Detection of the Sn(III) Intermediate and the Mechanism of the Sn(IV)/Sn(II) Electroreduction Reaction in Bromide Media by Cyclic Voltammetry and Scanning Electrochemical Microscopy

Abstract

Fast-scan cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) were used to investigate the reduction of Sn(IV) as the hexabromo complex ion in a 2 M HBr–4 M NaBr medium. CV at scan rates to 100 V/s and SECM indicated the reaction pathway involves ligand-coupled electron transfer via an ECEC-DISP process: (1) one-electron reduction of SnIVBr62– to SnIIIBr63–; (2) bromide dissociation of the reduced SnIIIBr63– to SnIIIBr52–; (3) disproportionation of the reduced 2SnIIIBr52– to SnIVBr5– and SnIIBr53–; (4) one-electron reduction of SnIIIBr52– to SnIIBr53–; (5) bromide dissociation from SnIIBr5 to SnIIBr42–. The intermediate Sn(III) species was confirmed by SECM3–, where the Sn(III) generated at the Au tip was collected on a Au substrate in the tip generation/substrate collection mode when the distance between the tip and substrate was a few hundred nanometers.