Reactions involved in the electrodeposition of hydrotalcite-type compounds on FeCrAlloy foams and plates

The cathodic electrodeposition of Mg/Al hydrotalcite-type (HT) compounds on FeCrAlloy plates and foams by the electro-base generation method, using nitrate salts as precursors, was studied. In order to characterize the main mechanisms governing the precipitation of HT compounds, potential sweeps or pulses were applied at both plates and foams dipped in nitrate and chloride baths, with and without Mg2+ and Al3+ precipitating cations. Moreover, nitrate reduction products were analyzed. The features of coatings and pH near foam supports were correlated to electrochemical results. Nitrate and oxygen reduction, as well as H2 evolution, contributed to a pH increase during the electrodeposition of HT compounds, but nitrate reduction was responsible for the highest pH increase at the electrode-electrolyte interface. FeCrAlloy showed a low activity in nitrate reduction to nitrite and ammonia. Mg2+ and Al3+ precipitating cations fostered electrochemical reduction and modified reaction products. The shape of the support, foam or plate, did not significantly alter the electrical conductivity and reduction potentials, but it did affect current density and H2 bubble formation. A higher current density was recorded at the foam, while H2 bubbles were smaller and dissipated rapidly; subsequently, a thicker coating was electrodeposited.