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 ≈2.8×10⁻⁴W 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.