Mn-Mo-W Oxide Anodes for Oxygen Evolution in Seawater Electrolysis for Hydrogen Production

Abstract

IrO₂/Ti-supported γ-MnO₂-type Mn-Mo-W triple oxide anodes were prepared by anodic deposition in MnSO₄-Na₂MoO₄-Na₂WO₄-H₂SO₄ solutions. The performance of anodes for oxygen evolution reaction during electrolysis of 0.5 kmol m⁻³ NaCl solution was examined at 1000 Am⁻². The stability, kinetics and physicochemical properties of the oxide deposit anodes were characterized by iR-corrected galvanostatic polarization, gravimetric, X-ray photoelectron spectroscopy and X-ray diffraction techniques. The addition of tungsten to the Mn-Mo oxide enhanced the oxygen evolution efficiency of anodes. The anode prepared in 0.2 kmol m⁻³ Mn²⁺-0.003 kmol m⁻³ Mo⁶⁺-0.006 kmol m⁻³ W⁶⁺ electrolyte of pH 0 showed the best performance among anodes prepared in this work. The high performance was attributed to the formation of single phase triple oxide with optimum composition, thickness and defect concentration. Tungsten addition beneficially exerts its effect via increasing the electrical conductivity of oxide deposits. The deposition mechanism of the oxides was discussed in terms of stability and population of Mn³⁺ species at the anode/electrolyte interface.