Electrochemical synthesis of metal phosphates by cathodic reduction

Acidified aqueous metal nitrate solutions containing dissolved phosphate io ns yield the corresponding metal phosphates upon cathodic reduction. In alk aline earth metal containing electrolytes [phosphate source, (NH4)(2)HPO4], the phase obtained is MHPO4 (M = Sr, Ba). Controlled growth of adherent mi crometer-thick coatings of SrHPO4 could be achieved on the cathode substrat e. In Mg, Co, and Ni containing electrolytes, electrosynthesis yields the h ydrates of the corresponding NH4MPO4 (M = Mg, Co, Ni) at low (25 mA cm(-2)) current densities, while at high (60 mA cm(-2)) current densities, X-ray a morphous metal orthophosphates are obtained. The use of Na3PO4 as the phosp hate source also yielded X-ray amorphous products. In the Co system, the el ectrosynthesized phase, (NH4CoPO4H2O)-H-. was different from that obtained by chemical precipitation. This study demonstrates the versatility of elect rosynthesis. (C) 2001 Elsevier Science Ltd. All rights reserved.