Methane synthesis from CO and HO 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 (CH 4 ) from CO 2 and H 2 O by using electricity at 120 °C. CH 4 was synthesized with a rate of 12 nmol s −1 cm −2 at a current density of 10 mA cm −2 with a CO 2 flow of 0.055 ml STP min −1 in the cathode vessel and with an Ar + H 2 O flow of 10 ml STP min −1 + 10 μL liquid min −1 in the anode vessel (STP; standard temperature and pressure at 0 °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 CH 4 compared to electrochemical CO 2 reduction systems at the electrode/electrolyte interfaces. Electrochemical CO 2 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 (CsH 2 PO 4 /SiP 2 O 7 ) at 250 °C and polymer electrolytes at 120 °C was performed and the possibility for practical applications of both systems was discussed. A polymer-electrolyte electrochemical cell, equipped with a Ru/ZrO 2 catalyst at 120 °C, converts CO 2 and H 2 O into CH 4 and O 2 with a current efficiency of 85%.