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/H_ads-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/H_ads-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.

 [1] S. Evers, M. Rohwerder, The hydrogen electrode in the “dry”: A Kelvin probe approach to measuring hydrogen in metals, Electrochem. Commun. 24 (2012) 85-88.

 [2] C. Larignon, J. Alexis, E. Andrieu, L. Lacroix, G. Odemer, C. Blanc, Combined Kelvin probe force microscopy and secondary ion mass spectrometry for hydrogen detection in corroded 2024 aluminium alloy, Electrochimica Acta 110 (2013) 484–490

 [3] G. Williams, H.N. McMurray, R.C. Newman, Surface oxide reduction by hydrogen permeation through iron foil detected using a scanning Kelvin probe, Electrochem. Commun. 27 (2013) 144-147

 [4] R.F. Schaller, S. Thomas, N. Birbilis, J.R. Scully, Spatially resolved mapping of the relative concentration of dissolved hydrogen using the scanning electrochemical microscope, Electrochem. Commun. 51 (2015) 54-58

 [5] M. Koyama, A. Bashir, M. Rohwerder, S. Merzlikin, E. Akiyama, K. Tsuzaki, D. Raabe, Spatially and kinetically resolved mapping of hydrogen in a twinning-induced plasticity steel by use of scanning Kelvin probe force microscopy, J. Electrochem. Soc. 162 (2015) 638–647

 [6] G. Schimo, W. Burgstaller, A. W. Hassel, Potentiodynamic hydrogen permeation on Palladium-Kelvin probe compared to 3D printed microelectrochemical cell, Electrochem. Commun. 60 (2015) 208-211

 [7] R.F. Schaller, J.R. Scully, Spatial determination of diffusible hydrogen concentrations proximate to pits in a Fe–Cr–Ni–Mo steel using the Scanning Kelvin Probe, Electrochem. Commun. 63 (2016) 5-9