Identifying operating mechanism in the electrochemical reduction of CO 2 on thin-film praseodymium-doped ceria electrodes

Dense thin-film electrodes of Ce0.9Pr0.1O1.95 (PDC) are tested for CO2 reduction in a solid oxide electrolysis cell (SOEC) with yttria-stabilized-zirconia (YSZ) electrolyte and La0.8Sr0.2MnO3-δ (LSM) air electrode. A spray pyrolysis technique is utilized to fabricate thin-film electrodes of PDC with an approximate thickness of 400 nm. Dense microstructure in the thin film is fabricated to understand the relative role and limitations offered by surface reaction and oxygen anion diffusion within the bulk of the PDC electrodes while disallowing any gas phase diffusion. Electrochemical tests are performed in a geometrically well-defined cell to ascertain the operating mechanism. Electrochemical reduction of CO2 is carried out in the SOEC mode on the PDC electrode. Cu is added to the surface of the dense thin film of PDC. Polarization resistance of the thin-film electrode measured at the open-circuit voltage, in an H2/CO2 (8% H2) environment, is observed to reduce by 45% on adding Cu at the surface of the electrode. This suggested that the electrocatalytic activity of the thin-film electrode is limited by sluggish surface activity, which is improved on adding the surface with Cu.