DFT study of CO₂ activation on pristine and vacancy-containing 2D-GeC monolayers

Designing a highly reactive adsorbent material for the catalytic conversion of carbon dioxide (CO₂) into valuable products to help ameliorate climate change and address the decreasing availability of fossil fuels is a widely explored application of two-dimensional (2D) nanomaterials. Herein, we present a 2D graphene-like monolayer (ML) of germanium (Ge) and carbon (C) atoms (2D GeC ML) for highly efficient CO₂ adsorption and activation. We have employed first-principles calculations based on the density functional theory (DFT) to investigate the adsorption behavior of CO₂ molecules at pristine GeC MLs and MLs containing defects/vacancies (C-vacancy V_C, Ge-vacancy V_Ge, and combined Ge- and C-vacancies V_Ge/C). We present a detailed description of the nature of the interaction and the mechanism of CO₂ conversion via in-depth projected densities of states, electronic band structures, charge density analysis, and Bader charge transfer analysis. The results show that CO₂ molecule weakly binds with the 2D GeC ML, with an adsorption energy (E_ads) of only −0.13 eV, rendering 2D GeC ML unsuitable for the reduction of CO₂. In contrast, CO₂ gas molecules show strong chemisorption on vacancy-defected GeC MLs with significant Bader charge transfer. The CO₂@GeC_V_Ge ML system displays a maximum E_ads of −4.46 eV, geometrical deformation, and a Bader charge transfer of −1.44 e⁻to the CO₂ molecule. Thus, V_Ge is the most promising candidate among all considered GeC systems to enable the electrochemical CO₂ reduction reaction.