Spatially resolved mapping of the relative concentration of dissolved hydrogen using the scanning electrochemical microscope

The scanning electrochemical microscope (SECM)was utilized to detect pre-dissolved hydrogen across an ultrahigh strength stainless steel surface. A high strength Fe–11Ni–12Cr–1Mo–0.005C–0.02Mn (wt.%) steel with a high diffusible hydrogen capacitywas first cathodically pre-charged to known concentrations of diffusible hydrogen. The steel was subsequently analyzed by the SECM in redox competition mode to detect the location of diffusible hydrogen by examining the effect of the hydrogen in pre-charged and uncharged areas on the oxygen reduction reaction at a platinummicro-electrode tip. The tip current significantly decreased in regions containing hydrogen. The presence of dissolved hydrogen results in enhanced consumption of O2 (by the oxygen reduction reaction) at the steel surface. Dissolved hydrogen can be detected and resolved at a sub-millimeter length scale.