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| Electrolyte material characteristics | Limitations and alternatives |
| Bismuth oxide (δ-Bi2O3) electrolytes with fluorite structure operate in the intermediate temperature range remaining stable within 730°C-804°C with the highest conductivity at 804°C [39] | Reduces to bismuth at the anode, and mechanical strength is low. Doped Bi2O3 combined with ceria electrolyte or doping with ZrO2the decomposition can be prevented [40] |
| Crystalline-structured perovskite material lanthanum gallate (LaGaO3) is chemically stable with high ionic conductivity at a low-temperature range. When doped with strontium and magnesium to form LSGM, it demonstrates better conductivity and stability having similar thermal expansion coefficient as YSZ [40] | Gallium is reactive to nickel oxides contained in the NiO-LSGM-based anodes and has poor mechanical strength [39] |
| Yttria addition to zirconia to form YSZ has enhanced conductivity. Reacts with electrodes made from lanthanum-based perovskite oxide electrodes at high temperatures. Codoping alumina increases the mechanical property of YSZ. Scandia-doped zirconia has better conductivity compared to YSZ at lower temperatures but is scarce and expensive [41] | Aging of both YSZ and ScSz occurs during operational life. Increasing the percentage of Scandia and codoping indium oxide in ScSz mitigates the aging rate [42, 43] |
| Ceramic material ceria with fluorite structure has been doped with rare earth elements for better conductivity and compatibility at low temperatures | However, cell voltage drops under a reducing environment. Samarium-doped ceria (CSO) and gadolinium-doped ceria (CGO) exhibit better ionic conductivity at intermediate temperatures [39] |
Yttrium-doped BaZrO3 [44, 45] and samarium-doped BaCeO3 [46] are proton-conducting compounds that can be a suitable alternative to SOFC-conducting protons due to their high conductivity, power density, and carbon tolerance.
For temperatures as low as 400°C, SDC carbonate can effectively transfer ions and protons which can be used for low-temperature range operation of SOFCs | — |
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| Cathode material characteristics | Limitations and alternatives |
| Lanthanum strontium manganite (LSM) is a perovskite material for anode appropriate in high-temperature applications for its highly conductive and electrochemically active feature [47, 48] | Low temperatures lower the LSM performance while it is reactive towards yttria-stabilized zirconia at high temperatures. LSM can be covered with ceria doped with gadolinium (GDC) for high-temperature performance [49] |
| La0.58 Sr0.4 Fe0.8Co0.2 O3 (LSFC) perovskite material has good ionic conductivity | Chemically unstable with YSZ electrolyte. Infusing LNF and MgO into GDC-coated LSFC increases chemical stability and electrochemical performance [50] |
| SmBaCo2-xNixO5+δ(SBCNx) [51] and LBSCO-40GDC (LaBa0.5Sr0.5Co2 O5+δ) [52] are cobalt-based perovskite material suitable for cathode materials at intermediate temperatures | Cobalt has a high thermal coefficient and is expensive due to which these cobalt-based materials are incompatible with SOFC parts. NdBa0.5Sr0.5Cu2 O5+δ(NBSCO) [53] and NdBaFe2-xMnx O5+δ [54] are perovskite material free of cobalt element suitable for intermediate temperature SOFC operations |
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| Anode material characteristics | Limitations and alternatives |
| Nickel material is a cheap and efficient electricity conductor. Combing with YSZ cermet to form Ni-YSZ ceramite acts as an excellent anode material for high-temperature applications | However, sulfur poisoning and coking when exposed to hydrocarbon are drawbacks for nickel-based materials. Alumina can also be added in appropriate proportions to improve stability, flexural strength and conductivity, and coking resistance [55]. The addition of silver also enhances conductivity and power density along with a reduction in carbon accumulation [56]. |
| Ceria can absorb sulfur, and Ni-SDC formed by doping nickel samaria with ceria can mitigate the impact of sulfur poisoning [57, 58] | For intermediate SOFC operation, mixing CaO and Cu to Ni-SDC further improves cell performance [59, 60] |
| Ti is chemically stable when exposed to a reducing environment. Nd0.5Sr0.5Ti0.5Mn0.5O3±d (NSTM) and SSTM are perovskite materials with enhanced conductivity at high temperatures suitable for high-range SOFC operations [61, 62]. Double perovskite material Sr2FeNb0.2Mo0.8O6-d (SFNM20) Pr0.5Ba0.5MnO3-d (PBMO3) and PrBaMn2O5þd (PBMO5) are some other nickel-free promising materials [63–65] | |
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