Highly Stable Transparent Conductive Silver Grid/PEDOT:PSS Electrodes for Integrated Bifunctional Flexible Electrochromic Supercapacitors

is relatively inexpensive and eco-friendly material that exhibits outstanding theoretical capacitance values with a distinct electro-polychromism. [17] However, studies exploiting their concurrent electropolychromism and energy-storing performance in devices are still aberrant. The main hindrance in V 2 O 5 electrode usage for potential commercial applications is their electrochemical instability, write-erase stability, and trapping-related degradations. [18] Constructing the thin film-based EESD electrodes needs a critical selection of components. In principle, the components should offer synergistic enhancements in the charge capacitance and also produce obvious color change during the charge insertion/extraction. Such bifunctionality could be used for either online charge level monitoring or in the energy storing smart window applications. Moreover, the electrochemical stability of transparent conductors must not be compromised by the adopted process as explained by the work of Cai et al. [19] Typically, researchers employ techniques like nanostructuring [20] or binary [21] /ternary [22] hybridizations of materials as effective ways to improve the capacitance of TMOs. The synergistic effect of a thin layer of TMOs on V 2 O 5 nanostructure in enhancing the capacitance and cyclic stability is described in some recent publications. [23,24] These reports highlighted the modifications in the electronic structure and chemical environment of V 2 O 5 that led to the electrode performance enhancements.Research on V 2 O 5 -based EESDs is still in its infancy with only a few reports appeared in the literature. An EC supercapacitor with V 2 O 5 in gyroid nanostructure is reported by Wei et al. [25] They observed a reduction in the initial specific capacitance to half of the value within the first few cycles before stabilization to a constant value of 155 F g −1 . This behavior was attributed to the structural instability of the gyroid nanostructure, which points to the fact that the capacitance retention is a serious issue even in a controlled nanostructuring of V 2 O 5 . In another paper, carbon nanosphere-decorated V 2 O 5 hybrid nanobelts were synthesized, and the effect of annealing on the capacitance and EC property was studied. [8] In the study, the film with higher capacitance is having a relatively slow response time. More attempts are required for the matured development/understanding of better V 2 O 5 based electrode materials V 2 O 5 electrochromic (EC) coatings are attractive for various photonic applications owing to their multiple oxidation states discernable by distinct colors. The material also shows massive potential for electrochemical energy storage because of their layered structure and high theoretical capacitance. Here, the solution processing of the electrodes composed of an ultra-thin layer of MnO 2 -encrusted V 2 O 5 (V 2 O 5 /MnO 2 ) nanowire mats on fluorinated tin oxide substrates is reported that offer much enhanced electrochemical stability along with a superior energy storage performance com...

The studied EC materials usually include viologens (as polymeric films), conjugated conducting polymers, transition metal oxides (e.g., WO 3 and NiO), metal coordination complexes (e.g., polymeric, evaporated, sublimed films). [7,11] Bene fitted by the diversity in composition/structure and the superior electrochromic performance, the electrochromism based on the thin-film transition metal oxides has become a hot topic. Recently, there have been some important breakthroughs in the transition metal oxide-based electrochromism, ranging from the development of new materials, [12] the introduction of new nanostructures, [13][14][15] element doping, [16,17] and composites [18][19][20][21] to novel designs and concepts of visible light and near-infrared radiation (NIR) dual-modulated smart windows [8,14,20] and the self-powered electrochromic batteries. [22,23] Therefore, the exploration of electrochromic devices with multifunctionalities and unique features by integrating both energy storage and electrochromism has been attracting great attention.There are several elaborate reviews serving as good references for this field, [1,3,4,6,[8][9][10] however, more comprehensive integration and up-to-date summaries embracing all relevant materials and applications are still lacking. Under such a background, as outlined in Figure 1, we attempt to provide a systematic and recapitulative review on the material developments and application status of electrochromism with a focus on transition metal oxides. Additionally, tailored synthesis and material design toward enhanced optical modulation and fast switching are also illustrated. Finally, an outlook on the future research trends in electrochromism is presented. This review will be very instructive and of special importance for directing other researchers in the future. Electrochromism: Fundamentals, Principles, and Device Structure Fundamentals and PrinciplesElectrochromism refers to the reversible change of colors and transparency under charge insertion/extraction or chemical reduction/oxidation induced by the application of an electrical current or a potential difference. [4][5][6] In the mid-1980s, the acceptance of electrochromism in fenestration technology as an approach to achieve energy efficiency in buildings captured the interest of researchers and the public. [3,24] This concept was coined as "smart window," which was capable of achieving Electrochromism has received increasing attention due to its unique electrochromic feature and the induced applications. This review provides an overview on the recent developments in the synthesis and application of the electrochromic metal oxides in smart windows, display devices, e-skins, and multifunctional energy storage devices. The main cathodic and anodic electrochromic metal oxides are surveyed here, with the discussion of representative examples in details. The current state-of-the-art research activities of the derived multifunctional electrochromic devices are highlighted, i.e., material systems, components, structures, m...

A well-designed flexible ITO-free electrochromic supercapacitor was obtained using a hybrid graphene/ CuS network on PET (G-CuS) as the transparent conductive electrode (TCE). This new type of TCE was produced by photolithography, chemical vapor deposition and a low temperature solvothermal reaction. The TCE achieves a sheet resistance (R s ) as low as $20 U sq À1 with a high transmittance of over 85%. In particular, the G-CuS TCE displays a remarkable flexible stability under bending stresses and an excellent chemical stability through the polyaniline (PANI) electrodeposition in acid solution. The PANI/G-CuS electrode gave a favorable area capacitance of 17.3 mF cm À2 at 0.025 mA cm À2 along with a large optical modulation of 40.1% (620 nm). More intuitively, a symmetrical supercapacitor of PANI/G-CuS was fabricated with H 2 SO 4 -PVA hydrogel as the electrolyte, and its noticeable color variation enables users to evaluate the level of stored energy by the naked eye in a predictable manner. This work may provide a practical route to the fabrication of stable TCEs in smart supercapacitors.