During my M.Sc. studies here in University of Iceland the following question came up:
'How do protons and electrons form hydrogen molecules during electrolysis?'
Two possible mechanisms were invoked. The solvated protons in the electrolyte may adsorb on the electrode surface where they recombine with electrons. Then, two adsorbed H atoms on the surface may combine into an H2 molecule. Alternatively, a solvated proton may directly react with a hydrogen atom and an electron on the surface and form a H2 molecule. Here the second proton never binds to the surface.
This fundamental question is interesting to answer and could help in the development of cheaper and/or better electrode catalysts than the Pt group metals used today in fuel cells in cars and for producing hydrogen gas from water. Also, in some cases we do not want to produce hydrogen molecules on the electrode. One example of this is in the electrochemical synthesis of ammonia where we would like to prevent the H2 evolution and only produce ammonia. This process has not yet been developed because of this fundamental problem. During my Ph.D. studies at DTU in Denmark, I continued these projects and the main results will be described in my presentation.
We model the interface between a charged electrode and an ionized liquid using density functional theory (DFT) calculations. A method is developed to vary the surface charge and the corresponding counter charge in the electrolyte. This is consistent with theoretical models of the electrochemical double layer introduced by Helmholtz over 150 years ago. With this new methodology we have calculated the rate of H2 formation on several electrode surfaces. The results will hopefully help in designing new types of electrodes, either to enhance the H2 formation or to block it.