Cathode Potentials during the Electrodeposition of Molybdenum Alloys from Aqueous Solutions

Abstract

Cathode potential measurements are used to explain the cathode reactions that result in the electrodeposition of molybdenum alloys. Potentials were measured by the direct method during the electrolysis of aqueous ammoniacal citrate solutions containing sodium molybdate and the sulfate of a codepositing metal, iron, nickel, or cobalt. The results indicate that the reduction of molybdate ion in this type of bath is probably not accomplished in one step with six electrons, but with one, two, or three electrons depending on the codepositing metal and its oxidation state in the bath. The results also indicate that hydrogen is involved in the molybdate reduction process. A two‐step mechanism for the reduction of molybdate ion in the presence of a codepositing metal is proposed and an explanation of why this metal must be iron, cobalt, or nickel rather than such metals as chromium, manganese, copper, or zinc is presented.

Local Atomic Structure and Catalytic Activities in Electrodeposited Mo-Ni Alloys

“…3) Its mechanism was studied by some workers. [4][5][6] Recently, Shinoda et al 7,8) studied the atomic structure of molybdenum ions in solutions by the anomalous X-ray scattering (AXS) method. This indicates that atomic structures of polymolybdate ions in electroplating bath change as a function of concentrations of complex forming reagents and the molybdenum alloy is electrodeposited only in a solution containing polymolybdate ions with a certain atomic structure.…”

Earth-abundant hydrogen evolution electrocatalysts

“…Work in the late 1950s and early 1960s showed that metallic molybdenum could be electrodeposited from aqueous solution as an alloy with iron-group metals, whereas pure molybdenum-containing solutions would only electrodeposit as the partially reduced oxide. 117,118 Furthermore, the cooperative deposition of metallic material only proceeded under conditions where hydrogen also was evolved, implying unique interactions between Ni, Mo, and H 2 or HER intermediates.…”

Role of Mo6+ during nickel electrodeposition from sulfate solutions

“…7. It has been proposed by some authors [28][29][30][31] that molybdate (MoO 4 2-) is initially electrochemically reduced to molybdenum oxide and subsequently undergoes chemical reduction with atomic hydrogen to form molybdenum in alloys. Thus it is likely that reduction of MoO 4 2-to Mo may take place either through Eq.…”

“…4 followed by Eq. 5 or by combination of chemical/electrochemical methods as suggested elesewhere [28][29][30][31]. Phosphomolybdate species exist in solutions containing both phosphate and molybdate at pH £ 7 [32][33][34][35][36].…”