Electroprecipitation of Ag(II)/Ag(III) tetraphenylsulfonate porphyrin and electrocatalytic behavior of the films

Abstract

The electrochemical precipitation on glassy carbon and gold electrodes of Ag(II) tetraphenylsulfonate porphyrin (Ag(II)TPPS) from aqueous HClO 4 solutions, is reported. Electrochemical quartz crystal microbalance (EQCM) results indicate the possible formation of an Ag(II)–Ag(III) porphyrin dimer species. This species is oxidized and reduced in two consecutive steps: oxidation at +0.31 and +0.36 V (vs. SCE) and reduction at +0.11 and +0.07 V. The films show catalytic behavior toward O 2 reduction in 10 −2 M HClO 4 at relatively low potentials ( E<−0.1 V) but catalyze NO reduction at relatively high-reduction potentials ( E<0.4 V). The electrochemical results seem to indicate that the catalytic cycle in the case of NO involves formation of Ag(II)TPPS–Ag(II)TPPS(NO) + and its electroreduction to regenerate Ag(II)TPPS–Ag(III)TPPS and NO-reduction products.