Help File Version 2.0
DigiElch Version 8.0, 8.F and 8.FD
Software for simulating and conducting electrochemical and spectro-electrochemical experiments
Author: Manfred Rudolph
Copyright (C) 2011 by ElchSoft.com, all rights reserved
Home page: http://www.ElchSoft.com
Note that DigiElch 8 requires Windows 7, 8 or later. Windows XP is no longer supported by DigiElch 8. Users still working with Windows XP have to stay with DigiElch 7.
DigiElch is a Windows program that computes the electrical current and the concentration profiles for any use-defined mechanism comprising an arbitrary number of charge transfer steps and first- or second-order chemical reactions. The program works for the most common electrode geometries including the simulation of thin layer cell experiments and the exact (two-dimensional) simulation of the electrical current response at band and disk micro-electrodes. Moreover, effects such as adsorption, IR-drop and/or double layer charging can be included in all these simulations. Version 8 includes simulation modules for the following electrochemical methods:
•Cyclic Voltammetry (CV)
•Square-Wave Voltammetry (SW)
•Fourier-Transform Cyclic Voltammetry (FT)
•Multi-sine Impedance (IMP)
•ComPosed-Scan Voltammetry (CPS)
•Modules for conducting CV, SW, CA, IMP, CPS and FT - experiments using a Gamry Reference 600, 600+ or Interface 1000 potentiostat
•Modules for conducting Spectro-Electrochemical or classical UV-VIS Spectroscopic Experiments and for evaluating such experiments by means of Factor Analysis (Singular Value Decomposition) and non-linear data fitting strategies.
This aforementioned modules enable the user to do measurements and simulations in a perfectly consistent way without requiring the export or import of data. When working with third-party hardware DigiElch enables the user to import experimental curves (stored in ASCII-file format) and to compare these curves with simulated ones. The determination of the thermodynamic and kinetic parameters involved in the underlying reaction scheme can be accomplished then either by "trial and error" ( DigiElch - Standard) or by making use of the non-linear fitting procedure implemented into DigiElch - Professional.
•Very fast and accurate simulation of the current response for any user-defined mechanism that can be composed of charge-transfer steps and first- or second-order chemical reactions.
•1D simulation of finite- and semi-infinite diffusion processes for the most common regular 1D-electrode geometries.
•Real 2D-simulations of such user-defined mechanisms for the band and disk electrode.
•Inclusion of IR-drop and double layer charging where the dependency of the double layer capacity from the electrode potential can be expressed by a fourth-order polynomial.
•Simulations of termolecular charge-transfer reactions of the type: Ox + P + e = Red + Q
•Simulation of adsorption processes
➢the kinetic of the adsorption processes can be formulated in a way that leads to the Frumkin isotherm under equilibrium conditions
➢CT-reactions may proceed either by direct electron transfer of the adsorbed species or via the desorption pathway
➢the heterogeneous rate constants of any CT-reaction can be linked to the surface coverage of a particular species. (Simulation of CT-reactions proceeding with different speed through the uncovered and covered part of the electrode)
➢reactions between adsorbed and desorbed species can be taken into consideration
•Two different simulation methods:
1.A very fast "fixed grid simulator" providing extremely high exponential convergence towards zero for the simulated flux error.
2.A relatively slow "adaptive grid simulator" that may be useful for simulating accurate concentration profiles and/or for checking the accuracy of the fixed grid simulator by an independent method.
•Options for displaying how the concentration profiles are changing in the course of the simulation.
•Options for displaying how surface concentrations or surface coverage are changing in the course of the simulation.
•Options for displaying the fundamental-, second and third-harmonics involved in the FT-CV current curve.
•Options for displaying the envelope of the fundamental-, second and third-harmonics involved in the FT-CV current curve.
•Option for displaying a user-defined harmonics involved in the FT-CV current curve and the envelope of the user-defined harmonics.
•Options for customizing colors and style of the screen display.
•Multi-core CPU support (process parallelization) for Data Fitting and 2D (micro-electrode)-simulations
•Export of the screen display in Windows enhanced meta file (*.emf) format.
•Export of simulated current curves and concentration profiles into ASCII-files. Several formatting options which enable the exported data to be imported into third-party presentation software.
•Import of experimental (or re-import of simulated) current curves. In this way (and by using the Copy/Paste command) any number of such curves can be simultaneously displayed on the screen for studying the effect of parameter variations simulated curves or for determining parameters yielding the "best fit" between experimental and simulated curves using a "trial and error" strategy.
•User defined import filters for importing experimental ASCII-data files produced by third-party instruments into DigiElch
Same features as reported above for DigiElch - Standard. Instead of determining the parameters yielding the "best fit" between experimental and simulated curves by "trial and error" the following tools are provided to manage this task in an automated way:
•A non-linear regression strategy can be used to optimize parameter values such as to minimize the standard deviation between simulated and experimental curves (measured with different scan rates, concentrations etc.) for an user-defined mechanism. The optimization is done iteratively by means of the Gaus-Newton method.
•Alternatively data fitting (or at least the determination of "good" starting values for the Gaus-Newton procedure) can be accomplished by means of a global minimum finder. The latter does not require starting values for the parameters to be optimized but only the definition of a physically sensible upper and lower limit for each parameter value. The optimization is done by searching the minimum standard-deviation between simulation and experiment using a low-discrepancy sequence of quasi-random numbers covering the range of sensible parameter values.
•Executing experiments with a Reference 600, Reference 600+ or Interface 1000 potentiostat (GAMRY Instruments) from within DigiElch in a way that is perfectly consistent with doing the simulations.
•The definition of scan segments used in the experiment is identical to those used in the simulations.
•"Run & Fit" i.e. current curves (or impedance data) measured in this way can be directly used for data fitting.
•One-click determination of uncompensated ohmic resistance, Ru, by measuring the impedance in a potential range where the faradaic current is negligible small.
•One-click "Measure IR-drop, Adjust IR-Compensation & Run Experiment". That means:
•the uncompensated ohmic resistance, Ru, is measured as described above.
•the IR-Compensation is automatically adjusted using the greatest possible value that is just a little bit smaller than the measure value of Ru.
•the experiment is started.
•Automatized approach for subtracting the experimental background current from measured current curves.
•Export of the screen display in Windows enhanced meta file (*.emf) format.
•Export of experimental current curves into ASCII-files. Several formatting options which enable the exported data to be imported into third-party presentation software.
•Execution of Spectro-Electrochemical (SPELCH) experiments using a Reference 600, Reference 600+ or Interface 1000 potentiostat (GAMRY Instruments) in combination with a diode array UV-VIS spectrometer. Currently spectrometers from GAMRY, Avantes and Mightex are supported by DigiElch 8. Both potentiostat and spectrometer are programmed and controlled from within DigiElch. The current response and the spectra measured in the course of the SPELCH-experiment are displayed in different TAB-windows. No need to move between different programs.
•SPELCH-experiments can be conducted either as potential sweep (CV ) or potential step (CA) experiment.
•Evaluation of recorded spectra by means of Factor Analysis to determine the number of colored species produced or erased during the SPELCH-experiment.
•Options for displaying and analyzing only spectra referring to a particular scan segment (i.e. to the forward or backward scan of a CV or to the first, second, third, etc. potential jump of a CA-experiment) .
•Studying chemical systems by classical UV-VIS spectroscopy and determining the significant number of colored species involved in a complex chemical equilibrium by means of Factor Analysis.
•Unique non-linear data fitting routine for minimizing the standard deviation between simulated and experimental spectra on the basis of a user defined mechanism in such a way that
➢ the simulated spectra of the colored species are linear combinations of the (significant) abstract mathematical factors
➢the linear combinations satisfy the constraint to avoid negative adsorption coefficients as much as possible
The execution of SPELCH experiments requires the activation of Modules for GAMRY-Potentiostats in DigiElch and access to the Dynamic Link Libraries (DLL) provided by the manufactures of the spectrometers. The measurement of classical UV-VIS spectra requires only access to the spectrometers DLL but no activation of Modules for GAMRY-Potentiostats.
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