According to the fact that the oxidation peak potential (Ep) shifted negatively with the increase of pH (4.00–6.00), showing that the higher the pH value, the more easily the UA and FA lost electrons to be oxidized, so their oxidation peak currents enhanced correspondingly. When the supporting electrolyte (PBS) changed from acidic (pH = 6.00) to neutral (pH = 7.00) or basic (pH > 7.00), the cathodic reaction of oxygen transferred from formulas (1-1) to another (1-2)