Cathodic electrodeposition of mixed molybdenum–selenium oxides

Abstract

Molybdenum–selenium oxides were electrochemically deposited onto indium–tin oxide (ITO) coated glass substrates from aqueous solutions containing molybdate ( Mo VI O 4 2 - ), selenate ( Se IV O 3 2 - ), and dimeric and tetrameric peroxo-polymolybdate (i.e., [Mo 2O 3(O 2) 4(H 2O) 2] 2−, [Mo 4O 9(O 2) 4] 2−) anions. Electrodeposition mechanisms were elucidated using chronocoulometry, cyclic voltammetry, spectroelectrochemistry, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical quartz crystal nanogravimetry (EQCN). At relatively positive deposition potentials from −0.1 V to −0.4 V (versus Ag/AgCl) a substoichiometric molybdenum oxide phase, Mo 3O 8, co-deposits with an insulating phase of Se 0. At more negative potentials, mixed molybdenum–selenium oxides (Mo x Se 1− x O y , 0 < x < 0.4) are deposited. Competing side reactions involving hydrogen and hydrogen selenide influence the structure, composition, and morphology of the mixed molybdenum–selenium oxide deposits.