Tuning Electrochemical Performance by Microstructural Optimization of the Nanocrystalline Functional Oxygen Electrode Layer for Solid Oxide Cells.

Further development of solid oxide fuel cell (SOFC) oxygen electrodes can be achieved through improvements in oxygen electrode design by microstructure miniaturization alongside nanomaterial implementation. In this work, improved electrochemical performance of an La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-d (LSCF) cathode was achieved by the controlled modification of the La 0.6 Sr 0.4 CoO 3-d (LSC) nanocrystalline interlayer introduced between a porous oxygen electrode and dense electrolyte. The evaluation was carried out for various LSC layer thicknesses, annealing temperatures, oxygen partial pressures, and temperatures as well as subjected to long-term stability tests and evaluated in typical operating conditions in an intermediate temperature SOFC. Electrochemical impedance spectroscopy and a distribution of relaxation times analysis were performed to reveal the rate-limiting electrochemical processes that limit the overall electrode performance. The main processes with an impact on the electrode performance were the adsorption of gaseous oxygen O 2 , dissociation of O 2 , and charge transfer-diffusion (O 2- ). The introduction of a nanoporous and nanocrystalline interlayer with extended electrochemically active surface area accelerates the oxygen surface exchange kinetics and oxygen ion diffusions, reducing polarization resistances. The polarization resistance of the reference LSCF was lowered by one order of magnitude from 0.77 to 0.076 Ω·cm 2 at 600 °C by the deposition of a 400 nm LSC interlayer at the interface. The developed electrode tested in the anode-supported fuel cell configuration showed a higher cell performance by 20% compared to the cell with the reference electrode. The maximum power density at 700 °C reaches 675 and 820 mW·cm -2 for the reference cell and the cell with the LSC interlayer, respectively. Aging tests at 700 °C under a high load of 1 A·cm 2 were performed.