Nanopore geometry governs osmotic energy conversion and rectification under coupled fields.

Understanding how nanopore geometry governs ion transport under coupled concentration, pressure, and electric potential gradients is critical for designing advanced nanofluidics and osmotic energy harvesters. A systematic computational study is conducted across eight realistic nanopore geometries. The dominant structural factors are identified, such as internal cavity volume, throat constriction, and axial curvature. Hydraulic permeability is controlled mainly by access resistance and axial smoothness, whereas ionic conductance depends on entrance aperture, cavity-assisted ion enrichment, and throat resistance. Hydraulic pressure acts as an operating modifier, which enhances current and power output but attenuates ion selectivity, rectification, and conversion efficiency. Parametric analysis further demonstrates that throat size is the primary structural determinant, while axial curvature mainly serves as a secondary fine-tuning parameter. However, expanded cavities in the bullet nanopore can promote co-ion enrichment under reverse bias, inducing selectivity inversion. Severe throat confinement may even reverse the membrane potential by shifting the zero-current balance in the cylinder and funnel nanopores at Rmin =5 nm. Finally, a comprehensive performance hierarchy and parameter dependence matrix are established. This framework provides guidelines for tailoring nanopore architectures to achieve enhanced ion current rectification and efficient osmotic energy harvesting.