Lattice Hydrogen Participation and Mass Transport Acceleration Improve CO₂ Electroreduction to C₂ Products

CO₂ electroreduction operated at high current densities typically face the critical issues of CO₂ 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 CO₂ 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 CO₂ 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 C₂₊ over HoSA-CuH is above 80% under 700-1200 mA cm^-2 and C₂ products account for 95% of all the C₂₊ products. Compared with the best-performing catalysts reported thus far, HoSA-CuH displays the broadest current density range for high FE_C2.