Germanene-Anchored Single-Atom Catalysts for CO2 Reduction: Insights from DFT

Rising atmospheric CO2 levels driven by extensive fossil fuel use underscore the urgent need for efficient CO2 utilization strategies. Electrochemical CO2 reduction (CO2RR) offers a sustainable route to valuable C1 products but faces challenges such as high overpotentials, limited selectivity, and competition from the hydrogen evolution reaction (HER). Single-atom catalysts (SACs) on two-dimensional (2D) supports provide a promising solution due to their tunable electronic structure and maximal atom efficiency. Motivated by the potential of germanene nanosheets (GeNS), this study employs density functional theory to screen ten 3d transition-metal-anchored systems (TM@GeNS) for CO2RR performance. Sc, Ti, V, Mn, Fe, and Co emerge as stable and catalytically viable dopants based on adsorption energetics, reaction free energies, and CO2 activation. Mechanistic evaluation of CO and HCOOH pathways, together with HER competition, shows that all TM@GeNS catalysts thermodynamically favor CO2 reduction. Among them, Mn@GeNS provides the most balanced stabilization of key intermediates while avoiding excessive H adsorption, enabling efficient CO2 conversion with minimal HER interference. These results identify Mn@GeNS as the most promising and energetically accessible catalyst in the TM@GeNS series and highlight the potential of germanene-based SACs for next-generation CO2RR electrocatalysts.