Electrochemical synthesis of metal phosphates by cathodic reduction

Acidified aqueous metal nitrate solutions containing dissolved phosphate ions yield the corresponding metal phosphates upon cathodic reduction. In alkaline earth metal containing electrolytes [phosphate source, (NH4)2HPO4], the phase obtained is MHPO4 (M = Sr, Ba). Controlled growth of adherent micrometer-thick coatings of SrHPO4 could be achieved on the cathode substrate. In Mg, Co, and Ni containing electrolytes, electrosynthesis yields the hydrates 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 amorphous metal orthophosphates are obtained. The use of Na3PO4 as the phosphate source also yielded X-ray amorphous products. In the Co system, the electrosynthesized phase, NH4CoPO4·H2O was different from that obtained by chemical precipitation. This study demonstrates the versatility of electrosynthesis.