Symmetrical solid oxide fuel cells (SOFCs) operate at high temperatures and consist of a dense electrolyte which is sandwiched between two electrodes. An anode acts as a fuel electrode where fuel is oxidised, while a cathode serves as an air electrode in which oxygen is reduced. However, the use of two different materials as electrodes poses several significant issues concerning durability, reliability and fabrication costs of SOFCs. Furthermore, at least two thermal steps are required for the sintering of both electrodes, thereby increasing energy usage. In overcoming these challenges posed by conventional SOFCs, the concept of symmetrical solid oxide fuel cells (S-SOFCs) has been introduced. S-SOFCs comprise of two identical materials for the anode and cathode. The use of two similar materials decreases the interfacial regions among the electrolyte and electrodes and consequently improves the compatibility among the components. Sulphur poisoning and carbon deposition at the fuel electrode can be solved by merely reversing the flow of oxidant and fuel to oxidise all the species that degrade the performance of SOFCs. Although, the electrode material for S-SOFCs requires some unique properties, such as high electrocatalytic activity for fuel oxidation and oxygen reduction, high electrical conductivity in oxygen and hydrogen/hydrocarbon environments, promising the capability to resist sulphur poisoning and carbon deposition in hydrocarbon fuels and good structural and chemical stability under actual fuel cell conditions. As the works related to S-SOFCs are limited in this respect, this paper reviews the available reports in this field to allow a better understanding of the operational mechanism and the potential of S-SOFCs.

LiCoO 2-based materials are well-known cathode materials used in lithium ion batteries. Moreover, these materials are currently utilized in low-temperature proton-conducting solid oxide fuel cells (SOFCs). Various dopants, such as Mn, Sr, and Zn, are introduced into LiCo 2-based materials to improve their properties and performance for proton-conducting SOFC applications. In this regard, Mn-, Sr-, and Zn-doped LiCoO 2 and LiCo 0.6 X 0.4 O 2 (X = Mn, Sr, or Zn) powders are synthesized via the glycine-nitrate combustion method. Their properties are characterized using different techniques. The precursor cathode powder is dried at 100 C and subjected to thermogravimetric analysis (TGA). The phase formation and morphology of calcined LiCo 0.6 Mn 0.4 O 2 (LCMO), LiCo 0.6 Sr 0.4 O 2 (LCSO), and LiCo 0.6 Zn 0.4 O 2 (LCZO) powders at 600 C to 700 C are examined via X-ray diffraction. At 600 C, both calcined LCSO and LCZO powders show few secondary phases, but these phases greatly decrease as calcination temperature increases to 700 C. By contrast, calcined LCMO powders exhibit a single phase structure at both calcination temperatures of 600 C and 700 C. The measured crystallite sizes of LCMO, LCSO, and LCZO powders are 23.32 ± 0.20, 21.08 ± 0.72, and 21.24 ± 0.32 nm, respectively. TEM images indicate that the particles in LCMO and LCZO powders highly agglomerate compared with those in LCZO powders. This result confirms that LCSO cathodes have the highest electrical conductivity (356.66 S cm −1) and the lowest area specific resistance (0.29 Ω cm 2 in humidified [3%] air) at 700 C. In conclusion, LCSO materials are the best cathodes with high potential for protonconducting SOFC applications.

The sustainable development goals concept towards zero carbon emission, set forth by the Paris Agreement, is the foundation of decarbonisation implemented in most developed countries worldwide. One of the efforts in the decarbonisation of the environment is through hydrogen fuel cell technology. A fuel cell is an energy converter device that produces electricity via the electrochemical reaction, with water as the by-product. The application of fuel cells is strongly related to the economic aspect, including local and infrastructure costs, making it more relevant to be implemented in a developed country. This work presents a short review of the development and progress of hydrogen fuel cells in a developed country such as Japan, Germany, USA, Denmark, and China (in transition between developing to developed status); which championed hydrogen fuel cell technology in their region.

In this study, the effects of different fabrication techniques on the electrochemical performance of solgel derived La 0.6 Sr 0.4 CoO 3-δ (LSC) cathode material for intermediate temperature proton-conducting fuel cells were investigated. Single-phase, sub-micron LSC powder was used to prepare cathode slurries by a simple grinding-stirring (G-S) technique and an advanced ball milling-triple roll milling (BM-TRM) technique. The prepared G-S and BM-TRM cathode slurries were brush painted and screen printed, respectively, onto separate BaCe 0.54 Zr 0.36 Y 0.1 O 2.95 (BCZY) proton-conducting electrolytes to fabricate symmetrical cells of LSC|BCZY|LSC. The thickness of LSC cathode layer prepared by brush painting and screen printing was 17 ± 0.5 µm and 7 ± 0.5 µm, and the surface porosity of the layers was 32% and 27%, respectively. Electrochemical impedance spectroscopy analysis revealed that the layer deposited by screen printing had lower area specific resistance measured at 700°C (0.25 Ω cm 2) than the layer prepared by brush painting of G-S slurry (1.50 Ω cm 2). The enhanced LSC cathode performance of the cell fabricated using BM-TRM assisted with screen printing is attributed to the improved particle homogeneity and network in the prepared slurry and the enhanced particle connectivity in the screen printed film.

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