Fuel Cells最新文献

In this work, we present a case where electrochemical impedance spectroscopy (EIS) on stack level enabled the identification of degradation and failure mechanisms in a 75-cell solid oxide electrolysis cell (SOEC) stack from Topsoe. In a blind test, a defective stack (stack not passing the quality control specifications) prone to degradation was investigated with EIS. The type of stack defects was not known a priori. The purpose of the stack EIS experiment was hence to serve as a proof-of-concept of using EIS on the stack level for identifying degradation mechanisms. An appropriate equivalent circuit model was applied and fitted to the experimentally obtained EIS data, which enabled the quantification of the different electrochemical contributions. We hereby identified which electrochemical contribution(s) to the overall stack resistance caused the stack to degrade. Furthermore, the data was plotted in a degradation space format, which further strengthened the identification of the cause of degradation. In this work, we are exploring and utilizing the potential of advanced EIS characterization and analysis; thereby successfully identifying some of the degradation and failure mechanisms taking place in the SOEC stack. This detailed type of degradation analysis has, to the best of my knowledge, not previously reported on the commercial stack level.

Mixed ionic electronic conductors (MIECs) oxides are used as electrode materials for solid oxide cell (SOC) application, as they combine high electronic conductivity as well as high oxygen diffusivity and oxygen surface exchange coefficients. The ionic transport properties can be directly determined thanks to the isotopic exchange depth profiling (IEDP) method. To date, the reported measurements have been performed at ambient pressure and below. However, for a higher efficiency of hydrogen production at the system level, it is envisaged to operate the cell between 10 and 60 bar. To characterize the MIEC oxides properties in such conditions, an innovative setup able to operate up to a total pressure of 50 bar and 900°C has been developed. The main goal of this study was to compare the behavior of two types of reference materials: the oxygen deficient La-Sr-Fe-Co perovskites, and the overstoichiometric lanthanide nickelates Ln₂NiO_4+δ (Ln = La, Pr, Nd). Diffusion and surface exchange coefficients obtained under 6.3 bar of oxygen are measured and their evolution discussed in light of the change in oxygen stoichiometries. This analysis allows better understanding of the dependency of the surface exchange coefficient with the oxygen partial pressure.

In this work, fundamental material properties of compounds in the system (La,Pr)₂(Ni,Co)O_4+δ as well as their performance as air electrodes in solid oxide electrolysis cells were investigated. Nickelates co-doped with Pr and Co were characterized on a material basis by means of X-ray diffraction and thermogravimetry. Conductivity and conductivity relaxation measurements were performed in order to obtain the electronic conductivity as well as the chemical surface exchange coefficient and the chemical diffusion coefficient of oxygen as a function of temperature and oxygen partial pressure. These parameters can be regarded as the most essential properties at the material level required to assess the suitability of mixed ionic-electronic conducting ceramics for application as air electrode in solid oxide cells. The electrode performance of the materials was then tested on fuel electrode-supported button cells at 800°C. The electrodes were applied by screen-printing and the effect of varying the Pr-content and Co-content of the electrode powder was investigated. Cell tests were performed by means of current-voltage measurements in electrolysis mode. While no significant impact of Pr-doping on the investigated material properties was observed, the electrode performance of Pr-containing materials was significantly better than for the Pr-free compound, which has been discussed in detail.

Different materials have been applied as anode in solid oxide fuel cell (SOFC). Perovskite structured materials are promising as an alternative electrode material to Ni. Here, we investigated perovskite-structured mixed ionic and electronic conducting material, lanthanum strontium ferrite (LSF), which has typically been used as a cathode material. LSF has also shown potential for an anode in SOFC. LSF films with two different compositions, La_0.6Sr_0.4FeO₃ (6LSF) and La_0.8Sr_0.2FeO₃ (8LSF) were fabricated by a polymeric precursor method. The effects of the phase content, surface chemistry, and microstructure on the anode performance were investigated. It was found that a mixture of the Ruddlesden–Popper phase, SrCO₃ phases, and rhombohedral perovskite exists in both cell structures. Both cells had Ruddlesden–Popper and SrCO₃ phases at their surface, in addition to the rhombohedral perovskite. Symmetrical half-cell measurements showed that the polarization resistance of 6LSF (0.34 Ω cm²) is lower than that of 8LSF (0.47 Ω cm²), mostly because of its highly porous microstructure as a result of slower A-site diffusion rates induced by higher Sr content.

The symmetrical 6LSF fuel and air electrodes exhibited ASR_electrode values of 0.34 and 0.14 Ω cm², respectively, at 800 ˚C.

A multiscale model has been used to optimize the microstructure of a classical hydrogen electrode made of nickel and yttria-stabilized zirconia (Ni-8YSZ). For this purpose, a 3D reconstruction of a reference electrode has been obtained by X-ray nano-holotomography. Then, a large dataset of synthetic microstructures has been generated around this reference with the truncated Gaussian random field method, varying the ratio Ni/8YSZ and the Ni particle size. All the synthetic microstructures have been introduced in a multiscale modeling approach to analyze the impact of the microstructure on the electrode and cell responses. The local electrode polarization resistance in the hydrogen electrode, as well as the complete cell impedance spectra, have been computed for the different microstructures. A significant performance improvement was found when decreasing the Ni particle size distribution. Moreover, an optimum has been identified in terms of electrode composition allowing the minimization of the cell polarization resistance. The same methodology has been also applied to assess the relevance of graded electrodes. All these results allow a better understanding of the precise role of microstructure on cell performances and provide useful guidance for cell manufacturing.

Strontium segregation (coupled to phase decomposition and impurity poisoning) and electrode delamination are two of the most important degradation mechanisms currently limiting the long-term stability of solid oxide fuel cell and electrolysis cell (SOFC and SOEC) air electrodes. The present study aims to demonstrate that air electrodes made of entropy-stabilized multi-component oxides can mitigate these degradation mechanisms while providing excellent cell performance. A SOEC utilizing La_0.2Pr_0.2Nd_0.2Sm_0.2Sr_0.2CoO_3-δ (LPNSSC) as an air electrode delivers −1.56 A/cm² at 1.2 V at 800°C. This performance exceeds that of a commercial cell with La_0.6Sr_0.4CoO_3-δ (LSC) air electrode, which reaches −1.43 A/cm². In a long-term electrolysis test, the LPNSSC cell shows stable performance during 700 h, while the LSC cell degrades continuously. Post-mortem analyses by scanning electron microscopy-energy dispersive X-ray spectroscopy indicate complete delamination of the LSC electrode, while LPNSSC shows excellent adhesion. The amount of secondary phases formed (esp. SrSO₄) is also much lower in LPNSSC compared to LSC. In conclusion, the high-entropy perovskite LPNSSC is a promising option for air electrodes of solid oxide cells. While LPNSSC can compete with ‒ or even outperform ‒ LSC air electrodes in terms of electrochemical performance, it could be particularly advantageous in terms of long-term stability in SOEC mode.