Linear sweep voltammetry coupled to a quartz crystal microbalance for investigating the catalytic activity of the Mg(II)-water electrochemical system and managing the Mg oxy-hydroxide hydration state

•Intramolecular water reduction of Mg(H2O)62 +•Electrogeneration of Mg(H2O)4(OH)2 ; ΔRG° = − 28 kJ/mol•Gradual dehydration of Mg(H2O)4(OH)2 to Mg(OH)2•Intramolecular dehydroxylation of Mg(OH)2 to MgO

This study provides an insight into the catalytic activity of the Mg(II)-water electrochemical system, from aqueous magnesium chloride hexa-hydrate to magnesium oxy-hydroxide electro-nucleation, growth and evolution, using Linear Sweep Voltammetry (LSV) coupled to a Quartz Crystal Microbalance (QCM) (− 0.80 > EV/SCE > − 1.80).Interfacial phenomena occur at the gold resonator during cathodic polarization (− 0.90 > EV/SCE > − 1.80).MgH2O62+→−0.90>EV/SCE>−1.25MgH2O4OH2→−1.25>EV/SCE>−1.50MgH2O2OH2→−1.50>EV/SCE>−1.70MgOH2From − 0.90 V, reduction of the intramolecular water of the hexa-coordinated Mg(H2O)62+ cluster enhanced the cathodic current i°MgH2O62+/i°H2O. In the range − 1.25 > EV/SCE > − 1.70, electrosynthesis of Mg(H2O)4(OH)2 and its simultaneous gradual dehydration to Mg(OH)2 take place. At lower potentials, experiments suggest intramolecular dehydroxylation of Mg(OH)2 to MgO. The applied potential thus allows fine control of the hydration state of the Mg oxy-hydroxide.

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