Designing Hydrogen Bond Network Inside Thermal‐Driven Multilayered Membrane for Sustainably Effective Energy Conversion from Seawater and WWTP Effluent

Abstract The natural phenomenon of ion permeation at the seawater‐freshwater interface harbors substantial untapped energy. However, freshwater scarcity and poor ion exchange membranes currently restrict salinity gradient energy conversion and its widespread application. In this study, a multilayered composite membrane through strategic integration of CNTC‐MOF intermediate layers with charge‐gradient sulfonated poly (ether ether ketone) (SPEEK) is designed and successfully prepared for effective energy conversion at the interface between seawater and wastewater treatment plant (WWTP) effluent, for the first time. Density functional theory (DFT) calculations demonstrated that incorporating an organic‐inorganic layer into the pristine membrane established a hydrogen bond network, improving water retention and enhancing cation transport. The output power density as high as 6.1 W m −2 is sustainably obtained at a 50‐fold KCl salinity gradient. Meanwhile, thermal‐osmotic synergy enabled 10.2 W m −2 , output through low‐grade heat integration (∆T = 30 K), which is hoped to open new avenues for waste energy utilization. Besides, the salinity conversion in real environments (seawater/WWTP effluent gradient) reached the maximum output power density of ∼3.0 W m −2 and compensated for the technical application limitations caused by insufficient freshwater resources. This study demonstrated that this synthesized composite membrane enables high energy conversion under a salinity gradient and shows excellent long‐term stability for harvesting blue energy.