Pressure retarded osmosis (PRO) is a new membrane technology to produce renewable energy from osmotic pressure difference of two solutions with different concentration. Membrane used in the PRO process requires high water permeability

effective rejection of salt and ideal mechanical strength in order to achieve an excellent energy production. This paper explains the basic requirements of PRO membranes and summaries the development of the widely-used asymmetric membranes from the aspects of active layer

support layer and pre-treatment

showing the effects of membrane material

preparation and pre-treatment on the membrane performance. Meanwhile

the paper induces the research status of symmetric and quasi-symmetric membranes

which could significantly mitigate internal concentration polarization (ICP) and become a research focus in the future.