Optimizing the Power Production in an Osmotic Engine via Microfluidic Fabricated and Surface Crosslinked Hydrogels Utilizing Fresh and Salt Water

Abstract

Salinity gradients between seawater and river water is a renewable source of energy having a worldwide potential capacity of about 3.1 TW. This energy can be extracted by e.g., an osmotic engine, using hydrogels with high water uptake capacity. Consecutive exposing hydrogels to fresh and saline water makes swelling–shrinking cycles, which can be utilized to move a piston in an osmotic engine. The production of power with this method is significantly suppressed by gelblocking, where voids between particles are blocked so that the water flow is limited and the absorbency significantly retarded. To improve the power production, the gelblocking is minimized within this article by using spherical mono-dispersed hydrogels made by microfluidic technique. In this study mono-disperse poly(acrylic acid-co-sodium acrylate) hydrogels with varying diameters (100-600 µm) and varying degrees of neutralization (DN = 10–75 mol%) are synthesized. In addition, hydrogels with different DN are utilized for additional surface crosslinking to fabricate core–shell particles. The maximum power of 0.67 W kg−1 is obtained for hydrogels with a diameter of 105 µm, degree of crosslinking (DC) = 1.7 mol%, DN = 75 mol%, and a core-shell architecture, which is three times higher compared to hydrogels having undefined size without a core–shell framework.