Abstract
AbstractConventional SOFCs use Nickel Yttria‐doped Zirconia cermet anodes, which are susceptible to degradation due to coking when operating with carbon containing fuels. Raman spectroscopy is a powerful tool for investigating surface chemistry and, when combined with electrochemical impedance spectroscopy under in situ conditions, the technique can report the real‐time material composition of the electrode during the EIS measurements. Studies described in this work used in situ Raman spectroscopy and electrochemical impedance spectroscopy to examine the carbon tolerance of novel ceramic anode materials comprised of niobium doped strontium titanate infiltrated with nickel or cobalt nanoparticles. The susceptibility of these electrodes to coking were tested with CO/CO2 mixtures and pure methane at 850 °C. Data show that nickel‐infiltrated STN electrodes are still prone to coking from methane. In contrast to STN electrodes infiltrated with nickel, cobalt‐infiltrated STN electrodes showed no susceptibility to carbon deposition during methane exposure within the detection limit of the Raman measurements. Neither anode showed evidence of coking from the CO/CO2 mixtures. Coking correlated closely with changes in EIS measurements, with the most noticeable effects appearing in the low frequency part of the spectrum. Ex situ SEM analysis of samples before and after operation illustrates the growth of the nanoparticles.
Highlights
Solid oxide fuel cells (SOFCs) are able to electrochemically oxidize a large variety of fuels
Studies described in this work used in situ Raman spectroscopy and electrochemical impedance spectroscopy to examine the carbon tolerance of novel ceramic anode materials comprised of niobium doped strontium titanate infiltrated with nickel or cobalt nanoparticles
The presence of NiO was inferred from the coke that formed during exposure of the reduced anode to methane and from the ex situ EDS and scanning electron microscopy (SEM) measurements performed after experimental operation
Summary
Solid oxide fuel cells (SOFCs) are able to electrochemically oxidize a large variety of fuels. One family of materials is based on donor-doped strontium titanate (SrTiO3) These perovskite ceramics are expected to be resistant to conventional SOFC anode contaminants, since they are tolerant to both carbon and sulphur impurities in the ambient fuel atmosphere. Ramos et al showed that materials such as B-site deficient Sr0.94Ti0.9Nb0.1O3 (STN94) could compete with state of the art Ni-YSZ cermet electrodes, if an electrocatalyst like ruthenium or palladium and a mixed ionic electronic conductor such as gadolinium doped cerium oxide (CGO) were co-infiltrated into an STN scaffold [7,8] Both ruthenium and palladium are precious metals and too costly to be used in any commercialization strategy. In combination with microscope optics, Raman spectra with a spatial resolution as fine as ~1 μm can be obtained and Raman spectroscopy is able to identify molecular and material species and their rates of formation/disappearance with temporal resolution down to one second or even faster [15]
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