Thermal‐Ionic Coupling in Transpiration‐Inspired Janus Nanofiber Membranes: Synergistic Dry‐Wet Interface Engineering for Solar‐Driven Electricity Generation

Harnessing solar evaporation for simultaneous steam and electricity generation is an emerging technology for sustainable energy-water systems, yet its development is fundamentally constrained by the inability to maintain a stable interfacial potential gradient in homogeneous materials. Here, we introduce a dry-wet interface engineering strategy that enables persistent thermal-ionic coupling for continuous electricity generation. Inspired by leaf transpiration, an asymmetric Janus nanofiber membrane is constructed to form a stable hydrophilic-hydrophobic interface that simultaneously regulates fluid distribution and interfacial charge dynamics. This architecturally confined interface induces hydration-triggered surface ionization on the hydrophilic layer, generating an intrinsic potential difference continuously reinforced by evaporation-driven directional ion transport. As a result, the Janus evaporator delivers a stable open-circuit voltage of 0.22 V under 1 sun illumination, 57% higher than natural evaporation, and exhibits scalable output up to 2.21 V via modular integration. Mechanistic investigations combining experiments and multiscale simulations reveal that the sustained electrical output arises from the synergistic coupling of interfacial potential modulation, ion-selective transport, and localized photothermal heating. The dry-wet interface plays a decisive role by stabilizing charge separation and suppressing potential dissipation. This work establishes a general framework for interfacial potential engineering in evaporation-driven systems, enabling simultaneous solar desalination and electricity generation.