Lattice Hydrogen Participation and Mass Transport Acceleration Improve CO ₂ Electroreduction to C ₂ Products

Abstract CO 2 electroreduction operated at high current densities typically face the critical issues of CO 2 depletion and competing reactions. Here we prepared CuH branched nanosheets stabilized with holmium single atoms (HoSA‐CuH). Finite‐element analyses show that the branched HoSA‐CuH structure could accelerate mass transport and alleviate CO 2 depletion under high current densities. In situ spectroscopies and theoretical calculations reveal that the introduced Ho single atoms increase the electron density at Cu surface, which is conducive to CO 2 enrichment and activation. Deuterium isotope labeling experiments confirm that the lattice hydrogen in CuH participate in the reaction, thereby lowering the energy barrier for the rate‐determining step in C–C coupling. Therefore, the selectivity for C 2+ over HoSA‐CuH is above 80% under 700–1200 mA cm −2 and C 2 products account for 95% of all the C 2+ products. Compared with the best‐performing catalysts reported thus far, HoSA‐CuH displays the broadest current density range for high FE C2 .