Efficient and Selective Electrochemical CO2 to Formic Acid Conversion: A First-Principles Study of Single-Atom and Dual-Atom Catalysts on Tin Disulfide Monolayers

Electrochemical CO2 reduction reaction (CO2RR), is a sustainable approach to recycle CO2 and address climate issues, but needs selective catalysts that can operate at low electrode potentials. Single-atom catalysts (SACs) and dual-atom catalysts (DACs) have become increasingly popular, due to their versatility, unique properties and outstanding performances in electrocatalytic reactions. In this paper, we used Density Functional Theory in combination with the computational hydrogen electrode methodology, to study the stability and activity of SACs and DACs by adsorbing metal atoms on SnS2 monolayers. With a focus on optimising the selective conversion of CO2 to formic acid, our analysis of the thermodynamics of CO2RR reveals that the Sn-SAC and Sn-DAC catalysts can efficiently and selectively catalyse formic acid production, being characterised by the low theoretical limiting potentials of approximately -0.25 V and an upper limit for the initial thermodynamic barrier for CO2 adsorption in gas phase of 0.5 eV. Investigation of the catalysts' stability suggests that structures with low metal coverage, with isolated metal centres, may be synthesised. Bader analysis of charge redistribution during CO2RR demonstrates that the SnS2 substrate primarily provides the electronic charges for the reduction of CO2, highlighting the substrate's essential role in the catalysis, which is also confirmed by further electronic structure calculations.