MoNi InducedCodeposition Mechanism

Abstract

Clean hydrogen produced from water electrolysis is an alternative to the use of fossil fuel precursors, though its rate is limited due to slow kinetics associated with electrode reactions. Molybdenum-nickel alloys are economical, practical and efficient catalysts. However, their fabrication by electrodeposition is difficult to control, and the reduction mechanism not well understood. MoNi alloys are characteristic of induced codeposition; molybdenum ions cannot be reduced without another metal codepositing at the same time, such as nickel. In this project, an examination of the MoNi induced codeposition mechanism is investigated. The experimental set-up is a stationary working electrode with a Pt anode and a Ag/AgCl reference. There is a trade-off of electrolyte components. High Mo content in the deposit can be achieved with little or no ammonia, but at a cost of current efficiency. Similarly, the rate of Mo(VI) reduction is limited by the amount of nickel in the electrolyte, however, too much nickel, while it can enhance the Mo(VI) reduction rate, can also result in a deposit with excess Ni. In view of both issues, our lab has determined conditions to deposit ultra high Mo content, 82 wt % Mo, the highest achieved world-wide with electrodeposition to date. The catalytic property of the Mo-rich, MoNi alloys were characterized in a sodium hydroxide electrolyte, and exhibited Tafel behavior consistent with their hallmark feature as a catalysts for electrolytic hydrogen evolution.