Double Layered CeO2-Co3O4-CuO Based Anode for Direct Utilisation of Methane or Ethanol in SOFC
Authors: Sarruf Bernardo Jordão Moreira , Hong Jong-Eun , Steinberger-Wilckens Robert , de Miranda Paulo Emílio Valadão 
Published: February 2020

Solid oxide fuel cells have been subject of many developments especially concerning alternative fuels such as hydrocarbons and alcohols, mainly because these devices can convert chemical potential into electricity with high efficiencies. In addition, the direct utilisation of hydrocarbons or alcohols as fuels increases the feasibility of SOFC market penetration. However, issues such as coking and clogging by carbon formation must be overcome before the technology can be safely delivered to final consumers. Therefore, the aim of this work was to develop an anode material capable of using methane or ethanol as fuels directly into the cell without any pre-reforming which could prevent carbon to deactivate the anode material.
A bimetallic Ceria-based electrocatalyst was thus prepared using Cobalt and Copper oxides to enhance catalytic activity and electrical conductivity. Two different compositions were produced, a Cerium-rich composition with the molar proportion of Ce:Co:Cu – 2:1:1 and a Cobalt-rich one, Ce:Co:Cu – 1:2:1. The electrocatalyst powder was synthesised by the amorphous citrate method and characterised by X-Ray diffraction (XRD), Rietveld refinement, and temperature-programmed reduction (TPR). The powders produced were pelletised, sintered, and then submitted to Van der Pauw 4-probe DC conductivity tests. ScCeSZr electrolyte-supported cells were produced with a Lanthanum Strontium-doped manganite cathode screen printed onto the electrolyte. The anode was comprised with a double layer of the aforesaid compositions and a Sc10Ce1Zr + CeO2 inner layer that provided more stability between the electrolyte and the anode. The cell was tested under hydrogen as fuel and oxygen as oxidant from 750 to 850 ˚C, and then with anhydrous methane and ethanol separately as fuels at 850 ˚C. After operation, the cell was submitted to Raman spectroscopy to assess any evidence of carbon deposition through the anode microstructure. Moreover, scanning electron microscopy was conducted to evaluate the anode morphology and conditions concerning its microstructure.
XRD spectra showed that the desired bimetallic CeO2-Co3O4-CuO oxide was formed and Rietveld refinement indicated that the formation of solid solutions did not occur. TPR demonstrated the ability of both compositions to absorb hydrogen by reducing its oxides as expected. DC conductivity tests presented suitable values since the tests were taken over the oxidised sample. The cell could operate in hydrogen, methane or ethanol as fuels showing maximum power densities of approximately 400, 100 and 160 mW.cm–2, respectively, at 850 ˚C. Raman spectroscopy was performed over several spots on the cell during post-mortem analysis and no evidence of carbon deposition was found on the anode. SEM images showed a homogenous microstructure concerning surface morphology and pore distribution. Finally, it was found that the bimetallic electrocatalyst anode could utilise hydrocarbon fuels directly without pre-reforming and produce a reasonable power density with no evidence of carbon coking which shows that this material configuration is promising as anode for carbonaceous fuels.