Comparison of Carbon Deposition and Removal from Ni-YSZ and Ni-BCZY Composites Using Operando Optical Methods

Solid oxide fuel cells (SOFCs) are attractive devices for power generation because they can operate with a variety of fuels, including H 2 , hydrocarbon fuels, biogas, and syngas. Conventional SOFC anode composites comprised of Ni-YSZ (YSZ = yttria-stabilized zirconia), however, suffer from performance degradation due to surface accumulation of carbon from hydrocarbon cracking. Alternative electrolyte materials such as yttria-doped barium cerate/zirconate mixtures (BCZY) offer the promise of reduced carbon formation over the Ni-BCZY electrode and lower operating temperatures by the conduction of protons instead of oxide ions. In this study, 50%-50% Ni-8YSZ and 50%-50% Ni-BCZY27 composites were exposed to CH 4 in the absence and presence of either CO 2 or H 2 O. The degree of carbon deposition and mechanism of carbon removal in the absence of fuel was estimated in the presence of steam using operando Fourier transform infrared emission spectroscopy (FTIRES) and near-infrared thermal imaging (NIRTI) at 750 °C. Upon exposure to each fuel condition, carbon removal using steam results in more CO 2 + CO product formation from Ni-8YSZ implying more carbon formation on Ni-8YSZ compared to Ni-BCZY27. Carbon removal of cells exposed to CH 4 alone indicate limited formation and fast depletion of CO over Ni-BCZY27; depletion of CO 2 , however, happens more slowly. Depletion of CO and CO 2 in the Ni-8YSZ system happens more gradually suggesting the deposition of carbon over Ni-BCZY27 occurs less readily and its removal is more facile through gasification. Interestingly, the cracking of CH 4 over Ni-8YSZ is accompanied by a larger degree of cooling compared to Ni-BCZY27 whereas both dry and wet reforming result in similar cooling over Ni-8YSZ and Ni-BCZY27. The results will be discussed in the context of recent work using operando spectroscopies to characterize CH 4 fuel utilization in Ni-8YSZ based SOFCs in the absence and presence of various reformers.