Thin Electrolyte Layer Research Articles

Theory of impedance for initial corrosion of metals under a thin electrolyte layer: a coupled charge transfer-diffusion model

Theory of impedance for initial corrosion of metals under a thin electrolyte layer: a coupled charge transfer-diffusion model

Effect of Second Phase on the Pitting Corrosion of ZL101A Aluminum Alloy in Thin Electrolyte Layer Environment Containing Cl

Effect of Second Phase on the Pitting Corrosion of ZL101A Aluminum Alloy in Thin Electrolyte Layer Environment Containing Cl

Numerical Analysis of Thermal Stress for a Stack of Planar Solid Oxide Fuel Cells

In this work, a 3D multi-physics coupled model was developed to analyze the temperature and thermal stress distribution in a planar solid oxide fuel cell (SOFC) stack, and then the effects of different flow channels (co-flow, counter-flow and cross-flow) and electrolyte thickness were investigated. The simulation results indicate that the generated power is higher while the thermal stress is lower in the co-flow mode than those in the cross-flow mode. In the cross-flow mode, a gas inlet and outlet arrangement is proposed to increase current density by about 10%. The generated power of the stack increases with a thin electrolyte layer, but the temperature and its gradient of the stack also increase with increase of heat generation. The thermal stress for two typical sealing materials is also studied. The predicted results can be used for design and optimization of the stack structure to achieve lower stress and longer life.

Practical considerations in designing solid state Li-S cells for electric aviation

The development of high-energy, high-safety, and high-power batteries beyond electric automotive standards is critical for future electric aviation applications. Non-volatile solid-state electrolytes (SSE) offer many promising advantages over traditional flammable liquid electrolytes. SSE may become an enabling technology for certain battery chemistries by preventing detrimental interactions that occur with liquid electrolytes, for example preventing dissolution of lithium-sulfur intermediates common in traditional liquid organic solvents. However, significant manufacturing challenges must be overcome before the adoption of such technology. One of the main challenges is the fabrication of sufficiently thin electrolyte layer to maximize specific energy of the solid-state cell. In this work we first show the feasibility in the assembly of an all solid-state battery via the development of composite SSE with ionic conductivity above 0.2mS/cm and thicknesses on the order of 40 micron through a tape-casting technique. With Li/Al alloy as the anode and TiS2 as the active cathode material, the resultant solid-state battery with a thin electrolyte layer and excellent cathode-electrolyte interface represents a prototype vision on a potential solid-state cell required for electric aviation. A detailed parameter analysis is further presented on the influence of the various cell metrics, such as electrolyte thickness, carbon content, active material utilization, and excess lithium, on the cell specific energy. The implications in the optimization of these required parameters to enable practical solid-state Li-S batteries for electric aviation are discussed.

Investigation on the SCC behavior of ZL101A aluminum alloy in simulated marine environments

Stress corrosion cracking (SCC) behavior of ZL101A aluminum alloy in solution and thin electrolyte layer (TEL) with different pH was investigated in detail. The results indicated that the precipitated phases of ZL101A were composed of α-Al/Si eutectic crystal phase and Si–Mg–Fe precipitated phase, which accelerated the formation of corrosion pits. ZL101A presented the highest SCC susceptibility in pH = 4 solution compared with pH = 7 and 10 solutions, which was mainly attributed to the enhanced synergistic effect of anodic dissolution, stress and hydrogen embrittlement. The basically similar SCC susceptibilities in TEL environments were mainly controlled by the anodic dissolution, which was attributed to the high diffusion rate of O2 in the thin electrolyte film.

Ammonia-fed reversible protonic ceramic fuel cells with Ru-based catalyst

The intermediate operating temperatures (~400–600 °C) of reversible protonic ceramic fuel cells (RePCFC) permit the potential use of ammonia as a carbon-neutral high energy density fuel and energy storage medium. Here we show fabrication of anode-supported RePCFC with an ultra-dense (~100%) and thin (4 μm) protonic ceramic electrolyte layer. When coupled to a novel Ru-(BaO)2(CaO)(Al2O3) (Ru-B2CA) reversible ammonia catalyst, maximum fuel-cell power generation reaches 877 mW cm−2 at 650 °C under ammonia fuel. We report relatively stable operation at 600 °C for up to 1250 h under ammonia fuel. In fuel production mode, ammonia rates exceed 1.2 × 10−8 NH3 mol cm−2 s−1at ambient pressure with H2 from electrolysis only, and 2.1 × 10−6 mol NH3 cm−2 s−1 at 12.5 bar with H2 from both electrolysis and simulated recycling gas.

Preparing Li‐garnet electrodes with engineered structures by phase inversion and high shear compaction processes

AbstractSolid‐state lithium batteries are promising for safety and energy density compared with traditional lithium‐ion batteries. However, the large interfacial resistance between the electrode and electrolyte is a bottleneck to achieving high‐performance solid‐state batteries. Engineered electrode structures with a porous scaffold of the solid electrolyte material are promising to lower the interfacial resistance and provide a mechanical support for a thin solid electrolyte layer. In this work, two ceramic processing techniques are used to fabricate porous/dense bilayer architectures based on a Li6.25Al0.25La3Zr2O12 (LLZO) Li‐garnet material. Finger‐like vertically aligned pores are created by the phase inversion (PI) process. A water bath presaturated with Li salt prevents Li loss during the PI solvent exchange step. Pore size and porosity can be optimized by adjusting the bath temperature. The high shear compaction process was used to prepare LLZO tapes with 40, 60, and 80 vol% poreformer. The porosity of the tapes after sintering is 39.5%, 58.4%, and 75.4%, respectively. Microtomography exhibits the porosity, pore shape, and pore distribution of the tapes. A typical cathode material LiNi0.33Mn0.33Co0.33O2 (NMC) is filled into the pores via vacuum infiltration, and a dense cathode layer is formed within the garnet scaffold.

Fabrication and Characterization of a Tubular Solid Oxide Fuel Cell with Impregnated Perovskite Electrodes

Thanks to large efficiency and ability to work in both fuel cell and electrolysis mode Solid Oxide Cells (SOCs) could become a vital technology in the transition to the carbon-neutral energy sector based on hydrogen. However, large cost and low durability constrain their full-scale commercialization. These challenges are tackled in the present work. Tubular cells are produced by a simple and inexpensive method, suitable for mass production. The cells showed excellent activity, stability and redox resistance due to tubular design and fully ceramic electrodes. Thermal shock resistance testing showed that the cell is resistant to rapid temperature changes.A thick supporting layer of the porous backbone was cast first, and a thin layer of electrolyte over it. After rolling into a tubular shape, the assembly was co-sintered and impregnated with functional perovskite materials. Co-casting allowed to achieve a strong interface and reduce the thickness of electrolyte. The impregnation gave the possibility to deposit a perovskite in temperature much lower than in state-of-art methods, preventing the undesirable reaction with zirconia electrolyte and reducing their densification, producing more active spatial microstructures with large surface area. Moreover, such electrodes are more thermally compatible with electrolyte as their bulk TEC is mainly controlled by the porous backbone made of the same material as the electrolyte.Yttria-stabilized zirconia (Zr0.92Y0.16O2.08, 8YSZ) is used as the electrolyte, for the fuel electrode nickel doped lanthanum calcium titanate (La0.43Ca0.37Ni0.06Ti0.94O3- γ, LCNT) was impregnated onto a porous 8YSZ backbone, while on the air electrode a lanthanum strontium ferrite (La0.8Sr0.2FeO3, LSF) was applied. These materials offer high activity and stability for a relatively low price. Electrochemical impedance spectroscopy (EIS), current-voltage (I-V) and potentiostatic measurements were carried out to characterize cell performance and cell’s stability during the test. The electrochemical testing showed improvement in the cell performances after electrochemical poling at high potential, due to facilitated LCNT reduction and exsolution of nickel nanoparticles.The cheap fabrication method, competitive performance, attracting redox stability and thermal shock resistance, braking the major limitation for SOFC applicability, making it even suitable to be used in portable applications.

Design and 3D Printing of Controllable and Gradient Porous Supports for Solid Oxide Fuel Cells

A controllable and gradient porous structure is desirable for many applications including solid oxide fuel cells (SOFC) electrodes. A SOFC contains a minimum three basic ceramic thin films with a thin yet dense electrolyte layer separates the adjacent porous anode and cathode layers. In general, the thinner the electrolyte layer, the smaller the ohmic resistance would be. The anode and cathode layers need to be porous so to allow gases (e.g. H2 and O2) to easily penetrate to the triple-phase boundary (TPB). At the same time the anode and cathode layers serve as the paths of removing the electrons generated at the TPBs. Properly design and fabricated porous electrode microstructure could greatly increase the connectedness of gas, electrons and/or protons/oxygen ions, and therefore reduce the gas diffusion and ohmic resistances of the SOFC electrodes and boost the overall fuel cell performance.Although there are electrolyte- and cathode- supported SOFC developers, the most used configuration is anode-supported or additional component-supported, for example metal-supported or ceramic-supported with a planar or tubular geometry. Conventionally, the porosity is generated by using sacrificial templates or pyrolyzable pore-formers for pore formation. Pores are formed after the burning off these sacrificial templates or pyrolyzable pore-formers at elevated temperatures. The size, shape and amount of the pore-formers can be controlled. However, the connectivity and orientation of these pores are not easily controllable, leaving significant amount of closed and isolated pores. These isolated and/or closed pores do not contribute to the TBP. Freeze casting of water-based suspension slurries could generate aligned pores, the low connectivity and weak mechanical strength challenges remain.This paper focuses on the design and fabrication of a desired gradient porous microstructure for use as a SOFC support. The pore size and shape, porosity and connectivity could be determined and strictly controlled by design. Tubular and planar parts with metal, cermet and/or ceramic materials are to be fabricated. Additive manufacturing (AM, or 3D printing) process enables the fabrication of the complicated parts with the desired microstructure directly from the computer-aided design (CAD) models. The morphology, porosity, permeability and tortuosity of the 3D printed parts are investigated and results are discussed.

Effects of Flow Channel Arrangement and Electrolyte Thickness on Thermal Stress for Planar Solid Oxide Fuel Cell Stacks

Typical operating temperature for solid oxide fuel cells (SOFC) is between 700~800°C. A large temperature gradient and thermal stress caused by internal losses and electrochemical reactions may cause SOFC stack performance degradation and even structural damage, which has become a hindrance to its applications.In this study, a three-dimensional multiphysics CFD (computational fluid dynamics) model is developed and applied for a planar SOFC stack to study the temperature and thermal stress distribution, as well as effects of structure and design parameters, including the flow channel arrangement (e.g., co- and count-flow) and thickness of the electrolyte layer. The stack is composed of three-unit cells, metallic interconnect layers, sealing and anode/cathode current collectors.The simulation results reveal that the temperature difference in the counter-flow mode is smaller and the thermal stress is lower than those in the co-flow mode. The overall performance of the stack is better when the electrolyte layer thickness becomes smaller, but the stack temperature and the temperature gradient become higher. In addition, a large temperature gradient due to the thin electrolyte layer leads to a significant increase of the thermal stress in the electrolyte. The findings and research method from this study can be applied to optimize the design of the stack structures, by consideration of the maximum thermal stress and its distribution.AcknowledgementsThis work is supported by the National Key Research and Development Project of China (2018YFB1502204), the Ningbo major special projects of the Plan “Science and Technology Innovation 2025” (2018B10048).

Fabrication and Characterization of a Tubular Solid Oxide Fuel Cell with Impregnated Perovskite Electrodes

The tubular cells were produced by a simple and inexpensive method, suitable for mass production. A porous YSZ backbone was co-cast with a thin layer of YSZ electrolyte over it. After rolling in tubular shape and co-sintering, the porous backbone was impregnated with functional perovskite materials, the nickel doped lanthanum calcium titanate LCNT (La0.43Ca0.37Ni0.06Ti0.94O3- γ) for the fuel side and the lanthanum strontium ferrite LSF (La0.8Sr0.2FeO3) for the air electrode. The LCNT perovskite was proposed as the alternative fuel electrode due to its mixed ionic and electronic conductivity (MIEC) properties and catalytical activity supplemented by exsolved Ni nanoparticles. The electrochemical poling at high potential, so-called 'switching', can increase the activity of LCNT due to facilitated reduction and exsolution. After switching at 2.1 V for 2 min, the tubular cell performance in fuel cell mode increased threefold. The impedance analysis indicated a reduction of ohmic and polarisation resistance on the whole frequency range and facilitated electrode kinetics under applied voltage.

Effects of Flow Channel Arrangement and Electrolyte Thickness on Thermal Stress for Planar Solid Oxide Fuel Cell Stacks

Typical operating temperature for a solid oxide fuel cell (SOFC) ranges from 700°C to 800°C. A large temperature gradient and thermal stress are induced by internal losses and electro-chemical reactions, resulting in significant structural damage and performance degradation of a SOFC stack, which has become a hindrance to its applications. In this study, a three-dimensional multi-physics CFD model is developed and employed to study the temperature and thermal stress distribution of a planar SOFC stack, then effects of the structure design parameters are investigated, including the flow channel arrangement (i.e., co- and cross-flow) and thickness of the electrolyte layer. The stack modeled is composed of three-unit cells, metallic interconnect layers, sealing components, and anode/cathode current collectors. The simulation results show that the temperature difference in the co-flow case is smaller and the thermal stress is lower than those predicted in the cross-flow. The overall performance of the stack improves as the thickness of the electrolyte layer decreases, but the temperature and its gradient inside the stack become higher. In addition, a large temperature gradient is observed inside the thin electrolyte layer, which leads to a significant increase of the thermal stress. The findings and the research methods in this study can be applied to design and optimize the stack structures by considering the temperature and the thermal stress distribution.

Fabrication and performance of anode-supported proton conducting solid oxide fuel cells based on BaZr0.1Ce0.7Y0.1Yb0.1O3-δ electrolyte by multi-layer aqueous-based co-tape casting

Although proton-conducting solid oxide fuel cells (PCFCs) is superior to traditional fuel cells,the two main challenges for restricting the experimental research and the commercialization of PCFCs application are its high manufacturing cost and difficulty in scale-up. In addition, the aqueous-based tape casting process as a novel strategy has been widely applied in fabricating thin, large-scale, cost-effective and environment-friendly electrolyte layer. In this paper, an 80 mm × 80 mm anode-supported proton-conducting solid oxide fuel cell is obtained through combining the multi-layer aqueous-based tape casting and co-sintering technology. The configuration of PCFCs is NiO-BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb)/BZCYYb (∼12 μm)/La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-BZCYYb. The performance of the cell with homogeneous microstructure reaches 389 mW cm−2 at 800 °C in condition of 3% humidified hydrogen as fuel and normal air as oxidant. Combined with the successful experience of previous work, this work can provide theoretical and statistical accumulation and reference for future assembly of large-scale PCFCs.

(Invited) Probing the Electronic Structure of Oxide Electrocatalysts and the Formation of Reaction Intermediates

Perovskite oxides (ABO3) are highly active for the oxygen evolution reaction (OER). Activity is observed to correlate with changes in bulk electronic structure parameters, such as metal-oxygen covalency and transition metal oxidation state. We employ spectroscopic approaches to consider such descriptors at the surface of perovskite oxides in situ, as well as their implications on the formation of surface adsorbates proposed to act as reaction intermediates during the OER.Many surface science techniques, such as X-ray photoelectron spectroscopy (XPS), collect information from inherently surface-sensitive low-energy processes, requiring operation in ultrahigh vacuum. This constraint is lifted for ambient pressure XPS, which can probe the surface in equilibrium with the gas phase at pressures up to ~a few Torr, or with thin liquid layers using a higher incident photon energy. This presentation will discuss the insights obtained with this technique regarding the electronic structure of oxide electrocatalysts in an oxidizing or humid environment, as well as the reaction intermediates of relevance to electrocatalysis.1 We will then extend the technique to probe electrocatalysts in operando,2 driving current through a thin layer of liquid electrolyte and employing a tender X-ray source.

Optimization of Tape Casting for Fabrication of Li6.25Al0.25La3Zr2O12 Sheets

Tape casting is an attractive technology for the scalable manufacturing of thin lithium garnet electrolyte (LLZO) layers for solid state battery applications. Processing of LLZO is complicated by m...

Thin layer electrolyte impregnation into porous anode-supported fuel cell by ultrasonic spray pyrolysis

An ultrasonic spray pyrolyzed thin layer electrolyte impregnates into a porous anode and extends the depth of triple phase boundaries (TPBs) to several times that of the dense thin-layer thickness. This process, without an anode functional layer, improves the conventional repeated impregnation that results in anode porosity blocking and difficult extending to the anode/electrolyte interface. A (La0.75Sr0.2Ba0.05)0.175Ce0.825O1.981 (LSBC) electrolyte thin layer (iLSBC) is deposited on a porous La0.3Sr0.7TiO3 (LST) anode by ultrasonic spray pyrolysis using 0.1 M LSBC precursor at a substrate temperature of 450 °C, while controlling the solution flow rate and spray volume. The spray pyrolyzed iLSBC/LST half-cells co-fired at 1350 °C/6 h exhibit no evident second phase in the X-ray diffraction analysis. The depth profile of iLSBC/LST indicates an approximately 2.75 μm-thick layer with the Ce element line scanning showing a significantly higher impregnation depth. Slight lattice distortion among the impregnated region may be due to the iLSBC diffusion, resulting in the extension of the TPB area and length. The half-cell reaches a low impedance and achieves a power density of 377 mW/cm2 at 750 °C.

Corrosion Evolution of High-Strength Aluminum Alloys in the Simulated Service Environment of Amphibious Aircraft in the Presence of Chloride and Bisulfite

The corrosion evolution of 2024-T351 and 7075-T651 aluminum alloys in the thin electrolyte layer (TEL) and wet–dry alternating cycle (WDAC) environment is studied in this work. The results show that in the TEL environment, the competitive effect between H+ that accelerates corrosion reactions and deposition of aluminum sulfate that impedes corrosion attacks exists during the corrosion exposure. The difference is that with increasing HSO3−, subsurface intergranular corrosion on 2024-T351 is promoted to form exfoliation corrosion eventually and the degree of exfoliation corrosion begins to decrease because the blocking effect of aluminum sulfate exceeds the expediting effect of H+. For 7075-T651, the corrosion area and the corrosion diameter decrease gradually, which is attributed to the HSO3−-enhanced deposition of corrosion products and their blocking effect. In the WDAC environment, the corrosion processes of 2024-T351 and 7075-T651 are the acidic dissolution of the matrix during the soaking phase. When the HSO3− concentration is high enough (0.1 M), the inhibiting effect of aluminum sulfate becomes the dominant factor.

Limiting Current Density of Oxygen Reduction under Ultrathin Electrolyte Layers: From the Micrometer Range to Monolayers

AbstractThe oxygen reduction reaction (ORR) under ultrathin electrolyte layers is a key reaction in many processes, from atmospheric corrosion to energy conversion in fuel cells. However, the ORR current under ultrathin electrolyte layers is difficult to measure using conventional electrochemical methods. Hence, reliable data are scarce for the micrometer range and totally missing for the sub‐micrometer range of the electrolyte layer thickness. Here, we report a novel hydrogen‐permeation‐based approach to measure the ORR current underneath thin and ultrathin electrolyte layers. By using a Kelvin‐probe‐based measurement of the potential, which results from dynamic equilibrium of oxygen reduction and hydrogen oxidation, and the corresponding hydrogen charging current density, the full current‐potential relationship can be constructed. The results shed a new light on the nature of the limiting current density of ORR underneath ultrathin layers of electrolyte.

Additive manufacturing of thin electrolyte layers via inkjet printing of highly-stable ceramic inks

Inkjet printing is a promising alternative for the fabrication of thin film components for solid oxide fuel cells (SOFCs) due to its contactless, mask free, and controllable printing process. In order to obtain satisfying electrolyte thin layer structures in anode-supported SOFCs, the preparation of suitable electrolyte ceramic inks is a key. At present, such a kind of 8 mol% Y2O3-stabilized ZrO2 (8YSZ) electrolyte ceramic ink with long-term stability and high solid loading (> 15 wt%) seems rare for precise inkjet printing, and a number of characterization and performance aspects of the inks, such as homogeneity, viscosity, and printability, should be studied. In this study, 8YSZ ceramic inks of varied compositions were developed for inkjet printing of SOFC ceramic electrolyte layers. The dispersing effect of two types of dispersants, i.e., polyacrylic acid ammonium (PAANH4) and polyacrylic acid (PAA), were compared. The results show that ultrasonic dispersion treatment can help effectively disperse the ceramic particles in the inks. PAANH4 has a better dispersion effect for the inks developed in this study. The inks show excellent printable performance in the actual printing process. The stability of the ink can be maintained for a storage period of over 30 days with the help of initial ultrasonic dispersion. Finally, micron-size thin 8YSZ electrolyte films were successfully fabricated through inkjet printing and sintering, based on the as-developed high solid loading 8YSZ inks (20 wt%). The films show fully dense and intact structural morphology and smooth interfacial bonding, offering an improved structural quality of electrolyte for enhanced SOFC performance.

Effect of Ni on the oxygen reduction reaction for low alloy steels in thin electrolyte layer conditions

The corrosion behavior of carbon and a Ni-containing steel is investigated in the environment of a thin electrolyte layer. Potentiodynamiccathodic polarization curves were determined using a thin electrolyte layer apparatus at ordinary and negative pressure environments. Oxygen reduction is an important cathodic reaction for carbon steel in the present study. However, the suppression of oxygen reduction occurred for Ni-containing steels. The inhibition of oxygen reduction was closely correlated with the formation of the amorphization of the corrosion product, which contained amount of Ni, formed on the Ni-containing steel.