Multi-component deep eutectic solvents achieve high stability zinc deposition and dissolution for electrochromic devices

Abstract

Electrochromic devices based on reversible metal deposition offer superior optical performance, with higher reflectivity and broader modulation ranges than conventional ion intercalation systems. Traditional devices use pre-deposited electrochromic layers on transparent conductive substrates, limited by material properties and ion migration rates. In contrast, metal deposition and dissolution devices achieve rapid, highly reversible color switching by directly controlling metal electrochemical deposition on transparent electrodes, expanding modulation range and response speed. This study proposes a multi-component deep eutectic solvent (MDES) electrolyte enabling reversible, efficient, dense zinc deposition, overcoming loose morphology, low transmittance, and low efficiency issues in aqueous electrolytes. MDES raises zinc nucleation overpotential, promotes fine, uniform particles, decreases light transmission, and enhances modulation depth; it also inhibits hydrogen evolution and zinc corrosion, improving stability and cycling. Trace Cu²⁺ further optimizes zinc kinetics, reduces interfacial polarization, and boosts reversibility and device efficiency. Using this electrolyte, a three-electrode multispectral device was assembled, showing four distinct optical states: fully transparent, semi-transparent blue, intermediate opacity, and nearly opaque. This enables dynamic visible and near-infrared light modulation, enhancing adaptive optical application potential. The work offers new design insights for metal-based reversible electrochemical systems, advancing smart windows, tunable filters, and energy-efficient displays with broad prospects.