Calcium hydroxide as a promoter of hydrogen absorption in 99.5% Fe and a fully pearlitic 0.8% C steel during electrochemical reduction of water

Calcium hydroxide (Ca[OH](2)) surface films were found to enhance the efficiency of hydrogen absorption over a range of hydrogen overpotentials for cold-worked 99.5% alpha Fe and isothermally transformed 0.8% C pearlitic steel (AISI 1080) during galvanostatic charging. Devanathan/Stachurski permeation experiments were conducted on Fe and AISI 1080 steelfoils in a range of solutions including sodium hydroxide (NaOH, pH 12.5), saturated Ca(OH)(2) (pH 12.5), saturated Ca(OH)(2) (adjusted to pH 9.2), ASTM artificial ocean water (pH 8.2), and a buffered Ca++/Cl- solution (pH 6). Additional permeation experiments also were conducted on foils with a mortar cover. The true surface overpotential was calculated by correcting for an increased pH at the surface caused by hydroxyl formation during water reduction. The steady-state hydrogen permeation flux was only enhanced over the range of true hydrogen overpotentials in high pH solutions containing Call. Auger and x-ray photoelectron spectroscopy (XPS) analysis of the surface of foils; charged in Call solutions were consistent with the presence of a Ca(OH)(2) surface film. The presence of calcium hydride (CaH2), calcium oxide (CaO), and calcium carbonate (CaCO3) was ruled out on thermodynamic grounds. Diagnostic experiments suggest that Ca(OH)(2) lowers the rate constant for H desorption and, possibly, raises the rate constant for absorption of H.