Enhancement of Ni–(Y₂O₃)_0.08(ZrO₂)_0.92 fuel electrode performance by infiltration of Ce_0.8Gd_0.2O_2−δ nanoparticles

Abstract

GDC nanoparticles reduce the reaction resistance associated with three-phase boundaries and improve oxygen transport in the Ni–YSZ electrode, as measured by electrochemical impedance spectroscopy under actual solid oxide cell operating conditions.

Effect of Nanoscale Ce0.8Gd0.2O2−δ Infiltrant and Steam Content on Ni–(Y2O3)0.08(ZrO2)0.92 Fuel Electrode Degradation during High-Temperature Electrolysis

“…However, some of the apparent R p degradation with time is actually the effect the varying the H 2 O fraction f . To illustrate this effect, Figure b also shows previously reported R p values obtained for Ni–YSZ and Ni–YSZ:GDC electrode cells; these were prepared identically to the present cells, and the values were measured during the early stages of testing so that no degradation was present . In Figure b, the lower dashed lines show the values for Ni–YSZ:GDC, and the upper dashed lines the values for Ni–YSZ.…”

“…The present values measured at time t = 0 agree very well with the reported values, as expected. The R p values generally increase with decreasing f , as is often observed for Ni–YSZ. − …”

“…To gain insight into electrode degradation mechanisms, the impedance spectra were analyzed using complex nonlinear least-squares fitting with an equivalent circuit model (Figure a) that was previously developed for Ni–YSZ symmetric cells . A transmission line model (TLM) was used to represent the porous percolated network of ionically conductive YSZ and electronically conductive Ni particles. ,,− The R rxn and Q rxn elements (resistance R in parallel with a constant phase element Q ) represent the hydrogen oxidation and steam reduction processes, respectively, at Ni–YSZ three-phase boundaries and on GDC surfaces in the Ni–YSZ:GDC electrodes. Noting that the electronic resistance is much lower than the ionic resistance ( R e – ≪ R O 2– ), the TLM impedance simplifies to where ζ represents the R rxn Q rxn element.…”

“…Noting that the electronic resistance is much lower than the ionic resistance ( R e – ≪ R O 2– ), the TLM impedance simplifies to where ζ represents the R rxn Q rxn element. Gas diffusion was modeled using a generalized finite length Warburg element as follows: , where R W is the dc diffusion resistance and n W is an exponent (0 < n W < 0.5) indicating the degree of nonuniform diffusion. The diffusion coefficient D i of the species i in the H 2 /H 2 O mixture is derived using the time constant τ W and the effective diffusion coefficient in the porous structure with thickness L s as where ε is the porosity and τ is the pore tortuosity for the Ni–YSZ support.…”

“…Gas diffusion was modeled using a generalized finite length Warburg element as follows: , where R W is the dc diffusion resistance and n W is an exponent (0 < n W < 0.5) indicating the degree of nonuniform diffusion. The diffusion coefficient D i of the species i in the H 2 /H 2 O mixture is derived using the time constant τ W and the effective diffusion coefficient in the porous structure with thickness L s as where ε is the porosity and τ is the pore tortuosity for the Ni–YSZ support. ε and τ were determined to be ∼0.35 and ∼1.52, respectively, by a stereological analysis using electrode images (in Figure S6).…”