Sintering Aid Strategy for Promoting Oxygen Reduction Reaction on High-Performance Double-Layer LaNi0.6Fe0.4O3-δ Composite Electrode for Devices Based on Solid-State Membranes

Abstract

Strontium and cobalt-free LaNi_0.6Fe_0.4O_3-δ is considered one of the most promising electrodes for solid-state electrochemical devices. LaNi_0.6Fe_0.4O_3-δ has high electrical conductivity, a suitable thermal expansion coefficient, satisfactory tolerance to chromium poisoning, and chemical compatibility with zirconia-based electrolytes. The disadvantage of LaNi_0.6Fe_0.4O_3-δ is its low oxygen-ion conductivity. In order to increase the oxygen-ion conductivity, a complex oxide based on a doped ceria is added to the LaNi_0.6Fe_0.4O_3-δ. However, this leads to a decrease in the conductivity of the electrode. In this case, a two-layer electrode with a functional composite layer and a collector layer with the addition of sintering additives should be used. In this study, the effect of sintering additives (Bi_0.75Y_0.25O_2-δ and CuO) in the collector layer on the performance of LaNi_0.6Fe_0.4O_3-δ-based highly active electrodes in contact with the most common solid-state membranes (Zr_0.84Sc_0.16O_2-δ, Ce_0.8Sm_0.2O_2-δ, La_0.85Sr_0.15Ga_0.85Mg_0.15O_3-δ, La₁₀(SiO₄)₆O_3-δ, and BaCe_0.89Gd_0.1Cu_0.01O_3-δ) was investigated. It was shown that LaNi_0.6Fe_0.4O_3-δ has good chemical compatibility with the abovementioned membranes. The best electrochemical activity (polarization resistance about 0.02 Ohm cm² at 800 °C) was obtained for the electrode with 5 wt.% Bi_0.75Y_0.25O_1.5 and 2 wt.% CuO in the collector layer.

Keywords: DRT; LNF; LaNi0.6Fe0.4O3–δ; SOFC; complex oxide; distribution of relaxation times; electrode; membranes; polarization resistance; sintering aids.

Figure 1

X-ray diffraction patterns for supporting electrolytes (a) and powders for the electrodes (b).

Figure 2

X-ray diffraction patterns of pLNF-SDC-electrolyte powders after firing at 1000 °C for 5 h in air.

Figure 3

Electrical conductivity of collector porous layers with different contents of sintering additives. The composition of the collector layers is shown in Table 1. In linear coordinates (a), in Arrhenius plot (b) and depending on the type and content of the sintering additive (c).

Figure 4

SEM images of collector layers with different proportions of sintering aids and maps of elements distribution.

Figure 5

Temperature dependences of polarization resistance of bilayer electrodes in contact with LSO electrolyte (a), temperature dependences of series resistance of electrochemical cells, the bottom dependence is taken from [41] (b), EIS spectra and DRT functions for 700 °C (c).

Figure 6

Temperature dependence of the polarization resistance of bilayer electrodes in contact with different electrolytes.

Figure 7

Time dependence of the relative series resistance of electrochemical cells and (a) polarization resistance of a double layer electrode with 5YDB–2CuO collector layer for (b) cells with different supporting electrolytes.