Dear All,
I've been thinking about how to simulate the cyclic voltammogram for electrocatalytic reaction (such as HER, ORR or formic acid oxidation).
I've read some papers on the subject, but what I've found is really confusing:
On one hand, there are plenty of works done on simple electron transfer reaction (e.g. Prof. R. G. Compton), they've used the electrochemical kinetics as the boundary condition for solving the diffusion equation.
On the other hand, M. Janik and Rossmeisl et al. have used DFT to calculate the CV for OH adsorption on Pt(111) and other surfaces. But they didn't use diffusion equation at all.
So I wish to start a discussion about what processes that must be considered in modeling the CV curve for electrocatalytic reactions? I think this is a very important topic in electrochemistry (especially in electrocatalysis since CV can tell us a lot of information) and wish to hear as many responses as possible.
Hope we can move the field forward by combining our wisdoms.
Thank you all.
Hello He Zhengda ,
You may find COMSOL useful - you can build up multiple sets of physics within a single model (MultiPhysics).
I apologise, I have not searched, but there may already be some examples of COMSOL being used for electrocatalysis modeling.
https://www.comsol.fr/electrochemistry-module
I remember talking to one of the key designers of the electrochemistry module, Dr. Edmund Dickinson, whom I believe was part of Richard Compton's group (along with my PhD supervisor Prof. Frank Marken). Therefore it may be worthwhile contacting COMSOL for guidance. Otherwise a simple search for the user manual for this module should reveal the equations that are solved within the model.
Digital simulation package is availble in all CHI instruments. You can use that.
If you're interested in writing your own simulation there are plenty of resources out there (on the echem side, Bard and Faulkner touch upon it, but you can find simulations that get down to single molecule random walk). If you are really looking for existing CV simulation programs DigiSim (older)/ DigiElch (current/updated version) has been around a while and is broadly used and accepted. That software lets you input multiple chemical and electrochemical reactions. DigiElch allows simulation of surface bound species. It also allows fitting to experimental data to extract things like rate constants. (Disclosure: ElchSoft is the owner of DigiElch, but that software is sold through Gamry Instruments).
Dear Zhengda,
In CV, the changed potential will accompany with the generation/consuming of the solute in solution phase.
If such generation/consuming of solute is large or sustaining, the concentration polarization will be established on the surface. The mass transport will hence become notable, thus greatly impact the measured current. In this case, the diffusion equation should be taken into the consideration. On the contrary, while generation/consuming of solute is tiny or not sustaining to establish the concentration polarization, it will be unnecessary to consider the diffusion.
As for CV of electrocatalytic reactions, if the associated reaction are HER/HOR or ORR/OER, generation/consuming of solute should be continuous, because a constant total Gibbs free energy deltaG=-nFU will always exists for these reactions. That is the reason the diffusion equation should be used.
On the other hand, for the DFT studied of OH* adsorption/desorption by, e.g. Rossmeisl et al, they just simulate the CV without the existence of O2/H2. And the reaction they simulate are quite reversible. Like H-upd region or OH adsopriton/desorption region on Pt111. Under this case, the generation/consuming of solute is not continuous. Because quasi-equilibrium of reaction establishes at any given potential. So in this case, the diffusion can be dismissed
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