The direct capture of energy from salinity gradient is limited by low energetic efficiency. Here we propose to investigate an original membrane for capture of osmotic energy based conical track-etched nanopore. In order to improve the surface charge at pH 7, the nanopore was functionalized with chitosan / poly(acrylic acid) self-assembly. We observed for single nanopore a large osmotic current around 0.6 nA for a concentration gradient c,(Tip)/c,(Base) = 1000. This corresponds to energy around 25 pW per nanopore. Then, we demonstrate that this result can be upscale for a multi-pore membrane in the case of a low density of nanopores.