Linking the Electrochemical Characteristics of Cr2O3-Ga2O3 on Glassy Carbon with the Electrocatalytic Reduction of CO2 to C2+ Products

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For years copper-based electrodes were believed to be the only ones capable of reducing CO2 (CO2RR) into C2+ products1. Recently however, Cu-free electrodes have proved their ability to carry out C-C coupling, in some cases out performing copper electrodes 2–4. We, in the Bocarsly Lab, developed a Ni-enhanced Cr2O3-Ga2O3 on glassy carbon electrocatalyst able to reduce CO2 to 1-butanol with a faradaic efficiency of 42% 5, more than 10 times larger than what has previously been reported 6. Our system operates with a 900 mV overpotential in a CO2-saturated 0.1 M KCl acidic solution (pH 4.10), a difference among most systems since acidic media favors hydrogen evolution 7. Mechanistic investigations, indicate that formate is a key building block instead of CO. This is a non-common route for multi-carbon product formation in CO2RR 6,8.These results raise important questions about the characteristics of the electrocatalysts that promote both carbon-carbon bond formation and multi-electron/proton charge transfer.The Ni-enhanced Cr2O3-Ga2O3 system is particularly intriguing because it is based on an oxide mixture which is non-conducting, although it is the major constituent of the electrode interface. Electron microscopy shows that the interfacial oxide layer forms in a series of islands, in what has been described as a ‘dry riverbed’. At the nanostructure, the oxide islands contain pores of around 5-200 nm and dendrites. We have hypothesized that the role of the oxide coating resides in the alteration of the electrical double layer of the electrode rather than the transport of the electrons. This would result in the modification of the local environment that could enhance the electrocatalysis9.To investigate this hypothesis, we have employed a series of electrochemical techniques, including cyclic voltammetry, chronocoulometry, rotating disc electrode and electrochemical impedance spectroscopy; in combination with ex-situ and operando spectroscopical techniques. From the electrochemical behavior of the oxide coated glassy carbon electrode, we look to establish the relationship between its electrochemical characteristics, the electrical double layer and its role in CO2RR. Results have shown a modulation in the electrochemical response of the coated surface according to the nature of electrochemical redox probes.