Although WO3 electrochromism exhibits remarkable optical modulation ability, its practical application is largely constrained by poor cycling durability in alkaline metal electrolytes. Herein, an NH4+ aqueous electrolyte with optimized concentration and acidity is proposed to improve the lifetime and electrochromic performance of WO3 films by leveraging the cation's unique hydrogen-bond intercalation chemistry. To construct full electrochromic devices, the electrolyte and counter electrode are further modified with NH4I and P10/ITO (polyquaternium-10/indium tin oxide nanoparticle) composite coating, respectively. The NH4I additive provides a reversible I0/I- couple for charge compensation, while the P10/ITO composite coating enhances the I0/I- conversion reversibility by adsorbing and immobilizing the polyiodide intermediates. More interestingly, the I0/I- conversion introduces an additional electrochromic ability on the counter electrode, and can therefore further improve the optical modulation amplitude in the 400-600 nm band. Thanks to these merits, the resulting WO3-iodine complementary device achieves an impressive optical modulation amplitude (45.5% at 633 nm) and impressive cycling durability (94.4% of the optical modulation ability remaining after 200 cycles).
Tan et al. (Sun,) studied this question.