Engineering d-band center of nickel in nickel@nitrogen-doped carbon nanotubes array for electrochemical reduction of CO2 to CO and Zn-CO2 batteries

Self-supported transition-metal single-atom catalysts (SACs) facilitate the industrialization of electrochemical CO₂ reduction, but suffer from high structural heterogeneity with limited catalytic selectivity. Here we present a facile and scalable approach for the synthesis of self-supported nickel@nitrogen-doped carbon nanotubes grown on carbon nanofiber membrane (Ni@NCNTs/CFM), where the Ni single atoms and nanoparticles (NPs) are anchored on the wall and inside of nitrogen-doped carbon nanotubes, respectively. The side effect of Ni NPs was further effectively inhibited by alloying Ni with Cu atoms to alter their d-band center, which is theoretically predicted and experimentally proved. The optimal catalyst Ni₉Cu₁@NCNTs/CFM exhibits an ultrahigh CO Faradic efficiency over 97% at ?0.7 V versus reversible hydrogen electrode. Additionally, this catalyst shows excellent mechanical strength which can be directly used as a self-supporting catalyst for Zn-CO₂ battery with a peak power density of ～0.65 mW/cm² at 2.25 mA/cm² and a long-term stability for 150 cycles. This work opens up a general avenue to facilely prepare self-supported SACs with unitary single-atom site for CO₂ utilization.