A Poly(3,4-ethylenedioxypyrrole)-Au@WO3-Based Electrochromic Pseudocapacitor

Application of Tungsten-Oxide-Based Electrochromic Devices for Supercapacitors

For making full use of the discoloration function of electrochromic (EC) devices and better show the charge and discharge states of supercapacitors (SCs), electrochromic supercapacitors (ECSCs) have attracted much attention and expectations in recent years. The research progress of tungsten-oxide-based electrochromic supercapacitors (ECSCs) in recent years is reviewed in this paper. Nanostructured tungsten oxide is widely used to facilitate ion implantation/extraction and increase the porosity of the electrode. The low-dimensional nanostructured tungsten oxide was compared in four respects: material scale, electrode life, coloring efficiency, and specific capacitance. Due to the mechanics and ductility of nano-tungsten oxide electrodes, they are very suitable for the preparation of flexible ECSCs. With the application of an organic protective layer and metal nanowire conductive electrode, the device has higher coloring efficiency and a lower activation voltage. Finally, this paper indicates that in the future, WO3-based ECSCs will develop in the direction of self-supporting power supply to meet the needs of use.

Reliable, High-Performance Electrochromic Supercapacitors Based on Metal-Doped Nickel Oxide

Herein, high-performance, reliable electrochromic supercapacitors (ECSs) are proposed based on tungsten trioxide (WO₃) and nickel oxide (NiO) films. To maximize device performance and stability, the stoichiometric balance between anode and cathode materials is controlled by carefully adjusting the thickness of the anodic NiO film while fixing the thickness of WO₃ to ∼660 nm. Then, a small amount (≤10 mol %) of metal (e.g., copper) is doped into the NiO film, improving the electrical conductivity and electrochemical activity. At a Cu doping level of 7 mol %, the resulting ECS exhibited the highest performance, including a high areal capacitance (∼14.9 mF/cm²), excellent coulombic efficiency (∼99%), wide operating temperature range (0-80 °C), reliable operation with high charging/discharging cyclic stability (>10,000 cycles), and good self-discharging durability. Simultaneously, the change in transmittance of the device is well synchronized with the galvanostatic charging/discharging curve by which the real-time energy storage status is visually indicated. Furthermore, the practical feasibility of the device is successfully demonstrated. These results imply that the ECS fabricated in this work is a promising potential energy storage platform and an attractive component for future electronics.

Flexible Conductive Cellulose Network-Based Composite Hydrogel for Multifunctional Supercapacitors

With the continuous development of energy storage devices towards sustainability and versatility, the development of biomass-based multi-functional energy storage devices has become one of the important directions. In this study, a symmetric dual-function supercapacitor was constructed based on a cellulose network/polyacrylamide/polyaniline (CPP) composite hydrogel. The presented supercapacitor, with excellent electrochemical performance and an areal capacitance of 1.73 mF/cm² at 5 mV/s, an energy density of 0.62 µW h/cm² at a power density of 7.03 µW/cm², a wide electrochemical window of 1.6 V and a promising cycling stability, can be achieved. The transmittance of the supercapacitor at 500 nm decreased by 9.6% after the electrification at 3 V, and the device can exhibit periodic transmittance change under the square potential input between 0.0 V and 3.0 V at regular intervals of 10 s. The present construction strategy provides a basis for the preparation of multifunctional devices with natural renewable materials and structures.

Fabry-Perot Cavity-Type Electrochromic Supercapacitors with Exceptionally Versatile Color Tunability

Electrochromic supercapacitors that can change their appearances according to their charged states are presently attracting significant interest from both academia and industry. Tungsten oxide is often used in electrochromic supercapacitors because it can serve as an active material for both benchmarking electrochromic devices and high-performance supercapacitor electrodes. Despite this, acceptable visual aesthetics in electrochromic supercapacitors have almost never been achieved using tungsten oxide, because, in its pure form, this compound only displays a 1-fold color modulation from transparent to blue. Herein, we defy this trend by reporting the first ever Fabry-Perot (F-P) cavity-type electrochromic supercapacitors based only on a tungsten oxide material. The devices were sensitively changeable according to their charge/discharge states and displayed a wide variety of fantastic patterns consisting of different, vivid colors, with both simple and complex designs being achieved. Our findings suggested a novel direction for the aesthetic design of intelligent, multifunctional electrochemical energy storage devices.

Intelligent electrochromic-supercapacitor based on effective energy level matching poly(indole-6-carboxylicacid)/WO3 nanocomposites

A high-quality electrochromic-supercapacitor based on poly(indole-6-carboxylicacid)/WO₃ nanocomposites can intelligently monitor the energy storage state by changing the color of the device.

High-Performance Asymmetric Electrochromic-Supercapacitor Device Based on Poly(indole-6-carboxylicacid)/TiO2 Nanocomposites

A difunctional porous network of poly(indole-6-carboxylicacid) (PICA)/TiO₂ nanocomposites is first prepared using TiO₂ nanorod arrays as the scaffold. Because of the synergistic effect of PICA and TiO₂, the nanocomposites show good electrochemical performance, a high specific capacitance value (23.34 mF cm^-2), and excellent galvanostatic charge-discharge stability. Meanwhile, this nanocomposite can be reversibly switched (yellow, green, brown) with a high coloration efficiency (124 cm² C^-1). An asymmetric electrochromic-supercapacitor device (ESD) is also constructed using the PICA/TiO₂ nanocomposites as the anode material and poly(3,4-ethylenedioxythiophene) as the cathode material. This ESD has robust cycle stability and a high specific capacitance value (9.65 mF cm^-2), which can be switched from light green to dark blue. After charging, the device can light up a single LED for 108 s, and the energy storage level can also be monitored by the corresponding color changes. This constructed ESD will have great potential applications in intelligent energy storage and other smart electronic fields.

Bifunctional Photo-Supercapacitor with a New Architecture Converts and Stores Solar Energy as Charge

Photo-supercapacitors (PSCs) combine functions of energy harvesting and storage in a single device, and in this study, a new architecture for a PSC is designed and implemented. Cadmium sulfide (CdS) quantum dots/hibiscus (hb) dye co-sensitized TiO₂ is used as the solar cell. Poly(3,4-ethylenedioxypyrrole) (PEDOP)@manganese dioxide (MnO₂) is employed as the counter electrode (CE) for the solar cell and also as the electrodes for the symmetric supercapacitor. The two ends of a long flat current collector support two spatially separated PEDOP@MnO₂ coatings, which serve as the CEs for the TiO₂/hb/CdS photoanode and yet another PEDOP@MnO₂ electrode in sandwich configurations. In this cell, under 1 sun (100 mW cm^-2) illumination, the TiO₂/hb/CdS photoanode undergoes charge separation and by channeling the photocurrent to the PEDOP@MnO₂ electrodes, the symmetric cell part is charged to a voltage of 0.72 V. The PSC delivers a specific capacitance of 183 F g^-1, an energy density of 13.2 Wh kg^-1, and a power density of 360 W kg^-1 at a discharge current density of 1 A g^-1. During the self-discharge process, PEDOP@MnO₂-based PSC retains a voltage of 0.72 V up to 500 s and maintains a stable voltage of 0.5 V thereafter. The TiO₂/hb/CdS photoanode with the PEDOP@MnO₂ CE in an aqueous polysulfide-silica gel electrolyte delivers a power conversion efficiency of 6.11%. This demonstration of a novel PSC opens up opportunities to develop new architectures for efficiently combining energy conversion and storage.

Fabrication of WO3·2H2O/BC Hybrids by the Radiation Method for Enhanced Performance Supercapacitors

In this study, we described a facile process for the fabrication of tungsten oxide dihydrate/bamboo charcoal hybrids (WO₃·2H₂O/BC) by the γ-irradiation method. The structural, morphological, and electrochemical properties of WO₃·2H₂O/BC hybrids were investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) techniques. The combination of BC (electrical double layer charge) and WO₃·2H₂O (pseudocapacitance) created a combined effect, which enhanced the specific capacitance and superior cyclic stability of the WO₃·2H₂O/BC hybrid electrode. The WO₃·2H₂O/BC hybrids showed the higher specific capacitance (391 F g⁻¹ at 0.5 A g⁻¹ over the voltage range from −1 to 0 V), compared with BC (108 F g⁻¹) in 6 M KOH solution. Furthermore, the hybrid electrode showed superior long-term performance with 82% capacitance retention even after 10,000 cycles. The experimental results demonstrated that the high performance of WO₃·2H₂O/BC hybrids could be a potential electrode material for supercapacitors.

Buckling Structured Stretchable Pseudocapacitor Yarn

Cable-type stretchable electrochemical pseudocapacitors based on multi-walled carbon nanotube (MWCNT) sheets and two different metal oxide nanopowders (NP), i.e., MnO₂ and RuO₂ are developed using a newly-devised dry painting method to mechanically fix the NP to the elastic rubber-based MWCNT electrode substrate, resulting in a porous buckling structured pseudocapacitor yarn. Highly stretchable stylene-ethylene/butylene-stylene (SEBS) is used as the supporting elastomeric core for wrapping with the MWCNT sheets and the electroactive NP. The dry painting can successfully deposit NP on the soft SEBS surface, which is normally an unfavorable substrate for coating alien materials. The resulting yarn-type pseudocapacitor, composed of eight-layered MWCNT sheets, three-layered RuO₂, and two-layered MnO₂, showing a diameter of approximately 400 μm with a porous buckling structure, records a specific capacitance of 25 F g⁻¹. After being stretched by 200% in strain with no sacrifice of the porous buckling structure, the cable-type stretchable electrochemical pseudocapacitor yarn retains its electrical capacity, and is potentially applicable to energy storage devices for wearable electronics.

Multifunctional Energy Storage and Conversion Devices

Multifunctional energy storage and conversion devices that incorporate novel features and functions in intelligent and interactive modes, represent a radical advance in consumer products, such as wearable electronics, healthcare devices, artificial intelligence, electric vehicles, smart household, and space satellites, etc. Here, smart energy devices are defined to be energy devices that are responsive to changes in configurational integrity, voltage, mechanical deformation, light, and temperature, called self-healability, electrochromism, shape memory, photodetection, and thermal responsivity. Advisable materials, device designs, and performances are crucial for the development of energy electronics endowed with these smart functions. Integrating these smart functions in energy storage and conversion devices gives rise to great challenges from the viewpoint of both understanding the fundamental mechanisms and practical implementation. Current state-of-art examples of these smart multifunctional energy devices, pertinent to materials, fabrication strategies, and performances, are highlighted. In addition, current challenges and potential solutions from materials synthesis to device performances are discussed. Finally, some important directions in this fast developing field are considered to further expand their application.