Hi all!
I am a beginner in applying DFT methods for water splitting and hydrogen evolution reactions. I have gone through several published articles in this regard. After reading them, I am with few unanswered questions with me. They are:
1. How to calculate H2O adsorption and activated H2O adsorption energies on a catalytic surface?
2. How to calculate Volmer step and Tafel steps separately, while H*-cat is the reactive center in the both steps with respect to calculations. So, how to calculate them separately?
3. How to calculate H adsorption and H evolution energies?
I would be glad to receive responses from experts to resolve them through DFT methods.
Thanking you in anticipation.
Hi Krishna Chaitanya Gunturu , Thanks for sharing your questions.
I have been studied HER for some time, if you are interested in how I did the calculations, please check this paper and the supporting materials there:
Article An Unusual Exchange Mechanism in the Tafel Reaction on Pt(11...
Now return to your questions:
1. How to calculate H2O adsorption and activated H2O adsorption energies on a catalytic surface?
My Answer: I'm not sure what you mean by "activated H2O". But if you want to calculate a water molecule on the surface, it is really easy. Just create the slab and put water molecule on it then its OK.
The formula for calculating the adsorption energies of water molecule (H2O) on a surface (let's say surf) is:
\Delta G_{ads}(H_2O_{ads}) = G(H_2O + surf) - G(H_2O) - E(surf)
when you calculate the Gibbs free energy, you can assume that:
G = E_{DFT} + ZPE - T*S, where E_{DFT} is the energy you directly get from DFT, ZPE is zero-point energy and S is the entropy term of adsorbates. You can get the formula in my paper.
I'm not sure what software is available to you and what is your experience, so that is all I can say (until I have more information about you and your specific questions)
2. How to calculate Volmer step and Tafel steps separately, while H*-cat is the reactive center in the both steps with respect to calculations. So, how to calculate them separately?
My Answer: You can calculate them separately. Tafel step is really easy since it is a surface reaction. VASP / Quantum Espresso + NEB method can do it. Heyrovsky reaction is a little bit tricky since it has proton and it is an electrocatalytic reaction. Prof. Wolfgang Schmickler has done some pioneer work in this field, you can check these papers:
* https://pubs.rsc.org/en/content/articlehtml/2011/cp/c0cp02748k
* https://pubs.rsc.org/en/content/articlehtml/2012/cp/c2cp40717e
3. How to calculate H adsorption and H evolution energies?
My Answer: This is basically the same procedure as I have mentioned in the answer of your first question. Please see the details in my paper.
If you have more questions or comments, please DM me through researchgate or send me an email through ([email protected]).
Hope these answers are helpful for you.
Best Regards,
Zhengda
He Zhengda Thanks for your reply. I will certainly contact you once I go through the suggested articles.