Fabrication of heterogeneous sulfonated poly(ether ether ketone) membranes for enhanced osmotic energy harvesting

Reverse electrodialysis (RED), a promising approach for harvesting sustainable energy from salinity gradients, relies on ion-selective membranes to optimize efficiency. Conventional polymer membranes, however, face limitations in achieving high power densities due to disordered ion transport pathways. This study introduces a novel heterogeneous sulfonated poly(ether ether ketone) (H-SPEEK) membrane synthesized via solvent-induced phase separation (SIPS). The membrane exhibits an ultrahigh negative surface charge density of −10.8 C m⁻², coupled with a heterogeneous architecture that amplifies hydrophilic domains, thereby accelerating ion flux. When tested in a RED system with natural river water and seawater, the H-SPEEK membrane delivers an exceptional output power density of 15.32 W m⁻², representing a substantial improvement over homogeneous membrane. Furthermore, under a 50-fold CaCl₂ salinity gradient, it maintains a robust performance of 12.0 W m⁻². These advancements are attributed to the membrane's dense ion-conductive channels and ion diode characteristics, which promote selective cation transport while minimizing ion concentration polarization. The results underscore the potential of heterogeneous SPEEK membranes as high-performance solutions for osmotic energy conversion.