Theoretical description of the electrode potential
The presence of the electrolyte and external electric fields represents a considerable challenge for the first-principles description of electrocatalytic systems. Although there are some promising approaches, there is still no generally accepted method to represent the electrode potential in periodic DFT calculations. There is a close correspondence between the applied electrode potential and the atomistic structure of the electrochemical double layer. On the one hand, the concentration of ions from the electrolyte in the electrochemical double layer is an explicit function of the electrode potential. On the other hand, the structure of the electrode-electrolyte interface contributes to the potential drop across the double layer and is thus related to the electrode potential through the work function of the interface.
After having finished the implementation of an explicite counter electrode in a periodic DFT code, we will concentrate on a more realistic description of the electrode-electrolyte interface and the electrode potential by particularly focusing on the role of ions in the electrochemical double layer. Depending on the electrolyte, typically either specifically adsorbed anions or non-specifically cations are present. Specific attention shall be given to an appropriate description of the solvation shell of the ions. Specifically adsorbed anions do not only lead to electrostatic effects, but they also modify the electronic structure of the electrode and thus additionally influence their electrocatalytic properties. The different effects of the ions shall be deconvoluted and thus a better understanding of the electrocatalytic activity obtained.
In a first step, different specifically adsorbed anions shall be addressed in a systematic manner, but also non-specifically adsorbed cations shall be considered. As an integral part, also a reliable derivation of the electrode potential for a given interface structure shall be developed.
Popular DFT functionals within the generalized gradient approximation (GGA) for the exchange-correlation effects yield a satisfactory description of the properties of water. However, there are some deficiencies such as the fact that GGA water is overstructured, i.e., too much ice-like as far as the pair-correlation distributions are concerned. Hence also the reliable first-principles description of the aqueous environment shall be assessed, especially by studying the effects of dispersion corrections on the properties of water on electrode-electrolyte interfaces.
Besides improving the first-principles description of electrochemical electrode-electrolyte interfaces, also electrocatalytic processes at these interfaces shall be addressed. In this project, we will focus on electrocatalytic processes in C1 chemistry, in particular on the electrooxidation of methanol. In the search for reaction steps, special attention shall be paid to the possible occurence of concerted reaction mechanisms.