Ion Selectivity Inversion in Nanotube‐Patterned Microchannels for Durable Osmotic Energy Harvesting

Small, vol. 21, pp. e2501396

Abstract

Abstract Ion‐selective membranes have long faced a trade‐off between nanoscale precision and macroscopic durability, especially in systems with large pores (>1 µm), where traditional overlapping electrical double layer mechanisms fail. Organic membranes offer high ion selectivity but poor stability, while inorganic membranes are durable yet limited by high internal resistance from ultralong, tortuous pathways. Here, these challenges are overcome by designing robust porous titanium membranes patterned with TiO2 nanotube arraysvia a simple electrochemical anodization process. Uniquely, these membranes reverse ion selectivity from cation to anion transport, enabled by the enhanced charge separation and high surface area of the TiO2 nanotubes.This allows cation adsorptionon channel walls and selective anion transport through the central tunnel—even in microchannels up to 100 µm, far beyond conventional nanoscale designs. The membranes demonstrate proof‐of‐concept osmotic energy conversion with remarkable durability of 110 days, attributed to the mechanical and chemical stability of TiO2 nanotubes. This work redefines the ion‐selective membrane design by bridging nanoscale control with macroscopic robustness and offers new insights into ion transport mechanisms within microchannels.

Authors 10

1. Kaiqi Zhao

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

2. Zhihao Li

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

3. Tengyu Chen

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

4. Dingyin Yin

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

5. Jun Yi Su

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

6. Wulyu Jiang Aachen Faculty of Mechanical Engineering

   RWTH Aachen University

   Affiliation as printed

   Faculty of Mechanical Engineering RWTH Aachen University 52056 Aachen Germany

7. Kaiwen Wang

   Beijing University of Technology

   Affiliation as printed

   Beijing Key Laboratory of Microstructure and Property of Advanced Materials Beijing University of Technology Beijing 100024 China

8. Qiannan Zhao

   Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

9. Lu Xia corresponding Aachen Faculty of Mechanical Engineering

   RWTH Aachen University · Chongqing University · State Key Laboratory of Mechanical Transmission

   Affiliation as printed

   Faculty of Mechanical Engineering RWTH Aachen University 52056 Aachen Germany

   State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China

10. Lidong Sun corresponding

    Chongqing University · State Key Laboratory of Mechanical Transmission

    Affiliation as printed

    State Key Laboratory of Mechanical Transmission School of Materials Science and Engineering Chongqing University Chongqing 400044 China