2D Covalent Metals: A New Materials Domain of Electrochemical CO₂ Conversion with Broken Scaling Relationship

Toward a sustainable carbon cycle, electrochemical conversion of CO₂ into valuable fuels has drawn much attention. However, sluggish kinetics and a substantial overpotential, originating from the strong correlation between the adsorption energies of intermediates and products, are key obstacles of electrochemical CO₂ conversion. Here we show that 2D covalent metals with a zero band gap can overcome the intrinsic limitation of conventional metals and metal alloys and thereby substantially decrease the overpotential for CO₂ reduction because of their covalent characteristics. From first-principles-based high-throughput screening results on 61 2D covalent metals, we find that the strong correlation between the adsorption energies of COOH and CO can be entirely broken. This leads to the computational design of CO₂-to-CO and CO₂-to-CH₄ conversion catalysts in addition to hydrogen-evolution-reaction catalysts. Toward efficient electrochemical catalysts for CO₂ reduction, this work suggests a new materials domain having two contradictory properties in a single material: covalent nature and electrical conductance.