Fig. 1 Carbonate fuel cell construction: low-cost stainless steel iron-base alloys are used for cell hardware construction

Fig. 2 DFC baseline cell hardware. CCC cathode current collector, BP bipolar plate, ACC anode current collector: >5-year (40,000 h) durability demonstrated

Fig. 3 Advanced surface protective coating demonstrated significantly improved hot corrosion resistance (in ~5700-h stack test). Coating approach can project >10-year service life

Fig. 4 DFC field stack operated for >5 years showing the formation of σ phase accelerated by temperature

Fig. 5 DFC field stack operated for >5 years showing the formation of σ phase accelerated by cold work

Fig. 6 σ-phase precipitation in a finer-grain and b coarser-grain austenitic stainless steel heat treated at 750 °C for 1700 h, c creep strength improvement with coarser-grain structure

Fig. 7 Aluminized coating demonstrating excellent wet seal protection in >5-year field service

Fig. 8 High-Cr stainless steel demonstrating excellent corrosion stability as gas manifold in field stack operated for >5 years. According to this corrosion rate (13 μm/year), more than 20-year service life can be projected

Fig. 9 Faster corrosion of medium-Cr stainless steel bellow a under fuel exit stream, whereas little corrosion of double-wall bellow b under oxidant exhaust stream, both after >5-year field service. Based on the corrosion rate shown in the figure, >10-year durability can be projected

Fig. 10 a Baseline vessel lining material showing significant oxide spallation in 15,000-h operation, b higher-Cr alloy reducing spallation significantly, c low-cost Al-coated ferritic alloy also reducing spallation significantly

Fig. 11 Stress corrosion cracking was observed on sensitized and embrittled stainless steel (in 14,500-h field service): reduction in stress and moisture condensation can eliminate such SCC fracture