Asymmetric Metal Oxide Electrodes for High-Efficiency Evaporation-Induced Energy Harvesting

In the domain of evaporation to electricity conversion, current research efforts are primarily focused on optimizing the permselectivity and evaporation efficiency of the fluid transferring medium. Here, we demonstrate that the output power of evaporation-induced energy harvesting devices can be significantly enhanced using suitable electrodes that complement the charge separation process and improve the ionic-electronic current conversion efficiency. The proof of concept was demonstrated by fabricating an energy device with the nanofluidic membrane of montmorillonite clay (MC-M). Upon replacing typically used Cu electrodes with surface-modified graphitic carbon strips with positively charged TiO₂ nanowires as the bottom electrode, and negatively charged Co₃O₄ nanowires as the top electrode, nearly 8000 times enhancement in the power output was observed. Unlike redox-active metals, metal oxide nanostructures applied in the MC-M device are not consumed in the charge conversion process. Finally, replacing liquid water with a modified block of pottery clay as a self-replenishing water source at the bottom of the MC-M device improved the long-term device stability (uninterrupted power output up to 8 h) in addition to addressing issues like inconveniences of water replacement, variations in water levels, and dissolution of the charge-selective medium.