Density functional theory study on the decomposition mechanism of HFC-32 on a Cu(111) surface: The impact of H2O and O-2

Density functional theory is employed to investigate the impact of water and oxygen on the dissociation of difluoromethane (HFC-32) on Cu(111) surfaces. Two initial dissociation reactions of the HFC-32 molecule on clean, oxygen atom- and water molecule-preadsorbed Cu(111) surfaces through the breakage of C-H and C-F bonds are studied in this work. The adsorption structures and adsorption energies of HFC-32 on the three types of Cu(111) surfaces are calculated to reveal the effect of the oxygen atom and water molecule on the adsorption characteristics of HFC-32. The results indicated that the presence of oxygen atoms and water molecules enhanced the interactions of the HFC-32 molecule with the Cu(111) surface. Moreover, the energy barrier and reaction energy of each reaction are obtained to illustrate the influence of O atom and H2O molecule on the dissociation of HFC-32. The energy barrier of each initial decomposition reaction for HFC-32 on the clean Cu(111) surface is higher than that on the oxygen atom and water molecule preadsorbed Cu(111) surfaces, which indicated that the decomposition reactions can be promoted by the oxygen atom and water molecule. Moreover, adjacent HFC-32 molecules will also affect the decomposition of each other. Therefore, the air in the organic Rankine cycle system should be emptied as much as possible to avoid promoting the cracking of HFC-32. (C) 2021 Elsevier B.V. All rights reserved.