Multifunctional electrochromic energy storage devices by chemical cross-linking: impact of a WO3\xb7H2O nanoparticle-embedded chitosan thin film on amorphous WO3 films

Bon-Ryul Koo,Myeong-Hun Jo,Kue-Ho Kim,Hyo-Jin Ahn

doi:10.1038/s41427-019-0193-z

Bon-Ryul Koo, Myeong-Hun Jo + Show 2 more

Open Access

https://doi.org/10.1038/s41427-019-0193-z

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Abstract

With the advent of multifunctional devices with electrochromic (EC) behavior and electrochemical energy storage, complementary design of film structures using inorganic–organic materials has shown great potential for developing EC energy storage devices. Herein, hybrid films consisting of WO3·H2O nanoparticle (WHNP)-embedded chitosan thin films on amorphous WO3 (a-WO3) films were designed. By exploiting the hybrid effect of chitosan and WHNPs to generate unique chemical cross-linking between them, the designed films exhibited attractive EC behaviors compared to bare a-WO3 films. These included fast switching speeds (4.0 s for coloration and 0.8 s for bleaching) due to enhanced electrical conductivity and Li-ion diffusivity, high coloration efficiency (62.4 cm2/C) as a result of increased electrochemical activity, and superb long-cycling retention (91.5%) after 1000 cycles due to improved electrochemical stability. In addition, hybrid films exhibited a noticeable energy storage performance with a high specific capacitance (154.0 F/g at a current density of 2 A/g) and a stable rate capability as a result of improved electrochemical activity and fast electrical conductivity, respectively. This resulted in brighter illumination intensity for the 1.5-V white-light-emitting diode due to improved energy density compared to a bare a-WO3 film. Therefore, the results suggest a new design strategy for materials to realize the coincident application of multifunctional devices with EC energy storage performance.

Highlights

Due to the growing energy demand with the increase in the world’s population, many researchers are investigating innovative technologies to accelerate energy savings or energy efficiency to improve quality of life[1,2,3]
For amorphous WO3 (a-WO3)/CH@WO3·H2O nanoparticle (WHNP), there is an absorption band in the visible region due to the existence of the WHNPs on the WO3 film[6]. These results indicate the successful introduction of chitosan thin films with WHNPs on a-WO3 films using a spincoating method
In summary, we successfully developed novel hybrid films consisting of a WHNP-embedded chitosan thin film on a-WO3 films, with enhanced EC energy storage performance

Summary

Introduction

Due to the growing energy demand with the increase in the world’s population, many researchers are investigating innovative technologies to accelerate energy savings or energy efficiency to improve quality of life[1,2,3]. The EC energy storage performance (optical modulation, coloration efficiency (CE), switching speed, long-cycling stability, specific capacitance, and rate capability) of multifunctional devices is believed to be attributed to the electrochemical double-behavior of electrons and cations on active materials. In this case, the optical modulation, CE, and specific capacitance are mainly related to the degree of insertion/extraction of electrons and cations into/from the active materials in response to the applied voltage and the degree of the switching speed, and the rate capability is directly determined by the ion diffusivity and electron conductivity on active materials[8,9]. Among the active materials of multifunctional devices classified as inorganic materials (transition metal oxides, Prussian blue-based materials, etc.)

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