Organic Molecule Functionalization Enables Selective Electrochemical Reduction of Dilute CO Feedstock.

The electrochemical conversion of low-concentration CO feedstock to value-added chemicals and fuels is a promising pathway for achieving direct valorization of waste gas streams. However, this is challenging due to significant competition from the hydrogen evolution reaction (HER) and lowered CO reduction (COR) kinetics as compared to systems that employ pure CO. Here we show that terephthalic acid (TPA) functionalization can boost selectivity towards COR and suppress HER over a range of catalysts including Bi, Cu and Zn. For instance, TPA functionalized Bi attained a formate Faradaic efficiency (FE) of 96.3 % at 300 mA cm with pure CO feedstock. Density functional theory simulations indicate that this is because TPA functionalization modulates the binding energies of the key reaction intermediates *OCHO and *H. With low-concentration feedstock (15 % CO) at 100 mA cm, we achieved a high FE of 85.8 %, which was double that of an unmodified Bi catalyst. Using an electrolyzer with a porous solid electrolyte layer, we successfully showcase 30 h of continuous high-purity formic acid production with a 5 % CO feed. Taken together, our findings demonstrate that molecular tuning of a catalyst can be an effective strategy for enabling selective COR using low-concentration feedstock.