PhD Student (graduated 2024)
Associate member of the GRK2516
Group: Prof. Friederike Schmid, JGU Physics

Research Project: Theory
Physical electrochemistry using molecular dynamics simulations

Recent electrochemical experiments reveal electrical conductivity and current density on the electrodes of acetonitrile(ACN)-water mixture solution flow cells without a supporting electrolyte and any ionic environment [1]. The physical mechanism of conductivity is still poorly understood; this study thus provides a first attempt to understand this mechanism, with support from the FOR2982 UNODE (UNusual anODE reactions in electrochemical energy conversion). Our working hypothesis is that a percolation phase transition occurs due to hydrogen bond network in the bulk when an external electric field is applied. Our results show that the hydrogen bond network is a fundamental tool in analyzing the formation of water nanodomains. We analyzed the polarization of acetonitrile-water mixtures under the effect of electric fields and found a linear response to small electric fields. In addition, the hydrogen bond network topology conserves its overall properties in the range of applied electric fields (10^-6 − 10^-1 V/nm). Moreover, in the non-linear response regime, at high electric fields (0.3 V/nm), we observe a change to a parallel orientation between acetonitrile molecules from the known antiparallel orientation at zero electric fields.

Fig. 1 Larger cluster representations of an ACN-water mixture at x_ACN = 0.75. a) Real space representation of molecules belonging to the hydrogen bond network. Oxygen atoms in water are red, nitrogen atoms in ACN are blue. These molecules are mainly water molecules partially surrounded by acetonitrile molecules. b) Hydrogen bond network graph of the largest cluster. Dangling ends correspond to ACN molecules.

Fig. 2 CDF between the COM of ACN first neighbor molecules.