A corrugated mesoscale structure on electrode–electrolyte interface for enhancing cell performance in anode-supported SOFC

Microtubular anode-supported solid oxide fuel cells (μt-SOFC) were created with a metallic coil embedded in the anode to act as current collector. The electrochemical performance was experimentally examined by comparing the power density (PD) of μt-SOFC with embedded coils of different turns per unit length and composition (nickel and palladium). It is shown that an increase in the turns per unit length results in a proportional current density increase and in a quadratic increment of PD. Additional performance improvement is found for the cell with palladium current collector due to the higher catalytic activity for hydrogen oxidation.

Enhancing the power of lithium ion batteries necessitates an understanding of the molecular processes governing Li+ ion transfer across the electrode–electrolyte interface. Here, employing enhanced sampling molecular dynamics simulations, we investigated the driving force and thermodynamic barrier of Li+ ion adsorption onto Li0.5CoO2 (104) electrode in LiClO4-, LiPF6-, and LiTFSI-based EC/EMC (3:7) electrolytes. The weaker cation–anion pairing in LiTFSI compared to LiClO4 was found to enhance the driving force for adsorption from −0.48 eV in LiClO4 to −1.26 eV in LiTFSI for an electrode–electrolyte interface with zero cation coverage, which was accompanied by an increased thermodynamic barrier from 0.33 eV in LiClO4 to 0.43 eV in LiTFSI at an equilibrium surface coverage of Li+ ions. The hindered diffusivity of the solvent molecules in the electric double layer (EDL) at the electrode–electrolyte interface was the main contributor to the thermodynamic barrier for ion transport. The entropic component of the thermodynamic barrier was found to be more than 1 order of magnitude smaller for ClO4– compared to TFSI–, which can be attributed to the presence of more ClO4– than TFSI– in the EDL, causing more structural changes in the EDL. The strong dependence of the entropic component of the thermodynamic barrier on the EDL structure enables its decoupling from the enthalpic components (e.g., ion-pairing that can be tuned independently) and thus can be used to control the kinetics of the interfacial transport. This work provides a fundamental understanding of the thermodynamic and kinetic parameters involved in Li+ ion adsorption, which is a crucial step in the performance of Li+ ion batteries.

For the analysis on the distribution of gas concentration during gas-purging in oil tank of a tanker, it is necessary to determine quantitatively the dispersion coefficient and the interception rate of gas-purging caused by existance of circulated gas flow and dead zones in tank.In this paper, the values of dispersion coefficients are calculated by use of the distribution of flow velocity and the interception rate ξ by stagnated flow is introduced in analytical method for one dimensional model. Besides, two dimensional analyses by finite element method are carried out to investigate the variation of distribution of flow velocity and gas concentration in tank using various conditions of decisive factors governing gas diffusion, i. e. position of inlet and outlet, volume of supplied gas and tank geometry. By the results of analyses, the relations between above-mentioned factors and dispersion coefficient or interception rate ξ are clarified.The actual values of dispersion coefficient and interception rate ξ are obtained from measured values of gas concentration in a 250, 000 DWT oil tanker by means of one dimensional analysis.

Long term durability was demonstrated on high-performance direct ethanol solid oxide fuel cell operating in gradual internal reforming. Anode supported single cells, fabricated at Forschungszentrum Jülich, composed of (La,Sr)MnO3 cathode, 8 mol% yttria-stabilized zirconia (YSZ) electrolyte, and YSZ-Ni anode were used for long term testing on anhydrous (direct) ethanol. Gadolinia-doped ceria (CGO), with 0.1 wt.% of Ir, catalyst was produced by the impregnation of Ir salt in commercial CGO (Praxair) and mixed with organic additives. The CGO-Ir suspension was deposited onto the surface of the YSZ-Ni anode support with an air brush. Such a catalytic layer acts both as a physical barrier to avoid direct contact of the fuel with Ni-based anode and to promote the gradual internal reforming of ethanol. The CGO-Ir catalyst was designed for the reforming of the main compounds resulting from the thermal decomposition of ethanol at high temperature and to inhibit the formation of ethylene, which is a known source of carbon deposits. After deposition the sample was heated at 850ºC in inert atmosphere to ensure good adhesion between the catalytic layer and the anode. Gold grid and paint were used as current collectors in both cathode and anode sides. The single fuel cells were mounted in the test apparatus, sealed with gold rings and alumina cement and heated to the measuring temperature (850°C) under inert atmosphere. After gas tightness was checked by flowing air on the cathode side and argon on the anode side, the anode was reduced under hydrogen. The fuel cell was kept at 0.6 V while monitoring the current drained from the cell at 850 °C. Samples were initially operated in hydrogen for a few hours and fuel was switched to dry ethanol, carried by nitrogen. It is important to mention that no oxidizing agent was added to the fuel and that water produced by the electrochemical reaction of hydrogen at the anode promoted the reforming of the ethanol in the CGO-based layer, in the so-called gradual internal reforming. In such conditions the current output was recorded and observed to not be significantly different form that under hydrogen. Moreover, the direct ethanol fuel cell was continuously operated for 650 hours without major losses due to carbon formation. The experimental results demonstrate that the water released by the electrochemical oxidation of reformate hydrogen at the electrolyte/anode active interfaces is sufficient for the reforming of the primary fuel in the catalytic layer, provided that a minimum fuel utilization is respected. After the durability tests, energy dispersive X-ray spectroscopy and scanning electron microscopy analyses of the samples revealed no carbon deposit formation in the anode. The experimental results provided compelling evidence for the viability of gradual internal reforming of ethanol in high performance solid oxide fuel cells.

In recent years, anode-supported solid oxide fuel cell (SOFC) technology gains greater attention. Kinetic and thermodynamic parameters play a pivotal role in influencing the overall efficiency and functionality of SOFCs. In present study, 3D model of a single cell anode-supported SOFC is developed using ANSYS fluent. Kinetic and thermodynamic parameters are optimized by comparison with experimental data. Optimized parameters are subsequently used to investigate the impact of pressure and fuel utilization on the overpotential. Simulation results indicate that optimized parameters give rise to an increased fuel consumption and hence water formation. This can be explained by the fact that optimized parameters give rise to an increased rate of reaction. Optimized parameters lead to a reduction in cell overpotential thereby increasing current and power densities at elevated pressure. Increased fuel utilization correlates with a decrease in power and current densities.

YSZ ( yttria-stabilized zirconia)-modified LSM composite cathodes were fabricated by formation of YSZ film on triple phase boundary (TPB) of LSM/YSZ/gas. The YSZ coating film greatly enlarged electrochemical reaction sites from the increase of additional TPB. The composite cathode was formed on thin YSZ electrolyte (about 30 Um thickness) supported on an anode and then I-V characterization and AC impedance analyses were performed at temperature between . As results of the impedance analysis on the cell at with humidified hydrogen as the fuel and air as the oxidant, R1 around the frequency of 1000 Hz represents the anode Polarization. R2 around the frequency of 100Hz indicates the cathode polarization, and R3 below the frequency of 10 Hz is the resistance of gas phase diffusion through the anode. The cell with the composite cathode produced power density of at air and oxygen atmosphere, respectively. The I-V curve could be divided into two parts showing distinctive behavior. At low current density region (part I) the performance decreased steeply and at high current density region (part II) the performance decreased gradually. At the part I the performance decrease was especially resulted from the large cathode polarization, while at the part H the performance decrease related to the electrolyte polarization.

We developed induction furnace brazed anode supported tubular and flat tube SOFCs to improve power density and studied basic technology of key components for making stacks from them. Performance of the flat tube cell showed 210 mW/cm 2 (0.7y 300 mA/cm 2 ) at 750°C. Induction furnace brazing was applied to connect ceramic and metal parts and their gas permeability was tested. The results indicated that the induction furnace brazing method could be used effectively for making anode supported tubular and flat tube cell stack. Through these experiments, we obtained basic technology of such cells and established a proprietary concept of the anode-supported tubular and flat tube cell stack.

Electrocatalytic reduction of CO2 to CO have been performed in a high temperature solid oxide electrolysis cell (SOEC). Solid oxide cell was fabricated using ceramic cathode, Ce0.9Pr0.1O2-δ (PDC), infiltrated into yettria stabilized zirconia (YSZ) scaffold. Lanthanum strontium manganite (LSM) as anode was brush coated on dense YSZ electrolyte. Physical characterization of infiltrated PDC cathode was performed by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). XRD pattern indicated the phase purity of PDC cathode, Figure 1(a). The porous cathode and dense electrolyte layers of thickness 600 µm and 700 µm respectively, were perfectly adhered as suggested by the SEM image of Figure 1(b). Electrochemical characterizations of SOEC were performed at 750 ºC, using impedance spectroscopy (IS) and current voltage (I-V) measurements. Open circuit impedance spectra of SOEC were obtained with varying ratio of CO2/CO gas in the inlet flow, as shown in Figure 1(c). As the CO concentration in the fuel side environment of SOEC was increased from 0% to 90%, the measured ohmic losses were observed to decrease from 3.5 to 1.5 Ωcm2. This might occurred because of the reducing environment in which Ce4+ may partially be reduced to Ce3+, resulting in mixed ion-electron conduction leading to higher ionic transport at the electrode-electrolyte interface. Similarly, the polarization resistances were decreased by increasing the CO content in reaction atmosphere (CO2/CO) on the cathode side. This might be because of the faster reaction kinetic of CO oxidation as compared to the CO2 reduction kinetics. Furthermore, open circuit potential (OCP) was observed to be increased from 0.06 V to 0.90 V as the CO2 percentage was decreased from 100 to 10%, possibly due to the same reason. Chronoamperometry (CA) were performed at certain a potential and corresponding reduction current was observed to be constant. Products of CO2 reduction reaction were analysed in gas chromatogram (GC). In order to understand the reaction mechanism of CO2 reduction on ceria, density function theory (DFT) calculations were performed to study the formation of CO from CO2 reduction on CeO2 surface. CO2 molecule adsorbed on the neighbor site of oxygen vacancy on the reduced surface, was activated and form a bent carbonate CO3 δ- like structure which ultimately dissociates into CO via the incorporation of the oxygen atom into the vacancy. The activation barrier and reaction energy for this redox mechanism, calculated from DFT studies, were of 258.9 kJ/mole and 238.6 kJ/mole respectively. The effect of lateral interactions were studied by performing calculations for the same reaction step on two oxygen vacancy (di-vacancy) on 2x2 supercell unit. The activation barrier and reaction energy on a di-vacancy were significantly reduced to 134.3 and 127.3 kJ/mole respectively. Furthermore, the hydrogen atom co-adsorbed on the surface could assist the CO2 dissociation reaction. In the presence of a hydrogen atom the dissociation reaction occurs in two exothermic steps: CO2+H→COOH, COOH→CO+OH. The intrinsic activation barriers of two hydrogen assisted elementary steps were 39.0 and 47.4 kJ/mole (Figure 1D) respectively, which were significantly lower than the barrier of redox mechanism of CO2 dissociation reaction. The experimental and theoretical studies could suggest a feasibility of CO2 reduction reaction on ceria based materials. Figure 1

This work addresses the development of anode-supported solid oxide fuel cells using alternative low-cost techniques such as cold die pressing of the anode substrates and spray deposition of electrolyte layers. The new techniques have been developed up to the fabrication of disc cells with a diameter of 120 mm consisting of a co-sintered anode support and the yttrium-stabilized zirconia electrolyte layer. The concept was demonstrated in a three-cell stack according to the Sulzer HEXIS design and operated successfully in steam-reformed natural gas at around 800°C. The cell performance reached 430 mW/cm 2 . Electrical efficiencies of >60% at a fuel utilization of 90% represent excellent performance for the non-sealed HEXIS stack design.

A systematic study was initiated of anode-supported solid oxide fuel cells (SOFCs) with Nd2NiO4 cathodes. This type of cathode, a mixed conducting K2NiF4-type material, can be considered as a candidate for SOFC applications. In this study, the influence of (1) the presence of a Ce0.8Gd0.2O1.9 (CGO) interlayer between the electrolyte and the cathode, (2) sintering conditions, and (3) the grain size of the powder on the performance of SOFCs with Nd2NiO4 cathodes was investigated in more detail. Results from current density-voltage characteristics and permeation and gas diffusion measurements showed that the electrochemical performance was promising for SOFCs including a CGO interlayer and a Nd2NiO4 cathode (prepared with a powder with a d50 of 0.5A∕cm2 or 0.8μm) sintered at 1100°C or higher; current density at 800°C and 700mV between 1.2 and 1.3A∕cm2. The microstructure of the cathode was such that no gas diffusion problems occurred.

Aluminum batteries with imidazolium-based electrolytes present a promising avenue toward the post-lithium-ion battery era. A critical bottleneck is the development of reversible aluminum metal anodes, which is hindered by sluggish battery charge–discharge characteristics due to the reversible/irreversible side reactions on the anodic and cathodic sides. The indispensable discernment of the stripping-plating mechanisms at the electrode–electrolyte interface is not well explored due to the complexity of the various reactions occurring at the surface of the aluminum anode. Herein, a high-fidelity physics-based model is coupled with density functional theory to explain the stripping-plating mechanisms that occur on the surface of the aluminum anode at different current densities. Sensitivity analysis is performed on the experimentally validated physics-based model using a machine-learning Gaussian process regression model to identify the most significant parameters for the plating-stripping mechanism of aluminum. The electrodeposition of aluminum is controlled by both diffusion and kinetics and is limited by the kinetics of the electrochemical reactions at a high current density. This work highlights the assurance of combining models at different scales, machine learning algorithms, and experiments to analyze the behavior of complex electrochemical systems.

Aqueous Zn‐ion batteries (AZIBs) hold great promise for large‐scale energy storage applications due to their low cost, intrinsic safety, and high theoretical capacity. However, the delivery of stable electrode–electrolyte interface becomes the main challenge for developing high‐performance AZIBs with long cycle life and high capacity. On the cathode side, the dissolution of active materials, formation of byproducts, and unsatisfactory interfacial compatibility frequently occur. Meanwhile, the Zn metal anodes usually suffer from inevitable Zn dendrites and parasitic reactions. Both the electrode–electrolyte interface issues for the cathodes and anodes will finally result in poor electrochemistry reversibility and fast capacity decay. With this perspective, this review focuses on the key scientific issues occurred at the electrode interfaces, and also proposes corresponding interfacial optimization strategies, including surface modification and electrolyte optimization, aiming at providing guidelines for the design of high‐performance AZIBs based on the understanding of interface improvement and practical application considerations.

The performance characteristics of high-performance Ni-YSZ (yttria-stabilized zirconia) anode-supported solid oxide fuel cells (SOFCs) are examined under typical fuel cell operating conditions over a period of ∼3000 h when hydrogen contaminated with different concentrations of H2S was used as the fuel. Analyses reveal some new insights into the sulfur poisoning behavior of a Ni-YSZ anode. First, an initial drop in power output upon exposure to H2S-contaminated fuels is more dramatic in an anode-supported cell (with small cell resistance) than in electrolyte-supported cell (with large cell resistance), creating an illusion that a high-performance cell appears to be less sulfur tolerant than a low-performance cell. Second, the transition time for this rapid performance drop to cease is much longer for an anode-supported cell (with a thicker anode) than an electrolyte-supported cell (with a thinner anode). Third, the degree of sulfur poisoning (or the cell resistance increase due to sulfur poisoning) diminishes with operating cell current density, suggesting that the water produced at the active sites on anode surface from electro-oxidation of hydrogen (or oxygen ions) may promote the oxidation and removal of adsorbed sulfur. This effect becomes less pronounced at higher concentration of H2S, but still significant at ∼1 ppm of H2S. Fourth, the subsequent slow degradation in performance after the rapid performance drop upon initial exposure to H2S can be avoided, indicating that the previously reported slow degradation is unlikely the inherent behavior of a Ni-YSZ anode, but associated with other complications. This further implies that sulfur poisoning may be reversible and the performance drop could be fully recovered when the fuel is switched back to clean hydrogen.

Micro-Solid Oxide Fuel Cell: A multi-fuel approach for portable applications

Anode-supported solid oxide fuel cells (SOFCs) offer the advantage of thinner electrolyte membranes which greatly reduce the ohmic loss and enables lower operating temperature and higher performance. However, a significant contribution to the polarization resistance is attributed to the anode, as the thickest component in the cell, which can influence the distribution of hydrogen partial pressure, p(H2) and water vapor pressure, p(H2O) especially when combined with current density to achieve high fuel utilization. To understand the degradation mechanism in long-term operation of a commonly used anode material, Ni/YSZ, commercial anode-supported cells were evaluated under varied current density (up to 1 A/cm2) and humidity (1-60%) using electrochemical impedance spectroscopy. The impedance spectra were analyzed using distribution of relaxation times (DRT) method to separate the resistance contribution from each component of the cell. The Ni/YSZ anode resistance was observed to increase with higher current density and humidity, suggesting that the degradation may be correlated to microstructural factors such as Ni agglomeration leading to reduced Ni interparticle contact, causing the increase in anode resistance. In addition, analysis using the 1-D transmission line model to determine the effective reaction length (ERL) of Ni/YSZ anode, revealed that the ERL moves further from the TPB with increasing degradation. Details of the post-test microstructural characterization of the cells will be discussed during the presentation.