Uncovering the performance of amorphous tungsten oxide electrodes within Zn-ion electrolytes toward stable aqueous...

Aqueous Zn-ion electrochromic devices (ZECDs) are attractive cheap, multifunctional and green energy saving technologies but are bottlenecked by limitations in ion diffusion kinetics within electrodes and the compatibility of electrolytes to achieve satisfactory stability. Here, key bulk properties (such as hydrogen bonding, ions conductivity, pH and electrochemical stability, etc.) of various aqueous Zn-ions electrolytes and the Zn-ions migration kinetics in amorphous WO₃ electrochromic electrodes were systematically investigated through combining experimental and theoretical analyses. Moreover, how the type and size of anions within the aqueous electrolyte affect the Zn-ions solvation structure and insertion/extraction processes were also demonstrated. Compared with SO₄^2- with double charge, the bulky CF₃SO₃^- anions can decrease the number of water molecules in the primary solvation sheath of Zn-ions, thus slowing down the hydrogen evolution side reactions and corrosion of electrodes. Benefiting from the weak solvent structure of Zn(CF₃SO₃)₂ solution, the amorphous WO₃ electrode possesses remarkable electrochromic and electrochemical performance at Zn(CF₃SO₃)₂ electrolytes, including robust electrochemical stability, superior rate performance and noticeable optical memory effects. Additionally, a prototype aqueous ZECD based on Zn(CF₃SO₃)₂ aqueous electrolyte demonstrates an impressive optical modulation (71.2 %@630 nm), remarkable cycling stability (over 1000 cycles) and a high areal capacity (170.2 mA h m^-2). This work is poised to provide invaluable foundational guidance for the development of novel Zn-ion electrolytes and for unraveling or mitigating the attenuation mechanisms that challenge high-performance aqueous ZECDs.