Reversible Electrochemical Mirror for Thermal Management Systems

Reversible electrochemical mirror devices function through reversible redox reactions that alternate between deposition of a highly reflective thin metallic film (hence the term mirror) and complete oxidation of the metallic film during the erasure cycle. These devices generally utilize transparent, conductive substrates such as those based on indium tin oxide type films applied to glass or plastic transparent substrates, though other substrate materials could be used in the build of these devices. Reversible electrochemical mirror devices may be built to either facilitate reflection and transmission or reflection and absorption of radiation sources depending on the nature of the counter electrode used. Reversible electrochemical mirror devices may be used in space based thermal management systems as well as terrestrial applications including auto-dimming mirrors for the automotive industry, electrochromic windows for the aviation industry, and smart glass for the architectural industry.

Room temperature ionic liquid electrolytes are an attractive for reversible electrochemical mirror devices used in space-based systems due to their ability to facilitate reversible electrodeposition reactions in addition to their negligible vapor pressure, excellent chemical and thermal stability and their large electrochemical windows. Simple, two electrode cells were built using transparent electrodes with electrically conductive films (i.e. indium tin oxide, platinum and silver) and air and moisture stable room temperature ionic liquid electrolytes for development of operating conditions that facilitate long cycle lifetimes in simple reversible electrochemical mirror devices. In this work, use of pulsed electric fields have been demonstrated to promote high cycle lifetimes when compared to operation under steady state (constant voltage electric fields). By tuning the pulse electric field, the mass transport properties and crystallization process are controlled, yielding fine grained silver deposits, which is expected to be important for the subsequent stripping process, which leads to long cycle lifetimes in comparison to steady state operation.