UC Berkeley

Methane’s abundance and low cost makes it an optimal raw material for chemical precursors and other energy dense fuels. Traditional methods of converting methane to methanol require large amounts of energy through thermal catalysis and high capital costs. However, electrochemical oxidation of methane is a cleaner and cheaper way to produce methanol, and a systematic study of an electrochemical cell could help assure selectivity over undesired products. Electrochemical oxidation of methane is an underdeveloped field, but electrochemical cells have been employed with high selectivity towards methanol.[1,2] Promising transition state metal-oxide catalysts have shown activity towards the selectivity of methanol over other by products, such as carbon dioxide, carbon monoxide, formic acid, formaldehyde.[2, 3] Further investigation of single site metal oxide catalysts is required to improve conversion and activity, but system optimization is also required. Reports of electrolyzer and fuel cell systems show varying assemblies, ranging from various solid and liquid electrolytes, temperatures, pressures, and current densities. [1-3] Few reports have been consistent on the operating current density and potential windows of such systems. Little work has been done on understanding how various components for these systems and understanding the phenomena of creating methanol in this partial oxidation pathway. In this study, we explore the activity, selectivity, efficiency of transition metal oxide catalyst in operation in an electrolyzer. The electrolyzer used was tested under a variety of relative humidity, operating temperatures, current densities, and membrane electrode assemblies. Through electrochemical and conductivity measurements, and gas phase analysis of the effluent, a better understanding of the partial electrochemical oxidation of methane to methanol is elucidated. The results of this study provide a systematic approach to this challenging problem and provide insights on new catalyst and electrochemistry pathways. References: Tomita, A., et. al., Direct Oxidation of Methane to Methanol at Low Temperature and Pressure in an Electrochemical Fuel Cell. Angewandte Chemie International Edition, 2008. 47: p. 1462–1464. Lee, B., et. al., Direct oxidation of methane to methanol over proton conductor/metal mixed catalysts, Journal of Catalysis, 271(2): p. 195-200. Rocha, R.S., et. al., Electrosynthesis of methanol from methane: The role of V2O5 in the reaction selectivity for methanol of a TiO2/RuO2/V2O5 gas diffusion electrode. Electrochimica Acta, 2013. 87: p. 606-610.