High‐Strength, Thin PBO Nanofiber Membrane with Long‐Term Stability for Osmotic Energy Conversion

Abstract Ion‐selective membrane embedded in a reverse electrodialysis system can achieve the conversion of osmotic energy into electricity. However, the ingenious design and development of pure polymer membranes that simultaneously satisfy excellent mechanical strength, long‐term stability, high power density, and increased testing area is a crucial challenge. Here, high‐strength, thin PBO nanofiber membranes (PBONM) with 3D nanofluidic channels and a thickness of 0.81 µm are prepared via a simple vacuum‐assisted filtration technology. The thin PBONM exhibits excellent mechanical properties: stress of 235.8 MPa and modulus of 16.96 GPa, outperforming the state‐of‐the‐art nanofluidic membranes. The obtained PBONM reveals surface‐charge‐governed ion transport behavior and high ion selectivity of 0.88 at a 50‐fold concentration gradient. The PBO membrane‐based generator delivers a power density of 7.7 and 40.2 W m⁻² at 50‐fold and 500‐fold concentration gradient. Importantly, this PBONM presents excellent stability in response to different external environments including various saline solutions, pH, and temperature. In addition, the maximum power density of PBONM reaches up to 5.9 W m⁻² under an increased testing area of 0.79 mm², exceeding other membrane‐based generators with comparable testing areas. This work paves the way for constructing high‐strength fiber nanofluidic membranes for highly efficient osmotic energy conversion.