Electrodeposition of Layered Double Hydroxides on platinum: Insights into the reactions sequence

The electrodeposition of four Layered Double Hydroxides (LDHs) has been attempted by applying different cathodic potentials to electrochemically pre-treated Pt surfaces soaked into solutions containing Al and four divalent cations (Co, Ni, Zn, Mg) in the form of nitrates. The syntheses have been performed in the presence (C1 condition) or in the absence (C2 condition) of KNO3 which acts both as supporting electrolyte and as additional source of nitrates necessary for the generation of the hydroxide anions. A systematic characterization of all the materials obtained in C1 condition has been performed to investigate the reactions sequence during precipitation. Two pathways for the LDHs electrodeposition have been demonstrated which are related to the OH- production rate. If it is slow the electrodeposition involves two steps: the first is the precipitation of Al(OH)3 and the second is the formation of LDH from the reaction between Al(OH)3 and M(II). On the other hand, the LDH is directly formed starting from M(II) and Al(III) when a high amount of OH- is generated at the electrode surface. In C2 condition only the most cathodic potential has been investigated. The obtained results indicate that in such a case both M(II) and Al precipitate simultaneously.