Influence of temperature on the capacitance of ionic liquid electrolytes on charged surfaces.

ABSTRACT

In this work using molecular dynamics simulations we examine the temperature dependence of the differential capacitance of room temperature ionic liquid electrolytes near electrified surfaces. For electrodes with atomically flat surfaces our simulations show very weak temperature dependence of the differential capacitance (DC) with a slight decrease of DC with increasing temperature. For atomically corrugated surfaces where the ion dimensions are comparable to the size of the surface corrugation patterns, the influence of temperature on DC is much more pronounced. At low temperatures the DC dependence on electrode potential shows large variations with well-defined maxima and minima. However, with increasing temperature these features are significantly flattened. Also for these corrugated surfaces an abnormal positive slope of DC vs. temperature is observed in the narrow range of relatively low voltages. Analysis of changes in the electric double layer structure as a function of temperature allowed us to propose a new mechanism explaining the observed trends in capacitance as a function of temperature and surface topography. The obtained simulation results are discussed in light of available experimental data and help to discriminate between contradictory experimentally observed trends in DC temperature dependence reported for ionic liquid based electrolytes in the literature.