(622e) Operando IR Spectroscopy of Electrocatalyst Surfaces for Temperature-Dependent Methane Adsorption and Selective Oxidation

Natural gas is one of the most abundant fuel sources in the world today. Methane, the primary component of natural gas, is difficult to transport due to its being a gas under standard conditions. This drawback has spurred interests and exploration into catalytic conversion of methane into liquid products, particularly, to enable easier transportation and utilization. We introduce a new concept of thermo-electrochemistry, in which both electrochemical potentials and temperatures are used to control methane adsorption and reaction on the catalyst surface, whereas in gas-phase catalysis, both these phenomena are governed solely by temperatures. Therefore, thermo-electrochemistry affords researchers an additional “knob” that assist methane adsorption onto catalytic sites at reduced temperatures. Polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS) is an ideal operando spectroscopic technique to monitor reaction intermediates and products on the electrode surface, thereby allowing for the mapping of reaction pathways and their associated rate constants. Adsorption and reactivity trends of metal surfaces such as gold, silver, iridium, copper, nickel, and platinum will be presented: surface-bound methoxy groups are indicative of methane oxidation occurring while methyl groups indicate chemisorption of methane to the surface. Finally, strategies for achieving electrochemical methane-oxidation selectivity will be discussed, analogous to published work for thermo-chemical systems.