Reverse Reaction Pathways for Efficient CO ₂ –to–Formic Acid Conversion at Cu ₂ O–Bi ₂ O ₃ Interfaces in Ionic Liquids

Although the electrochemical CO 2 reduction (CO 2 RR) to formic acid (HCOOH) is universally governed by the *OCHO intermediate, we demonstrate that a built-in electric field at a conventionally fabricated Cu 2 O–Bi 2 O 3 interface fundamentally reverses this pathway via a field-controlled microenvironment reconstruction (FCMR) mechanism. The FCMR process selectively stabilizes the *OCOH intermediate, and the addition of an ionic liquid further amplifies this shift by fine-tuning the interfacial environment. The resulting catalyst achieves >95% Faradaic efficiency for HCOOH over 140 h in an H-cell and maintains >91% efficiency at 350 mA cm –2 for 24 h without carbonate precipitation in a flow cell. This work establishes a general design principle: steering reaction pathways in composite catalysts via interfacial electric field control, thereby overcoming the thermodynamic constraints of traditional intermediates.