Alternating Current Electrolysis for Individual Synthesis of Methanol and Ethane from Methane in a Thermo-electrochemical Cell

The individual synthesis of methanol and ethane from methane was investigated using a thermo-electrochemical cell in gas flow mode over the temperature range of 150–200 °C. Methane was directly oxidized at an anode consisting of sub-10 nm Pt and Fe particles. In the electrolysis of humidified methane, methanol was produced through the formation of active oxygen intermediates from water vapor. In the electrolysis of unhumidified methane, ethane was produced via the dissociation of C–H bonds, followed by dimerization of the resultant •CH3 radicals. However, the formation rates for the target products decreased with time during electrolysis because of overoxidation of the anode by the direct-current (DC) voltage. The alternating current (AC) electrolysis of methane avoided this problem. Under optimized AC polarization conditions at a square waveform voltage of ±2.5 V with a pulse time of 5 s, this cell generated methanol and ethane at rates of 5.1 × 10–5 mol m–2 s–1 (92 mmol gcat–1 h–1) and 3.8 × 10–5 mol m–2 s–1 (69 mmol gcat–1 h–1), respectively, without a substantial loss of activity during continuous electrolysis.