Pressure retarded osmosis (PRO) is a way to generate electricity based on using the difference in osmotic pressure between two solutions. Fresh water and seawater have large differences in salt concentrations, and thus osmotic energy, and therefore energy can be harvested from these salinity differences. When two solutions with different salinities are placed on either side of a membrane that is permeable to water (but with limited permeability to salt), water will move from the fresh water through the membrane and into the salt solution until the salinities of the two solutions are similar. As fresh water enters, it pressurizes the salt water; that pressurized water can then be released through a turbine to make electricity. Reverse osmosis (RO) membranes are good for this purpose, but newer membranes are being developed especially for PRO or forward osmosis applications.
There is no research currently ongoing in the Logan lab on PRO. However, a comparison of PRO and RED is described in a review paper by Logan and Elimelech (2012), and there is information available on this from such sources as Wikipedia.