Reversible metal electrodeposition devices (RMEDs) operate via electrochemically controlled metal deposition and dissolution to modulate optical properties, representing an attractive platform for smart windows and adaptive displays. Unlike conventional electrochromic devices relying on ion insertion or organic redox processes, this reversible metal plating/stripping mechanism eliminates complex multilayer structures and enables superior optical and thermal management through reflection-based light control. Silver-based RMEDs have successfully demonstrated multicolor switching capabilities, yet their high material costs limit practical applications. Copper, with its abundance and lower electrodeposition potentials, presents a compelling alternative; however, previous Copper-based devices have achieved only monochromatic operation due to insufficient control over nucleation and growth dynamics. Here, we demonstrate a breakthrough copper-based RMED that overcomes these limitations through dual-electrode architecture combining nanoparticle-decorated ITO and smooth flat ITO electrodes. This design enables reversible switching among four distinct optical states: transparent, blue, red, and mirror, representing the first demonstration of achieving both blue and red coloration on a single electrode within a copper-based system. Tailored voltage protocols (constant voltage for blue, step voltage for red) produce wavelength-selective LSPR absorption at 700 nm and 550 nm respectively, while anodic deposition on the smooth electrode generates broadband reflection for the mirror state. The device achieves high optical modulation across all states (ΔT ranging from 55.8% to 72.2%), with the highest contrast observed at 550 nm corresponding to peak human visual sensitivity. Consistent coloration times (~10 s) and practical bleaching times (9.8-17.9 s) enable responsive switching suitable for smart window applications. Excellent cycling stability exceeds 80% retention after 100 cycles across all optical states. These findings establish copper-based RMEDs as a viable pathway for cost-effective multicolor electrochromic technologies in energy-efficient buildings and adaptive optical systems.
 

reversible metal electrodeposition,copper,step-voltage,multicolor,ITO nanoparticle