A nitrogen-stabilized single-atom catalyst containing low-valence zinc atoms (Znδ+ -NC) is reported. It contains saturated four-coordinate (Zn-N4 ) and unsaturated three-coordinate (Zn-N3 ) sites. The latter makes Zn a low-valence state, as deduced from X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory. Znδ+ -NC catalyzes electrochemical reduction of CO2 to CO with near-unity selectivity in water at an overpotential as low as 310 mV. A current density up to 1 A cm-2 can be achieved together with high CO selectivity of >95 % using Znδ+ -NC in a flow cell. Calculations suggest that the unsaturated Zn-N3 could dramatically reduce the energy barrier by stabilizing the COOH* intermediate owing to the electron-rich environment of Zn. This work sheds light on the relationship among coordination number, valence state, and catalytic performance and achieves high current densities relevant for industrial applications.
Keywords: CO2 reduction; coordination environment; electrocatalysis at scale; low valence; zinc single atoms.
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