Boosting oxygen-resistant CO2 electroreduction reaction in acidic media over conjugated frameworks

Abstract

The use of flue gas (containing 3–4% O₂) as the direct feed gas for the CO₂ electroreduction reaction (CO₂RR) is a promising protocol to reduce CO₂ purification costs. However, the competitive oxygen reduction reaction (ORR) and cathodic carbonate salt precipitation severely hinder its practical application. Here, we realize efficient CO₂RR towards CO under CO₂ containing 5% O₂ gas feed in conditions of acidic media. A conjugated cobalt polyphthalocyanine framework (CoPPc) shows outstanding performance in aqueous acidic electrolyte (H₂SO₄ + 0.4 M Cs₂SO₄, pH = 3.0) with a faradaic efficiency toward CO (FE_CO) exceeding 95% over a wide potential range from −1.0 to −1.9 V vs. a reversible hydrogen electrode (RHE), and a maximum CO partial current density (j_CO) up to −294 mA cm⁻² when using pure CO₂ gas. After coating with polyaniline (PANI), CoPPc@PANI shows a high FE_CO of up to 87.4% and a maximum industrial level current density of −270 mA cm⁻² at −2.1 V vs. RHE under 95% CO₂ + 5% O₂ feed gas in acidic media. The results of the oxygen reduction reaction, CO₂ adsorption capacity and the isosteric heat of adsorption (Q_st) demonstrate that CoPPc@PANI can adsorb and enrich CO₂ in comparison with oxygen, resulting in superior CO₂ reduction performance in the presence of O₂. This work will shed new light on the development of efficient electrocatalysts for CO₂RR using flue gas, which can reduce separation costs and avoid the formation of cathodic carbonate salt precipitates.