The role of ions in hydrovoltaic power generation†

Hydrovoltaic devices generate power from the transfer of ambient thermal energy involved in water evaporation. To date, hydrovoltaic research has focused mainly on identifying and optimizing materials for use in high-performing devices. While progress has been made towards the real-world application of hydrovoltaic devices, questions remain regarding the specific mechanism of power generation and the overall role of ions. Herein, we demonstrate that ions play an integral role in the functioning of graphite-based hydrovoltaic devices, and the presence of ions is essential for hydrovoltaic power generation in devices with both connected and disconnected electrodes. Probing the performance of devices in a variety of protic, aprotic, and organic solvents, we show that hydrovoltaic devices cease generating power in non-ionic liquids but can be ‘activated’ through the introduction of ionic salts. Recognizing the key role played by ions in hydrovoltaic devices provides further insight into the mechanism of power generation and can help guide the development of devices in the future.