Finite-Temperature Dihydrogen Adsorption/Desorption Thermodynamics on Metallo-Porphyrin Incorporated Graphene: Enthalpy versus Vibration

Gas adsorption is closely related to a variety of important physicochemical processes and technologies. Especially, hydrogen storage has been attracting much interest due to high energy density and the environmetally-friendly nature. Although a lot of theoretical studies have been carried out, the thermal vibration effect on hydrogen-sorbent interaction is relatively laking. Here we report the thermodynamics of H$_{\mathrm{2}}$ molecules adsorbed onto metallo-porphyrin-incoporated graphenes based on first-principles density-functional theory calculations. We found that the slow vibrations induced by weak binding tend to make the system more stable under finite temperature while the fast vibrations induced by strong binding disturb the adsorption. This tendency is expected to be universally found in various gas-sorbent systems.