Promoting Hydrogen Transfer in Electrochemical CO₂ Reduction via a Hydrogen on Demand Pathway

The proceeding of electrochemical CO₂ reduction reaction (CO₂RR) requires the formation of active hydrogen species for CO₂ protonation, while traditional catalysts fail to balance the rate of hydrogen supply and CO₂ protonation. Herein, we propose a "hydrogen on demand" mechanism, in which the polarity of the adsorbed CO₂ is enhanced to allow the capture of hydrogen from water without forming free hydrogen species, realizing the matching rate of hydrogen supply and CO₂ protonation. As a proof of concept, we construct Zn-N sites modified by Se atoms, allowing the proceeding of CO₂RR 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 7.6×10⁴ 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 CO₂ ^- with improved ability to acquire hydrogen species from water to facilitate the protonation process.