Electrochemical Oxidation of Syngas on Nickel and Ceria Anodes

Abstract

Fuel flexibility of solid oxide fuel cells enables the use of low cost and practical fuels like syngas. Understanding of the oxidation kinetics with syngas is essential for proper selection of anode material and its design optimization. Using nickel and ceria pattern anodes, we study the electrochemical oxidation of syngas in both dry and wet environments. In dry environment, the polarization resistance of CO oxidation drops drastically with the addition of small amounts of hydrogen to CO gas stream. In wet environment (4 % moisture), the polarization resistance of CO is only slightly higher than syngas and hydrogen. Observation in the first case is related to the hydrogen preferential oxidation whereas latter is a combined effect of water gas shift reaction and preferential oxidation of hydrogen. Kinetic modeling is also carried out to understand hydrogen and CO co-oxidation. Simulation suggests that CO, besides hydrogen, may also electrochemically oxidize depending upon its concentration in the syngas. At higher concentration, CO electrochemical oxidation may be non-negligible especially in case of ceria anodes.

Effect of H2S and HCl contaminants on nickel and ceria pattern anode solid oxide fuel cells

“…Unlike pattern electrode cells, Ni/GDC cermet cell performance remains unaffected at lower HCl concentrations (up to 60 ppm). The decrease in the polarization resistance of nickel and ceria pattern electrode cells possibly points towards the facilitating role of HCl for electrochemical hydrogen oxidation, and more specifically, the charge transfer step as the charge transfer step is the rate-determining in the oxidation process [35,37]. The same has not been observed in the Ni/GDC cermet cell case because the charge transfer resistance of the Ni/GDC electrode is generally small compared to the resistance offered by surface and gas-phase processes.…”

“…The impedance spectra are also easier to analyze. In previous works, we have used nickel and ceria pattern electrode cells to analyze the oxidation of hydrogen and carbon monoxide and mixtures thereof and highlighted the possible use of (un)doped ceria as an anode material in its reduced state [34,35]. Combined with modeling, this has proved to be a useful exercise in understanding the differences in the oxidation mechanism between nickel and ceria and, indeed, proposed possible reaction schemes [5,36,37].…”

“…Because of this, we use pattern anode cells, which have a well-defined topology and allow for localization of the reactions. Also, because the current drawn is so small, it is not envisaged that the gas diffusion impedance will significantly impact the response time [35]. The impedance spectra are also easier to analyze.…”

Opportunities and Challenges in Using SOFCs in Waste to Energy Systems

“…Pattern anodes are usually chosen for studying electrochemistry due to their advantages of easily quantifiable TPB length and the simplified 2D structure. The 2D structure of patterns eliminate the structural and even the gas phase effects which exist in the cermet anodes and can help in understanding the effect of fuel contaminants on the electrochemical reactions kinetics [27,28,29,30,31]. Experiments are then carried out porous symmetric cells and complete cells with anode and cathode to study these effects further [32,33].…”

Effect of Sn addition on improving the stability of Ni-Ce0.8Sm0.2O1.9 anode material for solid oxide fuel cells fed with dry CH4

“…In our previous work, Ni-Ce0.8Sm0.2O1.9 (SDC) was employed as the anode material of a direct CH4 SOFC. The SDC phase provided a high oxygen ionic conductivity and enlarged the region of three-phase boundaries [28]. A cell with a 120-μm-thick SDC electrolyte layer exhibited a Pmax of 670 mW cm -2 at 700 o C. Ni-SDC anodes have also been investigated with other hydrocarbon fuels such as methanol, ethanol and biomass gasification tar [29][30][31][32].…”