Toward a Working Mechanism of Fuel Oxidation in SOFCs: In Situ Optical Studies of Simulated Biogas and Methane

• Published in: Journal of physical chemistry. C 2015-06, Vol.119 (23), p.12781-12791
• Main Authors: Kirtley, John D, Pomfret, Michael B, Steinhurst, Daniel A, Owrutsky, Jeffrey C, Walker, Robert A
• Format: Article
• Language: English
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp511304x

Solid-oxide fuel cells (SOFCs) have potential as highly efficient, clean, and sustainable electricity sources. However, the current, limited state of understanding of the complex electrochemical processes that occur at the anode in these systems, particularly those that lead to anode carbon formation and degradation, are roadblocks to effective cell design and operation. A suite of noninvasive, in situ optical techniques has been developed to help identify these processes. Vibrational Raman spectroscopy, Fourier-transform infrared emission spectroscopy (FTIRES), and near-infrared thermal (NIR) imaging, along with electrochemical measurements, provide surface and gas-phase molecular-specific diagnostics with the requisite temporal, spatial, and thermal resolution to correlate in operando observations with model chemical mechanisms associated with oxidation and carbon formation on Ni-based, anode-supported cells. This present work expands upon earlier in operando studies to fully assess the performance of commercially available Ni-YSZ anode SOFCs from 700 to 800 °C and to provide a more comprehensive description of the anode chemistry involved. Methane and simulated biogas (BG) are used as fuel. Raman measurements show that carbon grows minimally only at the lower operational temperatures for BG; however under methane, carbon formation occurs at all temperatures. Subsequent electrochemical oxidation of deposited carbon revealed that carbon formation under both fuels varies differently as a function of temperature. FTIRES measurements show that CO x constituents increase with cell polarization only under methane fuel; this effect changes with temperature. NIR imaging indicates that the Ni anode surface cools significantly when cells are operated at 800 °C relative to 700 °C under BG, and only minimal cooling is observed when operating with methane.