pH-Resistant Nanofluidic Diode Membrane for High-Performance Conversion of Salinity Gradient into Electric Energy

The harvesting of the energy stored in the salinity gradient between seawater and river water by a membrane-scale nanofluidic diode for sustainable generation of electricity is attracting significant attention in recent years. However, the performance of previously reported nanofluidic diodes is sensitive to the pH conditions, which restricts their potential applications in wider fields with variable pH values. Herein, a pH-resistant membrane-scale nanofluidic diode with a high ion rectification ratio of ≈85 that demonstrates a stable ion rectification property over a wider pH range from 4 to 10 is reported. This pH-resistant ion rectification is explained quantitatively by a theoretical calculation based on the Poisson and Nernst–Plank equations. The nanofluidic diode membrane is integrated into a power generation device to harvest the energy stored in the salinity gradient. By mixing the simulated seawater (0.5 m KCl) and river water (0.01 m KCl) through the membrane, the device outputs an impressive power density of 3.15 W m ⁻² and demonstrates high stability over a wider pH range. The membrane-scale nanofluidic diode provides a pH-resistant platform to control the ion transport and to convert the salinity gradient into electric energy.