High Temperature Water Electrolysis Using Metal Supported Solid Oxide Electrolyser Cells (SOEC)

Metal supported cells as developed according to the DLR SOFC concept by applying plasma deposition technologies were investigated for use as solid oxide electrolyser cells (SOEC) for high temperature steam electrolysis. Cells consisting of a porous ferritic steel support, a diffusion barrier layer, a Ni/YSZ hydrogen electrode, a YSZ electrolyte and a LSCF oxygen electrode were electrochemically characterised by means of i-V characteristics and electrochemical impedance spectroscopy measurements including a long-term test over 2000 hours. The cell voltage during electrolysis operation at a current density of -1.0 A cm-2 was 1.28 V at an operating temperature of 850 °C and 1.4 V at 800 °C. A long-term test run over 2000 hours with a steam content of 43% at 800 °C and a current density of -0.3 A cm-2 showed a degradation rate of 3.2% per 1000 hours. The impedance spectra revealed a significantly enhanced polarisation resistance during electrolysis operation compared to fuel cell operation which was mainly attributed to the hydrogen electrode

Application of In-Situ Diagnostic Methods for the Study of SOFC Operational Behaviour

In order to optimise the operational behaviour of fuel cells and minimise cell degradation it is very helpful to use in-situ and ex-situ analytical methods. The application of advanced diagnostic methods by monitoring cell characteristics under real operating conditions provides valuable information to be used for the development of degradation mitigation strategies. The application of these methods in SOFC development is significantly limited mainly due to the experimental problems that are associated with the high operating temperature. However, an increasing effort in developing and implementing non-traditional analytical methods such as spatially resolved measurements and imaging techniques for SOFC development has been made in recent years. The presentation gives an overview of in-situ diagnostic methods that are applied at DLR Stuttgart for the study of SOFCs. It includes spatially resolved measurements with an experimental segmented cell configuration where different techniques such as IV characteristics, impedance spectroscopy, gas chromatography and temperature measurement are involved. The investigation by means of segmented cells aims at the determination of local effects and the identification of critical operating conditions during technically relevant SOFC operation. Recently, a new test setup with transparent optical access has been built up allowing for microscopic observation of processes within the cell as well as for application of in-situ laser Raman spectroscopy to determine highly resolved concentrations of gas species along a flow channel. Examples of analytical studies by applying these diagnostic methods are presented and potentials and limitations of the different techniques are discussed

A Novel Concept for In-Situ Gas-Phase Laser Raman Spectroscopy for SOFC

Gas-phase laser Raman spectroscopy has recently been adopted to determine the concentrations of relevant gaseous species within the anode flow channel with high spatial and temporal resolution during operation at technically relevant operating conditions. The paper describes the configuration of an optically accessible SOFC, the laser system and optical setup for 1 D Raman spectroscopy as well as the challenges associated with the measurements of an electrolyte supported cell of a size of 50 x 50 mm2. At different operating conditions Raman spectra were recorded and concentration profiles of gas species along the flow path in the anode were determined demonstrating this new experimental approach for a better understanding of SOFC processes

Electrochemical Impedance Analysis of Symmetrical Ni/Gadolinium-Doped Ceria (CGO10) Electrodes in Electrolyte-Supported Solid Oxide Cells

One of the most powerful tools in solid oxide cell (SOC) characterization is electrochemical impedance spectroscopy, which can unfold important insights into SOC performance characteristics and degradation behavior. To obtain a better understanding of the electrochemical behavior of Ni/CGO fuel electrodes, this work presents a comprehensive investigation of state-of-the-art Ni/CGO10- based electrolyte-supported cells. Commercial Ni/CGO10|CGO10|3YSZ|CGO10|Ni/CGO10 symmetrical cells were characterized between 550–975°C at pH2 = 0.8 bar and pH2O = 0.2 bar, and for different H2/H2O gas mixtures at 550°C. (i) Small electrode area, (ii) thin electrodes and (iii) large gas flow rates were used to minimize mass transport contributions. Based on distribution of relaxation times (DRT) analysis an equivalent circuit model was derived. Electrode process contributions on Ni/CGO were determined by means of a complex non-linear least square fit of the equivalent circuit model to the experimental data. One low frequency process at 0.1–1 Hz and one middle frequency process at 10–100 Hz were identified and correlated to a surface and a bulk process, respectively. Values for the apparent activation energy barriers and reaction orders with respect to steam and hydrogen content were determine

Synthesis and Evaluation of the A–site Deficient Perovskite La0.65Sr0.3Cr0.85Ni0.15O3-δ as Fuel Electrode for High Temperature Co–electrolysis Enhanced by In Situ Exsolution of Ni Nanoparticles

In this work, we focused on the lanthanum strontium chromite (LSC) matrix with the purpose to partially substitute the B-site with an electrocatalytic reducible transition metal that could be exsolved in situ. Therefore, nickel was considered at a substitution level of 15%. In addition, an A-site deficiency was formulated in order to enhance the exsolution capability of the electrocatalyst. A precursor was synthesized by wet-chemical method and further calcined in air. Single phase was obtained with the formulation La0.65Sr0.3Cr0.85Ni0.15O3-δ (L65SCN) which was characterized by X–ray diffraction (XRD) and Rietveld refinement analyses. Exsolution was investigated by means of thermogravimetric analysis (TGA) under reducing conditions and temperature-programmed reduction (TPR). Scanning electron microscopy (SEM) was used to study the particle morphology and its evolution. Ni particle exsolution was observed after exposure to a reducing atmosphere. The behaviour of the L65SCN perovskite was compared with the stoichiometric La0.70Sr0.3Cr0.85Ni0.15O3-δ (L70SCN). Aiming at evaluating the electrochemical performance, electrolyte-supported cells were manufactured by screen printing and sintering of composite L65SCN/CGO as fuel electrode and La0.58Sr0.4Fe0.8Co0.2O3-δ (LSCF) as air electrode on CGO-3YSZ-CGO substrates. The produced cells were tested in electrolysis and co–electrolysis mode and characterized by means of Electrochemical Impedance Spectroscopy (EIS) and polarization curves. Results will be presented with the perspective of SOEC applications

Polarised Quark Distributions in the Nucleon from Semi-Inclusive Spin Asymmetries

We present a measurement of semi-inclusive spin asymmetries for positively and negatively charged hadrons from deep inelastic scattering of polarised muons on polarised protons and deuterons in the range $0.003$1 GeV$^2$. Compared to our previous publication on this subject, with the new data the statistical errors have been reduced by nearly a factor of two. From these asymmetries and our inclusive spin asymmetries we determine the polarised quark distributions of valence quarks and non-strange sea quarks at $Q^2$=10 GeV$^2$. The polarised $u$ valence quark distribution, $\Delta u_v(x)$, is positive and the polarisation increases with $x$. The polarised $d$ valence quark distribution, $\Delta d_v(x)$, is negative and the non-strange sea distribution, $\Delta \bar q(x)$, is consistent with zero over the measured range of $x$. We find for the first moments $\int_0^1 \Delta u_v(x) dx = 0.77 \pm 0.10 \pm 0.08$, $\int_0^1 \Delta d_v(x) dx = -0.52 \pm 0.14 \pm 0.09$ and $\int_0^1 \Delta \bar q(x) dx= 0.01 \pm 0.04 \pm 0.03$, where we assumed $\Delta \bar u(x) = \Delta \bar d(x)$. We also determine for the first time the second moments of the valence distributions $\int_0^1 x \Delta q_v(x) dx$.Comment: 17 page

Spin asymmetries A1 and structure functions g1 of the proton and the deuteron from polarized high energy muon scattering.

Adeva B, Akdogan T, Arik E, et al. Spin asymmetries A(1) and structure functions g(1) of the proton and the deuteron from polarized high energy muon scattering. Phys.Rev. D. 1998;58(11): 112001.We present the final results of the spin asymmetries A(1) and the spin structure functions g(1) of the proton and the deuteron in the kinematic range 0.0008 < x < 0.7 and 0.2 < Q(2) < 100 GeV2. For the determination of A(1), in addition to the usual method which employs inclusive scattering events and includes a large radiative background at low x, we use a new method which minimizes the radiative background by selecting events with at least one hadron as well as a muon in the final state. We find that this hadron method gives smaller errors for x < 0.02, so it is combined with the usual method to provide the optimal set of results. [S0556-2821(98)07017-9]

Electrochemical Study of Interaction of Nickel and Alkaline Solutions

Nickel is an important material used as catalyst in electrochemical devices, e.g., as anode and cathode catalyst in alkaline electrolysers, as anode catalyst in alkaline fuel cells, in different batteries or as current collector grid in alkaline electrolyser. The reaction steps of heterogeneous electro-catalytic processes run at the solid-liquid interface. Therefore the understanding of the interaction of the electrolyte, especially of alkaline solutions, with the nickel surface is important. Depending on the technical application, Ni and different Ni alloys are used and therefore different oxide films are formed on the metal surface. To reduce the performance losses of the electrochemical device given by the low conductivity of such oxide films, much attention was paid to the understanding of the conduction mechanism of oxide films. The conductivity of nickel oxide surfaces is influenced by the thickness and the chemical composition of the oxide layer, as well as the gradients of the composition, depending on the applied potential and composition (purity) of the electrolyte. In particular, the influence of different contents of chloride ions (10 ppm, 100 ppm and 500 ppm) in alkaline solution (10 N NaOH) at 85°C was investigated. For the investigation of the electrochemical behaviour of nickel electrodes in 10 N NaOH with different Cl- content at 85°C, a polished rotating disk nickel electrode (>99,2% Ni) with 1 cm2 geometric surface was used. The used counter electrode was a platinum foil and a RHE (Hydroflex from Gaskatel-Kassel, Germany) as reference electrode. A first characterization of the Ni electrode was performed by recording cyclic voltammograms (CV) in the potential range from open cell potential (OCP) up to 1.5 V and down to 0 V with a scan rate of 100 mV/s. In addition, electrochemical impedance spectra (EIS) at OCP and impedance series measurements (18 spectra) over 3 h at 1.15 V in the frequency range from 50 mHz to 100 kHz were measured. From the impedance spectra one can conclude that with increasing Cl- content in the electrolyte the impedance modulus in the low frequency range decreases, corresponding to an increase of the corrosion current. The same conclusion can also be drawn from CV measurements, proving that the addition of Cl- ions enhances the formation of an oxide layer, especially in the potential range between 1 V and 1.4 V