Researchers develop efficient paired electrolysis system to produce formic acid from CO₂ and methanol feedstocks

In a study published in Angewandte Chemie International Edition, researchers developed an acid/alkali asymmetric electrolyzer for acidic CO₂ reduction reaction (CO₂RR) coupled with alkaline methanol electrooxidation (MOR) to concurrently produce valuable formic acid with high efficiency and stability.

The electrochemical reduction of CO₂using renewable energy to produce high value-added chemicals holds great promise.

In the conventional oxygen evolution reaction (OER) coupling system, the anode OER alone can consume about 90% of the input power for CO₂RR-OER coupling. On the other hand, alkaline and neutral electrolytes can inhibit the hydrogen evolution reaction (HER), thereby promoting CO₂RR.

However, due to the local high pH value during the cathodic reaction, more than 75% of CO₂ is lost by reacting with hydroxyl ions (OH^–) in the solution to form carbonates, and the service life of the catalyst is also reduced.

In this study, the researchers developed an efficient paired electrolysis system, i.e., coupling the cathodic acidic-CO₂RR with the anodic alkali-MOR. The cathode solution contained 3 M KCl + 0.1 M HCl and the anode solution contained 1.0 M KOH + 2.0 M methanol, which were separated by a cation exchange membrane.

The catalysts of Cu₂Se@CuO nanoflowers and Bi/BiOx nanosheets were synthesized respectively for cathode and anode.

The developed electrolyzer demonstrated stable operation at 1.9 V for more than 90 hours. The total Faraday efficiency of formic acid exceeds 190% in wide voltage range, and only 2.1 V is required to achieve a formic acid partial current density of ~130 mA cm^-2 while consuming three times less electricity compared to the acid/alkali coupled CO₂RR-OER system.

The superior performance of the acid/alkali hybrid electrolyzer can be attributed to the integration of excellent anode and cathode catalysts, the pairing electrolysis with MOR, and the effective harnessing of electrochemical neutralization energy.

This study illuminates innovative electron-efficiency and energy-saving techniques for CO₂ electrolysis, as well as the development of highly efficient electrocatalysts.

The research team included Prof. Wen Zhenhai and Assoc. Prof. Chen Qingsong from Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences.