3 research outputs found
Modular Flow-Through Platform for Spectroelectrochemical Analysis
A new
type of flow platform for electrochemical and spectroelectrochemical
measurements is presented. Finite element method simulations confirm
that the hydrodynamic profile within the device is not turbulent and
provides an analytical platform for the investigation of homogeneous
kinetics, radical lifetimes, and reaction mechanisms. The modular
āplug and playā configuration of the platform allows
one to carry out electrochemistry and spectroscopy individually or
simultaneously. Specific demonstrations of electroanalytical measurements
using the flow system platform includes voltammetric analysis of organometallic
compounds and quantitative analysis of ascorbic acid in commercial
orange juice samples. Combined spectroelectrochemical demonstrations
include electrochemical luminescence of ruthenium compounds and ligand
exchange reactions of iron complexes using UVāvis spectroscopy
Structural Correlations in Heterogeneous Electron Transfer at Monolayer and Multilayer Graphene Electrodes
As a new form of carbon, graphene is attracting intense
interest
as an electrode material with widespread applications. In the present
study, the heterogeneous electron transfer (ET) activity of graphene
is investigated using scanning electrochemical cell microscopy (SECCM),
which allows electrochemical currents to be mapped at high spatial
resolution across a surface for correlation with the corresponding
structure and properties of the graphene surface. We establish that
the rate of heterogeneous ET at graphene increases systematically
with the number of graphene layers, and show that the stacking in
multilayers also has a subtle influence on ET kinetics
Dual-Barrel Conductance Micropipet as a New Approach to the Study of Ionic Crystal Dissolution Kinetics
A new
approach to the study of ionic crystal dissolution kinetics
is described, based on the use of a dual-barrel theta conductance
micropipet. The solution in the pipet is undersaturated with respect
to the crystal of interest, and when the meniscus at the end of the
micropipet makes contact with a selected region of the crystal surface,
dissolution occurs causing the solution composition to change. This
is observed, with better than 1 ms time resolution, as a change in
the ion conductance current, measured across a potential bias between
an electrode in each barrel of the pipet. Key attributes of this new
technique are: (i) dissolution can be targeted at a single crystal
surface; (ii) multiple measurements can be made quickly and easily
by moving the pipet to a new location on the surface; (iii) materials
with a wide range of kinetics and solubilities are open to study because
the duration of dissolution is controlled by the meniscus contact
time; (iv) fast kinetics are readily amenable to study because of
the intrinsically high mass transport rates within tapered micropipets;
(v) the experimental geometry is well-defined, permitting finite element
method modeling to allow quantitative analysis of experimental data.
Herein, we study the dissolution of NaCl as an example system, with
dissolution induced for just a few milliseconds, and estimate a first-order
heterogeneous rate constant of 7.5 (Ā±2.5) Ć 10<sup>ā5</sup> cm s<sup>ā1</sup> (equivalent surface dissolution flux ca.
0.5 Ī¼mol cm<sup>ā2</sup> s<sup>ā1</sup> into a
completely undersaturated solution). Ionic crystals form a huge class
of materials whose dissolution properties are of considerable interest,
and we thus anticipate that this new localized microscale surface
approach will have considerable applicability in the future