Energy storage devices with the smart function of changing color can be obtained by incorporating electrochromic materials into battery or supercapacitor electrodes. In this review, we explain the working principles of supercapacitors, batteries, and electrochromic devices. In addition, we discuss the material candidates for electrochromic energy storages in detail. The challenges of the integrated electrochromic energy system for simultaneous realization of electrochromism and energy storage are specially highlighted.

The innovative core-ring structured NiCo 2 O 4 nanoplatelets were found to be novel and promising photocatalysts. The physical and photophysical properties of the photocatalyst were characterized by SEM, TEM, XPS, UV-vis absorption, and photoluminescence, respectively. The core-ring NiCo 2 O 4 nanoplatelets were composed of much smaller nanocrystallines, with an average size of 80-150 nm, compared to the ordinary NiCo 2 O 4 prepared through a conventional hydroxide decomposition method. Moreover, the optical band gap energies of the core-ring NiCo 2 O 4 nanoplatelets were estimated to be 2.06 and 3.63 eV from the UV-vis absorption spectra. The core-ring structured NiCo 2 O 4 photocatalyst exhibited a much higher photocatalytic activity for the degradation of methylene blue than the ordinary NiCo 2 O 4 and TiO 2 under visible light irradiation (>420 nm). This enhanced photocatalytic activity of the core-ring NiCo 2 O 4 nanoplatelets was attributed to their higher optical absorption ability, smaller particle size, and more active internal electron transitions. On the basis of all the results, the band structure of the photocatalyst was discussed.

The pursuit of harmonic combination of technology and fashion intrinsically points to the development of smart garments. Herein, we present an all-solid tailorable energy textile possessing integrated function of simultaneous solar energy harvesting and storage, and we call it tailorable textile device. Our technique makes it possible to tailor the multifunctional textile into any designed shape without impairing its performance and produce stylish smart energy garments for wearable self-powering system with enhanced user experience and more room for fashion design. The "threads" (fiber electrodes) featuring tailorability and knittability can be large-scale fabricated and then woven into energy textiles. The fiber supercapacitor with merits of tailorability, ultrafast charging capability, and ultrahigh bending-resistance is used as the energy storage module, while an all-solid dye-sensitized solar cell textile is used as the solar energy harvesting module. Our textile sample can be fully charged to 1.2 V in 17 s by self-harvesting solar energy and fully discharged in 78 s at a discharge current density of 0.1 mA.

Multifunctional glass windows that combine energy storage and electrochromism have been obtained by facile thermal evaporation and electrodeposition methods. For example, WO3 films that had been deposited on fluorine-doped tin oxide (FTO) glass exhibited a high specific capacitance of 639.8 F g(-1). Their color changed from transparent to deep blue with an abrupt decrease in optical transmittance from 91.3% to 15.1% at a wavelength of 633 nm when a voltage of -0.6 V (vs. Ag/AgCl) was applied, demonstrating its excellent energy-storage and electrochromism properties. As a second example, a polyaniline-based pseudocapacitive glass was also developed, and its color can change from green to blue. A large-scale pseudocapacitive WO3-based glass window (15×15 cm(2)) was fabricated as a prototype. Such smart pseudocapacitive glass windows show great potential in functioning as electrochromic windows and concurrently powering electronic devices, such as mobile phones or laptops.