The electrochemical conversion of CO₂ to CO has previously achieved nearly 100% CO selectivity by certain metal-based catalysts and has secured performance, one step closer to industrialization. In addition, the introduction of GDE-based MEA and flow cells overcomes the low CO₂ solubility and achieves currents of several hundred mA cm^-2. However, performance and stability that can be applied to industrialization beyond the lab scale are not yet guaranteed, so additional development is required.

Noble metal-based catalysts such as Ag, Au, and Zn have been intensively studied as electrocatalysts for CO generation from electrochemical CO₂ reduction reactions (eCO₂RR). Alloys and nanostructured catalysts are designed to control the unique properties of catalysts. Halides can also be another candidate for modifying the catalyst surface morphology. In addition to controlling the intrinsic properties of the catalyst, studies have been reported to improve the catalyst performance by controlling the relationship between the electrode and the electrolyte, such as hydrophobicity and porosity.

Here, AuAg alloy nanoparticles were simply prepared by galvanic replacement. The AuAg alloy catalyst prepared by incorporating Au species into Ag metal through the galvanic exchange has a high surface area with a hollow structure, and the surface-active sites controlled by Au significantly increased the catalytic activity with low overpotential and high current density. By controlling the diffusion rate of Ag⁺ ions through the synthesis reaction temperature, an AuAg alloy catalyst was synthesized in the form of AgCl on the catalyst surface and implemented between AuAg metals. In MEA cells, we demonstrate that the Au-on-Ag-modified intermetallic catalyst achieves 90% CO selectivity and 437.2 mA cm^-2. Through the reduction reaction, the AgCl-covered catalyst causes structural changes in nanoparticles, which greatly contributes to eCO₂RR selectivity and activity. Furthermore, by adding the carbon support, the mass diffusion limitation was greatly relaxed, resulting in a J_CO of > 700 mA cm^-2 at neutral pH electrolytes.