Asymmetric Micro-supercapacitors Research Articles

Printing pillar array structure of electrodes facilitating ion diffusion and electron transport for high-performance asymmetric microsupercapacitors

The asymmetric microsupercapacitors (MSCs) are appealing power sources for miniaturized electronic devices owing to their high capacitance and wider working voltage window. However, the sluggish ion diffusion and poor electron transport in pseudocapacitive electrodes result in confined electrochemical performance of devices. In this work, we propose the pillar array structure of electrodes via 3D printing V2O5 (VN) nanosheets and graphene composite inks to boost the electrochemical performance of asymmetric MSCs. The V2O5 (VN) nanosheets and graphene sandwich each other can deliver a high electrical conductivity. The pillar array structure of electrodes shortens ion diffusion pathway to endow the electrodes with fast kinetics. The asymmetric MSCs achieve an impressive energy density of 44.86 μWh cm−2 and power density of 1.78 mW cm−2, powering a pressure sensor for 20 000 s. This strategy developed here is very helpful to promote the practical applications of MSCs.

Nanoengineered micro-supercapacitors based on graphene nanowalls for self-powered wireless sensing system

This work presents a comprehensive investigation of micro-supercapacitors (MSCs) based on graphene nanowalls (GNWs), covering core material synthesis, device fabrication, evaluation, and application demonstrations. Three-dimensional hierarchical GNWs structures are grown successfully by a microwave plasma-enhanced chemical vapor deposition (MPECVD), with detailed descriptions of the synthesis process and underlying mechanisms. The structural and morphological properties of the GNWs are thoroughly analyzed. Several types of MSCs are reported, ranging from thin-film to three-dimensional (3D) MSCs, as well as symmetric to asymmetric MSCs. Thin-film MSC is developed by a novel micromachining process for one-step fabricating GNWs-Ni core-shell composite microstructures. A solid-state MSC utilizing 3D hierarchical electrode is created by a fully micro electro mechanical system (MEMS)-compatible process. This involves depositing GNWs-RuOx hybrid nanostructures onto microstructure scaffolds formed using deep reactive ion etching (deep RIE). Additionally, another 3D MSC utilizes GNWs-PANI electrode material deposited on silicon nanowires generated through metal-assisted chemical etching (MACE) method. To enhance MSCs performance, asymmetric MSC is proposed and realized, incorporating GNWs-MnO2 acting as the positive electrode and carbon black serving as the negative electrode. Furthermore, the successfully combination of the fabricated MSCs with an energy harvesting system is demonstrated. The self-powered sensing system driven by solar energy, with the harvested energy stored in MSCs, is effectively showcased, opening up new possibilities for futuristic MSCs to accumulate and store harvested energy as usable electricity. This demonstration has significant potential in fields such as self-powered wireless IoT sensing systems, offering valuable contributions towards sustainable and autonomous energy solutions.

Picosecond ultraviolet laser patterned in-plane asymmetric micro-supercapacitors with high-precision capacity matching

Extensive exploratory research on in-plane asymmetric micro-supercapacitors (AMSCs) involves developing various fabrication techniques for in-plane electrodes to streamline the manufacturing process and expanding the operating voltage window (OVW) to increase energy density. Herein, we prepare MXene (Ti3C2Tx) and laser-induced graphene (LIG) electrodes using picosecond ultraviolet laser etching and laser direct writing, respectively, to construct in-plane MXene//LIG AMSCs. The high precision of laser technology guarantees the preparation of in-plane asymmetric electrodes with an interelectrode spacing of 100 μm. Additionally, we adjust the electrode width ratio of the positive and negative electrodes to attain high-precision capacity matching. This capacity matching method not only broadens OVW to 1.2 V, but also increases the energy density up to 1.9 times. The picosecond laser patterning construction approach and the capacity matching method in this work provide new perspectives for in-plane asymmetric supercapacitors.

An inkjet-printing ink based on porous NiS/N-MXene for high-performance asymmetric micro-supercapacitors and self-powered microelectronics

An inkjet-printing ink based on porous NiS/N-MXene for high-performance asymmetric micro-supercapacitors and self-powered microelectronics

Laser maskless fast patterning for multitype microsupercapacitors

Downsizing electrode architectures have significant potential for microscale energy storage devices. Asymmetric micro-supercapacitors play an essential role in various applications due to their high voltage window and energy density. However, efficient production and sophisticated miniaturization of asymmetric micro-supercapacitors remains challenging. Here, we develop a maskless ultrafast fabrication of multitype micron-sized (10 × 10 μm2) micro-supercapacitors via temporally and spatially shaped femtosecond laser. MXene/1T-MoS2 can be integrated with laser-induced MXene-derived TiO2 and 1T-MoS2-derived MoO3 to generate over 6,000 symmetric micro-supercapacitors or 3,000 asymmetric micro-supercapacitors with high-resolution (200 nm) per minute. The asymmetric micro-supercapacitors can be integrated with other micro devices, thanks to the ultrahigh specific capacitance (220 mF cm−2 and 1101 F cm−3), voltage windows in series (52 V), energy density (0.495 Wh cm−3) and power density (28 kW cm−3). Our approach enables the industrial manufacturing of multitype micro-supercapacitors and improves the feasibility and flexibility of micro-supercapacitors in practical applications.

Flexible and alternately layered high electrochemical active electrode based on MXene, carboxymethylcellulose, and carbon nanotube for asymmetric micro-supercapacitors

Recent studies have shown that Ti-based MXene has great potential for electrochemical energy storage applications, including Li-ion batteries and micro-supercapacitors. However, self-stacking and weak interlayer interactions lead to poor electrochemical properties. Herein, a simple one-step vacuum filtration method was used to prepare a MXene/carboxymethylcellulose/carbon nanotube (Ti3C2Tx/CMC/CNT) hybrid membrane. Due to the unique adhesion and flexibility of CMC, it can be interwoven with CNT to form an interconnected mesh structure, which on the one hand mitigates the self-aggregation of CNT, and on the other hand, the CNT entangled on the surface of CMC imparts its electrical conductivity. Moreover, the –OH of CMC can form hydrogen bonds with the reactive terminal groups (-O, –OH, -F) of Ti3C2Tx, resulting in the tight anchoring of CMC and CNT to Ti3C2Tx nanosheet layers and bridging adjacent Ti3C2Tx nanosheets to form a complete conductive pathway. As a result, the mechanical property test indicates that the Ti3C2Tx/CMC/CNT hybrid film could achieve a maximum tensile strength of 64.9 MPa. Furthermore, an asymmetric micro-supercapacitor (MSC) using Ti3C2Tx/CMC/CNT as the cathode and reduced graphene oxide/carboxymethylcellulose/polypyrrole (RGO/CMC/PPy) as the anode was fabricated, which exhibited a high energy density of 258.8 μWh cm−2 at a power density of 750 μW cm−2, and an ultra-long cycle life (93.2% capacitance retention after 15,000 GCD cycles). The simple and scalable preparation process makes this MSC device very promising for commercial electronics applications.

2.5 V “water in salt” aqueous micro-supercapacitors based on polypyrrole-coated NiCo layered double hydroxides

Layered double hydroxides (LDHs) have been considered promising electrode materials in micro-supercapacitors (MSCs) for their high theoretical capacity, adjustable composition, designable function, and facile synthesis. However, the low energy density and disappointing cycle stability are still the main problems. Herein, water-in-salt (WIS) aqueous electrolyte and PPy coating of metal hydroxides are applied to broaden the working potential and stabilize the structure during the charge/discharge process. The asymmetric MSCs with PPy@NiCo-LDH@ITO NWs as the cathode, PPy@FeOOH@ITO NWs as the anode, and WIS electrolyte as the electrolyte have been assembled. The hybrid MSCs perform a high voltage window of 2.5 V, a high areal capacitance of 63.04 mF cm−2 at 0.4 mA cm−2, a maximum volumetric energy density of 32.2 mWh cm−3 (54.7 μWh cm−2) at a power density of 294.1 mW cm−3 (0.5 mW cm−2), and remarkable cyclic stability with 85 % capacitance retention after 8000 cycles at 5 mA cm−2. Remarkably, the series–parallel lighting tests demonstrate good device conformance. These results suggest a new perspective for applying WIS electrolytes for high-performance LDH-based MSCs.

Three-Dimensional Carbon Foam Based Asymmetric Assembly of Metal Oxides Electrodes for High-Performance Solid-State Micro-Supercapacitor

Micro-supercapacitors hold great attention as one of the promising energy storage devices satisfying the increasing quest for miniaturized and portable devices. Despite having impressive power density, superior cyclic lifetime, and high charge-discharge rates, micro-supercapacitors still suffer from low energy density, limits their practical application. The energy density (E=1/2CV2) can be increased either by increasing specific capacitance (C) or voltage range (V). Asymmetric micro-supercapacitors have attracted great attention by using two different electrode materials to expand the voltage window and thus increase the energy density. Currently, versatile fabrication technologies such as inkjet printing, lithography, laser scribing, etc., are used to directly or indirectly pattern the electrode material; these techniques still suffer from scalable production and cost inefficiency. Here, we demonstrate the scalable production of a three-dimensional (3D) carbon foam (CF) based asymmetric micro-supercapacitor by spray printing technique on an array of interdigital electrodes. The solid-state asymmetric micro-supercapacitor comprised of CF-MnO positive electrode and CF-Fe2O3 negative electrode achieves a high areal capacitance of 18.4 mF/cm2 (2326.8 mF/cm3) at 5 mV/s and a wider potential window of 1.4 V. Consequently, a superior energy density of 5 µWh/cm2 is obtained, and high cyclic stability is confirmed with retention of the initial capacitance by 86.1% after 10000 electrochemical cycles. The optimized decoration of pseudocapacitive metal oxides in the 3D carbon network helps in high electrochemical utilization of materials where the 3D interconnected network of carbon provides overall electrical conductivity and structural integrity. The research provides a simple and scalable spray printing method to fabricate an asymmetric micro-supercapacitor using a custom-made mask that can be integrated on a large scale.

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 (Ti3C2Tx) 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.

Multi-step electrodeposited Ni-Co-P@LDH nanocomposites for high-performance interdigital asymmetric micro-supercapacitors.

The development of high-performance electrode materials and the rational design of asymmetric structures are the two main keys to fabricating micro-supercapacitors (MSCs) with high energy density. Transition metal compounds, especially nickel-cobalt phosphides and hydroxides, are promising electrode materials with excellent pseudo-capacitance. However, they are rarely used in fabricating asymmetric MSCs (AMSCs) due to the limitations of the preparation method. In this work, we constructed hierarchical Ni-Co-P@LDH nanocomposites with outstanding mass specific capacitance (1980 F g-1 at 1 A g-1) via a multi-step electrodeposition method, which is employed with FeOOH to fabricate an interdigital AMSC device (Ni-Co-P@LDHs//PVA-KOH//FeOOH). The as-prepared device exhibits a high working voltage (1.4 V), a large specific capacitance (24.0 mF cm-2 at 0.14 mA cm-2), a high energy density (6.54 μW h cm-2 at a power density of 100 μW cm-2) and good cycling stability (86.5% of capacitance retention after 5000 cycles). This work may provide novel methods for the synthesis of high-performance nickel-cobalt composite materials and their potential applications in interdigital AMSC devices.

High Mass Loading Asymmetric Micro-supercapacitors with Ultrahigh Areal Energy and Power Density.

High mass loading asymmetric micro-supercapacitors (MSCs) are key components for the development of high-performance energy and power supply systems. Here, a concept for achieving high mass loading electrodes is presented and applied to high mass loading micro-supercapacitors with ultrahigh areal energy and power density. The positive electrode is made from porous carbon with birnessite coverage and multiwalled carbon nanotubes (CNTs) as conducting additives (PIC-CNTs-MnO2). The negative electrode is prepared from hierarchically porous active carbon mixed with CNTs (PICK-CNTs). Both positive and negative electrode materials are tailored to ensure a high content of macro- and mesopores. MSCs with an optimized mass loading of 13.9 mg·cm-2 (maximum: 23.6 mg·cm-2) provide an ultrahigh areal capacitance of 1.13 F·cm-2 (volumetric capacitance: 22.6 F·cm-3), an outstanding energy of 627.8 μWh·cm-2, and a maximum power density of 64 mW·cm-2. About 85% of the initial capacitance remained after 5000 cycles. Moreover, shunt and tandem device testing confirmed a high uniformity of these MSCs, meeting the requirements of adjustable output currents and voltages in microchips.

Electrochemically constructing V-doped BiFeO3 nanoflake network anodes for flexible asymmetric micro-supercapacitors

Bismuth ferrite (BiFeO3) with high specific capacity and wide voltage window, fundamentally stores charge through the reversible redox reactions of cations, but usually suffers from poor rate capability and bad cycling stability, due to its densely-packed crystal structure and multi-electron redox reaction kinetics. We present a novel route to regulate nanoflake network architectures and oxygen vacancy defects of BiFeO3 through V doping and electrochemical induction without annealing. After consecutive charge/discharge process of BiFe0.95V0.05O3 fabricated by electrochemical deposition, the cycled BiFe0.95V0.05O3 (c-BiFe0.95V0.05O3) retains better structural stability and more oxygen vacancies than those of the annealed BiFe0.95V0.05O3, revealing the outstanding superiority of electrochemical induction. The c-BiFe0.95V0.05O3 electrode provides high rate capability and Li+ diffusion coefficient, mainly attributed to its nanoflake network architecture and abundant oxygen vacancies. The first-principle calculation demonstrates V doping and oxygen vacancies can enhance built-in electric field and construct fast ion transport channels for boosting rate capability. Based on the c-BiFe0.95V0.05O3 anode and the PPyHG (polypyrrole hydrogel) cathode, flexible asymmetric micro-supercapacitors can deliver an extremely wide voltage window of 2.3 V and a high areal energy density of 7.33 µWh cm−2 at 63.7 µW cm−2, reflecting its huge potential for flexible energy storage micro-devices.

Asymmetric micro-supercapacitors based on electrodeposited Ruo2 and sputtered VN films

Research on micro-supercapacitors remains one of the most important activities in the area of electrochemical energy storage for powering smart and miniaturized electronic devices. Here we design an asymmetric micro-supercapacitor (A-MSC) combining sputtered vanadium nitride film (VN) and electrodeposited hydrous ruthenium oxide (hRuO2) film. Taking advantage of their complementary electrochemical potential windows in 1 M KOH electrolyte, the A-MSC achieves a cell voltage up to 1.15 V, associated to high specific capacitance values for the device (≈ 100 mF cm−2). The energy density of this asymmetric VN / hRuO2 micro-supercapacitor reaches 20 µWh cm−2 at a power density of 3 mW cm−2. Taking benefit from the asymmetric configuration, a 5-fold enhancement factor in energy density is demonstrated for the VN / hRuO2 asymmetric micro-supercapacitor as compared to symmetric VN / VN and hRuO2 / hRuO2 microdevices.

Selective deposition of metal oxide nanoflakes on graphene electrodes to obtain high-performance asymmetric micro-supercapacitors.

To meet the charging market demands of portable microelectronics, there has been a growing interest in high performance and low-cost microscale energy storage devices with excellent flexibility and cycling durability. Herein, interdigitated all-solid-state flexible asymmetric micro-supercapacitors (A-MSCs) were fabricated by a facile pulse current deposition (PCD) approach. Mesoporous Fe2O3 and MnO2 nanoflakes were functionally coated by electrodeposition on inkjet-printed graphene patterns as negative and positive electrodes, respectively. Our PCD approach shows significantly improved adhesion of nanostructured metal oxide with crack-free and homogeneous features, as compared with other reported electrodeposition approaches. The as-fabricated Fe2O3/MnO2 A-MSCs deliver a high volumetric capacitance of 110.6 F cm-3 at 5 μA cm-2 with a broad operation potential range of 1.6 V in neutral LiCl/PVA solid electrolyte. Furthermore, our A-MSC devices show a long cycle life with a high capacitance retention of 95.7% after 10 000 cycles at 100 μA cm-2. Considering its low cost and potential scalability to industrial levels, our PCD technique could be an efficient approach for the fabrication of high-performance MSC devices in the future.

3D Crumpled Ultrathin 1T MoS2 for Inkjet Printing of Mg-Ion Asymmetric Micro-supercapacitors.

Metallic molybdenum disulfide (MoS2), e.g., 1T phase, is touted as a highly promising material for energy storage that already displays a great capacitive performance. However, due to its tendency to aggregate and restack, it remains a formidable challenge to assemble a high-performance electrode without scrambling the intrinsic structure. Here, we report an electrohydrodynamic-assisted fabrication of 3D crumpled MoS2 (c-MoS2) and its formation of an additive-free stable ink for scalable inkjet printing. The 3D c-MoS2 powders exhibited a high concentration of metallic 1T phase and an ultrathin structure. The aggregation-resistant properties of the 3D crumpled particles endow the electrodes with open space for electrolyte ion transport. Importantly, we experimentally discovered and theoretically validated that 3D 1T c-MoS2 enables an extended electrochemical stable working potential range and enhanced capacitive performance in a bivalent magnesium-ion aqueous electrolyte. With reduced graphene oxide (rGO) as the positive electrode material, we inkjet-printed 96 rigid asymmetric micro-supercapacitors (AMSCs) on a 4-in. Si/SiO2 wafer and 100 flexible AMSCs on photo paper. These AMSCs exhibited a wide stable working voltage of 1.75 V and excellent capacitance retention of 96% over 20 000 cycles for a single device. Our work highlights the promise of 3D layered materials as well-dispersed functional materials for large-scale printed flexible energy storage devices.

On-chip 3D interdigital micro-supercapacitors with ultrahigh areal energy density

The great development of lightweight and portable smart electronic devices has significantly stimulated the interests in exploring and developing miniaturized energy storage systems. High-performance micro-supercapacitors (MSCs) with three-dimensional (3D) nanostructures show a great potential to improve energy storage capability, and these types of MSCs are regarded as ideal stand-alone power sources for smart microelectronics. Here, Cu0.56Co2.44O4@MnO2 core–shell nanoflowers and carbon nanotubes are integrated into a 3D hybrid asymmetric MSC with a fast, convenient, and scalable production fashion. Due to the hierarchical structure of the 3D electrodes and active materials, the hybrid MSC exhibits an improved specific areal capacitance of 665.3 ​mF ​cm−2 at 3.2 ​mA ​cm−2 and an excellent cycling performance of 89.8% retention after 8000 cycles. The MSC also shows an ultrahigh energy density of 182.3 ​μW ​h ​cm−2, which is higher than almost all the previously reported energy density values of on-chip interdigital-electrode MSCs. The efficient fabrication methodology of both the materials and the device demonstrated in this work show great potential in developing high-performance 3D MSCs.

MXene coupled with molybdenum dioxide nanoparticles as 2D-0D pseudocapacitive electrode for high performance flexible asymmetric micro-supercapacitors

Recently, two-dimensional (2D) transition metal carbides and carbonitrides (MXenes), have shown great potential in micro-supercapacitors (MSCs). However, the maximum voltage output of symmetric MXene MSCs is limited to 0.6 V due to the oxidation effects at high anodic potentials. Herein, we developed asymmetric micro-supercapacitors (AMSCs) based on titanium carbide MXene (Ti3C2Tx) and MXene-MoO2 electrodes with an enlarged voltage window of 1.2 V, which is twice wider than that of symmetric MXene MSCs. The 2D-0D MXene-MoO2 microelectrode is fabricated by homogenous dispersing zero-dimensional (0D) MoO2 nanoparticles into MXene layers to impede layers stacking and MoO2 nanoparticles aggregation. Notably, the AMSCs delivered good electrochemical performances of areal capacitance of ∼19 mF cm−2 and volumetric capacitance of 63 F cm−3 at a scan rate of 2 mV s−1, and high energy density of 9.7 mW h cm−3 at a power density of 0.198 W cm−3. The AMSCs also presented exceptionally mechanical flexibility under different bending states and excellent cyclic stability, with 88% capacitance retention after 10000 cycles at a discharge current density of 0.5 mA cm−2. For practical application, the serially connected AMSCs are fully affordable to power electronics, which is beneficial for soft and wearable power devices.

Self-Assembled Flexible and Integratable 3D Microtubular Asymmetric Supercapacitors.

The rapid development of microelectronics has equally rapidly increased the demand for miniaturized energy storage devices. On‐chip microsupercapacitors (MSCs), as promising power candidates, possess great potential to complement or replace electrolytic capacitors and microbatteries in various applications. However, the areal capacities and energy densities of the planar MSCs are commonly limited by the low voltage window, the thin layer of the electrode materials and complex fabrication processes. Here, a new‐type three‐dimensional (3D) tubular asymmetric MSC with small footprint area, high potential window, ultrahigh areal energy density, and long‐term cycling stability is fabricated with shapeable materials and photolithographic technologies, which are compatible with modern microelectronic fabrication procedures widely used in industry. Benefiting from the novel architecture, the 3D asymmetric MSC displays an ultrahigh areal capacitance of 88.6 mF cm−2 and areal energy density of 28.69 mW h cm−2, superior to most reported interdigitated MSCs. Furthermore, the 3D tubular MSCs demonstrate remarkable cycling stability and the capacitance retention is up to 91.8% over 12 000 cycles. It is believed that the efficient fabrication methodology can be used to construct various integratable microscale tubular energy storage devices with small footprint area and high performance for miniaturized electronics.

A Flexible Microsupercapacitor with Integral Photocatalytic Fuel Cell for Self-Charging.

With the rapid advancement in different kinds of portable electronics, self-powered systems with small volume and high-performance characteristics have attracted great attention in recent years. It would be rather exciting if one integrated system can not only convert recyclable energy or waste to electricity but also store energy at the same time. Here, flexible all-in-one energy chips composed of urea-based photocatalytic fuel cells (PFCs) and asymmetric microsupercapacitors (AMSCs) are designed on the same plane for powering small portable electronics. The planar PFC consisting of TiO2 photoanode and Ag counter electrode, utilizing urea as fuel, can produce a stable energy output (highest power density of 3.04 μW cm-2 in 1 M urea solution under a UV intensity of 30 mW cm-2) while purify this wasted water simultaneously. Besides, the AMSC comprised of NiCoP@NiOOH positive electrode and zeolite imidazolide framework derived carbon (ZIF-C) negative electrode achieves a high areal capacitance of 54.7 mF cm-2 at 0.5 mA cm-2 and an excellent energy density of 13.9 μWh cm-2 at the power density of 270.5 μW cm-2. Its stability can be confirmed by 86% capacitance retention after 8000 electrochemical cycles and almost no decay after 500 bending cycles. Four PFCs and two AMSCs can be easily constructed into an energy chip and power small electronics. This eco-friendly and self-sustainable system has great potential in future portable electronics.

One-step electrodeposited MnxCo1−x(OH)2 nanosheet arrays as cathode for asymmetric on-chip micro-supercapacitors

Constructing on-chip microsupercapacitors (MSCs) with an asymmetric structure is the predominant choice for applications in miniaturized electronic devices. However, the complex fabrication methods of electrodes and the assembling process of devices restrict the development of on-chip MSCs. Herein, a planar asymmetric MSC with MnxCo1−x(OH)2 nanosheet arrays as the cathode and Fe3O4 nanoparticles as the anode is fabricated via a facile one-step electrodeposition method combined with microfabrication technology. The planar asymmetric MSC exhibits a wider operation voltage window (up to 1.65 V), a higher capacitance (32 mC cm−2), and a higher energy density (7.78 μW h cm−2) than those of previously reported MSCs with an alkaline aqueous electrolyte. This work demonstrates a model of the excellent combination of material synthesis and device fabrication towards large-scale manufacture of on-chip microdevices.