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 CO 2 reduction reaction (ECRR) is limited due to the absence of synergistic active sites. Herein, Ni single atom (Ni SAs ) and Ni nanoparticles (Ni NPs ) are co-loaded on nitrogen-doped hollow carbon spheres (N-HCSs) by a one-step calcination method, which exhibits high CO selectivity in H-type cell with aqueous solution or an ionic liquid as electrolyte. Particularly, Ni SAs-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 Ni NPs can reduce the energy barrier of *COOH, thereby improving the ECRR performance, indicating the synergistic effect between Ni SAs and Ni NPs in the ECRR process. Moreover, Ni SAs-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 .