Transition Metal Carbides for Electrochemical CO2 Reduction

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Carbon dioxide (CO2) is the most notorious greenhouse gas that contributes to global warming. Converting produced CO2 into synthetic fuels represents thus a much sought route to reduce emissions and achieve a sustainable energy economy. Electrochemical CO2 conversion appears particularly advantageous, as it would draw the energy required to reduce the molecule directly from renewable electricity from wind, solar, or hydro power plants. It may furthermore be operated at ambient conditions and is therefore prone to small-scale decentralized utilization. Unfortunately, metal electrodes that are traditionally employed in electrochemistry show only an insufficient performance. The reaction runs too slow and too much energy is needed.These limitations are ascribed to a fundamental relation in the strength with which certain intermediate molecules that are formed in the course of the chemical reaction are bound to the metal electrodes. Modifying the metal electrode to optimize the binding of one such intermediate for the reaction automatically worsens the binding of another intermediate. There are first indications that this dilemma is broken when instead employing more complex electrode materials. Of interest are thereby either compound materials which mix metals with other elements or composite systems that comprise both a metal and another material. The objective of the present project is to assess the suitability of metal carbides in this respect, i.e. compounds formed of metals and the abundant element carbon. Specifically studied are molybdenum carbide and composite systems formed of molybdenum carbide and Au or Cu. Combining both experimental and computational approaches the ambitious goal is to analyze the electrochemical CO2 reduction at the atomic scale. Corresponding detailed insight is believed to provide a general understanding of how much and if so why the fundamental relation in the binding strength of the intermediate molecules is broken at these carbide based materials. This in turn will provide ideas of how to optimize carbides themselves for use as energy efficient electrodes in the electrochemical reduction of CO2, or design alternative materials for this purpose.