Recent decades witnessed the evolution of novel methods of energy conversion owing to the growing demand for clean energy. Nanofluidics, the study of fluid flow at nanometer scale, could contribute significantly in the field of energy conversion. For instance, the use of nanochannels for harvesting energy from pressure driven flow and from salinity difference between fresh water and sea water. The surface plays a crucial role in nanofluidics because of the high surface to volume ratio in such system, and the properties which are trivial in macroscale system becomes important. The failure of no slip boundary condition is one important surface effects and a non zero fluid velocity occurs at the interface depending on the wettability of the surface. The existence of interfacial slip, apart from increasing the fluid velocity also has a profound effect on the energy conversion in nanofluidic system based on the principle of electrokinetics. The hydrodynamic slip enhances the electrokinetic response which is quantified by the so called zeta potential which is the electric potential at the shear plane, i.e., at the interface where the fluid motion occurs. With this regard, our study aims to investigate the effect of concentration and alkali cation types (Li+ , Na+, and K+) on the hydrodynamic slip in non wetting (graphene) nanochannel to understand the influence of fluid slippage on electrokinetic energy conversion. To study the fluid behaviour at nanoscale, we used molecular dynamics simulation combined with the principles of continuum theory which is valid for channel heights approximately larger than five times the molecular diameter. Besides, our study is also trying to explore the applicability of nanofluidic system with different surface wettability (graphene and its counterpart, boron nitride) for energy conversion using pressure driven flow for three different salt solution with a wide range of salt concentration, particularly focussing on estimating the transport coefficient (zeta potential) relating the generated current density (streaming current) and the applied thermodynamic force (pressure gradient).