Evaluation of the effects of nanocatalyst infiltration on the SOFC performance and electrode reaction kinetics using the transmission line model

Abstract

In this work, the effect of nanocatalyst infiltration on the SOFC performance and electrode reaction characteristics was comprehensively investigated by the application of electrochemical impedance (EI) spectroscopy. The Ni-8 mol% yttria-stabilized zirconia (YSZ) anode-supported cell was fabricated using a YSZ electrolyte, and a mixed ionic electronic conductor (MIEC) La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (LSCF6428) cathode. The EI spectra were measured under various conditions (0.02 ≤ pO_2,cat./atm ≤ 1; 0.2 ≤ pH₂O_ano./atm ≤ 0.6) in the temperature range of 600–800 °C. With the application of the equivalent circuit model (ECM) fitting using a transmission line model (TLM), the parameters (R_s,el, R_p,el, C_p,el, and Q_W) expressing the activation polarization of the cathode and anode were analyzed, and the chemical diffusion coefficients (), the reaction constant (k), and the effective length of the electrode reaction were calculated. A similar anode-supported cell was fabricated in which the LSCF6428 cathode was infiltrated by a monodispersed Sm_0.5Sr_0.5CoFe_3−δ (SSC55) nanocatalyst using a sol–gel method. The cathode-infiltrated cell was measured under the same thermodynamic conditions. Each electrode was analyzed by using the TLM to evaluate the effect of the nanocatalyst on the SOFC performance and electrode reaction characteristics. With the application of nanocatalyst infiltration, the parameters (R_s,cat. and R_p,cat.) of the cathode were found to decrease by approximately one order and 40%, respectively. Similarly, C_p,cat. also fell by approximately one order of magnitude. From this investigation, it was confirmed that the diffusion of surface ions had a more significant contribution to conduction than the diffusion of bulk ions by the SSC55 nanocatalyst.