Comparison of two IT DIR-SOFC models: Impact of variable thermodynamic, physical, and flow properties. Steady-state and dynamic analysis

This paper compares two dynamic, one-dimensional models of a planar anode-supported intermediate temperature (IT) direct internal reforming (DIR) solid oxide fuel cell (SOFC): one where the flow properties (pressure, gas stream densities, heat capacities, thermal conductivities, and viscosity) and gas velocities are taken as constant throughout the system, based on inlet conditions, and one where this assumption is removed to focus on the effect of considering the variation of local flow properties on the prediction of the fuel cell performance. The refined model consists of mass, energy, and momentum balances, and of an electrochemical model that relates the fuel and air gas compositions and temperatures to voltage, current density, and other relevant fuel cell variables. Simulations for steady-state and dynamic conditions have been carried out and the results obtained from the two models compared. For a co-flow SOFC operating on a 10% pre-reformed methane fuel mixture, with 75% fuel utilisation, inlet fuel and air temperatures of 1023 K, average current density of , and an air ratio of 8.5, the results show that, although the error incurred in the prediction of the flow properties in the first model is significant, there is good agreement between both models in terms of the overall cell performance: the maximum difference in the local temperature values is about 7 K and the cell efficiency differs by less than 1%. However, the discrepancies between the two models increase, especially in the fuel channel, when higher current density values are assigned to the cell.     

Novel cobalt-free Pr2Ni1-xNbxO4 (x = 0, 0.05, 0.10, and 0.15) perovskite as the cathode material for IT-SOFC

The cobalt-free cathode materials with high activity is critical to the commercial application of medium temperature solid oxide fuel cells (IT-SOFC). Herein, a series of cobalt-free Nb-doped Pr₂Ni_1-xNb_xO₄ (x = 0, 0.05, 0.10, and 0.15) perovskite oxides were successfully prepared, and the effects of Nb-doping on the structure, thermal stability and electrochemical properties of the cathode material are studied in detail. The Pr₂Ni_1-xNb_xO₄ exhibits a K₂NiF₄ type structure with Fmmm space group. The Nb⁵⁺ cations that doped into Pr₂NiO₄ replaces the Ni site, which increases the surface oxygen content, then effectively eliminates the phase transition of Pr₂NiO₄ and significantly improves the ORR catalytic activity. The Pr₂Ni_0.9Nb_0.1O₄ was found to occupy the lowest polarization resistance of 0.057 Ω cm², and the peak power density of single cells supported by the electrolyte is 0.576 W cm^?2 at 700 °C, which has good long-term stability.     

Effects of Sn doping on the manufacturing,performance and carbon deposition of Ni/ScSZ cells in solid oxide fuel cells

This work demonstrates the effect of tin (Sn) doping on the manufacturing, electrochemical performance, and carbon deposition in dry biogas-fuelled solid oxide fuel cells (SOFCs). Sn doping via blending in technique alters the rheology of tape casting slurry and increases the Ni/ScSZ anode porosity. In contrast to the undoped Ni/ScSZ cells, where open-circuit voltage (OCV) drops in biogas, Sn–Ni/ScSZ SOFC OCV increases by 3%. The maximum power densities in biogas are 0.116, 0.211, 0.263, and 0.314 W/cm² for undoped Ni/ScSZ, undoped Ni/ScSZ with 3 wt% pore former, Sn–Ni/ScSZ and Sn–NiScSZ with 1 wt% pore former, respectively. Sn–Ni/ScSZ reduces the effect of the drop in the maximum power densities by 26%–36% with the fuel switch. A 1.28–2.24-fold higher amount of carbon is detected on the Sn–Ni/ScSZ samples despite the better electrochemical performance, which may reflect an enhanced methane decomposition reaction.     

Electrical characterization of co-precipitated LaBaCo2O5+δ and YBaCo2O5+δ oxides

REBaCo₂O_5+δ layered perovskite oxides (RE = Rare Earth) are promising cathodes for IT-SOFCs. In this work, a simple co-precipitation synthesis in aqueous medium was applied to prepare LaBaCo₂O_5+δ (LBC) and YBaCo₂O_5+δ (YBC) cathodes. The chemical and electrochemical properties of both materials were characterized via XRD, SEM, TPO, TG–DTA, 4-probe conductivity measurement, and EIS tests on symmetric cells. The coprecipitation synthesis revealed a promising preparation route: the measured ASR values of both materials were well comparable with the literature ones. A kinetic investigation of the O₂ reduction process was performed on LBC (600–800 °C, 5–100% O₂, v/v), whose results were analyzed with equivalent circuits. The main steps were identified (oxygen diffusion and charge transfer at high frequency, O₂ chemisorption at medium frequency), and their activation energy and reaction order were quantified. Aging tests (500 h time on stream, 500–800 °C) revealed quick deactivation for YBC and good stability for LBC.     

Ce0.8Sm0.1Gd0.1O1.9电解质的制备及其性能研究

采用共沉淀法合成了Sm、Gd共掺杂CeO2的Ce0.8Sm0.1Gd0.1O1.9（SGC）电解质粉末。研究了工艺条件等对粉末的相组成、结构、颗粒大小的影响。并对SGC烧结体的性能进行了研究。实验结果表明,共沉淀法成功制备出的SGC电解质粉末有良好的烧结性,1 400℃下得到的SGC烧结体的相对密度大于93%。电性能测试表明烧结体在中温范围内具有较高的氧离子电导率。     

Status and prospects of intermediate temperature solid oxide fuel cells

Compared with conventional electric power generation systems, the solid oxide fuel cell （SOFC） has many advantages because of its unique features. High temperature SOFC has been successfully developed to its commercial applications, but it still faces many problems which hamper large-scale commercial applications of SOFC. To reduce the cost of SOFC, intermediate temperature solid oxide fuel cell （IT-SOFC） is presently under rapid development. The status of IT-SOFC was reviewed with emphasis on discussion of their component materials. 2008 University of Science and Technology Beijing. All rights reserved.     

Electrochemical performance of a mechanochemically prepared submicron-sized crystalline Nd1.8Ce0.2CuO4±δ cathode for intermediate temperature solid oxide fuel cells

To produce a Nd_1.8Ce_0.2CuO_4±δ solid solution, the oxide form of the reagents were milled for 36 h and sintered at 1173 K for 8 h in a microwave furnace. The transition from a negative temperature coefficient (NTC) of conductivity to a positive temperature coefficient (PTC) was suppressed due to the submicron size of the crystallites. The low-frequency response in the complex impedance plane fit the Gerischer element. At 973 K, the area specific resistance (ASR) of Nd_1.8Ce_0.2CuO_4±δ/GDC/Nd_1.8Ce_0.2CuO_4±δ sintered at 1073 K for 2 h was 1.92 ohm cm².     

In situ high temperature neutron powder diffraction study of La2Ni0.6Cu0.4O4+δ in air: Correlation with the electrical behaviour

The knowledge of the thermal evolution of the crystal structure of a cathode material across the usual working conditions in solid oxide fuel cells is essential to understand not only its transport properties but also its chemical and mechanical stability in the working environment. In this regard, high-resolution neutron powder diffraction (NPD) measurements have been performed in air from 25 to 900 °C on O₂-treated (350 °C/200 bar) La₂Ni_0.6Cu_0.4O_4+δ. The crystal structure was Rietveld-refined in the tetragonal F4/mmm space group along all the temperature range. The structural data have been correlated with the transport properties of this layered perovskite. The electrical conductivity of O₂-treated La₂Ni_0.6Cu_0.4O_4+δ exhibits a metal (high T)-to-semiconductor (low T) transition as a function of temperature, displaying a maximum value of 110 S cm⁻¹ at around 450 °C. The largest conductivity corresponds, microscopically, to the shortest axial Ni–O2 distance (2.29(1) Å), revealing a major anisotropic component for the electronic transport. We have also performed a durability test at 750 °C for 560 h obtaining a very stable value for the electrical conductivity of 87 S cm⁻¹. The thermal expansion coefficient was 12.8 × 10⁻⁶ K⁻¹ very close to that of the usual SOFC electrolytes. These results exhibit La₂Ni_0.6Cu_0.4O_4+δ as a possible alternative cathode for IT-SOFC.     

Doping of scandia-stabilized zirconia electrolytes for intermediate-temperature solid oxide fuel cell: A review

The shortcomings of high-temperature solid oxide fuel cells necessitate research on SOFCs designs that are capable of operation at intermediate temperatures (600–800 °C), the so-called intermediate-temperature SOFCs. One of the limitations for the efficient operation of these fuel cells lies in insufficient ionic conductivity of the electrolyte material. This review briefly covers the types of ceramic electrolytes used in intermediate-temperature SOFCs and focuses on scandia-stabilized zirconia (ScSZ) electrolytes. It explores possibilities of control of phase stability and ionic conductivity of ScSZ by co-doping by various oxides, such as ceria, bismuth oxide, yttria, ytterbia, and several other co-dopants. It also covers a range of novel techniques applied to preparation of ScSZ electrolytes, which can be used to influence microstructure and phase composition of the electrolytes. The recommendations on the optimal ScSZ co-doping scheme are developed in the course of the present work.