Metal-Phase Protection Suppresses Bi Leaching for Durable Acidic CO₂ Electroreduction to Formic Acid

The electrocatalytic CO₂ reduction reaction (CO₂RR) in acidic electrolyte mitigates salt precipitation and carbon loss compared to that in alkaline and neutral electrolytes. However, the harsh acidic environments cause metal leaching and catalyst degradation, thereby impairing activity and long-term durability. Here we propose a metal-phase protection strategy that enables in situ formation of a BiCu catalyst (Bi_0.31Cu₁) with impressive durability for acidic CO₂RR to formic acid (HCOOH). The compressive strain of the Bi₂O₃ phase in Bi_0.31Cu₁, induced by its interaction with the CuBi₂O₄ phase, enhances Bi─O bond strength and mitigates Bi leaching during in situ electrochemical reconstruction, thus delivering highly desired activity and durability. The Bi_0.31Cu₁ catalyst achieves a HCOOH Faradaic efficiency (FE) of above 90% in a wide current density range from 200 to 650 mA cm^-2. In a 0.5 M KCl electrolyte with pH 2, the Bi_0.31Cu₁ catalyst can continuously produce HCOOH with a FE of around 90% at 200 mA cm^-2 for 500 h. This work showcases the great promise of the metal-phase protection strategy for minimizing metal leaching and improving the long-term durability of acidic CO₂ electrolysis.