Sebasian Oliver Klemm

Dissolution of Platinum: Limits for the Deployment of Electrochemical Energy Conversion?

Platinum stability: Dissolution of Pt, which is one major degradation mechanism in, for example, hydrogen/air fuel cells, was monitored under potentiodynamic and potentiostatic conditions. The highly sensitive and time-resolving dissolution monitoring enables the distinction between anodic and cathodic dissolution processes during potential transient and chronoamperometric experiments, and the precise quantification of the amount of dissolved Pt.

Element-Resolved Corrosion Analysis of Stainless-Type Glass-Forming Steels

Rust Resistance The rusting of iron and steel can be prevented through the addition of 11% or more chromium. The addition of molybdenum can enhance the corrosion resistance, with a complex interplay between the Cr and Mo atoms. However, if chemical variations exist, corrosion can still occur in localized regions or if the surface layer is mechanically abraded. Duarte et al. (p. 372) studied the corrosive failure of an iron-based glassy alloy. A combination of atom probe tomography, electron microscopy, and x-ray diffraction was used to build up a near atomistic picture of local variations in the metal as it was heated and allowed to crystallize, and the impact these processes have on the corrosion resistance. Measurements of the local composition of a steel alloy are correlated with the corrosion resistance. Ultrathin passive films effectively prevent the chemical attack of stainless steel grades in corrosive environments; their stability depends on the interplay between structure and chemistry of the constituents iron, chromium, and molybdenum (Fe-Cr-Mo). Carbon (C), and eventually boron (B), are also important constituents of steels, although in small quantities. In particular, nanoscale inhomogeneities along the surface can have an impact on material failure but are still poorly understood. Addressing a stainless-type glass-forming Fe50Cr15Mo14C15B6 alloy and using a combination of complementary high-resolution analytical techniques, we relate near-atomistic insights into increasingly inhomogeneous nanostructures with time- and element-resolved dissolution behavior. The progressive elemental partitioning on the nanoscale determines the degree of passivation. A detrimental transition from Cr-controlled passivity to Mo-controlled breakdown is dissected atom by atom, demonstrating the importance of nanoscale knowledge for understanding corrosion.

Electrochemical Etching of Zinc Oxide for Silicon Thin Film Solar Cell Applications

A novel approach is presented for introducing a surface morphology with beneficial light scattering properties to sputterdeposited ZnO:Al films, being used as front contact in Si thin film photovoltaic devices. Electrochemical anodization was used to trigger local corrosion, leading to interfacial structures complementary to those commonly prepared by an etching step in diluted HCl. By systematic variation of electrochemical etching conditions and electrolytes, sensible experimental parameters were evaluated for the preparation of ZnO films that can be applied in Si thin film solar cells. The prepared films were characterized by scanning electron microscopy, four-point resistance and Hall measurements. Furthermore, the kinetics of the heterogeneous interfacial reaction during the corrosion process were studied utilizing electroanalytical techniques. This allowed the identification of the processes occurring at the solid/liquid interface. Application of such films in microcrystalline Si single junction solar cells has shown promising initial results.