Hydrogen Permeation in Fusion Materials and the Development of Tritium Permeation Barriers

Fuel retention and hydrogen permeation in the first wall of future fusion devices are crucial factors. Due to safety issues and in order to guarantee an economical reactor operation, tritium accumulation into reactor walls and permeation through walls have to be estimated and prevented. Therefore, studies of permeation in the fusion materials are performed and the need for tritium permeation barriers (TPB) is verified. The development of TPB layers is explained. A reliable way of comparing different TPB layers and the estimation of the permeation reduction effect of a TPB layer on different bulk materials is enabled by calculation of the layer permeability

Quantitative Lithiation Depth Profiling in Silicon Containing Anodes Investigated by Ion Beam Analysis

The localisation and quantitative analysis of lithium (Li) in battery materials, components, and full cells are scientifically highly relevant, yet challenging tasks. The methodical developments of MeV ion beam analysis (IBA) presented here open up new possibilities for simultaneous elemental quantification and localisation of light and heavy elements in Li and other batteries. It describes the technical prerequisites and limitations of using IBA to analyse and solve current challenges with the example of Li-ion and solid-state battery-related research and development. Here, nuclear reaction analysis and Rutherford backscattering spectrometry can provide spatial resolutions down to 70 nm and 1% accuracy. To demonstrate the new insights to be gained by IBA, SiOx-containing graphite anodes are lithiated to six states-of-charge (SoC) between 0–50%. The quantitative Li depth profiling of the anodes shows a linear increase of the Li concentration with SoC and a match of injected and detected Li-ions. This unambiguously proofs the electrochemical activity of Si. Already at 50% SoC, we derive C/Li = 5.4 (< LiC6) when neglecting Si, proving a relevant uptake of Li by the 8 atom % Si (C/Si ≈ 9) in the anode with Li/Si ≤ 1.8 in this case. Extrapolations to full lithiation show a maximum of Li/Si = 1.04 ± 0.05. The analysis reveals all element concentrations are constant over the anode thickness of 44 µm, except for a ~6-µm-thick separator-side surface layer. Here, the Li and Si concentrations are a factor 1.23 higher compared to the bulk for all SoC, indicating preferential Li binding to SiOx. These insights are so far not accessible with conventional analysis methods and are a first important step towards in-depth knowledge of quantitative Li distributions on the component level and a further application of IBA in the battery community

Effects of Constant Load Operations on Platinum Bands Formation and Cathode Degradation in High-Temperature Polymer Electrolyte Fuel Cells

In this paper, Pt bands and cathode degradation are investigated in polybenzimidazole (PBI) membrane-based high-temperature polymer electrolyte fuel cells (HT-PEFC). A focused ion beam/scanning electron microscopy (FIB/SEM) system was used to characterize the cross-section morphologies of membrane electrode assemblies (MEA). A Pt band is observed in the FIB/SEM images of the MEA activated by a common break-in procedure (at 200 mA cm−2 for 70 h). Then, an identical MEA was subjected to an aging process that included static holding at 200 mA cm−2 for 100 h and an open circuit voltage (OCV) operation for another 100 h. FIB/SEM images of the aged MEA show that the band formed during the break-in procedure is strengthened. Moreover, a second Pt band is observed closer to the membrane/cathode interface, which is due to the increase of hydrogen crossover caused by membrane thinning during the OCV hold test. In situ electrochemical measurements show that the cell’s performance loss due to the formation of the Pt band during cell operation at 200 mA cm−2 is negligible. The decrease of cell performance is mainly attributed to the loss of electrochemically active surface area and membrane degradation during the OCV hold test

Plastic deformation of tungsten due to deuterium plasma exposure: Insights from micro-compression tests

Nanoindentation tests have shown that exposure to deuterium plasma causes a decrease in pop-in load and an increase in hardness of tungsten. In this work, we use micro-compression tests to investigate the plastic deformation and apparent strain hardening of tungsten exposed to deuterium plasma. In comparison with the pillars tested at reference state, the pillars tested after exposure showed an increased apparent strain hardening rate as well as an increased multitude of slip traces, which is attributed to the presence of deuterium. The micro-compression results are in agreement with the nanoindentation study on the pop-in and hardness of tungsten

Hydrogen embrittlement of tungsten induced by deuterium plasma: Insights from nanoindentation tests

Hydrogen exposure has been found to result in metal embrittlement. In this work, we use nanoindentation to study the mechanical properties of polycrystalline tungsten subjected to deuterium plasma exposure. For the purpose of comparison, nanoindentation tests on exposed and unexposed reference tungsten were carried out. The results exhibit a decrease in the pop-in load and an increase in hardness on the exposed tungsten sample after deuterium exposure. No significant influence of grain orientation on the pop-in load was observed. After a desorption time of td ≥ 168 h, both the pop-in load and hardness exhibit a recovering trend toward the reference state without deuterium exposure. The decrease of pop-in load is explained using the defactant theory, which suggests that the presence of deuterium facilitates the dislocation nucleation. The increase of hardness is discussed based on two possible mechanisms of the defactant theory and hydrogen pinning of dislocations