Abstract
Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. Examples of interface design based on single atom and surface science are, however, extremely rare. Here, we report Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO2 reduction. The unique geometric and electronic structure of the Cu–Sn surface alloys (Cu97Sn3 and Cu99Sn1) enables distinct catalytic selectivity from pure Cu100 and Cu70Sn30 bulk alloy. The Cu97Sn3 catalyst achieves a CO Faradaic efficiency of 98% at a tiny overpotential of 30 mV in an alkaline flow cell, where a high CO current density of 100 mA cm−2 is obtained at an overpotential of 340 mV. Density functional theory simulation reveals that it is not only the elemental composition that dictates the electrocatalytic reactivity of Cu–Sn alloys; the local coordination environment of atomically dispersed, isolated Cu–Sn bonding plays the most critical role.
Highlights
Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis
The ability to fabricate these complex structures in a single reaction step primarily stem from the sequential reduction processes, owing to the more negative standard electrode potential of Sn2+ relative to Cu2+ (Sn2+ + 2e− ⇌ Sn, E0 = −0.13 V vs. SHE; Cu2+ + 2e− ⇌ Cu, E0 = 0.34 V vs. SHE)
The atomic dispersion of Sn in Cu97Sn3 can be further identified from the distributed bright spots in the HAADF-STEM image (Fig. 1e and Supplementary Fig. 3), which is in sharp contrast to the clean crystal of Cu100 (Fig. 1d)
Summary
Direct experimental observations of the interface structure can provide vital insights into heterogeneous catalysis. We report Cu–Sn single-atom surface alloys, where isolated Sn sites with high surface densities (up to 8%) are anchored on the Cu host, for efficient electrocatalytic CO2 reduction. Surface alloys that comprise catalytically active single atoms (e.g., Au, Pt, Pd, etc.) anchored on the host surface have shown exceptional properties for various catalytic applications[22,23,24,25] With this design, no bonds form between foreign active sites; the intermetallic interactions occurring at the interfaces between two metals are fundamentally different from bulk alloys[26]. Density functional theory (DFT) simulations reveal the crucial role of the isolated Cu–Sn alloy-bonding geometry, which shows optimal absorption property of intermediates (COOH* and CO*) compared with pure Cu (too strong) or Cu70Sn30 bulk alloy (too weak)
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