Abstract
Electrochemically active oxide-based anodes capable of working in Single-Chamber Solid Oxide Fuel Cells (SC-SOFCs) were developed. Their performance is related to the selectivity of the electrodes. Tests are carried out on lab-scale devices with YSZ pellets as solid electrolytes in electrolyte supported cells. Selecting methane as a fuel, a gas mixture in the ratio CH4/O2 = 2 was chosen. The Ni-YSZ (NiO:YSZ=60:40) anode was optimized through CeO2 nanocatalysts infiltration to enhance the anode catalytic activity and make its reduction easier. Several infiltration amounts were compared, from null to 15% of the electrode weight. Both symmetric and complete cells (with LSCF-based cathodes) were tested in H2 and CH4/O2. For increasing amounts of infiltrated CeO2, symmetric cells tests describe an area specific resistance (ASR) reduction from 40 Ω cm2 to 1.7 Ω cm2 in hydrogen and from 11 Ω cm2 to 3.9 Ω cm2 in the methane/oxygen mixture. While complete cells tests displayed an ASR drop from 30 Ω cm2 to 2.9 Ω cm2 in H2, and from 8.7 Ω cm2 to 4.3 Ω cm2 in the methane/oxygen mixture, while OCP and power grew from 478 mV and 3.7 mW cm-2 to 766 mV and 13 mW cm-2.
Highlights
Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) represent a particular branch of SOFCs technologies that aims to overcome the main flows of the dual chamber devices, mainly due to the sealing, that makes the device design more complex and make it hard to be employed for portable applications [1]
The cell without CeO2 infiltration (0wt%), at 700°C delivers a spectrum that reaches about 300 Ω a value that discourages the exploitation of the material, despite the temperature is suited for YSZ electrolytes [2,3]
The semicircle on the right, is that for medium frequencies (MF), in a range around 104 Hz – 101 Hz. Sometimes it is visible a smaller arch at the highest measured Z’ values, for the low frequencies (LF), in the range 101 Hz – 10-2 Hz. These two semi-circles are generally associated with mass transfer processes, the one at MF depends on the micro-structure of the material and is due to gas diffusion through the electrode and the current collector, while the LF arch is associated to the diffusion of gases on top of the electrodes [31,33]
Summary
Single Chamber Solid Oxide Fuel Cells (SC-SOFCs) represent a particular branch of SOFCs technologies that aims to overcome the main flows of the dual chamber devices, mainly due to the sealing, that makes the device design more complex and make it hard to be employed for portable applications [1]. The main challenges bound to this technology are the intrinsic necessity for highly selective and catalytically active materials, the lower fuel utilization and efficiency, due to parasitic reactions, and the risk of explosion due to fuel and air being mixed together at high temperatures [4,5] These critical aspects made research on single chambers to become little appealing in the latest years [6], yet its employment for specific applications would make it a competitive technology, as in portable power applications [7], cogeneration [8] or in a context where the high fuel use efficiency is not a fundamental requirement, as sensors [9] or in residual fuel in engine exhaust [10]. The final cathode was LSCF:GDC (50:50) to avoid delamination of pure LSCF cathodes after thermal treatment
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