Promoting Hydrogen Transfer in Electrochemical CO 2 Reduction via a Hydrogen on Demand Pathway

Abstract The proceeding of electrochemical CO 2 reduction reaction (CO 2 RR) requires the formation of active hydrogen species for CO 2 protonation, while traditional catalysts fail to balance the rate of hydrogen supply and CO 2 protonation. Herein, we propose a “hydrogen on demand” mechanism, in which the polarity of the adsorbed CO 2 is enhanced to allow the capture of hydrogen from water without forming free hydrogen species, realizing the matching rate of hydrogen supply and CO 2 protonation. As a proof of concept, we construct Zn−N sites modified by Se atoms, allowing the proceeding of CO 2 RR under the “hydrogen on demand” mechanism with superior efficiency. The catalyst achieves an industrial CO current of −539.7 mA cm −2 , faradaic efficiencies of CO >90 % over a broad window from −0.5 to −1.1 V vs. reversible hydrogen electrode and a high turnover frequency of 7.6×10 4 h −1 in flow cell. In situ characterization and theoretical calculations reveal that the introduced Se sites enhance the electron localization around the Zn sites, thus increasing the polarity of adsorbed CO 2 − with improved ability to acquire hydrogen species from water to facilitate the protonation process.