Direct electrocatalytic CO2 reduction in a tubular protonic membrane reactor at high pressure
QUINA I. 1, ALMAR L. 1, CATALÁN D. 1, DAYAGHI A. 2, VIGEN C. 3, NORBY T. 2, SERRA J. 1, ESCOLÁSTICO S. 1
1 Instituto de Tecnología Química (Universitat Politècnica de València—Consejo Superior de Investigaciones Científicas), Valencia, Spain; 2 Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, Oslo, Norway; 3 CoorsTek Membrane Sciences AS, Oslo, Norway
Integration of membranes into reactors create the opportunity to increase the yield and boosting the performance for CO2 reactions shifting the thermodynamic equilibrium by water extraction as well as the potential to increase energy efficiency by coupling the exothermic and endothermic processes to produce carbon neutral synthetic liquid fuels.
In this work, developed in the frame of the eCOCO2 project, towards further process intensification via the direct electrochemical synthesis of long chain hydrocarbons, the CO2 electro-catalytic reduction into methane has been also studied in a tubular protonic membrane reactor. The protonic membrane was composed of (i) BaZr0.8Ce0.1Y0.1O3 as electrolyte and (ii) Ni+BaZr0.7Ce0.2Y0.1O3 as metallic electrodes that allows the proton injection in the reaction chamber and acts as methanation catalyst. Hydrogen pumping, CO2 conversion, CO and CH4 yield, impedance spectroscopy and voltage distributions were studied as a function of the applied current density and the operational conditions (at 450 ºC and pressures up to 30 bar). The maximum hydrogen pumping flow obtained was 22 NmL/min at 450 ºC and 20 bar that corresponds to a Faradaic efficiency of 100%. Total pressure plays an important role in both the electrochemical performance of the protonic cell and the catalytic performance. Distribution of relaxation times (DRT) analysis was employed to evaluate the different impedance contributions as a function of the frequencies and the operational conditions showing an improvement of the cell performance under pressurized operation due to (i) the higher electrolyte hydration boosting the protonic conductivity and (ii) the improvement of the surface kinetics and mass transfer of the electrodes. Regarding the catalytic performance, CO2 conversion and CH4 selectivity strongly increase due to the pressure, reaching values of 86% and 94% respectively for a stoichiometric H2/CO2 ratio of 4 at 450 ºC and 30 bar. Additionally, computational fluid-dynamics (CFD) simulations were employed to provide critical knowledge about the thermodynamics, transport phenomena and electrochemical performance of membrane reactor.
Acknowledgment: This study has received European Union’s Horizon 2020 Research and Innovation funding under grant agreement No 838077.