p-Block Indium Single-Atom Catalyst with Low-Coordinated In–N Motif for Enhanced Electrochemical CO2 Reduction

Electrochemical CO2 reduction represents a promising path toward the production of value-added chemicals. Atomically dispersed metal sites on nitrogen-doped carbon have demonstrated outstanding catalytic performance in this reaction. However, challenges remain in developing such catalysts beyond transition metals. Herein, we present two types of p-block indium single-atom catalysts: one with four nitrogen coordinated (In–N4) and another with three nitrogen coordinated with one vacancy nearby (In–N3–V). In electrochemical CO2 reduction, the In–N3–V site can achieve maximum CO Faradic efficiency (FECO) of 95% at −0.57 V vs reversible hydrogen electrode (RHE) in an aqueous medium. This outperforms the intact In–N4 catalyst with the maximum FECO of 80% at −0.47 V vs RHE. Density functional theory calculations on the mechanism suggest that structural change from In–N4 to In–N3–V brings the In orbital (s and pz) energies closer to the Fermi energy. These hybridized orbitals are responsible for lowering the energy barrier for COOH* intermediate formation, thus enhancing the catalytic performance. This work sheds light on the relationship between catalytic performance and structure of In single-atom sites, highlighting the importance of tailoring the electron state of s and pz orbitals in developing efficient p-block single-atom catalysts for electrochemical CO2 reduction.