MnO-Co Composite Modified Ni-SDC Anode for Intermediate Temperature Solid Oxide Fuel Cells

Significance Statement

Fuel cells have the ability to convert chemical energy in fuels to electric energy without the inhibition of the Carnot cycle. Conventional power generating devices are deficient in efficiency, low emissions and the potential for combined heat and power generation, critical features among which the fuel cell vehemently manifests. Solid oxide fuel cells (SOFCs) often operate at high temperatures which contributes to a higher efficiency and power density as compared to other types of fuel cells. More so, the high operating temperatures enable the SOFCs to utilize carbon monoxide as a fuel rather than a poison. SOFCs with Ni-YSZ (yttria-stabilized zirconia) cermet anodes often operate at a higher temperature which translates into higher synthesis cost. Conversely, SOFCs with Ni-SDC (samarium-doped ceria) cermet anodes have exhibited lower operating temperatures and excellent electrochemical performance at intermediate temperatures. Besides, efforts are still needed so as to promote the performance and stability of SOFCs of Ni-SDC anodes in hydrogen and/or methane.

Zhonghua Zhu and his group at The University of Queensland in Australia, proposed studies to enhance the electrochemical performance and/or stability of Ni-SDC anode in hydrogen and/or methane. The authors firstly modified the Ni-SDC anode with manganese oxide and cobalt (MnO-Co) composite in a bid to further promote its performance. The research team begun their empirical work by ball-milling NiO, SDC, dextrin (pore former) and synthesized manganese-cobalt spinel in ethanol for a specific period. They then prepared the anode-supported solid oxide fuel cells. The crystal structures of the synthesized powders and anode powders were characterized by x-ray diffraction. The microstructure of the fabricated solid oxide fuel cells was also examined by scanning electron microscopy.

After the successful fabrication of the Ni-SDC and MnO-Co composite modified Ni-SDC anode-supported SOFCs, the authors observed that when compared with the normal Ni-SDC anodes, the MnO-Co modified Ni-SDC anodes exhibited much higher peak power density and lower polarization resistance in dry hydrogen gas and dry methane gas at all of the temperatures investigated. The modified anode had higher porosity than the original anode. However, the team noted that the stability of MnO-Co modified Ni-SDC anodes was worse than that of Ni-SDC anodes in dry methane due to severer carbon deposition. This research work is now published in Fuel Processing Technology.1 After that, the authors applied a MnO-Co-SDC internal reforming layer over the Ni-SDC anode and observed significant improvement in its performance and stability in wet methane (3mol% H2O in methane). They found that the anode started to decline in 150 minutes without the reforming layer, but showed no indication of degradation over 900 minutes due to the methane pre-reforming process after the addition of the MnO-Co-SDC layer at 0.2A/cm2 and 650 oC and the peak power density was further increased by over 10%. This work has been published in Journal of Materials Chemistry A.2 On-going research is being carried out in Prof Zhu’s group.

Reference

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