Influence of NH4HCO3 on Microstructure of Ni/La10Si5.8Mg0.2O26.8 Anode

doi:10.15541/jim20140021

Abstract

Abstract:

Apatite-type lanthanum silicates are a new type of oxide-ion conductors. In the present research, nanosized apatite-type lanthanum silicate (La₁₀Si_5.8Mg_0.2O_26.8) powder was prepared through Sol-Gel method by using citric acid and nitrates. The nanosized lanthanum silicate powder was mixed with nanosized NiO powder according to weight ratio of 4:6, and with different amounts of NH₄HCO₃as pore-forming agent. Porous composite anodes of Ni/La₁₀Si_5.8Mg_0.2O_26.8 were fabricated through sintering at 1400℃ and then reduced in H₂ atmosphere at 600℃. Phases, surface morphology and porosity of the samples were characterized by XRD, FE-SEM and Archimedes method, respectively. Resistance of the anodes at room temperature was determined by ac impedance spectroscopy. The results show that the prepared Ni/ La₁₀Si_5.8Mg_0.2O_26.8 porous composite anodes are micro-crack free and the mean thermal expansion coefficient before reduction is 10.7×10^-6 K^-1. With increasing amount of pore-forming agent NH₄HCO₃, sizes of Ni grains, apatite-type silicate grains and pores decrease, but the porosity increases within the range of 30%-45%. The resistance of the anodes decreases at first and then increases as the amount of NH₄HCO₃ increases. Considering all these characteristics, including phases, surface morphology, porosity and resistance, the anode made with the pore-forming agent NH₄HCO₃ at ratio of 30wt% is the best.

Key words: Sol-Gel, apatite-type lanthanum silicate, anode, porosity, SOFCs

CLC Number:

TQ174

XIANG Li, DING Xiao-Fang. Influence of NH₄HCO₃ on Microstructure of Ni/La₁₀Si_5.8Mg_0.2O_26.8 Anode[J]. Journal of Inorganic Materials, 2014, 29(9): 924-930.

Figures/Tables 11

Table 1 Weight ratio of start materials for anode samples

Sample	Start materials	Weight ratio
0	La₁₀Si_5.8Mg_0.2O_26.8:NiO:NH₄HCO₃	4:6:0
1	La₁₀Si_5.8Mg_0.2O_26.8:NiO:NH₄HCO₃	4:6:1
2	La₁₀Si_5.8Mg_0.2O_26.8:NiO:NH₄HCO₃	4:6:2
3	La₁₀Si_5.8Mg_0.2O_26.8:NiO:NH₄HCO₃	4:6:3
4	La₁₀Si_5.8Mg_0.2O_26.8:NiO:NH₄HCO₃	4:6:4

Fig. 1 XRD patterns of start powders

Fig. 2 TEM image of La10Si5.8Mg0.2O26.8 powder

Fig. 3 FE-SEM surface micrographs of 60% NiO/La10Si5.8 Mg0.2O26.8 ceramic without NH4HCO3 (a) SEM image; (b) BE image

Fig. 4 Thermal expansion coefficient curve of 60% NiO/La10Si5.8Mg0.2O26.8 ceramic without NH4HCO3 Insert is the thermal expansion curve

Fig. 5 XRD patterns of samples with different amounts of NH4HCO3 before reduction (a) 10wt% NH4HCO3; (b) 20wt% NH4HCO3; (c) 30wt% NH4HCO3; (d) 40wt% NH4HCO3

Fig. 6 XRD patterns of samples with different amounts of NH4HCO3 after reduction (a) 10wt% NH4HCO3; (b) 20wt% NH4HCO3; (c) 30wt% NH4HCO3; (d) 40wt% NH4HCO3

Fig. 7 FE-SEM surface micrographs of samples with different amount of NH4HCO3 before reduction (a) 10wt% NH4HCO3; (b) 20wt% NH4HCO3; (c) 30wt% NH4HCO3; (d) 40wt% NH4HCO3

Fig. 8 FE-SEM surface micrographs of samples with different amount of NH4HCO3 after reduction (a) 10wt% NH4HCO3; (b) 20wt% NH4HCO3; (c) 30wt% NH4HCO3; (d) 40wt% NH4HCO3

Fig. 9 Relationship between porosity and amount of NH4HCO3

Table 2 Resistance of anodes with different amount of NH4HCO3

Amount of NH₄HCO₃	10wt%	20wt%	30wt%	40wt%
Resistance/Ω	2.38	2.17	1.78	1.4×10⁷

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Influence of NH₄HCO₃ on Microstructure of Ni/La₁₀Si_5.8Mg_0.2O_26.8 Anode

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