Hydrogen Entry into Ni-coated Steels in NaCl Solution

Abstract

This study aims to elucidate the hydrogen entry behavior into partially Ni-coated steel sheet in a 0.1 M NaCl aqueous solution. Electrochemical hydrogen permeation tests and hydrogen visualization tests using a polyaniline-based hydrogenochromic sensor were conducted to investigate corrosion-induced hydrogen entry. While the hydrogen permeation current was not detected during the electrochemical hydrogen permeation test, the hydrogenochromic sensor successfully visualized the hydrogen entry in situ. It was revealed that hydrogen entry is accelerated in the pits formed in the area where the steel substrate is exposed. Hydrogen entry was not confirmed in the Ni-coated area. The visualization tests also demonstrated time-lag between the corrosion initiation and the detection of hydrogen entry. The highly sensitive hydrogenochromic sensor provides insight into the spatial distribution of hydrogen entry sites, which is not readily detectable by conventional electrochemical hydrogen permeation methods. The findings clarified that the critical role of solution chemistry on the corroded area in hydrogen entry into Ni-coated steel.