Comparison of Different Synthesis Methods to Obtain GDC as Nanoparticulated Electrolytic Material for SOFCs Operating at Intermediate Temperature (~500°C)
Authors: Monterrosa Álvarez Laura Paulina , Santa Juan Felipe , Gonzalez Javier de Jesús , Ribadeneira Paz Rafael , Buitrago Robison 
Published: July 2021

The necessary global electrical energy demand employs a high amount of fossil fuels and produces emissions of polluting gases due to its combustion, which needs the improving of the electric power generation technologies friendlier with the environment. This technology must guarantee to be sustainable, economic and available for all people. The SOFCs represent a promising alternative in the production of electrical energy directly from chemical energy through a series of electrochemical reactions with the use of fuels as hydrogen, carbon monoxide, methane and several synthesis gases rich in hydrogen or methane.

The development of SOFCs has several challenges, related with thermic and electrochemical properties of the materials that constitutes anode, cathode and electrolyte. Several materials has been tested, for instance perovskites, aiming for facilitate the ionic conductivity inside these cells and reduce the operating temperatures, also looking for the increase of performance. To get similar thermal expansion coefficients (TEC) in anode, electrolyte and cathode, researchers have tested different chemical compositions to modify the perovskite structure of materials utilized in these components for SOFCs. Specifically for the electrolyte, these modifications could enhance the creation of oxygen vacancies, contributing to decrease TEC and also reduce the cathodic polarization, which are IT-SOFC operating challenges.

Aiming for solve these issues, in this work, the synthesis of a cobaltite of lanthanum type perovskite LSCF, as cathode material, is developed by the co-precipitation method, using nitrate precursors. Also GDC is synthetized by three synthesis methods, which is the main purpose of this work: co-precipitation, sol-gel combustion (SGC) and hydrothermal. The obtained compounds are characterized physical and chemically by FTIR, TGA, TEM, SEM-EDS, and XRD.

GDC synthesis was carried out by three different synthesis routes (SGC, Hydrothermal and Co-precipitation). The analysis of the mapping with EDS showed the uniform presence of each of the components Ce, Gd and O in the entire sample, in all the studied cases. In addition, the chemical composition in weight percent (% wt) by zones was evaluated to delimit the compositional homogeneity of the sample, but two different compositions were found that were replicated in all the extent of the powder, (1) Ce0,8Gd0,2O1,9 and (2) Ce0,7Gd0,3O1,85, as possible, which was corroborated with XRD analysis, in addition, the sample is crystalline and organized, the crystallinity decreases as follows SGC> Co-precipitation> Hydrothermal; this is defined as well, since the peaks are more defined and narrow in that order, whereas powders obtained by SGC are considered more crystalline than those obtained by the other two routes. Furthermore, similar stoichiometries of these compounds can be used in this type of fuel cell, since both have been used before.

In all the cases studied, FTIR analysis show the characteristic adsorption band of GDC, which is normally at 565 cm-1, and is assigned to vibrations by elongation between metal and oxygen, which in this case would be the Ce bonds, -O and / or Gd-O. On the other hand, with TEM analysis corroborate that all the powders obtained with GDC synthesis have a nanometric size. The particle size obtained in decreasing order was SGC> Co-precipitation> Hydrothermal.

The obtained results in this work show that GDC electrolytes are dependent of the synthesis route, but in general have adequate physical and chemical properties to be applied with good performance in IT-SOFCs. Considering this, currently we are building a single IT-SOFC with these materials to test at 500°C.