This project aims at understanding the role of the solvent in the electrocatalytic redox reactions of water, i.e. hydrogen oxidation and evolution, and oxygen reduction and evolution. Traditionally, the emphasis in heterogeneous catalysis is on the role of the catalytic material. In electrocatalysis, which in many ways may be viewed as heterogeneous catalysis at the solid-liquid interface, the role of the solvent has always been underexposed. However, for a complete fundamental insight into the aspects that determine the activity of a catalyst, the role of the medium needs to be accounted for properly. The proposed research aims at rectifying this situation by suggesting three different PhD research projects.

In the first project, the hydrogen evolution, the hydrogen oxidation, the oxygen reduction, and the water oxidation reaction will be studied electrochemically on a variety of different catalysts in different solvents. The variety of catalysts includes both the traditional metals such as platinum and gold, but also surface-immobilized molecular catalysts, that are often not water soluble. Our analysis will account for both thermodynamic and kinetic effects of the solvent, and is expected to shed light on why water often appears to be such a good medium for electrocatalysis. Moreover, we will study these reactions in non-aqueous solvents with the in situ vibrational spectroscopy tools available in our lab, to identify intermediates that may be difficult to observe in bulk water due to the overwhelming interference of the water itself.

In the second project, we will build on our recent successes in modeling aspects of electrochemical reactions in ultra-high-vacuum (UHV), by studying the dissociation of H ₂ and O ₂ on water-covered well-defined platinum surfaces. We will specifically focus on the role of steps in these processes. Our UHV lab is well suited for these challenging studies as we have a number of UHV setups, one of them equipped with a supersonic molecular beam. This project will also include some modeling of non-aqueous solvents, as studied in the first project, interacting with platinum and gold surfaces, in order to estimate the strength and the type of interactions of these molecules with the electrode surface.

In the third project, we will embark on a detailed computational study of the systems modeled in UHV in the second project. These first-principles DFT calculations should give us insight into the molecular basis of the H ₂ and O ₂ dissociation in the presence of water on stepped platinum surfaces. The simulations will employ ab initio molecular dynamics simulations as well as constrained total energy calculations to estimate barriers. In this project, we will also perform calculations of the some of the solvents considered in the first project and their strength of interaction with the relevant catalysts.
It is expected that the research will give new and fundamental insight into the role of solvent, water as well as other solvents, in the electrocatalytic reactions of water, that will be of significance for fuel cells and solar fuel production. The studies envisaged here are unique and novel and the environment of our group in Leiden is probably the only place in the world where this level of multidisciplinary (electro)catalysis research is currently possible. The project foresees collaborations with other expert groups in Leiden, Paris and Ulm.

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