STUDIES ON THE ELECTROCHEMICAL DEPOSITION OF NIOBIUM OXIDE

Various strategies for the electrodeposition of niobium oxide from bot h non-aqueous and aqueous solution are explored. The methods used were based on the electrochemical manipulation of the pH which leads to hy drolysis of soluble, well defined niobium precursors, leading to oxide deposition at the electrode. The reactions which proceed are believed to be closely related to those involved in conventional sol-gel proce ssing. In non-aqueous systems containing niobium alkoxides, hydroxide ions are generated by the two-electron reduction of tertiary alcohols (at < -2.5 V) and react with the niobium precursor to give a film of n iobium oxide on the dropping mercury electrode. Hydroxide generation v ia the reduction of oxygen to superoxide in O-2-saturated, non-aqueous solvents containing NbOCl3 did not, however, lead to niobium oxide fi lms. In acidic aqueous systems containing [NbOCl5](2-) species, raisin g the local pH around the electrode by hydrogen evolution does give ri se to niobium oxide deposition, but not at the electrode; In aqueous a lkaline solutions of the niobates K7H [Nb6O19] or (TMA)(6)[Nb10O28] (T MA = tetramethylammonium), protons generated by the electrochemical ox idation of water at > + 1.5 V cause the formation of mixed niobate and niobium oxide films on the electrode after > 30 min.