In this work, the influence of hydrogen bonds on structure and thermodynamic properties of binary mixtures of protic ionic liquids (PILs), sharing the same cation, are investigated with molecular dynamics simulation. The observed non-ideal mixing behavior can be explained with the formation of complex hydrogen-bonded clusters. With the help of a newly developed simple lattice model the clusters can be described. Furthermore, the model shows that the mixing process is enthalpy-driven, not entropy-driven as one would expect.<eng>
