Understanding the Electrokinetic Role of Ions on Electricity Generation in Droplet-Based Hydrovoltaic Systems

Hydrovoltaic is emerging as a promising energy harvesting technology with the remarkable capability of generating energy through the direct interaction of water and material. The hydrovoltaic generates volt-level potentials without any external force, and its electrical performance can be enhanced by using an aqueous solution. However, it is not clear how salt ions affect or interact with the material. Herein, the theoretical model was used to provide an in-depth analysis of working principles. The model, validated with experimental results, incorporates four physics: water flow in unsaturated porous media, transportation of ions, chemical reactions, and electrostatics. It was found that the distribution of ions is key to improving the voltage output. The higher gradient of ions’ concentration leads to strong potential differences, and its asymmetry of concentration is mainly governed by the water flow and concentration distribution. Additionally, we analyzed the parametric effects of substrate porosity and relative humidity under salt solution. The results showed that the presence of salt ions makes the electrical performance highly sensitive to porosity but less sensitive to relative humidity. Our findings improve the understanding of hydrovoltaic mechanisms and pave the way for the practical use of hydrovoltaic systems.