Electrokinetic energy harvesting over nanometer and sub-nanometer scales.

The article provides a comprehensive review of electrokinetic energy harvesting (EKEH), focusing on its mechanisms, materials, and challenges at nano- and sub-nanometric scales. EKEH exploits the movement of ionic species within charged fluid–solid interfaces, particularly through electrical double layers (EDLs), to convert pressure, concentration, and temperature gradients into electrical energy. Advances in nanofabrication and novel materials such as two-dimensional membranes, carbon nanotubes, and metal-organic frameworks have enabled enhanced ion selectivity and fluid permeability, addressing traditional tradeoffs and improving energy conversion efficiency. Despite promising applications ranging from small-scale wearable devices to large-scale salinity-gradient power generation, challenges remain in scalability, membrane fouling, fabrication costs, and maintaining performance in hypersaline environments. The review highlights future directions including angstrofluidics—the study of fluid behavior at angstrom-scale confinements—and the potential for bio-inspired designs to overcome current limitations and enable sustainable, carbon-neutral energy solutions.