Electrocatalysis of the charge-transfer process for the Sb(III)/Sb(V) couple at a platinum electrode in concentrated HCl

Electrocatalysis of the reduction of iron(III) by halides adsorbed at platinum electrodes in perchloric acid solutions

“…Davenport and Johnson (23) reported the electrocatalysis of the irreversible oxidation of Sb(III) by adsorbed T at Pt electrodes in dilute HC1 solutions. The value of k0¡app in 12 M HC1 was determined to increase by a factor of approximately 200 with addition of 2 µ I™ to the solution (24). The results were virtually the same for addition of I2.…”

Why halides enhance heterogeneous metal ion charge transfer reactions

“…15 The anion bridging mechanism has been invoked to explain rate enhancements for Cr 2+ /Cr 3+ , V 2+ /V 3+ , Sb 3+ /Sb 5+ , and Fe 2+ /Fe 3+ redox couples. 10,14,15,17,18 A two-step inner-sphere mechanism for how an adsorbed anion (*X) promotes oxidation of a metal ion (M n+ ) through the formation of an adsorbed metal-anion intermediate (*XM n+1 ) is written in eqn (1) and (2). Although here we write M n+1 as the product leaving behind *X, it is also possible that the halide becomes part of the desorbed complex as XM n+1 .…”

“…21 However, some studies have found that electrostatic effects alone are insufficient to explain the large increases (k halide /k no halides > 10) in the observed rate constants and postulated that anion bridging may be responsible. 8,10,15,18 Herein, we test our hypothesis that anion bridging on electrodes increases the kinetics for many metal redox couples by changing the energy of the surface intermediate (*XM n+1 ) and its adsorption and desorption barriers. The energy of *XM n+1 controls the fraction of active sites that the intermediate occupies and the apparent activation barriers for the redox reaction.…”

The Electrochemistry of Hydrocarbons in HF / SbF5: Some Mechanistic Conclusions Concerning the Super Acid “Catalyzed” Condensation of Hydrocarbons

“…There has been very little work reported on the electrochemistry of hydrocarbons and of antimony in such highly acidic media, especially that dealing with Sb(III)/Sb(V) couple. Most of the relevant work to be found in the literature concerns the reduction of Sb(III) in conventional acid solutions to form Sb(O), and the further reduction of the metal to stibine (SbH~) (14)(15)(16)(17)(18)(19)(20). A few reports have discussed the electrochemical reduction of Sb(V), which undergoes a 5-electron reduction directly to Sb(O).…”

“…A few reports have discussed the electrochemical reduction of Sb(V), which undergoes a 5-electron reduction directly to Sb(O). One of the few papers examining the Sb(III)/Sb(V) couple discusses the oxidation of Sb(III) on a platinum electrode (in 12m HC1) and describes an electrocatalytic effect produced by absorbing I-or I2 on the platinum surface (16). The aforementioned studies reveal that antimony exhibits very pronounced electrochemical behavior in acidic media.…”