Nonaqueous electrochemical reactive CO2 capture and conversion of 10 % CO2 feed to mixed carboxylic acids

Nonaqueous electrochemical systems offer many advantages, such as high selectivity, high conversion to C 2 compounds, and limiting the hydrogen evolution reaction (HER). However, they suffer from higher ohmic losses and lower current density under dilute CO 2 feed conditions. Herein, we develop a nonaqueous electrochemical CO 2 reduction (eCO2R) system that is flexible to operate in both pure and dilute CO 2 feeds, producing C 2 and C 4 products relevant to pharmaceuticals, hydrometallurgy, and cosmetology. Our system utilizes a CO 2 -soluble electrolyte that regulates the acidity of the microenvironment surrounding a selective mixed lead oxide catalyst, allowing for the reactive capture and conversion of CO 2 even from 10 % CO 2 feeds. While acidic microenvironments favor glycolate formation, reduced acidity facilitates dimerization of glyoxylate to tartrate. In situ electrochemical Raman spectroscopy confirms a CO 2 •− radical pathway stabilized by tetraethylammonium cations in the nonaqueous medium. With optimized microenvironment and potential, we achieve >100 mA/cm 2 current density with ~50 % selectivity toward oxalate and ~70 % overall selectivity to C 2 products under 100 % CO 2 , and ~80 % overall selectivity to C 2 /C 4 products under 10 % CO 2 feeds. Complementary DFT calculations reveal that selectivity over lead switches from C 2 to C 1 with increasing water content, with peak oxalate selectivity at ~1 mM proton concentration. Techno-economic analysis (TEA) indicates that electrochemical oxalate production can outcompete traditional routes. Our preliminary TEA further indicates that this process is ~50 % cheaper than commercial routes, while LCA reveals that coupling with solar PV can reduce net emissions to ~287 g CO 2 /kWh e per kg oxalic acid produced. Together, these results highlight the critical role of acidic microenvironments and integrated systems analysis in advancing nonaqueous eCO2R toward scalable, sustainable oxalate and multi-carbon products. • Demonstrates for the first time the electrochemical conversion of 10% CO₂ feed to mixed C₂–C₄ carboxylic acids in a nonaqueous system. • Utilizes a CO₂-soluble deep eutectic electrolyte (DEE) to tailor the acidity of the catalyst microenvironment. • Achieves record-high current density (>100 mA/cm 2 ) in nonaqueous CO₂ electroreduction, with ~70% selectivity to C₂ products at 100% CO₂ feed. • Controls product selectivity via microenvironment modulation on mixed Pb oxide nanoflakes, enabling glycolate, glyoxylate, and tartrate formation. • Integrates in situ Raman spectroscopy and pH measurements to reveal the phase behavior and mechanistic pathways of lead oxides under eCO₂R conditions.