The sputtering of wollastonite (CaSiO3) by solar wind-relevant ions has been investigated experimentally and the results are compared to the binary collision approximation (BCA) codes SDTrimSP and SRIM-2013. Absolute sputtering yields are presented for Ar projectiles as a function of ion impact energy, charge state and impact angle as well as for solar wind H projectiles as a function of impact angle. Erosion of wollastonite by singly charged Ar ions is dominated by kinetic sputtering. The absolute magnitude of the sputtering yield and its dependence on the projectile impact angle can be well described by SDTrimSP as long as the actual sample composition is used in the simulation. SRIM-2013 largely overestimates the yield especially at glancing impact angles. For higher Ar charge states, the measured yield is strongly enhanced due to potential sputtering. Sputtering yields under solar wind-relevant H + bombardment are smaller by two orders of magnitude compared to Ar. Our experimental yields also show a less pronounced angular dependence than predicted by both BCA programs, probably due to H implantation in the sample. Based on our experimental findings and extrapolations to other solar wind ions by using SDTrimSP we present a model for the complete solar wind sputtering of a flat wollastonite surface as a function of projectile ion impact angle, which predicts a sputtering yield of 1.29 atomic mass units per solar wind ion for normal impact. We find that mostly He and some heavier ions increase the sputtering yield by more than a factor of two as compared to H + bombardment only.

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Micro-structured thin-film electrodes were employed to investigate the capacitive behavior of nickel on yttria-stabilized zirconia (YSZ) electrolytes by means of electrochemical impedance spectroscopy. Electrodes with different shapes and electrode areas clearly showed a linear relationship between capacitance and the electrode area. Electrostatic double layer models, however, could not explain the observed area specific capacitance value of ca. 3 F/m 2 . This fact, the characteristic voltage dependence with a hysteresis, and the effect of H 2 S on the electrode capacitance indicate substantial contributions of a chemical capacitance. Solid oxide fuel cells (SOFCs) present a promising technology for direct conversion of chemical energy into electrical energy due to their high efficiency and fuel flexibility while causing little polluting emissions.1 Much research effort was devoted to the optimization of SOFC cathodes and cathodic polarization losses were substantially reduced.2 Consequently, in modern SOFCs the anode, which usually consists of a nickel/yttria stabilized zirconia (YSZ) cermet, may (again) contribute significantly to the overall cell losses. However, despite many investigations of the electrochemical anode behavior, fundamental properties of Ni/YSZ anodes are still far from being well understood. Therefore, considerable research still needs to be done to gain an in-depth understanding of the electrochemistry of Ni/YSZ electrodes, and to further optimize the performance of SOFC anodes.While having advantageous properties for application in operating SOFCs, Ni/YSZ cermet electrodes are often only of limited use for such fundamental research studies, since transport resistances due to ion conduction or gas diffusion and ill-defined geometry make data analysis very challenging. In contrast, model electrodes and in particular micro-structured thin-film electrodes -often referred to as pattern electrodes -are particularly suited for basic research studies.9-30 One of the main advantages of pattern electrodes is that their geometry can be controlled in a well-defined manner and thus geometry dependencies of electrochemical parameters can be obtained much easier compared to cermet electrodes. 31,32 So far, most research effort has been put into explaining the resistive behavior of Ni/YSZ model electrodes, while capacitive effects are still much less understood, despite their importance in impedance measurements. In previous literature high area specific capacitance (ASC) values of Ni/YSZ electrodes were reported, which could not be explained by a classical Helmholtz-type double layer. 12,33,34 A comparison of Ni, Pt and Au electrodes on YSZ also showed significantly higher capacitances of the Ni electrodes, further suggesting additional contributions to capacitive effects.12 Proposed mechanisms for the increased capacitance values were based on chemical processes at the electrode, such as proton ad/absorption 33 and valence changes of impurity ions. 34 Another capacitive model of metal electrodes on YSZ...

Micro-patterned metal/ceramic model thin film electrodes were used to investigate the hydrogen oxidation mechanism on various metal/ion conductor combinations such as Ni/yttria-stabilized zirconia (YSZ), Pt/YSZ, Ni/scandia-stabilized zirconia, Ni/titania/YSZ. For all electrode types besides those with a continuous titania interlayer a triple phase boundary (TPB) and an area pathway could be separated. Moreover, activation energies as well as hydrogen and water reaction orders were determined for both pathways and compared with previously published data on Ni/YSZ. It was found that when varying the electronically conducting phases on YSZ the activation energy of the TPB path remains virtually the same. However, changing the ion conductor significantly influenced the activation energy, indicating a rate-limiting step on the electrolyte. However, the stark difference in water reaction order of Ni/YSZ and Pt/YSZ electrodes shows that the metal phase is also actively participating in the reaction chain. It is suggested that the electrolyte surface is responsible for the ratelimiting electrochemical redox reaction while the metal interacts with the gas phase molecules and thus supplies the reactants. For samples with a thin mixed conducting titania layer on YSZ, the electrochemical behavior drastically changed, which can be explained by an extension of the reaction zone away from the TPB.