Oppositely charged MXene fibers as a highly efficient osmotic power generator from sea and river water

Abstract

Ion-exchange membrane-based reverse electrodialysis (RED) shows great potential for harvesting osmotic energy from seawater and converting it to electricity. However, their low energy conversion efficiency and huge ionic resistance hinder their application on large scales. The implementation of nanofluidic channels in RED devices can significantly improve the performance of osmotic power generators due to their selective and fast ion transport. However, technical challenges in scalable processing at the nanoscale and ion-selective membranes restrict their development in economically viable generators. Here, we report fibrous-based channels as positively and negatively charged MXene fibers (P-MF and N-MF) to extract osmotic energy from the natural and abundant conditions of the slat gradient of river and seawater. Due to the narrow (<2 nm), two-dimensional geometry and high surface charge densities (∼3.8 mC m⁻²) of nanochannels, the oppositely charged fiber membranes provide excellent transmissibility and ion selectivity and a stable output power density of 12.3 W m⁻² for a few months. This record is much higher than the commercialization benchmark (5 W m⁻²) and most state-of-the-art membranes of osmotic power harvesters. By connecting more cells, the output voltage ascends to a value of 1.7 V, which can be used for powering many electronic devices without an intermediary. The introduced membrane breaks the bottleneck of RED devices as practical osmotic power generators toward establishing blue energy as a sustainable and renewable energy source.