Dipole-programmed dynamic surface charge in covalent organic framework nanochannels for salinity-thermal energy conversion.

Ion-selective membranes for reverse electrodialysis typically rely on fixed charged groups to establish Donnan exclusion, yet their effective charge density is rapidly weakened by Debye screening under high-salinity conditions. Here we report hydrazone-linked covalent organic framework (COF) nanochannels with biomimetic dipolar pore-wall microenvironments for dynamic surface-charge regulation and coupled salinity-thermal energy conversion. Among hydroxyl-, methoxy- and non-functionalized COF membranes, the ortho-hydroxyl-functionalized COF-DhaBt/PAN establishes a cooperative hydroxyl-hydrazone dipolar network that preferentially restricts anion migration through ion-dipole interactions and hydrogen bonding, thereby generating an adaptive negative microenvironment for accelerated cation transport. Phosphate preadsorption further converts anion retention into a charge-amplification mechanism, increasing the power density from 41.7 to 116.6 W m-2 under a 0.5 M‖0.01 M NaCl gradient. When a 35 K temperature gradient is introduced, the phosphate-regulated membrane delivers a power density of 208.4 W m-2, accompanied by an increase in the ionic Seebeck coefficient from 0.72 to 0.82 mV K-1. This work establishes dipolar pore-wall programming as an effective strategy for overcoming charge-screening limitations and integrating salinity-gradient energy harvesting with low-grade heat utilization.