Single-Product Faradaic Efficiency for Electrocatalytic of CO 2 to CO at Current Density Larger than 1.2 A cm -2 in Neutral Aqueous Solution by a Single-Atom Nanozyme.

Electroreduction of CO 2 to CO is a promising approach for the cycling use of CO 2 , while it still suffers from impractical current density and durability. Here we report a single-atom nanozyme (Ni-N 5 -C) that achieves industrial-scale performance for CO 2 -to-CO conversion with a Faradaic efficiency (FE) exceeded 97 % over -0.8--2.4 V vs. RHE. The current density at -2.4 V vs. RHE reached a maximum of 1.23 A cm -2 (turnover frequency of 69.7 s -1 ) with an FE of 99.6 %. No obvious degradation was observed over 100 hours of continuous operation. Compared with the planar Ni-N 4 site, the square-pyramidal Ni-N 5 site has an increase and a decrease in the d z 2 ${{{\rm d}}_{{z}^{2}}}$ and d xz/yz orbital energy levels, respectively, as revealed by density functional theory calculations. Thus, the Ni-N 5 catalytic site is more superior to activate CO 2 molecule and reduce the energy barriers as well as promote the CO desorption, thus boosting the kinetic activation process and catalytic activity.