Oxidation behavior of porous P434L ferritic stainless steel, used for the fabrication of metal-supported solid oxide fuel cells (MS-SOFC), is studied under anodic and cathodic atmospheres. Temperature- and atmosphere-dependence is determined for as-sintered and pre-oxidized stainless steel. Pre-oxidation reduced the long-term oxidation rate. For pre-oxidized samples, the oxidation rate in air exceeds that in humid hydrogen for temperatures above 700 °C. The influence of PrOx, LSCF-SDC, and Ni-SDC coatings is also examined. The coatings do not dramatically impact oxide scale growth. Oxidation in C-free and C-containing anodic atmospheres is similar. Addition of CO2, CH4, and CO to humidified hydrogen to simulate ethanol reformate does not significantly impact oxidation behavior. Cr transpiration in humid air is greatly reduced by the PrOx coating, and a PrCrO3 reaction product is observed throughout the porous structure. A dense and protective chromia-based scale forms on steel samples during oxidation in all conditions. A thin silica enriched oxide layer also forms at the metal-scale interface. In general, the oxidation behavior at 700 °C is found to be acceptable.

High-entropy alloy (HEA) anode and reforming catalyst, supported on gadolinium-doped ceria (GDC), have been synthesized and evaluated for the steam reforming of methane under SOFC operating conditions using a conventional fixed-bed catalytic reactor. As-synthesized HEA catalysts were subjected to various characterization techniques including N2 adsorption/desorption analysis, SEM, XRD, TPR, TPO and TPD. The catalytic performance was evaluated in a quartz tube reactor over a temperature range of 700–800 °C, pressure of 1 atm, gas hourly space velocity (GHSV) of 45,000 h−1 and steam-to-carbon (S/C) ratio of 2. The conversion and H2 yield were calculated and compared. HEA/GDC exhibited a lower conversion rate than those of Ni/YSZ and Ni/GDC at 700 °C, but showed superior stability without any sign of carbon deposition unlike Ni base catalyst. HEA/GDC was further evaluated as an anode in a SOFC test, which showed high electrochemical stability with a comparable current density obtained on Ni electrode. The SOFC reported low and stable electrode polarization. Post-test analysis of the cell showed the absence of carbon at and within the electrode. It is suggested that HEA/GDC exhibits inherent robustness, good carbon tolerance and stable catalytic activity,‘ which makes it a potential anode candidate for direct utilization of hydrocarbon fuels in SOFC applications.

Proton-conducting solid oxide electrolyzers (H-SOEs) provide promising opportunity to produce pure and dry hydrogen in steam electrolysis at relatively low operating temperatures (550-700˚C) utilizing electricity and heat generated from renewable energy sources. Compared to traditional high temperature (750-1000˚C) oxygen-conducting solid oxide electrolyzers (O-SOEs), lower operating temperature of H-SOE offers ease of thermal management, active stack and BOP materials cost reduction and reduction in chromium evaporation from metallic components. Like O-SOEs, preserving the long-term stability of H-SOEs is one of the technical challenges for large-scale hydrogen production. In this technical contribution, results of experimental evaluation of H-SOEs under real-world operating conditions are presented. As fabricated and posttest cells have been characterized using operando electrochemical impedance spectroscopy, X-ray diffraction, focused ion beam-transmission electron microscopy and other bulk and surface characterization techniques to examine bulk, surface and interface stability of electrochemically active components. Phase and morphological changes, compositional uniformity and interfacial reaction products formation have been examined. Electrolyte/electrode materials stability, cell and gas seal fabrication processes, and gaseous impurities affecting long-term electrochemical performance will be discussed. H-SOE electrochemical performance model based on cell materials and operating conditions has been proposed and validated based on single cell testing data.

Mixed transition-metal oxide coatings are commonly applied to stainless steel interconnects for solid oxide cell stacks. Such coatings reduce oxidation and Cr evaporation rates, leading to improved degradation rate and stack lifetime. Here, the ChromLok™ MCO-based composition (Mn,Co)3O4 is applied to Crofer 22 APU stainless steel and evaluated specifically for application in solid oxide electrolyzer stacks operating around 800 °C and utilizing oxygen-ion-conducting solid oxide cells. The MCO coating is found to decrease the stainless steel oxidation rate by about one order of magnitude, and decrease the Cr evaporation rate by fourfold. The coating also dramatically lowers the rate of area-specific resistance increase for stainless steel coupons oxidized for 500 h with constant current applied, from 33 mΩ∗cm2 kh−1 for an uncoated coupon to less than 4 mΩ∗cm2 kh−1 for coated coupons. The coating is demonstrated on full-scale interconnects for single-cells, where the coating dramatically reduces degradation rate, and for a stack, which displays stable operation for 700 h.