A TOC- and deposition-free electrochromic window driven by redox flow battery

Under “green architecture” principles, electrochromic smart windows are employed to adjust optical transmittance and indoor temperature, yet their high costs limit the wide application. Here, an electrochromic window is driven by a redox flow battery (RFB), where TOC and deposition layers are no longer needed. The transmittance of the electrochromic window is modulated by the state of oxidation (SOC) of aqueous posolyte Fe(phen)₃Cl₂, which is coupled with BTMAP-Vi negolyte in RFB. Under optimized conditions, average CE, VE, and EE reach 93.25 %, 92.61 %, and 86.35 % for RFB with a capacity fading rate of 1.57 % per cycle. 88.66 % optical modulation and 9.36 cm²/C coloration efficiency are achieved in the electrochromic process, and 72.34 % optical modulation is maintained after 12000 s. Essentially, the indoor temperature declines 3 °C for posolyte with 100 % SOC when compared with the control experiment using circulating water for a model house. This means minimum electricity of 0.0185 kWh is saved when using an air conditioner to cool a 100 m³ house, which corresponds to declined CO₂ emission (COE) of 0.0185 kg. This work provides a novel and cost-efficient strategy for modulating indoor comfort via electrochromic windows driven by RFB.