Adsorption Characteristics of Refrigerants for Thermochemical Energy Storage in Metal–Organic Frameworks

The adsorption of fluorocarbons has gained significant importance as it is used as refrigerants in energy storage applications. In this context, the adsorption behavior of two low global warming potential refrigerants, R125 fluorocarbon and its hydrocarbon analogue R170, within four nanoporous materials, namely, MIL-101, Cu-BTC, ZIF-8, and UiO-66, has been investigated. By analyzing the validity of our models against experimental observations, we ensured the reliability of our molecular simulations. Our analysis encompasses a range of crucial parameters, including adsorption isotherms, the enthalpy of adsorption, and energy storage densities, all under varying operating conditions. We find remarkable agreement between the computed and observed adsorption isotherms for R125 within MIL-101. However, to obtain similar success for the rest of the adsorbents, we need to take into account a few considerations, such as the presence of inaccessible cages in Cu-BTC, the flexibility of ZIF-8, or the defects in UiO-66. Transitioning to energy storage properties, we investigated various scenarios, including processes with varying adsorption and desorption conditions. Our findings underscore the dominance of MIL-101 in terms of storage densities, with R125 exhibiting a superior affinity over R170. Complex mechanisms governed by changes in the pressure, temperature, and desorption behavior make for complicated patterns, demanding a case-specific approach. In summary, this study navigates the complex landscape of refrigerant adsorption in diverse nanoporous materials. It highlights the significance of operating conditions, model selection, and refrigerant and adsorbent choices for energy storage applications.