  Solid/liquid interfaces control various processes of technological relevance
in the process industry and many fundamental physicochemical phenomena. This
work examines the link between the atomistic description of mass transfer at
solid/liquid interfaces out of equilibrium and the constitutive mass transfer
equations typically used to model these processes at the mesoscale. In our
analysis, we discuss the microscopic inconsistencies apparent in simplified
models of mass transfer whenever non-idealities dominate the liquid phase in
the proximity of solid/liquid interfaces. Using C{\mu}MD - a molecular
simulation technique to investigate out-of-equilibrium, concentration-driven
processes with pseudo open-boundary conditions - we outline a strategy to
capture and quantify non-idealities induced by specific interactions between
the solid surface and molecules in the fluid phase. We demonstrate our approach
by studying electrolyte solutions in technologically important, multi-component
systems in which introducing a solid/liquid interface induces substantial
deviations in the composition and electrochemical properties compared to the
fluid phase bulk. To this aim, we analyse NaCl(aq) solutions in contact with i)
the graphite basal surface and ii) {100} NaCl(s) crystalline surfaces. We
uncover the tendency of the sodium cation to preferentially adsorb at the
surfaces considered, which induces local violations of electroneutrality that
leads to the emergence of an electric potential in the fluid phase at the
solid/liquid interface.
