Electrolytic Reduction of Aqueous Tungstate Solutions

A "catalytic reduction" theory is proposed to explain the electrolytic reduction of aqueous tungstate solutions in the presence of codepositing metals such as iron, nickel, and cobalt. Two cathode reactions are suggested as being essential to the reduction process: (A) (B) Reaction A proceeds until the cathode is covered with a thin deposit of metal, M, which then acts as a catalyst for reaction B. When this metal catalyst is covered with a layer of tungsten reaction B stops and reaction A again proceeds to give a new catalyst surface; thus alternate layers of metal (Ni, Co, or Fe) and tungsten are deposited on the cathode. Evidence for this postulated mechanism is based in part on polarographic studies, cathode potential measurements, and the laminated structure of the cathode deposits.