A simple Ce-doping strategy to enhance stability of hybrid symmetrical electrode for solid oxide fuel cells

Symmetrical solid oxide fuel cell (SSOFC) is a simple and very promising cell for the rest of the most important commercialization process, which has been longing for stable and efficient symmetrical electrodes, from single-phase perovskites to reducible perovskites with in-situ exsolved metal nanoparticles. Herein, we present a new-type hybrid symmetrical electrode consisting of two different perovskite phases for SSOFC, which interact by dynamic compositional change and accordingly improve the electrochemical activity. Furthermore, a simple Ce-doping strategy is successfully developed to solve the redox stability issue of the hybrid symmetrical electrode for SSOFC. Typical Gd_0.65Sr_0.35Co_0.25Fe_0.75O_3-δ (GSCF) consisting of a cubic perovskite phase and an orthorhombic perovskite phase is chosen as a proof-of-concept. Gd_0.65Sr_0.35(Co_0.25Fe_0.75)_0.9Ce_0.1O_3-δ (Ce-GSCF) with an optimized Ce content of only 10% exhibit the enhanced chemical and thermal stability, consisting of a cubic perovskite phase, an orthorhombic perovskite phase and an in-situ exsolved cubic fluorite phase (GDC). More importantly, Ce-GSCF exhibits very high stability in H₂ at 700 °C and a dramatical reduction of averaged thermal expansion coefficient from 19.5 × 10⁻⁶ K⁻¹ to 16.4 × 10⁻⁶ K⁻¹. The single-cell with Ce-GSCF hybrid symmetrical electrode reaches a high maximum power density of 224 mW/cm² at 700 °C, and can work stably for 180 h without any degradation, indicating that the simple Ce-doping strategy is promising to improve stability of hybrid symmetrical electrode for SOFCs.     

Exploring MnCr2O4–Gd0.1Ce0.9O2-δ as a composite electrode material for solid oxide fuel cell

Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr₂O₄–Gd_0.1Ce_0.9O_2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H₂O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y₂O₃ stabilized ZrO₂) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm⁻² at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.     

Efficient symmetrical electrodes based on LaCrO3 via microstructural engineering

Novel nanostructured electrodes, La_0.98Cr_0.75B_0.25O_3δ (B = Mn, Fe, Ti and Cu), are prepared by a single spray-pyrolysis deposition method directly on the electrolyte and a porous Ce_0.9Gd_0.1O_1.95 (CGO) scaffold. These perovskite-type electrodes without alkaline-earth metals exhibit low ionic/electronic conductivity; however, the polarization resistance is greatly enhanced by microstructural design. The best results are obtained for La_0.98Cr_0.75Mn_0.25O_3-δ deposited into a porous CGO-scaffold due to the synergetic effect of CGO, with high ionic conductivity, and doped-LaCrO₃ with a predominantly electronic conductivity. The materials are investigated as both air and fuel electrodes for solid oxide fuel cells (SOFCs) by different structural, microstructural and electrochemical techniques. Low values of polarization resistance are achieved for nanostructured La_0.98Cr_0.75Mn_0.25O_3-δ-CGO electrodes, i.e. 0.057 Ω cm² in air at 800 °C, compared to 0.96 Ω cm² for the same powder electrode obtained by screen-printing deposition. An electrolyte-supported symmetrical cell generates a stable maximum power output of 475 mW cm⁻² at 800 °C.     

Ta-doped PrBaFe2O5+δ double perovskite as a high-performance electrode material for symmetrical solid oxide fuel cells

Symmetrical solid oxide fuel cells (S-SOFCs) have received considerable attention due to fewer preparation steps in recent years. The PrBaFe₂O_5+δ (PBF) is a candidate material due to good catalytic activity and electrochemical stability. In this work, Ta-substituted PBF materials (PrBaFe_2-xTa_xO_5+δ, denoted as PBFTx, x = 0, 0.1, 0.2, 0.3) are prepared and evaluated as symmetrical electrodes on GDC(Gd_0.1Ce_0.9O_2-δ)-YSZ(yttria-stabilized zirconia)-GDC three-layer electrolyte. The PrBaFe_1.8Ta_0.2O_5+δ (PBFT0.2) symmetrical cell presents the lowest polarization resistance, and the value is 0.171 Ω cm² and 0.503 Ω cm² in air and hydrogen atmosphere at 800 °C, respectively. In addition, the PBFT0.2 cell shows a peak power density of 234 mW/cm² using humidified hydrogen as fuel gas and air as oxidant at 800 °C, which is enhanced by 68% compared with that of PBF (138 mW/cm²). The results indicate that the strategy of Ta doping can improve the electrochemical performance of PBF and PBFT0.2 is a potential electrode for S-SOFCs.     

Precursor of Pr2NiO4+δ as a highly effective catalyst for the simultaneous promotion of oxygen reduction and hydrogen oxidation reactions in solid oxide electrochemical devices

The electrochemical behaviour of a Sr₂Fe_1.5Mo_0.5O_6–δ based double-layer electrode decorated with a “symmetric” catalyst by the wet impregnation technique for the simultaneous acceleration of cathodic and anodic reactions was investigated for the first time. As a “symmetric” catalyst, a solution of precursor for the synthesis of praseodymium nickelate (Pr₂NiO_4+δ) was considered. Since the catalyst consists of NiO and Pr₆O₁₁ in an oxidizing atmosphere and of Ni and Pr₂O₃ in a reducing atmosphere, it effectively accelerates the rate of oxygen reduction at the cathode and hydrogen oxidation at the anode of solid oxide fuel cells with symmetric electrodes. It was shown that the rate of oxygen reduction after introduction of the catalyst into the electrode increased due to an increase in the rate of oxygen interfacial exchange between the electrode and the gas phase. The rate of hydrogen oxidation increased due to an increase in the rate of dissociation of adsorbed hydrogen. During tests of the fuel cell with a 300 μm LaGaO₃-based supporting electrolyte and decorated electrodes, a maximum power density of about 0.83 W cm^?2 at 800 °C under wet hydrogen/air condition was obtained.     

Performance of Pd-impregnated Sr1.9FeNb0.9Mo0.1O6-δ double perovskites as symmetrical electrodes for direct hydrocarbon solid oxide fuel cells

Symmetrical solid oxide fuel cell (SSOFC) is one of efficient ways to simplify preparation process, reduce manufacturing cost, and improve redox stability and reliability. Here, we report the performance of Sr-deficient Sr_1.9FeNb_0.9Mo_0.1O_6-δ (SFNM) double perovskites as symmetrical electrodes for direct-hydrocarbon solid oxide fuel cells and significant improvement of electrochemical performance. The SFNM exhibits good structural stability, suitable thermal expansion coefficient and highly chemical compatibility with Sm_0.2Ce_0.8O_1.9 (SDC) and La_0.9Sr_0.1Ga_0.8Mg_0.2O_3–δ (LSGM) electrolytes in both air and 5% H₂/Ar atmospheres. The area specific resistance of SFNM electrode is decreased by 3.6 and 8.4 times at 800 °C in air and H₂, respectively, as compared to the pristine Sr₂FeNbO_6-δ electrode. The electrochemical performance is further improved by introducing a small amount of Pd to form Pd-impregnated SFNM composite electrode (Pd-SFNM). The SSOFCs with Pd-SFNM after two-time impregnation treatments as the electrodes achieve impressive electrochemical performances in different fuels. The Pd-SFNM symmetrical electrode reveals good electrochemical stability operating on CH₄–CO₂ mixed gas.     

对称结构固体氧化物燃料电池研究进展

当采用碳氢化合物作为燃料时，具有同种电极材料的对称固体氧化物燃料电池(Symmetric Solid Oxide Fuel Cell ，SSOFC) 通过阴极和阳极的周期性转换，提高了阳极的抗焦化和抗硫中毒能力。通过对近几年来对称电极的分类和整理，总结了已有对称电极的优缺点。综合分析表明，发现适用于除了La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM)电解质的单相稳定氧化物对称电极或者开发出新的对称电极材料是必要的。