The most commonly used anode in development of solid oxide fuel cells (SOFCs) is currently a Ni/yttria-stabilized zirconia (YSZ) cermet. 1 Despite excellent properties for operation in hydrogen, the Nibased anode suffers from some disadvantages related to volume instability upon redox cycling and detrimental carbon formation caused by cracking of methane during operation in dry natural gas. For mixtures of CH 4 and H 2 O the catalytic properties of Ni cause total conversion over the first few millimeters of a cell. The endothermic nature of the steam reforming process can thus cause steep thermal gradients potentially capable of mechanically damaging the cell stack. 2 The basic requirements for an SOFC anode are as follows. 1. Electrochemical ability to oxidize methane directly without deposition of carbon, or alternatively adequate catalytic properties for steam reforming combined with the ability to oxidize H 2 and CO.2. Adequate electronic conductivity and preferably also oxide-ion conductivity to enhance electrode efficiency.3. Physical and chemical stability in oxidizing and reducing atmospheres, and chemical compatibility with the electrolyte during production and operation. 4. A thermal expansion coefficient (TEC) value comparable with that of the supporting element of the cell.Lanthanum-chromite (LC)-based materials have previously been investigated primarily as interconnect material, where typical dopants are Ca (LCC) and Sr (LSC). However, this group of materials may also be considered for use as anode material. The aim of this work has been to examine to which extent selected doped LC materials fulfill the listed requirements for anodes, and to which extent the problems faced with Ni/YSZ electrodes can be avoided. Key properties of selected LC materials are reviewed in the following.Electrochemical and catalytic properties.-Experiments reported in literature indicate little or no reforming activity or direct oxidation of CH 4 on lanthanum chromites, 3-7 disregarding experiments where a catalytic active current collector such as Pt has been applied. 8,9 Considering this, addition of a steam reforming catalyst to the LC electrode might be required. 4,7 Dissociation (cracking) of dry CH 4 occurs on LC materials at temperatures of 800 to 900ЊC, 5 but can apparently be avoided by addition of small amounts of water. 7 Preferably the reforming step should take place internally near the anode, where (i) water is evolved by the anode reaction and therefore does not have to be added or recycled, and (ii) heat for the endothermic steam reforming reaction is available from ohmic losses in the fuel cell during operation.Conductivity.-The electronic conductivity of LC is enhanced by the use of divalent doping on either A or B sites in the perovskite lattice. At high pO 2 , the charge balance is maintained by the formation of Cr 4ϩ . However, when the material is exposed to reducing conditions, the lattice looses oxygen, oxygen vacancies are formed, and the charge balance is now attained by reduction of Cr 4ϩ to Cr 3...

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In this study, electrochemical impedance spectroscopy (EIS) is applied in combination with cyclic voltammetry (CV) and current density -cell voltage curves (iV-curves) to investigate the processes contributing to the total impedance of a polymer electrolyte membrane electrolysis cell (PEMEC). iV-curves were linear above 0.35 A cm −2 implying ohmic processes to be performance limiting, however the impedance spectra showed three arcs indicating three electrochemical reactions at these conditions not to be purely ohmic, but also to have capacitive properties. A hypothesis that the composite IrO x /Nafion anode catalyst layer causes two of these arcs with a constant sum of resistance and current constrictions cause the third arc, is suggested. This hypothesis implies that the total differential cell resistance at current densities above 0.35 A cm −2 is purely ascribed to protonic resistance in Nafion in this type of PEMEC. The interest in renewable electrical energy obtained from e.g. wind turbines and solar cells have increased over the past years. However, the demand of electrical energy from society does not always correlate with the renewable electrical energy production, and a method to store the excess electrical energy for later use is needed. One such method is electrolysis of water into hydrogen and thus converts electrical energy into chemical energy bound in the hydrogen molecules, and thereby the energy can be stored. PEMECs have the ability to operate at high current densities, which reduces the operation costs.