High performance metal-supported solid oxide fuel cells with infiltrated electrodes

Abstract

High power density is required to commercialize solid oxide fuel cells for vehicular applications. In this work, high performance of metal supported solid oxide fuel cells (MS-SOFCs) is achieved via catalyst composition, electrode structure, and processing optimization. The full cell configuration consists of a dense ceramic electrolyte and porous ceramic backbones (electrodes) sandwiched between porous stainless steel metal supports. The conventional YSZ electrolyte and backbones are replaced with more conductive and thinner 10Sc1CeSZ ceramics. MS-SOFCs are co-sintered in a single step and subsequently infiltrated with nanocatalysts. Five categories of cathode catalysts are screened in full cells, including: perovskites, nickelates, praseodymium oxide, binary layered composites, and ternary layered composites. Various anode compositions are also tested. The conventional LSM cathode catalyst is replaced with more active Pr6O11 and the Ni content of the SDC-Ni anode is increased. The resulting cells achieve a peak power of 1.56, 2.0, and 2.85 W cm-2 at 700, 750, and 800 °C, respectively, with 3%H2O/H2 as fuel and 2 cathode exposed to air. Multiple cells show reproducible performance (Pmax=1.50 ± 0.06 W cm-2) and OCV (1.10 ± 0.02 V). The performance is further increased with cathode exposed to pure oxygen (2.0 W cm-2 at 700 °C).

Progress in durability of metal-supported solid oxide fuel cells with infiltrated electrodes

“…In the case of composite cathodes (see section 2.3), up to five infiltrations were implemented. For instance, a ternary composite cathode has three different layers [25], an electronic conductor that provides good electronic conduction at the triple phase boundary (TPB) and was infiltrated first and sintered at 850 ºC, an ionic conductor that provides good ionic conduction and was infiltrated second and sintered at either 600 ºC or 850 ºC, and the bulk catalyst for the oxygen reduction reaction (ORR) which was infiltrated three times and sintered at 600 ºC. XRD measurements on catalyst powders were obtained using a Bruker D2 Phaser powder diffractometer.…”

“…Catalyst performance and durability screening was performed on YSZ-based MS-SOFCs with 12 m YSZ electrolyte thickness [25], praseodymium oxide, (4) binary layered composites, and (5) ternary layer composites. The initial OCV was 1.12 ± 0.03 V (theoretical value is 1.12 in 3% humidified hydrogen), and remained within 2% of the initial value after 100 h of operation at 700 °C and 0.7 V. The overall peak power density and degradation at 700 °C are grouped by cathode family in Table 1.…”

“…Although the intrinsic transport properties of nano-scale ceramics remain to be investigated, the high peak power density in cells with PrO x cathode was attributed to enhanced oxygen ion transport properties [25]. The peak power density and degradation for different cathode catalysts are summarized in Table 1 and Fig 1a. The binary composite cathodes exhibit the highest overall peak power density and the lowest degradation rates, Fig.…”

“…Small passenger vehicles, however, require high power due to limited volume to house the MS-SOFC stack, and immediate response during rapid vehicular acceleration and transient driving conditions, such as intermittent fuel flow and continuous load variation. 3 In our preceding report [25], the cell specification (catalyst precursor chemistry, thickness of each cell layer, cell sintering conditions, backbone porosity, and catalyst firing temperature) was optimized, and YSZ electrolyte was replaced with higher-conductivity and thinner 10Sc1CeSZ (SCSZ).…”

“…Following substantial progress in improving performance [25], in this work we focus on increasing the longevity of MS-SOFCs. The expected lifetime of MS-SOFC stacks in vehicles is ~10,000 h; hence, fabrication of high performing and durable cells is crucial for commercialization of this technology.…”