La_0.8Ca_1.2Fe_0.9Co_0.1O_4-δ (LCFC) perovskite oxides were prepared by using sol-gel method. Symmetrical solid oxide cells LCFC|GDC|YSZ|GDC|LCFC were assembled by using Y_0.15Zr_0.88O_2-δ (YSZ) as the electrolyte, while LCFC was simultaneously used as the fuelelectrode and airelectrode and Gd_0.1Ce_0.9O_2-δ (GDC) as a barrier to prevent the reaction between the electrode material and electrolyte. Phase structure and chemical stability of the LCFC material were studied by using X-ray diffraction method, high temperature electrical conductivity of the material was measured by using the four-probe method, and the thermal expansion coefficient of the material was also characterized. Electrochemical performance and stability of the symmetrical cell in fuel cell mode (SOFC) and electrolytic cell mode (SOEC) were evaluated, while the microstructure of the cell after testing was observed by scanning electron microscope. In SOFC mode, the maximum power density can reach 0.11 W·cm^-2 at 850 ℃ with wet H₂ as fuel and the electrolysis current density of pure CO₂ electrolysis can reach 0.75 A·cm^-2 at 850 ℃ and 2 V. Meanwhile, the cell has strong structural stability. Therefore, LCFC is a promising symmetrical cell electrode material.

CH₄ concentration of underground drainage coal mine methane is rather low, which is of the explosion risk and difficult to be used. Therefore, a safe and high-efficiency power generation method of low concentration coal mine methane (LC-CMM) was proposed based on the solid oxide fuel cell (SOFC). The deoxygenation and methane enrichment experiment based on the pressure swing adsorption (PSA) was conducted to eliminate the explosion risk of LC-CMM, the large-scale SOFC single cell experiment using the LC-CMM was carried out, and the multi-physics coupling model of SOFC was developed. The results show that the CH₄ concentration can be increased by 1.36 times, the deoxygenation ratio can reach 84.5% through the PSA experiment, and the produced gas can meet the requirement of safe and efficient power generation of SOFC. The power density of large-scale single cell using LC-CMM can reach 110.2 mW/cm², but the anodic carbon deposition occurs after the long-term discharging, thus causing the SOFC performance degradation. The results of numerical simulation show that the decrease of discharging voltage, the increase of volume ratio between O₂ and CH₄ of fuel and the decrease of fuel inlet rate can decrease the carbon deposition, but reducing the power generation performance of SOFC.

Joule-heating reactors have the higher energy efficiency and product selectivity compared with the reactors based on radiative heating. Current Joule-heating reactors are constructed with electrically-conductive metals or carbon materials, and therefore suffer from stability issue due to the presence of corrosive or oxidizing gases during high-temperature reactions. In this study, chemically-stable and electrically-conductive (La_0.80Sr_0.20)_0.95FeO₃ (LSF)/Gd_0.1Ce_0.9O₂ (GDC) ceramics have been used to construct Joule-heating reactors for the first time. Taking the advantage of the resistance decrease of the ceramic reactors with temperature increase, the ceramic reactors heated under current control mode achieved the automatic adjustment of heating to stabilize reactor temperatures. In addition, the electrical resistance of LSF/GDC reactors can be tuned by the content of the high-conductive LSF in composite ceramics and ceramic density via sintering temperature, which offers flexibility to control reactor temperatures. The ceramic reactors with dendritic channels (less than 100 µm in diameter) showed the catalytic activity for CO oxidation, which was further improved by coating efficient MnO₂ nanocatalyst on reactor channel wall. The Joule-heating ceramic reactors achieved complete CO oxidation at a low temperature of 165 ℃. Therefore, robust ceramic reactors have successfully demonstrated effective Joule heating for CO oxidation, which are potentially applied in other high-temperature catalytic reactions.

High-entropy double perovskite SmBa(Mn_0.2Fe_0.2Co_0.2Ni_0.2Cu_0.2)₂O_5+δ(HE-SBC) as a cathode material was prepared by a modified Pechini method, and the performance of HE-SBC with 10% (in mole fraction) Gd₂O₃-doped CeO₂ (GDC) (HE-SBC-GDC) was optimized. The results show that the thermal expansion of Co ions caused by the change of valence state can be reduced due to the formation of high-entropy at B-site, thereby reducing the thermal expansion coefficient of SBC. The polarization impedance (R_p) of the HE-SBC symmetrical cell with yttria-stabilized zirconia (YSZ) as an electrolyte is 1.04 Ω·cm² at 800 ℃ and the maximum power density and R_p of the anode-supported single cell are 683.53 m W/cm² and 0.46 Ω·cm², respectively. Furthermore, the catalytic activity of HE-SBC is improved by the addition of GDC[m(HE-SBC):m(GDC)=7:3] due to the enlarged three-phase interface. The polarization resistance of HE-SBC-GDC composite cathode symmetric cell is only 0.09 Ω·cm² at 800 ℃ and the maximum power density and R_p of the anode-supported single cell are 838.66 m W/cm² and 0.12 Ω·cm², respectively.

New two-layer Ruddlesden-Popper (RP) oxide La_0.25Sr_2.75FeNiO_7-δ (LSFN) in the combination of Sr₃Fe₂O_7-δ and La₃Ni₂O_7-δ was successfully synthesized and studied as the potential active single-phase and composite cathode for protonic ceramics fuel cells (PCFCs). LSFN with the tetragonal symmetrical structure (I4/mmm) is confirmed, and the co-existence of Fe³⁺/Fe⁴⁺ and Ni³⁺/Ni²⁺ couples is demonstrated by X-ray photoelectron spectrometer (XPS) analysis. The LSFN conductivity is apparently enhanced after Ni doping in Fe-site, and nearly three times those of Sr₃Fe₂O_7-δ, which is directly related to the carrier concentration and conductor mechanism. Importantly, anode supported PCFCs using LSFN-BaZr_0.1Ce_0.7Y_0.2O_3-δ (LSFN-BZCY) composite cathode achieved high power density (426 mW·cm^-2 at 650 ℃) and low electrode interface polarization resistance (0.26 Ω·cm²). Besides, distribution of relaxation time (DRT) function technology was further used to analyse the electrode polarization processes. The observed three peaks (P1, P2, and P3) separated by DRT shifted to the high frequency region with the decreasing temperature, suggesting that the charge transfer at the electrode-electrolyte interfaces becomes more difficult at reduced temperatures. Preliminary results demonstrate that new two-layer RP phase LSFN can be a promising cathode candidate for PCFCs.