An eco-friendly sodium-based thermoplastic starch solid electrolyte for energy-efficient and sustainable electrochromic devices

Abstract

This study presents an eco-friendly electrochromic device (ECD) utilizing a sodium-based thermoplastic starch solid electrolyte, in which carboxymethyl cellulose (CMC) enhances mechanical stability, sodium acetate serves as an ion source, glycerol acts as a plasticizer, and citric acid functions as a cross-linking agent. This system addresses the increasing demand for sustainable materials in energy-saving applications. The proposed sodium-based electrolyte offers a low-cost, abundant, and biodegradable alternative to conventional lithium-based systems. The ECD was fabricated using an “all-in-one” method, simplifying the assembly process with the composite electrolyte layer sandwiched between two ITO glass electrodes. The device demonstrated a fast coloration switching time of just 6 seconds at 90% modulation and 120 seconds at 99% modulation. Electrochemical analysis confirmed stable redox performance and efficient ion diffusion, while spectro-electrochemical measurements indicated a significant transmittance change of 58.5% at 520 nm. Moreover, the ECD exhibited excellent long-term stability, with minimal degradation in optical contrast of 6.0% over 80 hours of continuous operation. The self-bleaching time, without power, was recorded as 11.5 hours at 90% modulation and 16.5 hours at 99% modulation, showing efficient passive transparency recovery. These findings highlight the potential of sodium-based solid electrolytes for scalable, environmentally friendly and energy-saving ECDs.