Electrochemical reduction of HNO sub(2) or oxidation of benzyl alcohol by electrocatalyst coatings consisting of alternating layers of [P sub(2)Mo sub(18)O sub(62)] super(6-) anions and Os(II)- or Ru(II)-polypyridine cations

• Published in: Electrochimica acta Vol. 44; no. 13; pp. 2271 - 2279
• Main Authors: Kloster, Grant M, Anson, Fred C
• Format: Journal Article
• Language: English
• Published: 01.01.1999
• ISSN: 0013-4686

A previously described procedure for coating electrodes with multiple layers of heteropolyanions and charge-balancing dipositive cations was extended to incorporate catalytically active reactants in the coatings. Clear electrocatalytic activity was demonstrated for both anionic ([P sub(2)Mo sub(18)O sub(62)] super(6-)) and cationic ([cis-Ru(dcbpy) sub(2)(OH sub(2)) sub(2)] super(2+) (dcbpy identical with 6,6'-dichloro-2,2'-bipyridine)) components of coatings on roughly polished edge plane pyrolytic graphite electrodes. However, the stacking of multilayers on top of the first layer of [P sub(2)Mo sub(18)O sub(62)] super(6-) adsorbed on the electrode produced almost no increase in catalytic currents for the reduction of HNO sub(2) to N sub(2)O and the activity of [cis-Ru(dcbpy) sub(2)(OH sub(2)) sub(2)] super(2+) in coatings toward the catalytic oxidation of benzyl alcohol was short-lived. The behavior observed provided insight into the features that must be controlled to obtain useful coatings consisting of multilayers of electrocatalysts. The kinetics of the reduction of HNO sub(2) by [H sub(2)P sub(2)Mo sub(18)O sub(62)] super(6-) with both reactants present in solution were also examined. The reaction produces N sub(2)O and a rate constant for the process of 3.5x10 super(2) M super(-1) s super(-1) was estimated from rotating disk voltammetric measurements. O sub(2) does not react with the reduced complex, [H sub(2)Mo sub(18)O sub(62)] super(6-), but during its reaction with HNO sub(2) any O sub(2) also present undergoes catalytic reduction. The intermediate proposed to be involved in both catalytic reactions is an adduct formed by the reaction of HNO sub(2) with [H sub(2)P sub(2)Mo sub(18)O sub(62)] super(6-).