Osmotic energy harvesting with soft-etched nanoporous polyimide membranes

[EN] We present the study of osmotic energy harvesting with soft-etched nanoporous polyimide membranes for a wide range of salt concentration differences, ion irradiation fluences, and multipore orientations (parallel or network). The effect of solution pH and divalent cations on the membrane performance is also investigated. The membrane behavior is evaluated in terms of the reversal potential (V-rev), the maximum power generation (P-max), and the energy conversion efficiency (eta(max)). For an exposed membrane area of similar to 1 cm(2), the maximum values obtained for these parameters are V-rev = 123 mV, P-max = 0.45 mu W, and eta(max )= 40%, respectively. A significant decrease in the membrane performance is observed for membrane samples obtained with ion fluences higher than 4 x 10(9) ions cm(-2) because of pore overlapping and the diffusional resistance of the external solution boundary layers at very low ionic concentrations. The soft-etched membranes are able to hold the reversal potential for several days.