Preparation And Properties Of Cellulose Nanofibers Paper-based Flexible Electrochromic Supercapacitors

Cellulose nanofibers （CNFs） paper with excellent optical transmittance, goodflexibility, low thermal expansion is considered to be a good potential substrate forsupercapacitors. In this study, Layer-by-Layer （LbL） assembly method and in-situpolymerization process is used to prepare hybrid multilayer thin film electrodes withtransparent CNFs paper as the substrates, poly（3,4-ethylenedioxythiophene: poly（styrenesulfonate））（PEDOT:PSS） and reduced graphene oxide （RGO） as the transparent conductivematerials and polyaniline （PANI） as the electrochromic materials. And then, differenttransparent flexible thin film supercapacitors were successfully fabricated by these thin filmelectrodes. According to a series of testing, the properties of the electrodes andsupercapacitors were analyzed. Our work demonstrates that the process of electrolyte ionsdiffusion is associated with the microstructures of the electrodes and the electrochemicalproperties of the supercapacitors may be affected by ion diffusion.CPP-n electrodes are prepared with CNFs paper, PEDOT:PSS suspension and PANIsuspension by LbL assembly method. The transparency of them is good and the surface ofthem is uniform and smooth, but the compact structure of them will block the diffusion ofelectrolyte ions. The transparency of supercapacitor S-PP-8which is fabricated by CPP-8electrodes is good. The transmittance is about47.1%（at550nm）, but the electrochemicalproperties of it is unsatisfactory.CPG-n films are prepared with CNFs paper, graphene oxide （GO） suspension andPANI suspension by LbL assembly method. CPG-n films were transformed to conductiveCPRG-n electrodes by the chemical reduction with hydroiodic （HI） acid. The surface ofCPRG-n film is rugged and the interspace in the CPRG-n film can provide channels forions to diffuse to the electrochemical active materials, which will improve the performanceof supercapacitors fabricated by the CPRG-n film electrodes. The electrochemicalproperties of supercapacitor S-PG-8which is fabricated by CPRG-8electrodes are good.Benefiting from the EDL capacitive behaviour of RGO and pseudocapacitive property ofPANI synergistically, S-PG-8exhibits good cyclic stability and capacitive behavior. Owingto RGO’ color （black）, the transmittance of S-PG-8is only30.6%（at550nm） and theelectrochromic phenomenon could not be seen directly.CRGP electrodes are prepared with CNFs/RGO5and aniline by in-situ polymerization process. The surface of CRGP films is nonuniform. The interspace beween PANI canprovide channels for the diffusion of electrolyte ions. At a low scan rate of2mV·s-1, thecapacitance of supercapacitor S-RGP which is fabricated by CRGP electrodes is19.76mF·cm-2. However, the transmittance of S-RGP is only16.8%（at550nm）.CNFs/[Cu²⁺-GO]₅/[PANI-PEDOT:PSS]10films was prepared with CNFs paper,PEDOT:PSS suspension, GO suspension and PANI suspension by LbL assembly. They aretransformed to CRGPP-10electrodes by the chemical reduction with HI acid. The surfaceof CRGPP-10is uniform and smooth, but the compact structure of them will block thediffusion of electrolyte ions. Benefiting from RGO, the electrochemical properties ofsupercapacitor S-RGPP which is fabricated by CPRG-8electrodes are better than that ofS-PP-8. The transmittance of S-RGPP is37.8%（at550nm）.