Synergistic effect between Ni single atoms and Ni nanoparticles for effectively boosting sustainable co-electrolysis of CO2 and hydrazine

The intrinsic performance of single atom catalysts (SACs) to electrochemical CO2 reduction reaction (ECRR) is limited due to the absence of synergistic active sites. Herein, Ni single atom (NiSAs) and Ni nanoparticles (NiNPs) are co-loaded on nitrogen-doped hollow carbon spheres (N-HCSs) by a one-step calcination method, which ex-hibits high CO selectivity in H-type cell with aqueous solution or an ionic liquid as electrolyte. Particularly, NiSAs-NPs-N-HCSs demonstrate a CO selectivity of 98.98%, yielding an industrial level CO current density of 152.7 mA cm-2 in flow cell. In situ Raman spectroscopy and in situ infrared characterization technology confirm that *COOH and *CO are important intermediates in the ECRR process. Theoretical computations suggest that coexisting NiNPs can reduce the energy barrier of *COOH, thereby improving the ECRR performance, indicating the synergistic effect between NiSAs and NiNPs in the ECRR process. Moreover, NiSAs-NPs-N-HCSs is applied to the membrane electrode assembly system coupling the hydrazine oxidation reaction (HzOR), which can significantly reduce the voltage about 836 mV at 100 mA cm-2.