Thin Anodic Layers Research Articles

30 μm Thin Anode Gas Diffusion Layers for Optimized PEM Fuel Cell Operation at 120 °C and Low Relative Humidity

Achieving higher temperature operation above 100 °C, while increasing the volumetric power density are key targets in current fuel cell development. In this work, a novel type of polyvinylidene fluoride and graphite based microporous film of only 30 μm thickness, acting as thin alternative to typical gas diffusion layers (GDLs) on the anode side of a hydrogen fuel cell is reported. Ex situ measurements (contact angle, electric conductivity, gas permeability measurements, and scanning electron microscopy (SEM)) reveal that the thin, porous layers achieve comparable chemical, electrical, and transport properties to commonly employed and significantly thicker gas diffusion layers. In‐situ fuel cell tests reveal considerable improvements, particularly in the target operation range beyond 100 °C: At 120 °C and 30% RH and 0.65 V cell voltage, the best thin anode layer enables a 51% higher current density (1342 vs 885 mA cm−2) and a 9% lower high frequency resistance (76 vs 84 mΩ cm−2) compared to a commercial state‐of‐the‐art GDL.

Fabrication of Low-Temperature Solid Oxide Fuel Cells via Development of Magnetron Sputtering Process

We herein report the development of the sputtering process for the fabrication of thin film low-temperature solid oxide fuell cells (LT-SOFCs) supported by anodized aluminum oxide (AAO). The process development has been conducted for each component, anode, electrolyte, electrolyte/cathode interlayer, and cathode to achieve not only high performance but also durability. In order to fabricate catalyst-ion conducting anode cermet, Ni and GdCe co-sputtering is utilized. Since the AAO is an electrical insulator, the electrons produced from the anode requires to pass through the thin anode layer to be collected which can lead to high current collecting resistance. Therefore, sputtering conditions such as power, pressure, and time are adjusted to produce the anode with minimal ohmic loss stemming from current collection. For the electrolyte (YSZ) and interlayer (GDC), a ceramic sputtering recipe has been developed to achieve high density and uniformity, which are the most critical requirement for these components. Through optimization of the gun angle, power, pressure, and the target to substrate distance (TSD), a highly dense and uniform ceramic electrolyte can be deposited on various AAO substrate sizes. For the cathode, a mixed ionic electronic conducting cathode sputtering recipe has been developed to enhance oxygen reduction reaction (ORR) at low operating temperatures. We have been developing the sputtering process to fabricate a nanocrystalline and highly porous LSC-GDC cathode with desired microstructure to enhance the ORR activity. Through the integration of the aforementioned sputtering process development, durable and high performance LT-SOFCs have been successfully fabricated on AAO substrates up to 15cm x 15cm size. Suppered thin film cells have shown superior performance at low operating temperatures, e.g., peak power density of 1.5W/cm2 at 550oC with hydrogen fuel.

Fabrication and Characterization of Thin-Film SOFC Supported by Microchannel-Structured Zirconia Substrate for Direct Methane Operation

Ni-cermet anode demonstrates excellent catalytic activity and electrical conductivity but suffers from carbon deposition issue. To utilize Ni-cermet anode while preventing carbon deposition, a synergic strategy is employed to design anode electrode. In particular, Zr is incorporated into Ce0.8Sm0.2O2-δ lattice to tailor oxygen storage and catalytic properties of Ni-Ce0.8-xSm0.2ZrxO2-δ anode for improving electrochemical oxidizations of various fuel species. An inert thick YSZ microtubular substrate with radially well-aligned microchannels open at the inner surface is used to support multi thin functional layers of solid oxide cell, i.e., Ni current collector, Ni-Ce0.8-xSm0.2ZrxO2-δ anode, YSZ/SDC electrolyte, and LSCF cathode. The thick YSZ substrate is able to inhibit the ratio of fuel to product gases in the thin anode functional layer, which favors the prevention of carbon buildup in the thin anode layer when synergistically combined with Ni-Ce0.8-xSm0.2ZrxO2-δ anode material. The microchannels embedded in the YSZ substrate can also avoid too much dilutions of the fuel in the anode functional layer. The cell is fabricated and tested with both hydrogen and methane as the fuel. A short-term test is conducted with methane as fuel and good stability is obtained. The fundamental mechanisms for the prevention of carbon buildup in anode functional layer are also discussed.

Anode supported SOFC fabricated with functional anode: role of variation of fuel and oxidants

The present study focuses on the efficacy of core-shell nickel (Ni) @ stabilized zirconia (SZ) functional anode towards the oxidation of both hydrogen and reformed methane as fuel in presences of steam as one of the important component. The redox reaction is processed by adsorption on anode catalyst followed by decomposition and charge transfer reaction. This is further accelerated by the extension of triple phase boundary (TPB) regions (Ni/SZ/gas) within (intra-) and inter-anode involving electrolyte. Core-shell Ni@SZ cermet enables the extension of TPB regions in contrast to conventional matrix. Authors have reported four configurations for anode support, wherein the layered structure involving conventional Ni-SZ is placed at the fuel side and layers of Ni@SZ on the top. The thin anode layer in vicinity to the electrolyte with optimized Ni content of 28/32 vol % acts as the primary electrocatalytic layer and shows a maximum current density of ∼4 A.cm−2@0.7 V, 800°C with moist hydrogen as fuel. Multifuel capability in the cell with similar functional anode is demonstrated using 20 % reformed methane with optimum steam/carbon ratio (2:1) having current density of ∼ 1.13 A.cm−2 under similar condition. The findings are correlated using impedence spectroscopy and corroborated with morphological findings.

A Micromachined Flexible Hollow Cathode Discharge Device

This paper presents the fabrication and test of a flexible hollow cathode discharge device. The discharge device consists of three layers; a thin anode layer, an insulation layer and a hollow cathode layer. The hollow cathode discharge is characterized by its high current density. The discharge device is fabricated by micromachining technology. The anode and cathode are made of aluminum and nickel, respectively. Polyimide is chosen as an insulating material because of its excellent dielectric properties and good mechanical stability. The device has an array of 10 ×10 holes for the discharge. The hole diameter and depth are 70 and 110 µm, respectively. The size of the flexible discharge device is 9 ×9 ×0.13 mm3. The discharge test was performed in an argon gas chamber at room temperature. The current is measured during the discharge at various applied voltages. At a pressure of 510 Torr, the discharge appears at an operating voltage of 270 V. The discharge is also observed at atmospheric pressure.

Reforming of methane, ethylene, and desulfurized kerosene over Ni-8YSZ catalyst

Abstract For solid oxide fuel cell (SOFC) systems fueled by kerosene, reforming of methane, ethylene, and desulfurized kerosene was investigated over Ni-8YSZ catalyst at 750 °C and steam-to-carbon ratio (S/C) = 3 as a function of gas hourly space velocity (GHSV). At temperatures higher than 650 °C, a thick Ni-8YSZ layer exhibited a high catalytic activity for reforming of methane, ethylene, and kerosene of which gas concentration in a pre-reformate gas was less than 1%. On the other hand, thin anode layer will require some modification of the catalytic activity. Carbon was formed as particles in the inlet quartz wool via pyrolysis of ethylene at flow-stagnation points, which will cause pore closure in Ni-anode catalysts. This type of carbon formation would bring about inhomogeneous flow-and-voltage distribution in a cell. Direct feed of steam and kerosene to Ni-8YSZ was examined at GHSV = 2400 h −1 , S/C = 3 and 550–750 °C. Gas composition analysis and FTIR spectra indicate that high kerosene conversion (≥95%) could be attained at 650–750 °C over Ni-8YSZ assuming relatively thick Ni-anode layer. The catalytic activity was deteriorated at lower temperatures. Clear carbon deposition on Ni-8YSZ or inlet quartz wool was not observed on the experimental condition. The direct feeding system may be possible only at high temperatures and high S/C. As long as a temperature of anode-supported SOFCs is kept over 650 °C, small amount of methane, ethylene, and kerosene will not harm performance of the SOFCs.

TDS study of the anodic layer on emersed polycrystalline platinum

Polycrystalline platinum electrodes emersed from H2SO4 and HClO4 solutions were transfered to ultrahigh vacuum for study by thermal desorption spectroscopy (TDS). The double layer was generated at potentials between 0.05 and 2.75 V. Our interest was focused on the surface coverage with water, oxygen and sulphate as a function of the applied electrode potential. The desorption of O2 from polycrystalline Pt starts 500 mV earlier (at 700 mV/RHE) than the value obtained earlier on Pt(100). The chemical state of thin films generated for 30 s at positive potentials seems to be a mixture of hydroxides and oxides. Whereas water desorption signals increase in parallel with those of oxygen, the sulphate coverage decreases with increasing potential.The growth of anodic layers induced by a square-wave cycling method was monitored by thermal desorption of water and oxygen as well as by cyclic voltammetry. In contrast with thin anodic layers, anions are incorporated into thick layers generated in H2SO4 and HClO4.

The formation of anodic layers on annealed copper surfaces in phosphate-containing solutions at different pH

The electrochemical behaviour of Cu in different phosphate buffers is studied through electrochemical techniques combined with scanning electron microscopy and energy dispersive X-ray analysis. At pH 6.0 and 8.0 the onset of passivation is due to the anodic formation of a basic Cu(II) phosphate, whereas at pH 11.5 the passivating layer corresponds to a duplex Cu(I) oxide-Cu(II) oxide layer. The potentiostatic anodic current transients can be reproduced by a model involving the initial growth of a thin anodic layer and the simultaneous electrodissolution of Cu. The electrodissolution of passivated Cu takes place through the passivating layer. This reaction contributes to the thickening of the outer part of the passivating layer.

Ellipsometric changes produced by oxidation—reduction potential cycles applied to cadmium in sodium hydroxide solutions

Ellipsometry data obtained for the CdNaOH solution interface under the influence of potential cycles in the potential window where the Cd(OH) 2CdO layer can be electroformed and electroreduced, are particularly sensitive to both the layer thickness and the upper electroformation potential limit. The best fitting of the experimental results is obtained for two limiting situations. For thin anodic layers ( d ⩽ 6 nm) the ellipsometric data fit the equation ñ=1.55− i 0.005, whereas for relatively thicker anodic layers ( d > 7 nm) data can be adjusted through the equation ñ=2.6− i 0.10. These equations are consistent with the electroformation of a hydrous cadmium oxide layer at low potentials, and a cadmium oxide layer with a lower water content which grows beneath the former one at high potentials. Otherwise, the electroreduction of the anodic oxide layer yields a cadmium overlayer which exhibits a shift of the corresponding ellipsometric data as compared to the starting cadmium surface. This shift is presumably related to the development of different metal surface textures resulting from the different electroreduction conditions.

Growth and dissolution of thin anodic layers on GaAs: A photoelectrochemical study

Thin anodic oxide films were allowed to grow on the surface of n-type GaAs electrodes. The dissolution rate of these films was controlled by the rotating electrode technique. Thickness and formation field of the oxide were evaluated by means of chroanoamperometry. The potential distribution across the semiconductor-electrolyte junction was analysed by means of capacitance measurements. Ring-disc experiments were performed in order to study the influence of the oxide film on the redox reactions at the semiconductor electrode.

Anodic oxide/GaAs and InP interface formation

The initial stages of anodization of GaAs and InP were investigated in order to determine the factors which affect the oxide–semiconductor interface formation. This was accomplished by ESCA profiling thin anodic layers grown on chemomechanically polished wafers. Oxides on both InP and GaAs appear to be initiated by a nucleation and island growth process with the film becoming continuous at a thickness of approximately 40 Å. The oxide/GaAs interface was found to be composed of a Ga2O3 layer with indications of elemental As near the substrate. The oxide/InP interface had a uniform distribution of In2O3 and P2O5. The data indicates that dissolution of As2O3 or P2O5 is not a significant factor in the interface formation but the thermodynamic stability of the oxide could be important.