Methane synthesis from CO₂ and H₂O using electrochemical cells with polymer electrolyte membranes and Ru catalysts at around 120 C: a comparative study to a phosphate-based electrolyte cell

Electrochemical cells with fluorine-based polymer electrolyte membranes (PEMs) and Ru catalysts have been investigated for the production of methane (CH4) from CO2 and H2O by using electricity at 120 degrees C. CH4 was synthesized with a rate of 12 nmol s(-1) cm(-2) at a current density of 10 mA cm(-2) with a CO2 flow of 0.055 ml(STP) min(-1) in the cathode vessel and with an Ar + H2O flow of 10 ml(STP) min(-1) + 10 mu L-liquid min(-1) in the anode vessel (STP; standard temperature and pressure at 0 degrees C and 101.3 kPa, respectively). This rate was corresponding to the current efficiency of ca. 85%, and unreacted H-2 and subproducts of CO were obtained with current efficiencies of ca. 14 and 1%, respectively. The properties of temperature and current density dependence were discussed in this article. The present system exhibits significantly higher selectivity in synthesizing CH4 compared to electrochemical CO2 reduction systems at the electrode/electrolyte interfaces. Electrochemical CO2 reduction did not take place in the present system, and the importance of the combination of water electrolysis and catalytic methanation at solid/gas interfaces was proposed. A comparative study between phosphate (CsH2PO4/SiP2O7) at 250 degrees C and polymer electrolytes at 120 degrees C was performed and the possibility for practical applications of both systems was discussed.