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

• Addresses mapping and resolution of H containing zones using redox competition
• Unique technique that maps H at mm to μm lateral length scale; suitable to μm scale
• SECM H mapping that can be conducted ex situ, in situ, or in charging solutions
• Novel measurement concept applicable to a broad range of materials containing H
• Material conditions that limit measurement and govern resolution are discussed.

The scanning electrochemical microscope (SECM) was utilized to detect pre-dissolved hydrogen across an ultra-high strength stainless steel surface. A high strength Fe–11Ni–12Cr–1Mo–0.005C–0.02Mn (wt.%) steel with a high diffusible hydrogen capacity was 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 platinum micro-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.