Study of the electrocatalytic reduction of nitrite with silicotungstic heteropolyanion

Three couples of reversible redox waves of the SiW₁₂O^4?₄₀ anion which are composed of two one-electron and one two-electron processes occur in the potential range +0.1 to ?0.7 V in aqueous solutions. The first (most positive) and third (most negative) redox waves exhibit good electrocatalytic activities for nitrite reduction in acid solutions with pH < 2 for the former and with $\text{pH}\text{? 4}$ for the latter. The behavior of the third catalytic wave, which is quite unusual, was studied in detail. The rate constant governing the reduction of NO^?₂ by the first wave of SiW₁₂O^4?₄₀ was measured by an ultramicrodisk electrode as 3.73 × 10³ M^?1 s^?1.