A detailed kinetic model for the reduction of oxygen on LSCF-GDC composite cathodes

• Published in: Electrochimica acta 2020-03, Vol.335, p.135620, Article 135620
• Main Authors: Donazzi, Alessandro, Cordaro, Giulio, Baricci, Andrea, Ding, Zhao-Bin, Maestri, Matteo
• Format: Article
• Language: English
• Subjects: Adatoms; Cathodes; Computer simulation; Conservation equations; EIS; Electric arcs; Electrodes; Gaseous diffusion; GDC; Impedance; LSCF; Microkinetics; ORR; Oxygen reduction reactions; Pressure effects; Sensitivity analysis
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2020.135620

A kinetic investigation of the Oxygen Reduction Reaction (ORR) is performed on LSCF-GDC composite cathodes (La0.4Sr0.6Co0.2Fe0.8O3-δ/Ce0.9Gd0.1O2-δ 50/50) spanning a wide range of operating conditions. EIS tests are carried out on symmetric cells between 700 °C and 560 °C at OCV, with O2/N2 mixtures at varying O2 molar fraction (5–21%). A dynamic, one-dimensional, physic model of the LSCF-GDC electrode is applied to rationalize the experimental results. The model simulates the spectra by solving mass and charge conservation equations, including terms for gas diffusion in the porous electrode and solid state transport in both the LSCF and the GDC lattice. A thermodynamically consistent, detailed kinetic scheme is applied to describe the ORR mechanism, which takes into account elementary steps of adsorption and desorption, first and second electronation at the gas/electrode interface, interfacial and lattice ion transfer. A full set of rate parameters (pre-exponential factors and activation energies) is derived by fitting to inhouse-measured impedance data, and validated against a well-established literature dataset. The sensitivity analysis supports the prevailing role of the TPB route over the 2PB route, and highlights that the transfer of a single-charged oxygen adatom from the LSCF surface to the GDC lattice governs the ORR. The model clarifies the origin of distortions in measured impedance arcs, and captures the effect of O2 pressure on the observed electrochemical activity. [Display omitted] •A dynamic heterogenous and physic model of composite LSCF-GDC cathodes is presented•Electrochemical impedance spectra are simulated with a detailed kinetic ORR scheme•Consistent rate parameters are derived by fitting to experimental spectra•Simultaneous oxide ion flow in LSCF and GDC occurs at high applied current density•The transfer of a single-charged oxygen adatom from LSCF to GDC is the RDS