MOF derived carbon embedded NiO for an alkaline Zn‐NiO electrochromic battery

Transparent-to-Brown-Black Patterned Electrochromic Metal-Organic Frameworks

Metal-organic frameworks (MOFs) exhibit promising electrochromic (EC) performance owing to their porous structure, regular channel, and tunable component characteristics. However, few reports focus on MOF materials with the EC performance of a transparent to brown-black (neutral colored state) change that is more suitable for smart windows. In this work, we proposed a strategy for synthesizing MOF (named Ni-BPY) EC materials and corresponding films fabricated via a low-cost electrostatic spray deposition technique. The obtained film exhibits excellent EC performance with a neutral color change from transparent to brown-black, a large optical modulation of 70% at 430 nm, and a fast response within 10 s. Benefiting from good electrical and chemical stability, the Ni-BPY film can be cycled over 500 times. Notably, the Ni-BPY MOF film also delivers a stepwise-controlled process during the bleached state due to its porous characteristics. In addition, the unique color variation of the Ni-BPY film derives from the redox reaction of the Ni metal node between Ni2+ and Ni3+, which is verified by the in situ potential-dependent Raman and X-ray photoelectron spectroscopy (XPS) measurement. As a proof of application, the patterned Ni-BPY EC films and devices are additionally constructed to demonstrate their potential application in electronic tags and logo displays.

A multi-chromic supercapacitor of high coloration efficiency integrating a MOF-derived V2O5 electrode

Modern technological trends in smart electronic devices demand more intelligent automation. Simultaneous integration of energy storage and multicolor electrochromism in a single device improves user-device interfacing based on a salient human-readable output. In this work, primarily metal-organic framework (MOF) derived V₂O₅ was synthesized which, as an electrochromic material, shows high optical modulation of 35% at 485 nm, with very fast switching speeds (2.9/3.4 s for coloring/bleaching). The multiple coloration states of the V₂O₅ electrode make it worthy for further integration as a smart negative electrode in a multicolored electrochromic asymmetric supercapacitor, where the electrochromic polyaniline electrode serves as the counter electrode. The device demonstrates a high coloration efficiency of 137.2 cm² C^-1 and an areal capacitance of 12.27 mF cm^-2 and an energy density of 2.21 × 10^-3 mW h cm^-2 at a current density of 0.05 mA cm^-2. By virtue of its different chromatic states during charging and discharging, smart visual tracking of the state of charge of the supercapacitor can be realized. Such a design of energy storage devices will have promising practical application in futuristic smart multifunctional electronic devices.

In situ grown hierarchical NiO nanosheet@nanowire arrays for high-performance electrochromic energy storage applications

Electrodes with hierarchical nanoarchitectures could promote electrochemical properties due to their largely exposed active sites and quick charge transfer. Herein, in situ grown hierarchical NiO nanosheet@nanowire films are reported by a one-step hydrothermal process followed by heat treatment. The unique NiO hierarchical nanostructures, which are composed of NiO nanowires grown on the surface of a nanosheet array, show improved electrochromic properties such as large optical modulation in different light regions (95% at 550 nm and 50.6% at 1000 nm), fast color change (9.8/5.4 s) and better coloring efficiency (91.2 cm² C^-1) with long-term cycling properties (82.2% after 700 cycles). Simultaneously, the hierarchical nanostructures possess optimal areal capacitance (117.2 mF cm^-2), rate performance and cycling properties. The enhanced electrochemical properties are due to the pretreated seed layer and the synergistic effect between the unique in situ grown ultrathin nanowire and the underlying vertical nanosheet layer which can strengthen the mechanical adhesion of the nanoarray film to the substrate and make both nanosheets and nanowires more exposed to the electrolyte, enhancing charge transfer and mass diffusion. This work provides a promising pathway towards developing high quality electrochromic energy storage devices.

Organic electrochromic energy storage materials and device design

While not affecting electrochemical performance of energy storage devices, integrating multi-functional properties such as electrochromic functions into energy storage devices can effectively promote the development of multifunctional devices. Compared with inorganic electrochromic materials, organic materials possess the significant advantages of facile preparation, low cost, and large color contrast. Specifically, most polymer materials show excellent electrochemical properties, which can be widely used in the design and development of energy storage devices. In this article, we focus on the application of organic electrochromic materials in energy storage devices. The working mechanisms, electrochemical performance of different types of organics as well as the shortcomings of organic electrochromic materials in related devices are discussed in detail.