In situ optical studies of methane and simulated biogas oxidation on high temperature solid oxide fuel cell anodes.

Novel integration of in situ near infrared (NIR) thermal imaging, vibrational Raman spectroscopy, and Fourier-transform infrared emission spectroscopy (FTIRES) coupled with traditional electrochemical measurements has been used to probe chemical and thermal properties of Ni-based, solid oxide fuel cell (SOFC) anodes operating with methane and simulated biogas fuel mixtures at 800 °C. Together, these three non-invasive optical techniques provide direct insight into the surface chemistry associated with device performance as a function of cell polarization. Specifically, data from these complementary methods measure with high spatial and temporal resolution thermal gradients and changes in material and gas phase composition in operando. NIR thermal images show that SOFC anodes operating with biogas undergo significant cooling (ΔT = -13 °C) relative to the same anodes operating with methane fuel (ΔT = -3 °C). This result is general regardless of cell polarization. Simultaneous Raman spectroscopic measurements are unable to detect carbon formation on anodes operating with biogas. Carbon deposition is observable during operation with methane as evidenced by a weak vibrational band at 1556 cm(-1). This feature is assigned to highly ordered graphite. In situ FTIRES corroborates these results by identifying relative amounts of CO2 and CO produced during electrochemical removal of anodic carbon previously formed from an incident fuel feed. Taken together, these three optical techniques illustrate the promise that complementary, in situ methods have for identifying electrochemical oxidation mechanisms and carbon-forming pathways in high temperature electrochemical devices.

Identification of a Methane Oxidation Intermediate on Solid Oxide Fuel Cell Anode Surfaces with Fourier Transform Infrared Emission.

Fuel interactions on solid oxide fuel cell (SOFC) anodes are studied with in situ Fourier transform infrared emission spectroscopy (FTIRES). SOFCs are operated at 800 °C with CH4 as a representative hydrocarbon fuel. IR signatures of gas-phase oxidation products, CO2(g) and CO(g), are observed while cells are under load. A broad feature at 2295 cm(-1) is assigned to CO2 adsorbed on Ni as a CH4 oxidation intermediate during cell operation and while carbon deposits are electrochemically oxidized after CH4 operation. Electrochemical control provides confirmation of the assignment of adsorbed CO2. FTIRES has been demonstrated as a viable technique for the identification of fuel oxidation intermediates and products in working SOFCs, allowing for the elucidation of the mechanisms of fuel chemistry.