Direct CO2 conversion to syngas in a BaCe0.2Zr0.7Y0.1O3- δ-based proton-conducting electrolysis cell

Abstract

Electrolysis of steam and CO2 is considered to be a promising instrument for energy storage via sustainable H2 and hydrocarbon production. A model electrolysis cell was assembled using a thick BaCe0.2Zr0.7Y0.1O3-δ (BCZY27) electrolyte and two distinct electrodes, i.e., a (H2-cathode) porous Pt layer; and (steam-anode) a composite made of 60 vol. % La0.8Sr0.2MnO3-δ (LSM) and 40 vol. % BCZY27. The as-sintered steam electrode was catalytically-activated with Pr6O11-CeO2 nanoparticles. The cell was characterized by means of voltamperometry and impedance spectroscopy. Different operation parameters were analyzed: temperature; water concentration in the anode chamber; and H2 and CO2 concentration in the cathode chamber. Increasing H2O concentration (in the anode) and presence of CO2 (in the cathode) positively affected the electrode performance giving rise to lower cell overpotential and, consequently, substantial improvement in Faradaic efficiency. The high electrolyte thickness and the non-optimized Pt cathode limited the range of current density and the achieved peak power densities. The Faradaic efficiency for water electrolysis reached a value of 39% at 10.4 mA/cm2, as determined by the analysis of the H2 production. During co-electrolysis, the CO2 reaction was fostered by co-feeding a minimum H2 amount. CO formation took place through the reverse water gas shift (RWGS) reaction. When the current density was applied, CO2 conversion increased due mainly to the non-Faradaic electrochemical modification of catalytic activity (NEMCA effect) that allowed for the improvement of CO2 hydrogenation kinetics.