7.15) A Data Analysis Service for Steady-State Voltammetry via the World Wide Web
Description
This article is from the Electrochemistry FAQ, by Zoltan Nagy nagy@anl.gov with numerous contributions by others.
7.15) A Data Analysis Service for Steady-State Voltammetry via the World Wide Web
A service has been set up via the World Wide Web
(http://physchem.ox.ac.uk/~rgc/datan/datan.htm)
which permits the analysis of steady-state
experimental data (limiting currents or half-wave potentials) at:
* Spherical Electrodes
* Microdisc Electrodes
* Rotating Disc Electrodes
* Channel Electrodes
* Channel Microband Electrodes
This analysis is available for a range of common electrochemical mechanisms (E,
EC, EC2, EC2E, DISP1, DISP2 and EC' processes). The software interpolates the
simulated response from a series of working curves and surfaces. These were
generated from fully-implicit steady-state numerical simulations using
expanding
grids for Channel and Channel microband electrodes[1] and in conformal space
for Microdisc[2], Spherical and Rotating Disc[3] electrodes. The simulations
employed multigrid[4] and preconditioned Krylov subspace[5] methods for the
efficient solution of the large sparse linear systems resulting from finite
difference discretisation and global linearisation via Newton's method.
The user simply selects a geometry and mechanism, enters the cell parameters
and
the limiting current/half-wave potential as a function of radius/rotation
speed/flow rate. Data may be entered directly via a WWW interface, or uploaded
as a file by FTP. For each experimental data set, the theoretical response is
predicted for the chosen mechanism and plotted as a function of mass transport
appropriate to the electrode geometry.
The variance is computed between the experimental and theoretical sets of data.
This may be minimised to 'fit' (i.e. optimise) unknown parameters such as rate
constants or diffusion coefficients. A Golden Section Search[6] may be used to
find a local minimum in one dimension. Downhill Simplex minimisation[6] may be
used for multidimensional searches. One-, two- and multi-dimensional sampling
routines are also available so that the variance curve or surface may be
visualised allowing the global minimum to be discerned from local minima.
Analysis for wall-jet electrodes and heterogeneous chemical and electrochemical
processes at channel electrodes will be added shortly. The service is
available
free of charge.
References
[1] J.A. Alden and R.G. Compton, J.Phys. Chem. B, 101, (1997), 9751.
[2] J.A. Alden and R.G. Compton, J.Phys. Chem. B, 101, (1997), 9606.
[3] R.G. Compton, M.E. Laing, D. Mason, R.J. Northing, P.R. Unwin, Proc. R.
Soc.
Lond. A, 481, (1988), 113.
[4] J.A. Alden and R.G. Compton, J. Electroanal. Chem., 415, (1996), 1.
[5] J.A. Alden and R.G. Compton, J.Phys. Chem. B, 101,(1997), 8941.
[6] W.H. Press, S.A. Teukolsky, W.T. Vetterling and B.P. Flannery, Numerical
Recipes in C: The Art of Scientific Computing, 2nd Edition, Cambridge
University Press, 1992.
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This service is courtesy of Richard G. Compton,
Physical and Theoretical Chemistry Labortatory, Oxford University
With problems/questions contact: RICHARD.COMPTON@CHEMISTRY.OXFORD.AC.UK
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