First-principles study of CO₂ activation on pristine and defected XO₂ (X= Pd, Pt) monolayers

Carbon dioxide (CO₂) capture is crucial to address both energy and environmental challenges. In this study, density functional theory (DFT) calculations are performed to investigate the adsorption behaviour of the CO₂ molecule on pristine (P-XO₂) and vacancy-defective (V-XO₂) XO₂ (X = Pd, Pt) monolayers (MLs). XO₂ MLs exhibit a semiconducting natureand to study vacancies, we created X monovacancy (V_X-XO₂), O monovacancy (V_O-XO₂), and X-O divacancy (V_X/O-XO₂). Our findings reveal that CO₂ adsorbs physically on PdO₂ and PtO₂ MLs with adsorption energies (E_ad) of -18.67 and -19.83 kJ/mol, respectively, and minimal Bader charge transfer (-0.004 e^- in both cases). Creation of Pd and O vacancies in PdO₂ ML increases the magnitude of E_ad for CO_2, while the nature of adsorption remains the same. On the other hand, the CO₂ molecule adsorbs chemically on V_Pd/O-PdO₂ ML with an E_ad of -55.47 kJ/mol and Bader charge transfer of 0.668e^-. Also, the CO₂ molecule bends after adsorption, which confirms its activation for further conversion. Similarly, CO₂ adsorption on V_O-PtO₂ and V_Pt-PtO₂ MLs falls in the category of physisorption due to E_ad of -23.18 and -21.56 kJ/mol, respectively. Presence of Pt and O divacancy increases E_ad to -29.89 kJ/mol. Thus, among all XO₂ MLs, V_Pd/O-PdO₂ ML appeared as a promising catalyst for activation and further electrochemical conversion of CO₂.