In Situ-Activated Indium Nanoelectrocatalysts for Highly Active and Selective CO₂ Electroreduction around the Thermodynamic Potential

Developing electrocatalysts for electrochemical CO₂ reduction reaction (CO₂RR) with pre-eminent activity and high selectivity at low overpotentials is very significant, but it still remains a formidable challenge. Herein, we report an in situ-activated indium nanoelectrocatalyst derived from InOOH nanosheets for active and selective CO₂RR at ultralow overpotentials. Such a catalyst delivers near-unity CO₂RR selectivity with formate as the main product, in a wide low-overpotential window of −0.25∼−0.49 V versus reversible hydrogen electrode (vs RHE). Significantly, the CO₂RR activity reaches 151 mA cm^–2 at −0.45 V vs RHE, comparable to the state-of-the-art Au-based catalysts. Impressively, full-cell CO₂ electrolysis implements a record-high electricity-to-fuel energy-conversion efficiency of 76.0% and solar-to-fuel energy-conversion efficiency of 20.7%. Furthermore, in situ synchrotron X-ray diffraction reveals the dynamic formation of nanosized metallic indium, correlating well with CO₂RR activity, also evidenced by cyclic voltammetry. Combined with theoretical calculations, it is confirmed that the in situ-generated metallic indium plays a dominant role in promoting formate formation by accelerating the second proton-coupled electron transfer process (*OCHO+ H⁺ + e^– → *HCOOH). Consistent with experimental results, operando Raman spectra further demonstrate that in situ-activated indium nanocatalysts can facilitate formate production even at the thermodynamic potential. This work uncovers nanosized metallic indium as the highly active site and sheds light on the design of superior indium-based catalysts for CO₂ electroreduction.