Ionic liquids (ILs) have emerged as suitable solvents for a number of energy-related applications. This research provides the necessary thermodynamic and thermophysical properties to evaluate and design ionic liquids for these industrial applications. Post-combustion carbon capture would be an efficient way of reducing the carbon dioxide (CO2) emissions to the atmosphere, thus slowing down the effect of climate change. The enthalpy of absorption of CO2, ∆HCO2, directly impacts the solvent regeneration cost of the carbon capture unit. In addition it provides valuable information on the physicochemistry with CO2. This work presents a new method to directly measure the ∆HCO2 in ionic liquids by calorimetry. Experimental enthalpies of absorption of CO2 in a series of anion functionalized ionic liquids with phosphonium and imidazolium cations were obtained using this novel technique. These results demonstrate the ability of tuning the aprotic heterocyclic anion (AHA)-based ILs, showing great potential for the design of cost efficient carbon capture technology. As ILs are likely to be combined with other solvents in industrial processes, deep knowledge of their mixing behavior is needed. The excess properties of mixtures provide important information on the mixture non ideality and give insights into the IL and solvent interactions in the solution. Therefore, these properties were experimentally determined for the binary mixtures of trimethylbutylammonium bis(trifluoromethylsulfonyl) imide, [N1114][Tf2N], with ethanol, 1-propanol and N,N-dimethylformamide. In order to assess the vialibility of ILs for heat transfer fluid application, their thermophysical properties (i.e. viscosity, density and thermal conductivity) must be well understood. Our study of these properties is followed by the investigation of mixtures of two ILs for this application. Expanding the ability of tuning the fluid, mixtures of ILs with two different cations and anions exhibit unique characteristics.