Understanding Ionic Flow in Nanofluidic Blind‐Hole Anodic Aluminum Oxide (AAO) Membranes for Osmotic Energy Generation

The use of anodic aluminum oxide (AAO) membranes in osmotic energy generation has been limited to structural support to other ion exchange membranes based on a range of nanomaterials. However, recent investigations have demonstrated the potential of blind‐hole AAO membranes to be used as an active ion selective platform to harvest renewable osmotic energy from saline electrolyte gradients. These membranes provide simplicity and unique dynamic ion transport properties that can be tailored by engineering the structure of their nanopores. Herein, we harness the inherent iontronic properties of as‐produced blind‐hole AAO membranes with engineered structural features and study their potential for osmotic energy generation. Analysis of the performance of these model membranes reveals that a balanced tuning of membrane resistance, and ion selectivity, and flux results in an enhancement of their osmotic energy generation capability, making it possible to extract a maximum power density of 5.16 ± 0.26 W m −2 in FeCl 3 ‐based electrolyte. This study provides new fundamental knowledge on the iontronic properties of blind‐hole AAO membranes and how these can be engineered, building a foundation framework to design nanofluidic membranes with optimal capability for osmotic energy generation.