Spatially Resolved Mapping of Hydrogen Permeation with a Novel in-Situ Scanning Kelvin Probe (SKP) Based Setup
Authors: Wu Chun-Hung , Krieger Waldemar , Rohwerder Michael 
Published: February 2020

The detection of localized diffusible hydrogen is a key issue in investigating hydrogen embrittlement and crucial energy conversion issues. Several methods based on SKP and SECM techniques have been developed so far to trace diffusible hydrogen [1]-[7]. Most of these methods use pre-charged samples, through this way important information is usually lost due to the escape of diffusible hydrogen before the measurement can start and also it takes long time for a single measurement.
The use of a “static” SKP based permeation setup inspired by the Devanathan-Stachurski electrochemical double cell was reported before [1],[5] using Pd thin film at the exit side for a potentiometric hydrogen measurement by Kelvin Probe. However, once H/Pd reaches the atomic ratio ~ 0.02 at room temperature, the onset of palladium hydride formation (i.e. of the binary phase region) will pin the potential value and all information of further hydrogen permeation will disappear. This drawback is overcome by using a dynamic ORR/Hads-H+ redox competition, which prevents reaching the binary phase point and provides a potential output value determined by a dynamic equilibrium of the redox competition. Furthermore, the potential output value measured can be correlated to the permeation rate obtained in electrochemical double cell under same charging condition. With the combination of Scanning Kelvin Probe and the ORR/Hads-H+redox competition method, localized hydrogen permeation maps can be obtained in an oxygen-purged atmosphere. Here on as an example the study of three differently microstructured samples with same composition will be presented (A: annealed, CR: cold-rolled, RK: recrystallized), and it was found that in large area scan (2000μm*2000 μm) A & RK showed no big difference in spatial permeation rate, but CR revealed strong differences. In a detailed investigation, it was found that in areas where blisters formed the hydrogen diffusion through the material was significantly decreased. The results showed that the resolution of this novel technique is from mm to μm scale range.
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