Zn-N_x Doping in Carbon Nanotubes Boosts Selective CO₂ Electroreduction to CO

Electroreduction of CO₂ to CO is attractive target to store energy from intermittent sources, as it requires the transfer of only two electrons and two protons. Metal-based catalysts (Au, Ag, Ni, Fe, etc.), especially metal- and N-co-doped carbon materials have been proven to show high selectivity for CO production. However, for Zn-based catalysts, the critical active site is still intensely debated. Herein, we synthesize a series of carbon nanotube-supported Zn-based catalysts with a tunable ratio of isolated ZnN_x sites and Zn-based nanoparticles. We identify ZnN_x moieties anchored on the surface of carbon nanotubes are catalytically highly active for the selective CO₂ electroreduction to CO, with the Faradaic efficiency (FE) as high as 97.3 %. In contrast, N-doped carbon nanotubes (NCNTs) and Zn-containing nanoparticles supported on NCNTs exhibit inferior selectivity with the CO FEs of 56.7 % and 72.9 %, respectively, suggesting that Zn doping in carbon and the existing forms are of significant importance for improving the ability of Zn-based catalysts for electrocatalytic reduction of CO₂.