Enriching Metal–Oxygen Species and Phosphate Modulating of Active Sites for Robust Electrocatalytical CO₂ Reduction

Abstract Direct electrochemical reduction of CO₂ (CO₂RR) into value‐added chemicals is a promising solution to reduce carbon emissions. The activity of CO₂RR is influenced deeply by the reaction microenvironment and electronic properties of the catalysts. Herein, the surface PO₄³⁻ anions are tuned to modulate the local microenvironment and the electronic properties of the indium‐based catalyst with abundant metal–oxygen species enabling efficient electrochemical conversion of CO₂ to HCOO⁻. Indium nanoparticles coupled with PO₄³⁻ anions (PO₄³⁻‐In NPs) achieve a high selectivity of HCOO⁻ up to 91.4% at a low potential of −0.98 V versus reversible hydrogen electrode (versus RHE) and a high HCOO⁻ partial current density of 279.3 mA cm⁻² at −1.1 V versus RHE in the electrochemical flow cell. In situ and ex situ characterizations confirm the PO₄³⁻ anions keep stable on the surface of indium during CO₂RR, accelerating the generation of OCHO^* intermediate. From density functional theory calculations, PO₄³⁻ anions enrich the metal–oxygen species on the substrate to optimize the electronic structure of the catalysts and induce a local microenvironment with massive K⁺ ions on the interface, thus reducing the activation energy barrier of CO₂RR.