Nanocrystalline Manganese-Molybdenum-Tungsten Oxide Anodes for Oxygen Evolution in Acidic Seawater Electrolysis

Abstract

In an attempt to tailor new oxygen evolution anodes for acidic seawater electrolysis, manganese-molybdenum-tungsten oxide anodes were prepared by anodic deposition on IrO₂/Ti substrate using 0.2 kmol m⁻³ MnSO₄-(0.00–0.006) kmol m⁻³ Na₂MoO₄-(0.0–0.03) kmol m⁻³ Na₂WO₄ electrolytes at pH −0.1∼+1.0 and 363 K at 600 Am⁻². The deposits consist of a nanocrystalline single γ-MnO₂ type phase in the form of triple Mn_1−x−yMo_xW_yO_2+x+y oxide. Anodic deposition in 0.2 kmol m⁻³ Mn²⁺-0.003 kmol m⁻³ Mo⁶⁺-0.006 kmol m⁻³ W⁶⁺ electrolyte at pH 0.0 resulted in the formation of an electrode with 100% and 99.8% oxygen evolution efficiencies before and after electrolysis for 691.2 ks in 0.5 kmol m⁻³ NaCl solution of pH 2 at 1000 Am⁻². Thus, Mn_1−x−yMo_xW_yO_2+x+y electrodes were promising oxygen evolving anodes for acidic seawater electrolysis. It has been concluded that additions of both tungsten and molybdenum beneficially bring about an increase in the real electro-catalytic activity along with the formation of deposits with optimum thickness and good adherence to the IrO₂/Ti substrate.