Anodic processes on a titanium-supported Ruthenium dioxide electrode at high potentials in a mixture of sulfuric acid and ammonium sulfate

The anodic polarization behaviours of Ti-supported RuO₂ electrode at high potentials and the electrode reactions, especially oxygen evolution and peroxydisulfate ion formation, were investigated in H₂SO₄(NH₄)₂SO₄ mixed aqueous solutions. The effects of NH₄F addition to the solutions on the anodic processes were also examined.The anodic polarization curve is clearly divided into three parts: in the first linear region only oxygen evolution occurs and in the second one peroxydisulfate ion formation takes place, accompanied by oxygen evolution. The transitional region lies between these two linear regions. However, the oxygen evolution reaction proceeds predominantly in all regions in H₂SO₄(NH₄)₂SO₄ mixed aqueous solutions. The current efficiency for peroxydisulfate ion formation depends on the concentration of (NH₄)₂SO₄ and the current density. The current efficiency is greatly increased by adding NH₄F to the mixed solutions. The formation reaction of peroxydisulfate ion in the NH₄F-containing solutions is controlled by the step of the primary discharge of sulfate ion or hydrogensulfate ion.