Ultrathin Electrolyte Research Articles

Thermo-mechanical stability of multi-scale-architectured thin-film-based solid oxide fuel cells assessed by thermal cycling tests

The thermo-mechanical stability of a thin-film and nanostructure-based SOFC (TF-SOFC) is assessed by thermal cycling tests. An ultrathin bi-layer electrolyte composed of 150-nm-thick yttria-stabilized zirconia (YSZ) and 450-nm-thick gadolinia-doped ceria (GDC) is successfully built on a NiO-YSZ anode support the microstructure scale of which changes from μm to nm (multi-scale architecture). The concept of multi-scale architecture in the TF-SOFC not only enables the reliable implementation of thin-film electrolytes and nanostructured electrodes to improve the critical low-temperature performance of the SOFC but also secures the thermo-mechanical stability of TF-SOFC. Competent cell performance is obtained, including a peak power density about 1.4 W cm−2 at 600 °C. The TF-SOFC survives 50 thermal cycle tests between 600 and 400 °C over 124 h without suffering a drastic failure. Although some cell output degradation is observed after the thermal cycling tests, the cell sustains a peak power density over 1 W cm−2 at 600 °C, which indicates the superior thermo-mechanical stability of the multi-scale-architectured TF-SOFC.

Three-Dimensional Nanostructured Bilayer Solid Oxide Fuel Cell with 1.3 W/cm2 at 450 °C

Obtaining high power density at low operating temperatures has been an ongoing challenge in solid oxide fuel cells (SOFC), which are efficient engines to generate electrical energy from fuels. Here we report successful demonstration of a thin-film three-dimensional (3-D) SOFC architecture achieving a peak power density of 1.3 W/cm(2) obtained at 450 °C. This is made possible by nanostructuring of the ultrathin (60 nm) electrolyte interposed with a nanogranular catalytic interlayer at the cathode/electrolyte interface. We attribute the superior cell performance to significant reduction in both the ohmic and the polarization losses due to the combined effects of employing an ultrathin film electrolyte, enhancement of effective area by 3-D architecture, and superior catalytic activity by the ceria-based interlayer at the cathode. These insights will help design high-efficiency SOFCs that operate at low temperatures with power densities that are of practical significance.

Methane-fueled thin film micro-solid oxide fuel cells with nanoporous palladium anodes

Methane-fueled thin film micro-solid oxide fuel cells (μSOFCs) based on palladium (Pd) anodes are discussed in this article. The μSOFCs are composed of porous platinum (Pt) cathodes, 8mol.% yttria-stabilized zirconia (YSZ) ultrathin electrolytes, and Pd anodes – specifically, a Pt/YSZ/Pd heterostructure synthesized by physical vapor deposition. The Pt/YSZ/Pd μSOFCs exhibit a power density of 385mWcm−2 and an open circuit voltage of 0.77V at 550°C. A detailed study on synthesis, microstructure and functional properties of the nanoporous Pd films is presented. Possible anodic methane reactions, carbon deposition on Pd anodes, and carbon suppression approaches are discussed. The results are of potential relevance to advancing low temperature micro-fuel cell technology using hydrocarbon fuels.

A facile and environment-friendly method to fabricate thin electrolyte films for solid oxide fuel cells

A facile and environment-friendly method, the so-called vertical deposition (abbreviated as VD) method, is used to prepare thin yttria-stabilized zirconia (YSZ) films (≤5 μm) for solid oxide fuel cells (SOFCs). The YSZ films are self-assembled by VD process based on capillary force. The influence of experimental conditions (e.g. concentration of YSZ dispersion, deposition times, and sintering procedure) on the morphology of the films produced and thereby on the performance of SOFC devices is investigated. The single cell utilizing a 5 μm dense YSZ film as solid electrolyte achieves a high open circuit voltage of 1.05 V which remains stable at 700 °C for 4 h. The peak power density is 0.4 W cm −2 at 800 °C for the phase inversion anode-supported fuel cell composed of an YSZ electrolyte film of 5 μm thick. The VD method developed herein is promising for preparing ultra-thin electrolyte films for SOFCs.

Periodical Nanostructured Multiline Copper Films Self-Organized by Electrodeposition: Structure and Properties

Nanoscale patterned electrodeposition of metals on flat substrates has become a topic of great interest both scientifically and technologically in recent years. Here, we demonstrate the self-organized growth of extended arrays of parallel nanoscale copper wires on flat glass chips from an ultrathin aqueous electrolyte layer. Regular, periodic patterns of copper nanowires with diameters in the range of 40 nm-400 nm were grown, forming parallel arrays of alternating lines of copper and cuprous oxide at periodicities down to approx. 80 nm, depending on the deposition parameters such as voltage and pH. The resulting multiline films are investigated with respect to their structure and electrical properties using Electrical Force Microscopy, Scanning Electron Microscopy and Scanning Auger Electron Spectroscopy. The results of the experiments show a strongly anisotropic behavior of the electrical properties of multiline nanostructures corresponding to their strongly anisotropic geometry.

PbTe/Pb quasi-one-dimensional nanostructure material: controllable array synthesis andside branch formation by electrochemical deposition

A periodic PbTe/Pb nanostructure material with quasi-one dimension has been electrodeposited ontoa SiO2/Si substrate by fabricating an ultra-thin electrolyte layer. The emergence of side branches atthe edge of the nanowire array results from the non-uniform electric field distribution andthe polycrystalline structure of the nanowires. The measurement of the electricalcharacteristics indicates that the crystal boundaries and defects in the nanowirecould influence the change of resistance in the branch parts. This research shouldfacilitate the acquisition of high-quality nanowire arrays by electrodeposition.

Growth and Branching Mechanisms of Electrochemically Self-Organized Mesoscale Metallic Wires

Electrochemical metallization with copper has been developed for on-chip interconnection in microelectronics. Therefore, the need for a detailed understanding of copper electrodeposition on the micrometer and nanometer scale is essential. In particular, approaches for the self-organized growth of mesoscale wires have become ofgreat interest recently. Here, we investigate the details of the deposit morphology of such mesoscale self-organized copper wires, focusing especially on the origin of the branching mechanism. The details of the morphology inform how the wires develop and why the branching occurs. It also shows that branching is not only associated with system noises but also with the electrical and concentration field and their coupling with interface growth. We demonstrate that by carefully adjusting the growth parameters branching can be avoided. In this way, highly ordered, periodic parallel arrays of metallic mesoscale wires were fabricated using this novel approach for self-organized growth by electrodeposition in ultrathin electrolyte layers. The results provide a general explanation for morphology formation during nonequilibrium electrocrystallization in thin electrolyte layers. This knowledge helps to develop processes for the controlled fabrication of micro- and nanostructured metallic patterns by electrochemistry.

Low-Temperature Anode-Supported SOFC with Ultra-Thin Ceria-Based Electrolytes Prepared by Modified Sol-Gel Route

The utilization of anode-supported electrolytes is a very promising strategy to improve the electrical performance in solid oxide fuel cells (SOFCs) application, because it is possible to decrease considerably the electrolytes thickness. In this paper, ultra-thin ceria-based electrolyte films were successfully prepared on porous NiO/GDC anode support. The electrolyte films with thickness of 0.5-1 µm were deposited by a novel citrate sol-gel route combined with a suspension spray coating technique. The characterization and microstructure of the ultra-thin films were investigated by DTA/TGA, XRD and FE-SEM. The results showed that ceria-based films prepared were pure fluorite type nanocrystalline, homogenous and almost fully dense. Electrochemical performance of single cells based on the ultra-thin electrolyte films was also tested. The single cell with electrolyte thickness of 1 µm provided an OCV of 0.832 V at 500 °C which was close to that of the reported single cell with thicker ceria-based electrolyte film of 10 µm, and maximum power densities of 59.6, 121.9 and 133.8 mW/cm2 at 500, 600, and 700 °C, respectively. These ultra-thin electrolyte films showed good combination with the porous NiO/GDC anode supports, and good insulating ability for inactive electron migration at temperatures less than 600 °C.

Ultra-thin Y-doped Zirconia Electrolyte Membranes Synthesized under Photon Irradiation: Structure Evolution and High Temperature Electrochemical Transport Studies

Synthesis and characterization of Y-doped zirconia (YDZ) thin films grown under UV-photon irradiation are reported in this article. Zr-Y metal precursor alloy thin films were successfully oxidized into cubic crystalline zirconia at room temperature under ultra-violet (UV) irradiation. Detailed transmission electron microscopy studies reveal that films are pin-hole free and form distinct grain boundaries upon high temperature annealing. In-plane ac impedance spectroscopy studies indicate that UV grown films have comparable electrochemical properties to the YDZ films grown by other methods. UV synthesis would be an attractive route to grow high quality ultra-thin oxide electrolytes at relatively low temperatures.

Synthesis and Phase Stability in Ultra-thin Solid Electrolytes: The Case of Zirconia Thin Films

Phase stability in 9.5 mol % yttria doped zirconia (YDZ) and pure zirconia thin films have been studied by transmission electron microscopy (TEM). Through detailed in-situ TEM analysis, we found that phase stability in nanoscale zirconia thin film depends on film thickness, grain size, and annealing ambient. Pure zirconia thin films of ~ 52 nm thickness were stabilized without any dopants at room temperature, while it transformed into a tetragonal phase upon heating to 400 oC. On the other hand, 9.5 % Yttria doping enables stabilization of the cubic structure regardless of grain growth. Annealing of poor crystalline YDZ films in air (oxygen rich) leads to tetragonal phase formation, while ultra-high vacuum (oxygen-deficient) annealed samples display cubic phase at high temperature.

Synthesis and High Temperature Electrochemical Properties of Y-Doped Zirconia Thin Films Synthesized under Photon Irradiation: A Route to Ultra-Thin Electrolyte Membranes

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Development of thin-film nano-structured electrolyte layers for application in anode-supported solid oxide fuel cells

This paper reports a study on the deposition of sol particles for the preparation of thin and ultra-thin electrolyte membrane layers (thickness < 5 μm–50 nm), which cannot be produced with regular powder-based processes. For the deposition process, a range of coating liquids with varying particle sizes, covering the complete range between standard suspensions with a particle size of several 100 nm and nano-particle sols, was prepared. In the first part, it is demonstrated that a colloidal sol route can be used for membrane formation on a regular macroporous SOFC anode (NiO/zirconia), when the sol particle size is adapted to the pore structure of the anode (particle size ∼ 200 nm). SEM characterization indicated a thickness in the range 3–4 μm after calcination at 600 °C and ca. 2 μm after sintering at 1400 °C, far below the limit for conventional powder-based deposition methods. In the second part, ultra-thin zirconia and ceria membrane films are prepared by spraying sols containing nano-particles (average size 5–6 nm). The layers show a thickness of ∼ 100 nm, a very narrow particle size distribution and tight ultra-microporous structure, which allows a sintering treatment below 1000 °C, and can be used as an additional electrolyte layer for improving the leak rate of the cell or as diffusion barrier.

Long-range ordering effect in electrodeposition of zinc and zinc oxide

In this paper, we report the long-range ordering effect observed in the electro-crystallization of Zn and ZnO from an ultrathin aqueous electrolyte layer of ZnSO4 . The deposition branches are regularly angled, covered with random-looking, scalelike crystalline platelets of ZnO. Although the orientation of each crystalline platelet of ZnO appears random, transmission electron microscopy shows that they essentially possess the same crystallographic orientation as the single-crystalline zinc electrodeposit underneath. Based on the experimental observations, we suggest that this unique long-range ordering effect results from an epitaxial nucleation effect in electrocrystallization.

Self‐organization of periodically structured single‐crystalline zinc branches by electrodeposition

AbstractWe report here the electrodeposition of periodically structured single‐crystalline zinc branches from an ultrathin aqueous electrolyte layer of ZnSO4. The main trunk and side branches of electrodeposits are regularly angled, and each branch is made of periodic bead‐like structures. Layered morphology has been observed on each bead. During electrodeposition, spontaneous oscillation of electric current occurs when constant voltage is applied across the electrodes, and the oscillation leads to periodic patterns on deposit branches. According to electron diffraction of transmission electron microscopy (TEM), the whole branch of electrodeposits has the same crystallographic orientation despite the fact that the branch looks like an assembly of beads. We interpret this unique growth behavior to the epitaxial nucleation in the transport‐limited growth system. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Nanoscale Polymer Electrolytes: Ultrathin Electrodeposited Poly(Phenylene Oxide) with Solid-State Ionic Conductivity

Incorporating ions within electrodeposited polymer dielectric films creates ultrathin solid electrolytes on a length scale (<50 nm) that bridges molecular electronics and conventional electrochemical devices. Electrooxidation of phenol in basic acetonitrile generates electrodeposited nanoscale (21 ± 2 nm), pinhole-free poly(phenylene oxide), PPO, films on indium−tin-oxide substrates. Solid-state electrical measurements using top electrode contacts (vapor-deposited Au, liquid Hg, or liquid Ga−In eutectic) confirm that these PPO films are electronically insulating (7 ± 2 × 10-12 S cm-1) with a high dielectric strength (1.7 ± 0.1 × 106 V cm-1). The insulating film is converted to an ultrathin solid polymer electrolyte by soaking in a solution of LiClO4−propylene carbonate and then heating under vacuum to remove solvent. Atomic force microscopy establishes that the salt-impregnated film is thicker (43 ± 10 nm) than the as-prepared PPO film. The X-ray photoelectron spectroscopic measurements suggest minimal retention of solvent in the film. Electrochemical impedance measurements demonstrate that the incorporated ions are mobile in the solid state with an ionic conductivity of 7 ± 4 × 10-10 S cm-1. Such ultrathin solid polymer electrolytes should enable progress toward nanoscopic solid-state ionic devices and power sources.

Spontaneous formation of periodic nanostructured film by electrodeposition: Experimental observations and modeling.

In this paper we report the spontaneous formation of a nanostructured film by electrodeposition from an ultrathin electrolyte layer of CuSO4. The film consists of straight periodic ditches and ridges, which corresponds to the alternating deposition of nanocrystallites of copper and copper plus cuprous oxide, respectively. The periodicity on the film may vary from 100 nm to a few hundred nanometers depending on the experimental conditions. In the formation of the periodically nanostructured film, oscillating voltage/current has been observed across the electrodes, and the frequency depends on the pH of the electrolyte and the applied current/voltage. A model based on the coupling of [Cu2+] and [H+] in the electrodeposition is proposed to describe the oscillatory phenomena in our system. The calculated results are in agreement with the experimental observations.

ChemInform Abstract: Investigation of the Corrosion of Metals Covered with Adsorbed Electrolyte Layers. A New Experimental Technique.

AbstractThe new method developed allows to measure the corrosion rate and the corrosion potential of metals covered by ultrathin electrolyte layers without a direct contact with the electrolyte film by using a Kelvin probe and a differential pressure meter, respectively.

The investigation of the corrosion properties of metals, covered with adsorbed electrolyte layers—A new experimental technique

A new method is described, which allows the investigation of the corrosion of metals, covered by ultrathin electrolyte layers. The corrosion rate and the corrosion potential are measured free of a direct contact with the electrolyte film using a Kelvin probe and a differential pressure meter, respectively.

A 14% efficient nonaqueous semiconductor/liquid junction solar cell

We describe the most efficient semiconductor/liquid junction solar cell reported to date. Under W-halogen (ELH) illumination, the device is a 14% efficient two-electrode solar cell fabricated from an n-type silicon photoanode in contact with a nonaqueous electrolyte solution. The cell′s central feature is an ultrathin electrolyte layer which simultaneously reduces losses which result from electrode polarization, electrolyte light absorption, and electrolyte resistance. The thin electrolyte layer also eliminates the need for forced convection of the redox couple and allows for precise control over the amount of water (and other electrolyte impurities) exposed to the semiconductor. After one month of continuous operation under ELH light at 100 mW/cm2, which corresponds to the passage of over 70 000 C/cm2, thin-layer cells retained over 90% of their efficiency. In addition, when made with Wacker Silso cast polycrystalline Si, cells yield an efficiency of 9.8% under simulated AMl illumination. The thin-layer cells employ no external compensation yet surpass their corresponding experimental (three-electrode) predecessors in efficiency.