Permeability of gases In the anode of An anode-supported SOFC

International audienceIn the high current density regime, the performance of SOFCs is limited by concentration overpotentials when the demand for reactants exceeds the capacity of the porous cermet anode to supply them by gas diffusion mechanisms, and when the rate at which water is produced exceeds the ability of the anode to evacuate water. A compromise should be found between maintaining a high level of activation in the anode, which means a high density of Triple Phase Boundaries (TPB) usually associated with small grains size and small pores, and high gas permeability generally associated with large interconnected pores. The present work aims at determining experimentally the gas permeability of the anode as a function of the percolation, tortuosity and volume fraction of the pores. Anodes with varying porosity ensured by different quantities of pore former were obtained by cold pressing and sintering. SEM image analysis, mercury intrusion porosimetry and permeability measurements for different gases were performed. However, non-linearity as a function of the gases molecular weight is observed

Dual cells with mixed protonic-anionic conductivity for reversible SOFC/SOEC operation

International audienceThe dual cell concept is a novel design for solid oxide fuel cells operating at intermediate temperature. The cell comprises a series of five layers with different compositions, alternating two dense electrolytes and three porous layers, i.e. the outer electrodes and a central membrane. The dual cell concept makes it possible to separate the compartment for water formation from both fuel and oxidant chambers. Such a three-chamber configuration gives many advantages related to fuel dilution, materials corrosion, and reversibility between fuel cell and electrolyser operational modes (SOFC/SOEC) at high temperature. Dual conductivity (protonic/anionic) can be achieved by joining two dense BaCe0.85Y0.15O3-δ (BCY) and Ce0.85Y0.15O2-δ (YDC) electrolytes through a porous ceramic central membrane made up of both materials. Complete anode-supported dual cells have been fabricated by a combination of pressing, casting, printing, wet spraying, and plasma spraying techniques. Electrochemical tests carried out by impedance spectroscopy showed the feasibility of the concept and successful reversible operation of the dual cell. The fabrication route, the microstructural and electrochemical testing results are reported in this work, and partially compared to simulated results from an electrochemical model developed describing the dual cell concept

Hydrogen Evolution on Ni Electrode During Synthetic Tap Water Electrolysis

The current research attempts to investigate the influence of the contaminants in the tap water on the hydrogen as well as oxygen evolution reaction (HER/OER) on Ni electrodes. Steady-state galvanostatic polarization, potentiodynamic curves and Electrochemical Impedance Spectroscopy were applied to evaluate the electrochemical kinetic parameters of the reaction ¿ Tafel slope, charge transfer coefficient, exchange current density as well as the activation energy. Long-term stability test results are also included.JRC.DDG.F.2-Cleaner energ

Hydrogen evolution on nickel electrode in synthetic tap water - alkaline solution

The effect of tap water contaminants on the kinetics of the hydrogen evolution reaction on a nickel electrode in 1 mol dm3 KOH was investigated by galvanostatic polarization and electrochemical impedance spectroscopy techniques. It was found that the tap water contaminants lead to an increase in the overpotential of the hydrogen evolution reaction, especially at low temperatures. The combination of electrochemical techniques, as well as physicochemicals such as SEM and EDAX ones, confirmed that the contaminants are specifically adsorbed and blocked the available electrode surface for the reaction. It was concluded that they do not participate in an electrochemical reaction in the potential region where HER occurs. Besides the short term negative impact on the rate of hydrogen evolution, a 55 h test revealed that the overpotential shows a steady increase over time in presence of tap water contaminants, while in absence of these contaminants the overpotential is constant.JRC.F.2-Cleaner energ

Hydrogen evolution on nickel electrode in synthetic tap water - alkaline solution

The effect of tap water contaminants on the kinetics of the hydrogen evolution reaction on a nickel electrode in 1 mol dm(-3) KOH was investigated by galvanostatic polarization and electrochemical impedance spectroscopy techniques. It was found that the tap water contaminants lead to an increase in the overpotential of the hydrogen evolution reaction, especially at low temperatures. The combination of electrochemical techniques, as well as physicochemicals such as SEM and EDAX ones, confirmed that the contaminants are specifically adsorbed and blocked the available electrode surface for the reaction. It was concluded that they do not participate in an electrochemical reaction in the potential region where HER occurs. Besides the short term negative impact on the rate of hydrogen evolution, a 55 h test revealed that the overpotential shows a steady increase over time in presence of tap water contaminants, while in absence of these contaminants the overpotential is constant. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved

Impedance Behavior of LSCF/YDC/LSCF Symmetrical Half Cell Prepared by Plasma Spray

Impedance studies of electrolyte supported symmetrical half cells La0,6Sr0,4Co0,2Fe0,8O3- /Ce0,85Y0,15O2-/La0,6Sr0,4Co0,2Fe0,8O3- with electrodes deposited by atmospheric plasma spraying (APS) show that the applied technique influences reversibly the substrate properties, introducing additional contribution to the interface substrate/electrode. After thermal treatment in temperature range 100-800oC during the impedance measurements, an annealing effect is observed. It eliminates the additional increase of the electrolyte resistivity and increases slightly the polarization resistance. The observed effect could be related to thermally and/or mechanically induced local microstructure defects, caused by the APS procedure. The obtained results show that for stabilization of the cell’s performance, annealing should be performed after the APS deposition. It can be supposed that an appropriate annealing atmosphere may prevent the electrodes deactivation

Towards Understanding the Dual Membrane Fuel Cell (IDEAL-Cell) Using a Metallic Central Membrane

This work presents results of a measurement setup which was constructed for understanding the performance contributions of the individual compartments and reactions taking place in the patented concept of IDEAL-Cell (described in detail in(1)). By inserting a third measurement point at the central membrane of an ideal cell it was possible to measure the cell in three different modes corresponding to hydrogen, oxygen compartment and the full cell. Recorded maximum power densities of (~4, ~7, 11, 16) mW/cm² at (600, 650, 700, 750) °C in H2-O2 atmosphere respectively were observed which were similar to the values of proof of concept ideal cell samples tested so far. Moreover in this setup it was possible to record higher maximum power densities for the hydrogen (proton conducting) compartment which was (~14, 22, 33*, ~38*) mW/cm² at (600, 650, 700, 750) °C

Pile à combustible avec cathode avec canaux

L'invention concerne une pile à combustible comprenant - une anode (10) apte à oxyder un premier composé Ml en premiers ions M(m+), - un premier électrolyte (20) en contact avec cette anode, - une cathode (50) apte à réduire un second composé N2 en seconds ions N(n_), - une membrane centrale (30) poreuse dont une des faces (32) est en contact avec ce premier électrolyte (20), et dont la face opposée (35) est en contact avec cette cathode, le premier électrolyte (20) étant constitué d'un matériau apte à conduire les ions M(m+), la membrane centrale (30) étant constituée d'un matériau apte à conduire à la fois les ions M(m+) et les ions N(n_). La cathode (50) est traversée par un réseau de canaux (52) qui débouchent chacun sur la membrane centrale (30) et sur une surface libre de la cathode (50), la dimension minimale d'une section transversale d'un quelconque de ces canaux (52) étant supérieure à 20 μm de telle sorte que l'évacuation du produit P résultant de la réaction des ions M(m+) et des ions N(n_) depuis la membrane centrale (30) vers l'extérieur de la pile à combustible (1) au travers de ces canaux (52) est possible

Differential analysis of SOFC current-voltage characteristics

Solid Oxide Fuel Cells (SOFCs) are regarded as a promising technology for economic power generation due to their high efficiency and large fuel flexibility. Durability is a severe hurdle towards their deployment. The near future Targets in respect to Degradation Rate (DR) are about 0.1%kh-1, which needs improved monitoring and diagnostics.This work aims at introducing a new approach based on Differential Analysis of the i-V curves, named DiVA. It operates with the Differential Resistance Rd and its evolution during long term testing. Two new performance indicators are introduced. Since derivatives are more sensitive to small deviations, the Differential Resistance Analysis (DRA) ensures increased sensitivity and information capability in respect to degradation monitoring and diagnostics, which is demonstrated on a small stack during thermal cycling conditions - before and after first thermal cycle, on button cells tested up to 9000 h, as well as on button cells operating in fuel cell and in electrolysis mode. The results show that DRA is several times more sensitive in comparison with the classical DR evaluation based on registration of the voltage decrease at constant current