Stable Aqueous Ammonium-Ion Electrochromic Devices via Electrolyte Concentration Modulation Strategy

Ammonium-ion electrochromic devices (AECDs), featuring intuitive color display functionality and constructed with tailored electrolytes, have emerged as promising ″visual windows″ for next-generation smart electronic systems. However, most contemporary studies prioritize the development of novel electrochromic materials, while lacking in-depth analysis of the correlation between morphological characteristics and the cycling performance of electrodes, treating the electrolyte as a static ″background″ parameter without systematic optimization. Herein, the electrochemical behaviors, electrochromic properties, and post-long-cycle-testing SEM surface morphologies of Prussian blue (PB) electrodes with different concentrations of NH4Ac and (NH4)2SO4 electrolytes were systematically compared. Moreover, a more in-depth exploration of the ammonium storage mechanism within PB electrodes is conducted via analysis of the reaction kinetics. It was found that the ammonium storage behavior of the PB electrode reached the optimal equilibrium state in 0.25 M (NH4)2SO4 solution, and after 5000 consecutive cycles, there were no significant cracks on the surface morphology. On this basis, this work assembled PB (positive electrode), Nb18W16O93 (negative electrode), and an ammonium-ion hydrogel electrolyte to construct a quasi-solid-state AECD. The device achieved a transmittance modulation of 63.8% at 630 nm and retained 93.0% of its initial capacity even after 2000 cycles. Given that the AECD technology is still in the development stage, this work provides a solution for next-generation ammonium-ion electrochemical devices for intelligent displays.