K+ selectivity modulation in non-aqueous CO2 electroreduction on lead catalysts: from oxalic to tartaric acid production

Abstract

Here, we show that the presence of potassium ions in the catholyte modulates the selectivity of a Pb plate electrode, leading to the formation of tartrate, a C₄ compound, from CO₂ reduction. A faradaic efficiency of 60% was achieved at −2.3 V (vs. Ag/Ag⁺) for tartrate using a proton exchange membrane and a high concentration of potassium-based supporting anolyte. The electrode microenvironment with a higher potassium concentration also inhibits cathode corrosion and deactivation. Remarkably, the electroreduction of CO₂ changes the selectivity with the cationic availability in the anolyte. Higher FE to formic acid is observed with an increase in the proton concentration, and by increasing anolyte K⁺ availability, C–C coupled products (oxalate, C₂, and tartrate, C₄) are formed in the majority. Our results prove that controlling potassium ions and the proton concentration in the catholyte regulates the selectivity of the Pb plate electrode and can lead to the formation of a C₂₊ product from CO₂ reduction.