Cascade-Heterostructured Nanofluidics for Photo-Enhanced Upscaling Osmotic Energy Generation

Ensuring energy and resource availability constitutes a fundamental pillar of sustainable socioeconomic development. Nanofluidics hold great promise for energy and resource harvesting. However, a critical bottleneck hinders commercialization, namely, that upscaling nanofluidic areas to boost ion currents triggers severe potential drop and concentration polarization, causing a drastic degradation in selectivity. Here, we engineered cascade-heterostructured nanofluidics (CHS-NFs) featuring numerous atomic-level type-I semiconductor heterojunctions and Schottky junctions to create continuous, ultrafast pathways for coupled electron-ion transport. The heterointerfaces generate nanoscale localized asymmetric electric fields that mitigate concentration polarization and offset potential drops, thereby realizing high ion selectivity and flux. As a result, the CHS-NFs achieve a record-high energy conversion efficiency of 49.5%-approaching the theoretical limit of 50%-over a large area (28 mm², 933 times larger than prior areas), with an exceptional Na⁺/Cl^- selectivity of 332.3. The electricity produced by CHS-NFs-based osmotic cells is effectively stored in capacitors and ion batteries under simulated solar irradiation, exhibiting a 68.8% capacity increase compared with a non-irradiated one. Notably, the cells can generate a high ionic current (467.6 µA), enabling the selective electrochemical recovery of gold from solutions with near-100% purity, as well as other valuable metals, significantly reducing the energy footprint of industrial metallurgy.