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 ameliorate climate change and decreasing deposits 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 VC, Ge-vacancy VGe, and combined Ge- and C-vacancies VGe/C). We present a detailed description of the nature of the interaction and the mechanism of CO₂ conversion via in-depth projected densities of state, electronic band structures, charge density analysis, and Bader charge transfer analysis. The results show that CO₂ molecules weakly bind with the 2D GeC ML, with an adsorption energy (Eads) of only −0.13 eV, rendering 2D GeC ML unsuitable for the reduction of CO₂. In contrast, CO₂ gas molecules show strong chemisorption on V-GeC MLs and the required negative Bader charge transfer. The CO@GeC_VGe ML system displays a maximum Eads of −4.46 eV, geometrical deformation, and a Bader charge transfer of −1.440 e− at the CO₂ molecule. Thus, VGe is the most promising candidate among all considered GeC systems to enable the electrochemical CO₂ reduction reaction.