Sr_2−xGd_xFe_1.5Mo_0.5O_6−δ (x=0, 0.1, 0.2, 0.3, 0.4) (SG_xFM) powders as anode of solid oxide fuel cell (SOFC) were synthesized by using a sol-gel method. Electrolyte supported SOFC single cell was assembled. XRD, XPS, SEM, TGA and electrochemical test were used to characterize the samples. The anode materials exhibited single phase double perovskite structure. With increasing concentration of Gd³⁺, the XRD diffraction peak shifted, which indicated that Gd³⁺ has well incorporated into Sr₂Fe_1.5Mo_0.5O_6−δ. SG_0.1FM had higher Fe²⁺/Fe³⁺ and Mo⁵⁺/Mo⁶⁺ ratios. According to TGA results, SG_0.1FM showed the highest oxygen loss, indicating that it has the highest concentration of oxygen vacancy. The electrode material presented a loose and porous microstructure, while the electrolyte was dense. The cell was tested at 550–800 ℃, with H₂ as fuel and static air as oxidant. At 800 ℃, the anode had a polarization impedance of 0.021 Ω·cm², while the maximum power density reached 264 mW·cm⁻². Therefore, Gd³⁺ ion doping can improve the performances of SFM.

Sr₂Fe_1.5−xMn_xMo_0.5O_6−δ (x = 0, 0.1, 0.2, 0.3, 0.4) (SFM_xM) anode materials were prepared by using a sol-gel method. The samples were characterized by using XRD, SEM, electrochemical test and other methods, in order to screen out anode materials with high catalytic activity and high electrical conductivity. XRD results revealed that the samples are all of double perovskite structure without the presence of secondary phases. With increasing doping content of Mn, the XRD diffraction peaks were split, indicating the occurrence of cubic to tetragonal perovskite phase transition. SEM observation showed that the GDC electrolyte is compact and both the anode and cathode are of three-dimensional porous structure. Using H₂ as fuel and static air as oxidant, the single cell performance was tested in the temperature range of 550‒800 ℃. The performance is optimized at the Mn doping concentration of x = 0.2. The polarization impedance of the anode is 0.015 Ω·cm² at 800 ℃ and the maximum power density of the cell reaches 192 mW·cm⁻². Therefore, b-site doping is an effective way to improve the performance of SFM materials. Specifically, SFM0.2M is a potential candidate of SOFC anode.

Solid oxide cells (SOCs) are promising energy conversion technology for carbon-neutral direction. Although impressive progress has been made in developing mixed ionic and electronic conductor (MIEC) composite electrodes and perovskite fuel electrodes, Ni-YSZ is the best option for commercial application, because of its excellent catalytic effect for both hydrogen oxidation reaction (HOR) in SOFC and hydrogen evolution reaction (HER) in SOEC. However, the degradation of Ni-YSZ electrodes is still an important issue restricting the development of SOCs. Ni-YSZ electrode materials are briefly introduced and the typical phenomena related to Ni-YSZ electrode degradation in SOFC and SOEC are summarized. Also, the reason of degradation of the Ni-YSZ electrode is examined, based on which improvement strategies are proposed. Finally, an outlook on the optimization for the long-term stability of Ni-YSZ electrodes is presented.

La_0.75Sr_0.25Cr_0.5Mn_0.5O_3−δ (LSCM) is an attractive candidate for perovskite-type anode of SOFC, in which hydrocarbon can be used directly as fuel. However, the poor electrochemical performance limits its practical applications. LSCM nanorods with aspect ratios of 20–40 were prepared by using a sol-gel method combined with electrostatic spinning process, which were subsequently used to form LSCM-GDC composite anode, in order to optimize microstructure and improve performance of the electrode. It was found that the LSCM nanorods tended to be single perovskite phase, as compared with the LSCM powders prepared by sol-gel method. Also, LSCM nanorods showed stronger resistance to agglomeration during the sintering process. By using LSCM nanorods, the porosity of the anode of LSCM-GDCǁYSZǁLSM-YSZ button cells was 50% higher than that of the one made of LSCM powder. The button cells were tested using 97%H₂+3%H₂O as fuel at 850 ℃, with maximum power density of 195.1 mW·cm⁻² and polarization impedance of 0.31 Ω·cm². In comparison, the values were 174.4 mW·cm⁻² and 0.31 Ω·cm² for the anode of LSCM powder.

The relationship between the thickness and electrochemical performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ-Gd_0.1Ce_0.9O_1.95 oxygen electrode was studied by using a symmetrical oxygen electrode cell. Electrochemical impedance spectroscopies of the oxygen electrode with thicknesses of 5–22 μm were measured at various open-circuit voltages. The electrochemical impedance spectra and cyclic voltammetry curves of the fuel supported button cells with oxygen electrodes of different thicknesses were also tested. It is found that the total polarization impedance (R_p) changes with thickness change of the oxygen electrode. The total polarization impedance is derived from oxygen ion transfer, oxygen surface exchange and oxygen diffusion. By analyzing the impedances of different processes, it can be found that the high frequency oxygen ion transport process has a weak dependence on the oxygen electrode thickness. The surface exchange and diffusion of oxygen are strongly dependent on thickness of the oxygen electrode. The electrochemical performance of the oxygen electrode can be improved by optimizing the thickness. The lowest value of resistance is reached at 12 μm, which is 0.034 Ω·cm² at 750 ℃. Accordingly, the maximum power density of the fuel electrode supported button cell (NiO-YSZ||YSZ||20GDC||LSCF-10GDC) is 1098 mW·cm^-2, with 3 vol.% H₂O + 97 vol.% H₂ as fuel and static air as oxidant at 800 ℃. Because the optimal thickness of the oxygen electrode obtained is only about half of the thickness of the currently similar oxygen electrode, the concept of “thin film oxygen electrode” was proposed for possible commercialization.

Lowering the working temperature of solid oxide fuel cells is an inevitable trend for their commercialization. The increase in polarization resistance of cathode caused at reduced temperature is the key problem that should be solved urgently. In the application of composite cathode, CeO₂-based materials have two roles as “electrolyte” and “cathode”, which can not only increase the conductivity of oxygen ions, extend the three-phase interface, adjust the thermal expansion coefficient of cathode, but also accelerate the cathodic oxygen reduction reaction as a synergistic catalyst. The research progress of CeO₂-based materials in promoting cathodic oxygen reduction reaction is reviewed, in which their synergistic catalytic mechanism is analyzed and the design and development of cathode materials for low-temperature solid oxide fuel cells are discussed.

The development and preparation of high-performance electrolyte materials will promote the commercialization of proton conductor solid oxide fuel cell (PCFC). BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3-δ (BZCYYb) is a promising PCFC electrolyte material, which has sufficient chemical stability and high ionic conductivity in low and intermediate temperature range (400–700 ℃). However, the low sintering activity of BZCYYb hinders its application in PCFC. BZCYYb powder was synthesized by using an improved Pechini method, with inorganic salt Li₂CO₃ as the sintering aid, which was introduced using a mechanical ball milling mixing process. The addition of Li₂CO₃ significantly promoted densification process of the electrolyte, without changing the crystalline structure and phase composition of BZCYYb. After adding 8 mol%Li₂CO₃ and sintering at 1350 ℃ for 3 h, the sample exhibited relative density and linear shrinkage of 95.37% and 17.90%, respectively. The sample with 8 mol% Li₂CO₃ had the highest conductivity in wet hydrogen gas, reaching 1.922×10^-2 S·cm^-1 at 700 ℃, while the BZCYYb sample sintered at 1450 ℃ for 5 h had a conductivity of 1.493×10^-2 S·cm^-1. The introduction of an appropriate amount of Li₂CO₃ can significantly reduce the sintering temperature of BZCYYb, with desirable increment in the conductivity.

Reversible solid oxide cells (RSOCs) could be alternately operated in SOFC/SOEC mode, which could realize sustainable cycle of clean energy and electric energy, thus realizing “peak shifting and valley filling”. Because of the advantages of high efficiency and long-time/large-scale energy storage etc., RSOCs have broad application prospects in the construction of Energy Internet. Conventional Ni-YSZ fuel electrode materials are prone to sulfur poisoning when using fuel gases containing sulfur impurities and carbon accumulation, such as hydrocarbon fuels. Strontium titanate (SrTiO₃) perovskite has been the most widely studied RSOCs fuel electrode material, due to its highly adjustable structure and properties, high structural stability and thermochemical stability, and strong anti-carbon accumulation and anti-sulfur poisoning ability.Research progress of SrTiO₃-based RSOCs fuel electrodes are reviewed, while the related mechanisms are described. The challenges of SrTiO₃-based fuel electrode in the future application of RSOCs are discussed.

Owing to adjustable thermal expansion performance, BaO–CaO–Al₂O₃–B₂O₃–SiO₂ (BCABS) glass has a promising commercialization prospect for intermediate temperature-solid oxide fuel cells (IT-SOFCs) sealing. Herein, Al₂O₃ with two different contents was added into the same glass formulation, referred to as A and B glass, respectively. In terms of the non-isothermal crystallization kinetic behavior, the effect of Al₂O₃ as the unique intermediate was innovatively studied on the long-term performance of BCABS sealing glass. After the heat treatment at 1023 K for 100 h, the change of the network structure and the expansion coefficient of the glass were characterized. The results showed that the addition of Al₂O₃ as a network forming body could enhance the structure of glass, and increase the activation energy for glass transition, which could effectively inhibit the crystallization ability of sealing glass. Therefore, the B glass with the higher Al₂O₃ content showed the better long-term sealing ability, which was greatly beneficial for IT-SOFCs sealing.