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

Abstract

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 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 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 (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 vacancy-defected GeC MLs with significant Bader charge transfer. The CO2@GeC_VGe ML system displays a maximum Eads of −4.46 eV, geometrical deformation, and a Bader charge transfer of −1.44 e−to the CO2 molecule. Thus, VGe is the most promising candidate among all considered GeC systems to enable the electrochemical CO2 reduction reaction.