(308c) Ionic Liquids As Novel Electrolytes for Energy and Green Chemistry Applications

Ionic liquids (ILs) offer opportunities to tune electrochemical systems beyond what can be done with traditional electrolytes and solvents. The properties of ILs, salts with melting points below 100°C, can be altered by modifying the anion-cation pair. Beyond the favorable traits many ILs are touted for in general applications, such as a minimal vapor pressures, tunable solubilities, wide thermal windows, etc., there are additional properties that make them desirable for electrochemical use. These include wide electrochemical potential windows (EWs) and moderate conductivities. Traditional electrochemical systems are commonly limited by either the EW or conductivity. In aqueous solutions the conductivities can be high by dissolving appreciable quantities of electrolyte, but the EW is small due to water splitting. This small EW prevents many electrochemical redox potentials from being accessed. In organic solutions, the EW can be increased but solubility of electrolyte salts is limited, reducing conductivity significantly. With the use of ILs, the EW can be substantially widened compared to aqueous systems while having higher conductivities than what is possible in many organic systems, potentially creating a more favorable electrochemical environment. Examples of IL use in electrochemistry include electrolytes for electrodeposition, batteries and double-layer capacitors, and as co-catalysts in electrochemical reactions.

Two applications where ILs hold promise for use will be presented in more detail – electrodeposition of palladium in ILs for nanoparticle synthesis and use of IL-like solvents as switchable electrolytes for use as battery safety switches. The electrochemistry and electrodeposition phenomena of palladium and its impact on the resulting morphology of the deposited nanoparticles will be reported. Through the IL used and the electrochemical parameters, the size and shape of the Pd nanoparticles can be dramatically changed. With secondary batteries, as the energy density of electrochemical devices increases, so does the risk for runaway reactions which can lead to fires and explosions of the devices. By use of an in situ safety switch that when triggered by heat will significantly lower the conductivity, the device can shutoff prior to incident. It is also important that when the device cools again that it can return back to an operating state. Silylamine reversible ionic liquids can serve as a switchable electrode through the use of heat and CO₂ as the switching stimuli between a conductive RevIL state and a non-conductive molecular liquid state.