Optimizing Electrochemical Thermal Control Devices: Investigating the Effect of Water Contamination on Reversible Silver Thin-Film Plating

Abstract

Reversible Electrochemical Mirror (REM) technology describes a variable emissivity system that can switch between reflective and transmissive states through the application of a voltage to electrodeposit and remove a reflective mirror film. Such a system is an ideal replacement for traditional thermal control methods in space (louvres and radiators), because it is lighter, has no moving parts, and offers a finer degree of tunability. We have investigated various silver-plating systems that achieve this switching effect, including (1) AgNO3 in DMSO solvent, as well as (2) AgI and LiBr salts in γ-Butyrolactone. The effect of water contamination on these systems was determined, and the subsequent enhancement or degradation of the system quantified. While silver nucleation occurs more readily in water-contaminated systems, the presence of water may be detrimental to the stability and reversibility of the system such as more ready oxidation of the deposited film. For the DMSO/AgNO3 system, the addition of water also results in an increase in current during deposition (Figure 1). This is hypothesized to be a result of easier dissociation of AgNO3 in the presence of water which leads to greater silver ion conductivity. Thin film growth will be carried out on various substrates (indium tin oxide (ITO), silver, and gold) to determine the ways in which small amounts of water contamination affect the microstructure, optical reflectivity, reversibility, and stability of the system. Figure 1: Silver plating at -0.05 V in DMSO/AgNO3 systems (WE: ITO, CE: ITO, RE: Ag/AgNO3/0.1M AgNO3 in DMSO) with various amounts of water-doping. As the concentration of water increases, current increases. Figure 1