Operando Thermal Imaging Study of Internal Partial Methane Oxidation in Ni-YSZ Anodes of Commercial SOFCs

Thermal imaging is employed to study internal partial methane oxidation in a Ni-YSZ anode of a commercial, button-style solid oxide fuel cell at 800 °C in real time. When a stoichiometric 2:1 mixture of methane and oxygen is delivered to the anode, thermal imaging reveals formation of two distinct zones on the exposed surface of the anode: a smaller zone of increased temperature near the fuel delivery inlet and a larger zone of decreased temperature occupying the rest of the anode. We assign the former to exothermic complete oxidation of some methane to steam and carbon dioxide and the latter to endothermal reforming of the remaining methane with the steam and carbon dioxide generated in the hot zone. Simultaneous detection of catalytic products using mass spectrometry indicates that when combined the two sequential reactions convert almost 80% of the delivered methane, with the main products being carbon monoxide and hydrogen. Cell polarization during partial methane oxidation delivers an oxide ion flux to the anode-electrolyte interface. As the oxide flux is significantly lower than the oxygen gas flux delivered in the methane and oxygen mixture, the former is used to probe the catalytic products of partial methane oxidation. Our results reveal negligible amounts of unreacted methane and accumulated carbon on the anode surface during the partial oxidation process.