In Situ Spectroscopic Determination of Faradaic Efficiencies in Systems with Forced Convection under Steady State: Electroreduction of Bisulfite to Dithionite on Gold in an Aqueous Electrolyte
Abstract:The reduction of bisulfite on Au electrodes in buffered aqueous solutions (pH ) 5.25) was examined by in situ near-normal-incidence UV-visible reflection absorption spectroscopy on a rotating disk electrode (RDE) and in situ transmission UV-visible spectroscopy downstream from a channel-type electrode. The currents associated with dithionite (S 2 O 4 2-) formation obtained from the spectroscopic measurements were found to be lower than those expected for a one-electron, diffusion-controlled process. Faradaic e… Show more
“…Sulfur dioxide is known to undergo reversible reduction in strongly acidic media on a variety of electrode materials at around −0.4 V vs SCE; − ,, it seems, thus, conceivable that at pH > 3, SO 2 is also the electroactive species in this potential region, as was recently proposed in this laboratory . In this pH range, however, the amount of free SO 2 in the solution is low and the current would become limited by the rate of its formation from bisulfite (eq 1, Scheme 1)…”
Section: Brief Backgroundmentioning
confidence: 79%
“…As indicated, the values of i lim for the electroreduction dropped significantly as the pH increased. The faradaic efficiency for dithionite production, as determined by in situ UV−visible reflection−absorption spectroscopy at a RDE, was 100% down to the onset of hydrogen evolution, indicating that no further reduction or decomposition of this product occurs under these conditions. 1 Polarization curves for bisulfite reduction obtained with a Bi RDE in 0.10 M citric acid + x M NaOH + (0.50 − x )M NaClO 4 + 10 mM Na 2 SO 3 solutions, at the specified pH values (0.1 < x < 0.4).…”
Section: Resultsmentioning
confidence: 96%
“…Both the optical and electrochemical instrumentation have been described in detail in ref . A Ag/AgCl in 3 M NaCl (BAS) separated by a closed (wet) glass stopcock and connected to the working electrode compartment through a Luggin capillary was used as the reference electrode.…”
The reduction of bisulfite on a bismuth rotating disk electrode (RDE) was studied in aqueous buffered
electrolytes over the pH range 3−6. Clearly defined limiting currents were observed in all solutions examined;
however, their magnitudes were not only smaller than those expected for a process limited by the diffusion
of bisulfite from the bulk solution, but were also found to decrease as the media became less acidic. This
behavior was attributed to a preceding homogeneous process that generates sulfur dioxide, the actual
electroactive species. UV−visible absorption−reflection spectroscopy measurements at a RDE showed that
in the potential region in which such limiting currents are observed, dithionite is produced with 100% faradaic
efficiency. Results of rotation rate staircase scan amperometric RDE experiments were found to be consistent
with the conversion of bisulfite into SO2 proceeding via a general acid catalysis mechanism, and allowed
values for the rate constants for the following reactions to be determined: SO2 + H2O → HSO3
- + H3O+,
k
b
= (1.6 ± 0.2) 107 s-1; HSO3
- + H3O+ → SO2 + H2O, k
f
H
= (1.2 ± 0.15) 109 M-1 s-1; HSO3
- +
CH3COOH → SO2 + H2O + CH3COO-, k
f
HA
= (1.7 ± 0.5) 104 M-1 s-1. On this basis, and assuming
diffusion-controlled rates for proton transfer from strong acids to oxygen bases, a more detailed mechanism
involving formation of sulfurous acid as an intermediate is discussed and some thermodynamic and kinetic
properties of the latter are estimated.
“…Sulfur dioxide is known to undergo reversible reduction in strongly acidic media on a variety of electrode materials at around −0.4 V vs SCE; − ,, it seems, thus, conceivable that at pH > 3, SO 2 is also the electroactive species in this potential region, as was recently proposed in this laboratory . In this pH range, however, the amount of free SO 2 in the solution is low and the current would become limited by the rate of its formation from bisulfite (eq 1, Scheme 1)…”
Section: Brief Backgroundmentioning
confidence: 79%
“…As indicated, the values of i lim for the electroreduction dropped significantly as the pH increased. The faradaic efficiency for dithionite production, as determined by in situ UV−visible reflection−absorption spectroscopy at a RDE, was 100% down to the onset of hydrogen evolution, indicating that no further reduction or decomposition of this product occurs under these conditions. 1 Polarization curves for bisulfite reduction obtained with a Bi RDE in 0.10 M citric acid + x M NaOH + (0.50 − x )M NaClO 4 + 10 mM Na 2 SO 3 solutions, at the specified pH values (0.1 < x < 0.4).…”
Section: Resultsmentioning
confidence: 96%
“…Both the optical and electrochemical instrumentation have been described in detail in ref . A Ag/AgCl in 3 M NaCl (BAS) separated by a closed (wet) glass stopcock and connected to the working electrode compartment through a Luggin capillary was used as the reference electrode.…”
The reduction of bisulfite on a bismuth rotating disk electrode (RDE) was studied in aqueous buffered
electrolytes over the pH range 3−6. Clearly defined limiting currents were observed in all solutions examined;
however, their magnitudes were not only smaller than those expected for a process limited by the diffusion
of bisulfite from the bulk solution, but were also found to decrease as the media became less acidic. This
behavior was attributed to a preceding homogeneous process that generates sulfur dioxide, the actual
electroactive species. UV−visible absorption−reflection spectroscopy measurements at a RDE showed that
in the potential region in which such limiting currents are observed, dithionite is produced with 100% faradaic
efficiency. Results of rotation rate staircase scan amperometric RDE experiments were found to be consistent
with the conversion of bisulfite into SO2 proceeding via a general acid catalysis mechanism, and allowed
values for the rate constants for the following reactions to be determined: SO2 + H2O → HSO3
- + H3O+,
k
b
= (1.6 ± 0.2) 107 s-1; HSO3
- + H3O+ → SO2 + H2O, k
f
H
= (1.2 ± 0.15) 109 M-1 s-1; HSO3
- +
CH3COOH → SO2 + H2O + CH3COO-, k
f
HA
= (1.7 ± 0.5) 104 M-1 s-1. On this basis, and assuming
diffusion-controlled rates for proton transfer from strong acids to oxygen bases, a more detailed mechanism
involving formation of sulfurous acid as an intermediate is discussed and some thermodynamic and kinetic
properties of the latter are estimated.
“…On the other hand, it is known that gold is one of the most stable metals, that can be used as an inert electrode material, and can be processed to give different shapes of electrode for electroanalysis, e.g. gold disk electrode, 17 gold ring-disk electrode, 18 gold microband electrode array, 19 gold wire electrode. 20 It also possesses very high stability in nanoscale, even in several atoms.…”
We report a new application of gold nanoparticles for visual detection of copper ions with high sensitivity and selectivity based on the colorimetric difference due to the strong and specific inhibition of Cu(NH 3 ) 62+ to the corrosion of gold nanoparticles at low concentration.
“…Scherson has recently compared the two techniques for the determination of the faradaic efficiency of dithionite (S 2 O 4 2− ) generation from HSO 3 − (bisulfate) reduction. The RDE was judged to be better for this measurement since the measured absorbance is not dependent on the kinetics of follow-up reactions [208].…”
Section: Forced Convection Rde and Channel Flowmentioning
The sections in this article are
Introduction and Principles
Introductory Remarks
Theory and Techniques: Steady State Measurement
Cell Transmission for a Simple Electron Transfer Reaction: Determination of
E
and
n
Effect of Follow‐up Reactions in
OTTLE
Cells
Theory and Techniques: Kinetic Measurements
Chronoabsorptometry
Instrumentation for Chronoabsorptometry
Slow Heterogeneous Kinetics
Effect of Follow‐up Reactions
Derivative Cyclic Voltabsorptometry (
DCVA
)
Galvanostatic Conditions
Adsorption
Cell Geometries, Design, Techniques, and Instrumentation
General Considerations
Transmission under Thin‐layer Conditions:
OTTLEs
and Flow‐cells
Variations on and Alternatives to the Basic
OTTLE
Design
OTTLE
Cells Intended for Both
UV
‐visible and
FTIR
Use
OTTLE
Cell Electrochemical and Spectroscopic Response
Semi‐infinite Cells: Optically Transparent Electrodes (
OTEs
)
Reflection from Electrodes and Liquid–Liquid Interfaces
Glancing Incidence Reflection, Near‐parallel or Parallel Reflection, and Diffraction
Liquid–Liquid Interface and Attenuated Total Reflection
Long Optical Path‐length Thin‐layer Cell (
LOPTLC
)
Forced Convection,
RDE
and Channel Flow
UV
‐vis Combined with Other Spectroscopic Techniques
Applications
Solution Studies of Inorganic Species
Solution Studies of Organic Species
Molten Salts Spectroelectrochemistry
Studies of Species of Biological Interest
Inorganic Thin Films and Modified Electrodes
Conducting Polymers and Oligomer Models
Conclusions
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