Sulfide corrosion of Cu is rapid, and hydrogen atoms produced by its cathodic half-reaction could adsorb on the Cu surface and diffuse into the Cu, potentially leading to hydrogen embrittlement. However, in solutions with low concentrations of SH⁻, absorption of hydrogen into Cu is not observed by ex situ hydrogen analysis, although it is unclear whether this is due to the lack of absorption, the outgassing of hydrogen from the Cu before it can be measured, or another mitigation mechanism. Herein, hydrogen uptake into Cu and the development of Cu2S layers during corrosion by SH⁻ were studied by in situ neutron reflectometry and electrochemical impedance spectroscopy. The method relies on a 4-nm Ti layer beneath 50 nm of Cu to trap hydrogen that may penetrate the Cu. Additionally, elastic recoil detection analysis and Rutherford backscattering spectrometry were used to measure hydrogen. While no increase in hydrogen was detected in either the Ti or Cu layers, a higher concentration of hydrogen was observed in the outer Cu2S layer (2560 ppm) than in the underlying Cu (244 ppm), demonstrating that bisulfide-driven corrosion does not lead to hydrogen absorption into the Cu. These results have implications for deep geological repositories utilizing Cu corrosion barriers.

One concern regarding the used nuclear fuel containers proposed for use in a Canadian deep geological repository (DGR) is the possibility that a small amount of hydrogen might be absorbed into their copper coating, potentially altering its mechanical properties. Reported herein is a study of hydrogen absorption into 50 nm of copper, coated on 4 nm of Ti using in situ neutron reflectometry (NR) and electrochemical impedance spectroscopy (EIS). NR results show that hydrogen is absorbed when the copper is cathodically polarized below the threshold for the hydrogen evolution reaction (HER), but that the hydrogen concentrates in the underlying titanium layer rather than concentrating in the copper coating. The hydrogen concentration in titanium rapidly rose when the HER was initiated and was observed to reach a steady state at TiH_1.5. Over the course of 55h of cathodic polarization, the concentration of hydrogen in the copper remained below the NR detection limit (2 at %). The portion of hydrogen atoms produced that diffused through the copper layer was initially 3.2%, suggesting a possible upper limit for hydrogen uptake by the copper coating of the UFC, although definitive conclusions can only be drawn from studies on 3 mm copper-coated steel samples.