Effects of Applied Voltage on Morphology and Crystal Orientation of Mg(OH)[sub 2] Coating on Pt by Electrochemical Synthesis

Magnesium hydroxide [ Mg ( O H ) 2 ] coatings have been successfully prepared via electrochemical synthesis on Pt in aqueous Mg ( N O 3 ) 2 solution. Two major reactions corresponding to various applied voltage regions were identified: ( i ) O 2 + 2 H 2 O + 4 e − → 4 O H − ( ∼ 0.5 to − 0.77 V ) and ( ii ) 2 H 2 O + 2 e − → H 2 + 2 O H − ( − 0.77 to − 3 V ) . The efficient deposition was carried out at the second region, because H + ions were depleted and many O H − ions were provided to form Mg ( O H ) 2 on the cathodic surface. Through thermogravimetric differential thermal analysis, X-ray diffraction, Fourier transform IR spectroscopy, and scanning electron microscopy, it was found that the crystal orientation and morphology of Mg ( O H ) 2 on Pt was linked to the applied voltage. The more negative the applied voltage was and the more the O H − concentration was, finally resulted in the more (001) preferred orientation and various surface appearances. Therefore, the controllable fabrication of highly dense and uniform Mg ( O H ) 2 films could be carried out by tuning deposition potential. The uniform coating film deposited at − 1.2 V was densely packed flat Mg ( O H ) 2 particles and condensed into MgO around 340 ° C . Compared to microarc oxidation, which is only restricted to Mg alloy, this electrochemical synthesis can be applied to other metals. Also, the reported method, with a low cost, is simple and environmentally benign.