Low-Valence Zn delta+ (0<delta<2) Single-Atom Material as Highly Efficient Electrocatalyst for CO2 Reduction

A nitrogen-stabilized single-atom catalyst containing low-valence zinc atoms (Zn delta+-NC) is reported. It contains saturated four-coordinate (Zn-N-4) and unsaturated three-coordinate (Zn-N-3) 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. Zn delta+-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 Zn delta+-NC in a flow cell. Calculations suggest that the unsaturated Zn-N-3 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.