Graphene Oxide Composite Electrode Research Articles

(Invited) Structural Lithium-Ion Battery Based on LiFePO4/Reduced Graphene Oxide Composite Cathode and Graphene Anode Prepared via Electrophoretic Deposition on Carbon Cloth

Structural lithium-ion batteries based on binder-free LiFePO4/reduced graphene oxide composite cathode electrode and graphene anode electrode are prepared respectively via electrophoretic co-deposition of LiFePO4, reduced graphene oxide, and carbon black on carbon cloth substrate for the cathode, and graphene oxide and carbon black on carbon cloth substrate for the anode. Following deposition, the electrode materials were dried. The graphene oxide of the anode was reduced to graphene via rapid thermal annealing. Possessing excellent stiffness, strength-to-weight ratio, and good electrical conductivity, the carbon cloth substrate serves multifunctional roles in the battery: as structural reinforcement and mechanical load bearing element and as current collector. Given its good electrical conductivity, high aspect ratio, and high surface area, reduced graphene oxide improves electrical conductivity within the cathode and provides sites for hosting LiFePO4; this enhances reversible Li ion extraction from the host during cycling. Graphene with its good electrical conductivity and high aspect ratio provides sites for insertion of Li ions in the anode; this enhances the aerial lithiation capacity of the battery system. Carbon black enhances conductivity within the two electrodes and reduces interfacial impedance. The electrochemical properties of the electrodes are strongly correlated to their microstructure and phase composition. Electrochemical characterization of the electrodes and their performance in half-cell and full cell configurations are evaluated. Additionally, Li-ion diffusivity within the materials is evaluated with three independent electroanalytical methods, including potentiostatic and galvanostatic and intermittent titration techniques, and electrochemical impedance spectroscopy.

Melamine foam scaffolded 3D porous polyaniline/reduced graphene oxide composite electrode for flexible supercapacitor

Graphene composite foam with enhanced mechanical and electrochemical properties holds great promise for flexible supercapacitors. This work developed a cost-effective method for massive production of three-dimensional (3D) porous graphene composite using melamine foam (MF) as a flexible scaffold. The MF was coated reduced graphene oxide (RGO) to form an interconnected conductive layer by dip-coating and vapor reduction, and loaded with polyaniline (PANI) by in-situ polymerization. The resulted PANI/RGO/MF, as self-supporting electrode, exhibits extraordinary mechanical flexibility and a high specific capacitance of 806.2 mF cm−2 at 0.5 mA cm−2. Furthermore, the assembled solid-state supercapacitor exhibits an outstanding capacity of 299.1 mF cm−2 at 0.5 mA cm−2, a high energy density of 26.6 μWh cm−2 at 200 μW cm−2, nearly 100 % capacitance retention at 0°–180°, and good cycling stability. This study provides a scalable strategy for fabricating graphene composite foam suitable for flexible energy storage application.

Conducting Nickel Hydroxide Thin Film on Molybdenum Disulfide – Reduced Graphene Oxide Composite Electrode for Simultaneous Detection of Uric Acid, Dopamine and Ascorbic Acid

AbstractHerein we report the fabrication of a simple electrochemical sensor based on an electrode containing reduced graphene oxide and molybdenum disulphide (RGO/MoS2) as a conducting film onto the glassy carbon electrode (GCE) via a drop dry method to form GCE‐RGO/MoS2. The surface (GCE‐RGO/MoS2) was further modified with nickel hydroxide thin film using electrodeposition method to form GCE‐RGO/MoS2/Ni(OH)2. The materials and modification steps were thoroughly characterized using microscopy and spectroscopy methods. The composite electrode, GCE‐RGO/MoS2/Ni(OH)2, showed excellent electrocatalytic potential separation for the detection of dopamine, uric acid, and ascorbic acid. The electrocatalytic oxidation peak potentials were at 3 mV, 157 mV and 303 mV for AA, DA and UA, respectively. The composite electrode was also selective towards the determination of ascorbic acid (AA), dopamine (DA), uric acid (UA), and simultaneously in mixture of analytes. The low detection limits for AA, DA and UA were 1.17 μM, 0.15 μM and 1.15 μM, respectively. The composite electrode was applied for the detection of AA, DA and UA in spiked newborn calf serum samples with high percentage recoveries ranging from 96.6–100.8 % for AA, 92.8–104.2 % for DA and 99.4–102.3 % for UA.

Ti─O─C Bonding at 2D Heterointerfaces of 3D Composites for Fast Sodium Ion Storage at High Mass Loading Level.

3D composite electrodes have shown extraordinary promise as high mass loading electrode materials for sodium ion batteries (SIBs). However, they usually show poor rate performance due to the sluggish Na+ kinetics at the heterointerfaces of the composites. Here, a 3D MXene-reduced holey graphene oxide (MXene-RHGO) composite electrode with Ti─O─C bonding at 2D heterointerfaces of MXene and RHGO is developed. Density functional theory (DFT) calculations reveal the built-in electric fields (BIEFs) are enhanced by the formation of bridged interfacial Ti─O─C bonding, that lead to not only faster diffusion of Na+ at the heterointerfaces but also faster adsorption and migration of Na+ on the MXene surfaces. As a result, the 3D composite electrodes show impressive properties for fast Na+ storage. Under high current density of 10mAcm-2, the 3D MXene-RHGO composite electrodes with high mass loading of 10mgcm-2 achieve a strikingly high and stable areal capacity of 3mAhcm-2, which is same as commercial LIBs and greatly exceeds that of most reported SIBs electrode materials. The work shows that rationally designed bonding at the heterointerfaces represents an effective strategy for promoting high mass loading 3D composites electrode materials forward toward practical SIBs applications.

Bi2O3@reduced graphene oxide and NiCo2@Ni3Co electrodes for all-electrodeposited high-performance supercapacitors

A novel α-Bi2O3@reduced graphene oxide (rGO) composite negative electrode is designed using an electrodeposition technique, exhibiting an activation process during the first 100 charge-discharge cycles. The bismuth compounds in an initial adsorbed state gradually transformed into a dissolved state, resulting in a distinctive morphological change and the formation of a porous nanosheet structure. At a current density of 1 A/g, the α-Bi2O3@rGO achieves a specific capacitance of 1144 F/g (317 mAh/g), representing 92.18 % of its theoretical value. Even when the current density is increased by 20 times, the capacitance still maintains at 91.71 %. Additionally, a multi-layered composite cathode of NiCo2@Ni3Co is prepared. Based on these two electrodes, an all-electrodeposited soft-packaged supercapacitor (AESPS) is assembled, reaching an energy density of 107.8 Wh/kg at a power density of 800 W/kg, and 73.8 Wh/kg at 16 kW/kg. These outstanding electrochemical performances strongly demonstrate their potential in novel energy storage devices.

Effect of hydrothermal time on catalyst activity of counter electrode Cu2S-rGO composite to enhance the efficiency of quantum dot solar cells

In this study, a high-efficiency reduced graphene oxide and Cu2S composite counter electrode for quantum dot-sensitized solar cells is investigated via various hydrothermal times (12, 24, and 36 h). Besides, for comparison, Cu2S CE was fabricated by hydrothermal and chemical bath deposition methods. The morphology of the nanocomposites was studied using a field emission scanning electron microscope and high-resolution transmission electron microscopy. It confirms the formation of nanoflower-like Cu2S intermixed with rGO sheets. The presence of Cu2S and rGO in rGO/Cu2S composites was identified by X-ray diffraction, selected area electron diffraction, Fourier-transform infrared spectroscopy, and Raman spectra. The chemical composition and purity of rGO/Cu2S were examined by X-ray photoelectron spectroscopy. The electrochemical property of the as-fabricated counter electrode was studied by cyclic voltammetry analysis using the sulfide/polysulfide-based electrolyte. The optimum hydrothermal time was 24 h. The power conversion efficiency of 5.187 % for rGO/Cu2S 24-h counter electrode is higher than that of reduced graphene oxide (4.013 %), synthesized chemical bath deposition (3.466 %), and hydrothermal Cu2S (3.112 %) counter electrodes, respectively. The main reason is the Cu2S nanoflower morphology and the conductive reduced graphene oxide network, which provide more catalytically active sites and a rapid electron transport pathway. Overall, the ease of synthesis, low cost, time efficiency, and excellent electrocatalytic characteristics of the rGO/Cu2S composites demonstrated a promising counter electrode.

Insight on magnetic nitrogen-doped graphene oxide composite electrode constructing heterogeneous Electro-Fenton system for treating organophosphorus pesticide wastewater

The treatment of organic phosphorus pesticide (OPP) wastewater faces challenges such as incomplete degradation and low reaction efficiency. While heterogeneous electro-Fenton (Hetero-EF) has emerged as the preferred technology for addressing these issues due to its high treatment efficiency, further optimization is still necessary. This study used a one-pot hydrothermal method to prepare magnetic nitrogen-doped graphene oxide (Fe3O4@N-GO) composite electrodes to construct a novel Hetero-EF system. Dimethoate (DIM) was chosen as the representative pollutant to investigate the effects of parameters such as current density, pH, electrode spacing, and loading amount on degradation efficiency. The results demonstrated complete degradation of DIM within 40 min. Density functional theory (DFT) calculations and intermediate product analysis revealed that the reactive sites for DIM degradation were the P=S and P=S bonds, involving both hydrolysis and •OH pathways, with a decrease in toxicity of degradation products observed. Compared to graphite electrodes, Fe3O4@N-GO composite electrodes significantly increased H2O2 production, achieving complete DIM degradation even after 5 cycles, with a phosphate conversion rate of 30–40 %. This study highlights the innovative strategy of the Hetero-EF system in its significant application value for OPP treatment.

Self-standing bacterial cellulose-reinforced poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) doped with graphene oxide composite electrodes for high-performance ionic electroactive soft actuators.

Flexible electrode films with good film-forming properties, large deformation ability, high conductivity, and strong charge and discharge capabilities are crucial for ionic electroactive polymer soft actuators. However, there are still challenges in preparing high-quality electrode films that can combine well with the intermediate polyelectrolyte to form high-performance soft actuators. Herein, we propose an advanced sandwich ionic electroactive actuator utilizing self-standing bacterial cellulose (BC) reinforced poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PP) doped with graphene oxide (GO) conductive composite electrodes and a Nafion ion-exchange membrane via a hot-pressing method. The prepared BC-PP-GO electrodes have good film-forming properties with a Young's modulus of 1360 MPa and a high conductivity of 150 S cm-1. The hot-pressed BC-PP-GO/Nafion ionic actuator exhibited a large bending displacement of 6.2 mm (1 V, 0.1 Hz) with a long-term actuation stability up to 95% over 360 cycles without degradation. Furthermore, we introduced the actuator's potential applications including bionic grippers, flies, and fish, providing more opportunities for the development of next-generation micromanipulators and biomimetic microrobots in cm-scale space.

In situ biosynthesized polyphosphate nanoparticles/reduced graphene oxide composite electrode for highly sensitive detection of heavy metal ions

The development of an effective sensing platform is critical for the electrochemical detection of heavy metal ions (HMIs) in water. In this study, we fabricated a newly designed sensor through the in situ assembly of reduced graphene oxide (rGO) and polyphosphate nanoparticles (polyP NPs) on a carbon cloth electrode via microorganism-mediated green biochemical processes. The characterization results revealed that the rGO produced via microbial reduction had a three-dimensional porous structure, serving as an exceptional scaffold for hosting polyP NPs, and the polyP NPs were evenly distributed on the rGO network. In terms of detecting HMIs, the numerous functional groups of polyP NPs play a major role in the coordination with the cations. This electrochemical sensor, based on polyP NPs/rGO, enabled the individual and simultaneous determination of lead ion (Pb2+) and copper ion (Cu2+) with detection limits of 1.6 nM and 0.9 nM, respectively. Additionally, the electrode exhibited outstanding selectivity for the target analytes in the presence of multiple interfering metal ions. The fabricated sensor was successfully used to determine Pb2+/Cu2+ in water samples with satisfactory recovery rates ranging from 92.16% to 104.89%. This study establishes a facile, cost-effective, and environmentally friendly microbial approach for the synthesis of electrode materials and the detection of environmental pollutants.

The combination of MoS2/reduced graphene oxide composite electrode and ionic liquid for high-temperature supercapacitor

Increasing the temperature range of electrochemical energy storage devices represents one of the most interesting sectors in the energy field. In fact, there are countless applications in which the current temperature range is not able to satisfy the applicant's requests and, unfortunately, traditional energy storage devices are not able to sustain these harsh conditions. Among all, supercapacitors emerged as possible candidates to solve this problem, but a lot of research efforts should be spent to overcome the actual limitations. Herein we report on the fabrication of a supercapacitor able to achieve the working temperature of 200 °C exploiting a 3D graphene aerogel decorated with nanostructured MoS2 in combination with an ionic liquid electrolyte able to warranty an effective energy storage performance even at high temperature. The proposed device exhibits capacitance values up to 210 F/g (corresponding to 365 mF/cm2) at 200 °C with a voltage window equal to 2.1 V, resulting in a 20 % improvement of performance from RT to 200 °C, overcoming the existing literature in the field. In fact, the rated value corresponds to an energy of 0.22 Wh dm−3 in a coin-cell embodiment, one order of magnitude higher compared to the device which reaches the highest temperature commercially available of 175 °C. Moreover, the same device can practically be employed in the whole temperature range from 25 °C up to 250 °C with small performance fluctuations.

Graphene modification with chrysin molecules as a high performance electrode material for supercapacitor

In this study, chrysin (CHY) molecules are immobilized on the surfaces of graphene oxide (GO) via π-π interactions to obtain organic molecular-modified reduced graphene oxide (RGO) composite electrode material (CHY/RGO) by one-step hydrothermal. On one hand, CHY molecules can contribute to capacitance through faradic reactions. On the other hand, they act as spacers that impede the accumulation of graphene nanosheets and promote electrolyte ion migration. As a result, CHY/RGO exhibits excellent capacitance performance. The specific capacitance is up to 707F g−1 (1 A g−1), and the capacitance remains 100% after 10 000 circles. In addition, the symmetrical supercapacitor (CHY/RGO//CHY/RGO) displays excellent energy storage performance, achieving an energy density of 38 Wh kg−1 at a power density of 800 W kg−1. Two CHY/RGO//CHY/RGO devices in series is capable of lighting 50 LEDs. Density functional theory (DFT) calculations show that CHY molecules are adsorbed parallel to the RGO by the π-π stacking. The DFT calculations also indicate that the modification of CHY molecules alters the charge distribution on the surface of RGO. Therefore, CHY/RGO composites offer a higher capacitance and superior cycle stability, making them a promising choice for future energy storage electrode materials.

Performance of The Composite Electrode of Reduced Graphene Oxide Palm Oil Shell - Zinc Oxide (rGOCKS - ZnO) as a Chemical Oxygen Demand (COD) Sensor by Photoelectrocatalysis

The preparation of reduced graphene oxide composite electrodes from palm shells (rGOCKS-ZnO) as a chemical oxygen demand (COD) sensor by photoelectrocatalysis has been successfully carried out. The preparation of rGOPS - ZnO electrodes by thermal reduction method and modified Hummer. The XRD results showed several peaks of rGOCKS - ZnO namely 23.287 º, 26.781 °, 29.889 °, 32.468 °, 35.109 °, 37.14 °, 39.822 °, 43.559 °, 47.927 °, and 48.537 °. SEM-EDX analysis reveals the surface of graphene sheets containing aggregates in the shape of small particles attached to graphene sheets. The results of the EDX analysis consisted of C 67.82 %, O. 19.2 %, Zn. 7.85 % and 5.13 % impurity. The CV and LSV tests showed that the rGOAK - ZnO electrode with a variation of 1 gram: 0.3 gram had a good response to the oxidation process under visible light. The profile tests of these organic dyes (methylene blue) in concentrations of 0.5 ppm, 1.0 ppm, 2.0 ppm, and 3.0 ppm were applied by Multi Pulse Amperometry (MPA). The performance of the rGOPS - ZnO electrode has been in determining the value of COD by photo electrocatalytic good sensitivity, linearity, limit of detection, repeatability, and service life. The COD value was determined using the rGOPS - ZnO electrode and obtained 2.97897 mg/LO2 close to the theoretical value.

Planar on-chip micro-supercapacitors based on reduced graphene oxide and carbon nanotube by liquid–air interface self-assembly and photolithography

Recently, the development of miniaturized electronic devices has accelerated the demand for the rate capability of planar on-chip micro-supercapacitors (POMSs). The POMSs based on reduced graphene oxide and carbon nanotube (rGO/CNT) composite electrodes (rGO/CNT-POMSs) were manufactured in the work and detailed electrochemical tests of devices were carried out over a wide range of scanning rates (0.01–10000 V s−1). The rGO/CNT composite electrode films without binder were prepared on silicon substrates by a modified liquid–air interface self-assembly method and a hydroiodic acid reduction method. The electrodes were fabricated into interdigital structure with 50 μm width of electrode and gap of electrode by photolithography. Interdigital POMSs based on different electrodes were prepared by gold sputtering on the electrode lugs. The area capacitance of the rGO/CNT-POMSs was 28.62 μF cm−2. They also had 0.004 μWh cm−2 of energy density and 1.068 μW cm−2 of power density. In addition, the charge–discharge time constant of the device was only 5.6 μs, and the charge–discharge rate was very quick. After 10,000 cycles of charge–discharge, the capacitance retention rate was still above 88%. At the ultra-high scan rate of 10000 V s−1, the devices still worked well. Compared with the POMSs based on reduced graphene oxide electrodes (rGO-POMSs) and the POMSs based on carbon nanotube electrodes (CNT-POMSs), the introduction of the CNT significantly increased the area capacitance, energy density and power density of rGO/CNT-POMSs, and significantly shortened the charge–discharge time constant. This indicated that the rGO/CNT composite electrodes had a good application prospect in the micro-chip accumulator devices.

One-step hydrothermal preparation of bi-functional NiS2/reduced graphene oxide composite electrode material for dye-sensitized solar cells and supercapacitors

To screen out suitable electrode materials and overcome the shortcomings of the existed electrode materials for the application in dye-sensitized solar cells and supercapacitors, NiS2/reduced graphene oxide (NiS2/rGO) composite material was prepared by a simple one-step hydrothermal method in this paper and applied in the field of both dye-sensitized solar cells and supercapacitors as electrode material. In an electrolyte of 6 M KOH, the NiS2/rGO composite material with bilayer capacitance characteristics exhibited a high specific capacitance of 259.20 F g−1 at the current density of 0.6 A g−1, which was significantly higher than that of rGO (188.94 F g−1). Moreover, at a current density of 2 A g−1, the NiS2/rGO composite material had 92.85% capacitance retention after 2000 cycles. When applied as counter electrode material for the dye-sensitized solar cells, the NiS2/rGO composite material counter electrode exhibited a satisfactory photoelectric conversion efficiency (η) of 3.16% under standard simulated sunlight (AM 1.5 G), which was significantly higher than that of single rGO counter electrode (improved by 90.40%). The NiS2/rGO composite electrode material prepared by a simple one-step hydrothermal method is a potential bi-functional composite electrode materials for both dye-sensitized solar cells and supercapacitors.

F and N Codoped Bimetallic Oxide‐Reduced Graphene Oxide Composite Electrode FN‐NA‐CLDH@RGO for Electrocatalytic Reduction of CO2 to CO

Currently, there is considerable interest in developing cost‐effective, high‐performance electrocatalysts for electrocatalytic carbon dioxide reduction (ECR). Due to their low electrical conductivity and relatively weak catalytic activity, layered bimetallic oxides have rarely been applied in ECR studies. However, they contain a large specific surface area and are rich in Lewis bases, which are favorable for CO2 adsorption. Herein, F and N co‐doped layered bimetallic oxide and reduced graphene oxide composites with precisely controlled morphology are deposited directly on carbon paper using a simple constant current electrodeposition method (FN‐NA‐CLDH@RGO‐X, X denotes the deposition time). Notably, the doping of F helps to suppress the hydrogen precipitation reaction, while the doping of N enhances the adsorption and conversion of CO2. The CO2 reduction study in an H‐type electrolytic cell shows that the FN‐NA‐CLDH@RGO‐100 s electrode‐reduced CO2 to CO at an applied potential of −1.1 V with an efficiency of 87.9% (compared to the reversible hydrogen electrode). In addition, the doping of F favors the reduction of overpotential and the improvement of catalytic activity, while the synergistic effect of F and N enhances the catalytic activity without significant decay in more than 6 h of continuous testing.

Electrostatic self-assembled MXene–graphene oxide composite electrodes for planar supercapacitors

MXene based layered materials have exhibited excellent performance in supercapacitor applications owing to their high conductivity. However, device planarization hinders their broader ability in a film-based energy storage device. Here, we have demonstrated the fabrication of self-assembled MXene–graphene oxide (M-GO) composites based on the electrostatic interaction between MXene and GO solutions. The as-prepared M-GO composite possessed homogeneous structures and tunable conductivities according to different GO contents, which benefit both charge storage and ions transmission. The first-assembly sandwiched supercapacitors based on these M-GO composites showed a maximum specific capacitance value of 39.0 mF/cm2 (10.9 mF/cm2 for MXene based devices). The enhanced electrochemical performance after self-assembly was due to the improved interface effect between electrodes and electrolytes. Additionally, the introduction of GO guarantees the completeness of designed M-GO patterns without the need for additives, and it is worth noting that with the assistance of a laser fabrication technique, planar supercapacitors based on the most suitable M-GO (with mass ratio of M:GO = 1:1) composite could be obtained by ablating the unwanted areas. Additionally, planar M-GO based supercapacitors also exhibited excellent electrochemical performance, which demonstrated the great potential of M-GO composite supercapacitors in wearable electronic applications.

Ultra-long MnO2 nanowire-entrenched reduced graphene oxide composite electrodes for energy storage

Ultra-long MnO2 nanowire-entrenched reduced graphene oxide composite electrodes for energy storage

An Ultrafast, High‐Loading, and Durable Poly(p‐aminoazobenzene)/Reduced Graphene Oxide Composite Electrode for Supercapacitors

AbstractAlthough challenging, the fabricated supercapacitor electrodes with excellent rate capability, long cycling stability, and high mass‐loading are crucial for practical applications. Herein, a novel 3D porous poly(p‐aminoazobenzene)/reduced graphene oxide hydrogel is designed and prepared as an ultrafast, high‐loading, and durable pseudocapacitive electrode through a facile two‐step self‐assembly approach. Owing to abundant stable redox‐active sites, fast electrolyte diffusion, and efficient charge conduction, the PRH electrode (5 mg cm−2) shows a high specific capacitance (701 F g−1 at 2 A g−1) and ultrafast rate (97% capacitance retention at 100 A g−1). Furthermore, even with a mass‐loading of 10 mg cm−2, the electrode still exhibits comparable high performance and excellent long‐term cycling life (only 6.7% capacitance loss after 10 000 cycles). This work demonstrates novel polyaniline analog composites for constructing novel electrodes, promising to open an avenue toward practical applications.

A High Performance Triboelectric Nanogenerator Based on MXene/Graphene Oxide Electrode for Glucose Detection.

A smart sensing platform based on a triboelectric nanogenerator (TENG) possesses various advantages such as self-powering, convenience, real-time and biocompatibility. However, the detection limit of the TENG-based sensor is required to be improved. In this study, a high performance TENG-based glucose sensor was proposed by using the Ti3C2Tx (MXene)/graphene oxide (GO) composite electrode. The MXene and GO nanosheets are popular 2D materials which possessed high conductivity and a rich surface functional group. The MXene/GO thin films were prepared through electrostatic self-assembly technology, which can effectively impede the agglomeration of two nanoflakes. The as-prepared MXene/GO film presented outstanding mechanical property. To figure out the relationship between the nanostructure of MXene/GO film and the TENG, a series of MXene/GO-based TENG with different GO sizes was characterized. As a result, the TENG with 400 nm GO demonstrated the highest output performance. Subsequently, the optimized TENG was used in glucose detection application without the assistance of a glucose enzyme. This simple and flexible TENG shows promising potential in biosensors and non-invasive health monitoring.

Aramid Nanofibers/Reduced Graphene Oxide Composite Electrodes with High Mechanical Properties

In this work, aramid nanofibers (ANFs)/reduced graphene oxide (ANFs/RGO) film electrodes were prepared by vacuum-assisted filtration, followed by hydroiodic acid reduction. Compared with thermal reduced ANFs/RGO, these as-prepared film electrodes exhibit a combination of mechanical and electrochemical properties with a tensile strength of 184.5 MPa and a volumetric specific capacitance of 134.4 F/cm3 at a current density of 0.125 mA/cm2, respectively. In addition, the film electrodes also show a superior cycle life with 94.6% capacitance retention after 5000 cycles. This kind of free-standing film electrode may have huge potential for flexible energy-storage devices.