Copper Silver Thin Films with Metastable Miscibility for Oxygen Reduction Electrocatalysis in Alkaline Electrolytes

• Published in: ACS applied energy materials Vol. 1; no. 5; pp. 1990 - 1999
• Main Authors: Higgins, Drew, Wette, Melissa, Gibbons, Brenna M, Siahrostami, Samira, Hahn, Christopher, Escudero-Escribano, Marı́a, García-Melchor, Max, Ulissi, Zachary, Davis, Ryan C, Mehta, Apurva, Clemens, Bruce M, Nørskov, Jens K, Jaramillo, Thomas F
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 29-05-2018; American Chemical Society (ACS)
• Subjects: chloroalkali process; electrocatalysis; electrochemistry; ENERGY STORAGE; fuel cells; oxygen reduction; physical vapor deposition; sustainable energy; thin films; chloroalkali process; electrochemistry; physical vapor deposition; fuel cells; sustainable energy; electrocatalysis; oxygen reduction; thin films
• ISSN: 2574-0962; 2574-0962
• DOI: 10.1021/acsaem.8b00090

Increasing the activity of Ag-based catalysts for the oxygen reduction reaction (ORR) is important for improving the performance and economic outlook of alkaline-based fuel cell and metal–air battery technologies. In this work, we prepare CuAg thin films with controllable compositions using electron beam physical vapor deposition. X-ray diffraction analysis indicates that this fabrication route yields metastable miscibility between these two thermodynamically immiscible metals, with the thin films consisting of a Ag-rich and a Cu-rich phase. Electrochemical testing in 0.1 M potassium hydroxide showed significant ORR activity improvements for the CuAg films. On a geometric basis, the most active thin film (Cu70Ag30) demonstrated a 4-fold activity improvement vs pure Ag at 0.8 V vs the reversible hydrogen electrode. Furthermore, enhanced ORR kinetics for Cu-rich (>50 at. % Cu) thin films was demonstrated by a decrease in Tafel slope from 90 mV/dec, a commonly observed value for Ag catalysts, to 45 mV/dec. Surface enrichment of the Ag-rich phase after ORR testing was indicated by X-ray photoelectron spectroscopy and grazing incidence synchrotron X-ray diffraction measurements. By correlating density functional theory with experimental measurements, we postulate that the activity enhancement of the Cu-rich CuAg thin films arises due to the non-equilibrium miscibility of Cu atoms in the Ag-rich phase, which favorably tunes the surface electronic structure and binding energies of reaction species.