Comparative Performance of Anode-Supported SOFCs Using a Thin Ce[sub 0.9]Gd[sub 0.1]O[sub 1.95] Electrolyte with an Incorporated BaCe[sub 0.8]Y[sub 0.2]O[sub 3−α] Layer in Hydrogen and Methane

Abstract

Multilayered Ce 0.9 Gd 0.1 O 1.95 /BaCe 0.8 Y 0.2 O 3−␣ /Ce 0.9 Gd 0.1 O 1.95 ͑GDC/BCY/GDC͒ electrolytes were prepared by tape casting on a Ni-Ce 0.8 Sm 0.2 O 1.9 anode support. The overall electrolyte thickness ranged from 30 to 35 m, including a 3 m thick BCY layer. When the multilayered electrolyte cell was tested with hydrogen at the anode and air at the cathode in the temperature range of 500-700°C, it yielded open-circuit voltages ͑OCVs͒ of 846-1024 mV, which were higher than the OCVs of 753-933 mV obtained for a single-layered GDC electrolyte cell under the same conditions. The corresponding peak power densities reached 273, 731, and 1025 mW cm −2 at 500, 600, and 700°C, respectively. The multilayered electrolyte cell could also be applied to direct methane solid oxide fuel cell ͑SOFC͒ and single-chamber SOFC operating in a mixture of methane and air. These SOFCs yielded OCVs of 880-950 mV and reasonable power densities without coking.There has been considerable recent interest in solid oxide fuel cells ͑SOFCs͒ operating at intermediate temperatures of 700°C or less. 1 Compared with polymer electrolyte fuel cells ͑PEFCs͒, the intermediate-temperature solid oxide fuel cells ͑IT-SOFCs͒ can tolerate CO even at high concentrations and they can work with much higher electrode reaction rates. 2 Unlike conventional hightemperature SOFCs, the IT-SOFCs allow for the direct use of a hydrocarbon fuel, significantly reducing the complexity of the fuelcell systems. 3,4 A key issue in the development of IT-SOFCs is the use of a highly ion conductive electrolyte, because the operation of SOFCs under such conditions results in excessive electrical resistance in the cell. Ceria-based oxide-ion conductors are promising electrolytes that exhibit much higher ion conductivities than yttriastabilized zirconia ͑YSZ͒. Combined with advanced anodesupported cell structures, ceria-based SOFCs can maintain acceptable performance at intermediate temperatures. [5][6][7][8][9][10][11][12][13] The primary problem encountered in using ceria-based electrolytes for IT-SOFCs is the partial reduction of ceria in fuel atmospheres. 14 This results in n-type electronic conductivity, causing partial internal electronic short circuits in the cell. It also results in expansion of the crystal lattice, leading to mechanical degradation inside the electrolyte or at the electrolyte-electrode interface. Therefore, ceria-based SOFCs must be processed at temperatures below 500°C, where the reduction of ceria is thermodynamically suppressed. 15 We recently proposed an effective approach to avoid partial reduction of ceria. 16,17 The surface of a Sm 3+ -or Gd 3+ -doped ceria substrate with a thickness of 0.5 mm was coated with a thin BaO film and then heated up to 1500°C. Consequently, a solid-state reaction between the film and the substrate formed a ϳ10 m thick BaCe 1−x Sm x ͑or Gd x ͒O 3−␣ layer on the substrate surface. Using the coated electrolyte, a hydrogen-air SOFC showed open-circuit voltages ͑OCVs͒ above 1 V in the temperature range of 600-950°C. ...

Anode‐supported SOFC Operated Under Single‐chamber Conditions at Intermediate Temperatures

“…On the other hand, our cell performances are lower than those reported under similar cell conditions (anode-supported, 10-20 lm electrolytes) by Shao et al and Zhang et al [8,22]. The use of cathode LSC instead of BSCF, LSCF or SSC can partially explain these differences in performance, because the LSC overpotential is higher than those of BSCF, LSCF or SSC [12,23]. However, there are other reasons that could justify the low performance of our cell.…”

Single-Chamber Solid Oxide Fuel Cell Technology—From Its Origins to Today’s State of the Art

“…Tomita et al [163] found that the addition of a thin BaCe 0.8 Y 0.2 O 3- (BCY) layer between two layers of GDC increased the stability of ceria-based electrolytes in reducing atmospheres. The laminated three-layer electrolyte impeded electronic short circuiting which occurs from electronic conductivity due to reduction of GDC at low oxygen partial pressure.…”

New Stack Design of Micro‐tubular SOFCs for Portable Power Sources

“…Doped ceria displays mixed conductivity (ionic and electronic) when it is placed in the reducing atmosphere, and this elecronic conduction causes leak current, leading to lower OCV. However, there are several reports to minimise the efficiency drop and they should be taken into account for the use of ceria-based electrolyte for application use [28,29]. Figure 4 shows the output current at the voltage of 2.1 V (0.7 V per bundle) for various fuel flow rates at 500°C operating temperature.…”