreducing end of a series of glycans. Meanwhile, A200Y/S232Y remains flexible donor substrate specificity and is able to transfer Neu5Ac, Neu5Gc, and KDN.

High-precision underwater positioning must eliminate the influence of refraction artefacts. Since a Time Of Arrival - Global Navigation Satellite System Intelligent Buoys (TOA-GIB) system does not measure incident beam angles, common refraction correction methods cannot be directly used for refraction artefacts. An Equivalent Sound Speed (ESS) iteration method is proposed and is based on the transformation relations between depth, the ESS gradient and the incident beam angle. On this basis, a TOA/AOA-GIB system without a real-time Sound Speed Profile (SSP) is proposed to estimate the target position and the ESS gradient as unknown parameters. The results from a simulation experiment show that the positioning accuracy of a TOA/AOA-GIB system is better than 0·07% of water depth when the accuracy of the incident beam angle is 0·1°.

The development of sodium (Na) ion capacitors marks the beginning of a new era in the field of electrochemical capacitors with high-energy densities and low costs. However, most reported negative electrode materials for Na+ storage are based on slow diffusion-controlled intercalation/conversion/alloying processes, which are not favorable for application in electrochemical capacitors. Currently, it remains a significant challenge to develop suitable negative electrode materials that exhibit pseudocapacitive Na+ storage for Na ion capacitors. Herein, surface-controlled redox reaction-based pseudocapacitance is demonstrated in ultradispersed sub-10 nm SnO2 nanocrystals anchored on graphene, and this material is further utilized as a fascinating negative electrode material in a quasi-solid-state Na ion capacitor. The SnO2 nanocrystals possess a small size of