  Osmotic transport in nanoconfined aqueous electrolytes provides new venues
for water desalination and "blue energy" harvesting; the osmotic response of
nanofluidic systems is controlled by the interfacial structure of water and
electrolyte solutions in the so-called electrical double layer (EDL), but a
molecular-level picture of the EDL is to a large extent still lacking.
Particularly, the role of the electronic structure has not been considered in
the description of electrolyte/surface interactions. Here, we report enhanced
sampling simulations based on ab initio molecular dynamics, aiming at
unravelling the free energy of prototypical ions adsorbed at the aqueous
graphene and hBN interfaces, and its consequences on nanofluidic osmotic
transport. Specifically, we predicted the zeta potential, the diffusio-osmotic
mobility and the diffusio-osmotic conductivity for a wide range of salt
concentrations from the ab initio water and ion spatial distributions through
an analytical framework based on Stokes equation and a modified
Poisson-Boltzmann equation. We observed concentration-dependent scaling laws,
together with dramatic differences in osmotic transport between the two
interfaces, including diffusio-osmotic flow and current reversal on hBN, but
not on graphene. We could rationalize the results for the three osmotic
responses with a simple model based on characteristic length scales for ion and
water adsorption at the surface, which are quite different on graphene and on
hBN. Our work provides first principles insights into the structure and osmotic
transport of aqueous electrolytes on two-dimensional materials and explores new
pathways for efficient water desalination and osmotic energy conversion.
