Atmospheric Pressure Plasma Jet Synthesis and Characterization of Copper-Silver Bimetallic Materials as Electrocatalysts for CO2 Reduction
Authors: Agrotis Stefanos , Caruana Daren J. , Handoko Albertus Denny , Sener Mustafa Emre , Hagger Oliver S. J. 
Published: August 2024

Copper-silver (Cu-Ag) bimetallics and alloys are attractive due to their enhanced performance compared to their parent metals in various fields including electronics, batteries, biomedicine, solar technology, energy storage, and catalysis.[1] Existing methods for synthesizing Cu-Ag bimetallics suffer from major drawbacks such as intense temperature and pressure conditions, pre and post-treatment processes, and multiple time-consuming steps.[2, 3]

In this work, Cu-Ag bimetallic films were synthesized under various ratios for the first time using a newly developed Atmospheric Pressure Plasma Jet (APPJ) system. Synthesis was done in a single step, in under 15 minutes. The samples exhibited strong adhesion onto various substrates such as glass and glassy carbon. This direct-deposition technique requires low power input (<50 W) without the need for any pre- or post-treatment processes and with little to no waste. This contrasts with wet chemistry, where deposition normally takes 12-24 hours followed by thermal processes that produce several waste products.[4] Considering the high melting points (MP) of pure Cu and Ag (MP of Cu is ca. 1,085 °C and MP of Ag is ca. 962 °C), and the fact that they are immiscible, the formation of Cu-Ag alloys usually requires a high amount of energy under intense conditions.[5]

These Cu-Ag films were characterized via cyclic voltammetry (CV), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Here, we demonstrate that by only mixing low-concentration metal salt solutions and using a neutral gas (helium), we can readily synthesize metal alloys while controlling their thickness, shape, composition, and metal ratios. From an electrochemical point of view, APPJ drives the reduction of metal cations from the presence of free electrons. This suggests the presence of a medium that is considered either as an electrode, due to the presence of electrons, or as an electrolyte, due to their electrical conduction.[6]

These plasma-synthesized materials were tested as electrocatalysts for reducing atmospheric carbon dioxide (CO2) under various potentials. The performance of these catalysts was assessed via electrochemical surface area (ECSA), electrochemical impedance spectroscopy (EIS), and pulse voltammetry techniques. Copper is the only heterogeneous catalyst that converts CO2 into valuable chemicals, such as hydrocarbons, aldehydes, and alcohols.[7] Interestingly, we illustrate that the addition of silver improves the catalytic activity of copper toward CO2 reduction under low potentials. This is a desirable property given the anticipated transition to green energy.

References

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