The electrochemical transformation of CO2 to formate, is an attractive target in terms of a potentially energy efficient synthesis of a bulk chemical that could consume environmental CO2. However, this process is hindered by an excessive activation barrier. We have previously reported that C1 products can be efficiently formed at low overpotential from CO2 using an aromatic amine as a molecular electrocatalyst at a variety of electrode surfaces. We have also suggested that certain aromatic amines are catalysts for the formation of carbon-carbon bonds, leading to products such as isopropanol and butanol. Thus, electrocatalytic reduction of CO2 can provide commercially useful products while removing CO2 from the environment as long as the process is driven by a non-fossil energy resource. Our investigation of catalyzed systems has led to the finding that the nature of the electrode interface is a critical parameter. To further understand the role of this component, we have undertaken a study of post-transition metal electrode materials. Materials such as indium and tin have been found to reduce aqueous CO2 to formate with modest overpotential and good faradaic efficiency in the absence of a dissolved electrocatalyst. Detailed FTIR spectroelectrochemical investigations point to a meta-stable surface oxide as a key catalytic component. The outer layer of this oxide is terminated with hydroxyls. Insertion of CO2 into the surface hydroxide to form a surface bicarbonate/carbonate forms the catalytic component on these electrode interfaces. Improved electrocatalytic performance and time stability can be obtained when a thick oxide layer is placed on the electrode surface prior to CO2 electrolysis. The indium-based system is sufficiently stable to be considered for development as a commercial system. To this end, eered CO2 to formate flow electrochemical reactor has been engineered. A short stack of 3-cells has been powered solely by a silicon photovoltaic array to produce formate from CO2 and natural sunlight (AM1.5) with a maximum observed thermionic efficiency of 2.5%. This system demonstrates the viability of a solar driven process for the efficient conversion of CO2 to C1 products.

Electrocatalytic reduction of carbon dioxide to organic oxygenates: From chemical concept to scaled-up electrochemistry

251st National Meeting (2016)

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