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

Abstract Electrolysis of steam and CO 2 is considered to be a promising instrument for energy storage via sustainable H 2 and hydrocarbon production. A model electrolysis cell was assembled using a thick BaCe 0.2 Zr 0.7 Y 0.1 O 3-δ (BCZY27) electrolyte and two distinct electrodes, i.e., a (H 2 -cathode) porous Pt layer; and (steam-anode) a composite made of 60 vol. % La 0.8 Sr 0.2 MnO 3-δ (LSM) and 40 vol. % BCZY27. The as-sintered steam electrode was catalytically-activated with Pr 6 O 11 -CeO 2 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 H 2 and CO 2 concentration in the cathode chamber. Increasing H 2 O concentration (in the anode) and presence of CO 2 (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/cm 2 , as determined by the analysis of the H 2 production. During co-electrolysis, the CO 2 reaction was fostered by co-feeding a minimum H 2 amount. CO formation took place through the reverse water gas shift (RWGS) reaction. When the current density was applied, CO 2 conversion increased due mainly to the non-Faradaic electrochemical modification of catalytic activity (NEMCA effect) that allowed for the improvement of CO 2 hydrogenation kinetics.