The electroreduction of carbon dioxide (CO₂) into valuable chemicals and fuels typically operates under alkaline or neutral conditions, but the carbonation side reaction causes carbon loss. Besides, the main product is formate, which requires additional treatment such as acidification to obtain formic acid.

Acidic CO₂ electroreduction can effectively mitigate carbonation issues and directly produce formic acid. However, harsh acidic environments often lead to problems such as rapid catalyst degradation and metal leaching, limiting both the activity and long-term durability of the catalyst.

In a study published in Angewandte Chemie International Edition, a research team led by Prof. GAO Dunfeng and Prof. ZHOU Xukai from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences proposed a metal-phase protection strategy, and achieved durable acidic CO₂ electroreduction to formic acid.

This metal-phase protection strategy enabled the in situ formation of a Bi-Cu bimetallic oxide catalyst (Bi_0.31Cu₁). The Bi_0.31Cu₁ catalyst delivered a Faradaic efficiency (FE) of above 90% for formic acid in a wide current density range from 200 to 650 mA cm⁻². In a 0.5 M KCl electrolyte at pH 2, it continuously produced formic acid with a FE of around 90% at 200 mA cm⁻² for 500 h.

Researchers found that the interphase interaction between Bi₂O₃ phase and CuBi₂O₄ phase within the Bi_0.31Cu₁ catalyst induced compressive strain and lattice contraction in Bi₂O₃ phase and strengthened Bi-O bond, which effectively suppressed Bi leaching during catalyst reconstruction and enhanced long-term durability.

"Our study showcases the promise of the metal-phase protection strategy for developing highly efficient catalysts with long-term durability for acidic CO₂ electrolysis," said Prof. GAO.