Harnessing the Intrinsic Ionic Rectification Properties of Blind-Hole Nanoporous Anodic Alumina for Osmotic Energy Generation

The full potential of blue energy as a sustainable technology for high-performance energy generation remains elusive. Nanoporous anodic alumina (NAA) is extensively used as a passive structural support to develop a broad variety of ion exchange membranes based on other materials for osmosis-driven energy generation. However, the intrinsic ionic current rectification (ICR) properties of the inherited hemispherical barrier oxide layer (BOL) closing the bottom tips of NAA's nanopores are overlooked. As-produced NAA provides new avenues to control ionic transport through its BOL, acting as an ICR model system to study electric current associated with the selective flow of ions across anodic oxides. This study explores the intrinsic capability of NAA membranes for osmotic energy generation. NAA membranes with a working area of 13.4 mm2 can generate a power density yield of approximate to 2.8x10-4 W m-2 when subjected to a 105-fold salinity ratio at a pH 3 in CaCl2 electrolyte, achieving a high efficiency of 7%. With better understanding of the mechanism of ion transport on osmotic generation, the intrinsic properties of NAA membranes can be tailor-engineered to maximize blue energy yield, paving the way for future developments in a scalable technology suited for real-life applications. Harnessing the barrier oxide layer of nanoporous anodic alumina for blue energy generation. The native barrier oxide layer of blind-hole nanoporous anodic alumina membranes enables selective flow of ions when this system is subjected to a salinity gradient. This selectivity, which can be engineered by tuning the electrolyte characteristics, is translated into osmotic energy power via ionic flow rectification. image