Bimodal Droplet-Based Electricity Generation Through Semi Cassini Oval Dynamic Morphology Control

Droplet-based electricity generator (DEG) is the promising energy harvesting technology applicable in versatile scenarios. Despite numerous optimizations in DEG's materials and structures, few has paid attention to the droplet dynamics and morphology control. Here the droplet's spread-retraction dynamics and the resultant semi Cassini oval (SCO) morphology are reported, characterized by convex at both ends and concave in the middle. The lifted top electrode (LTE) is designed to respond to the dynamic SCO morphology in two steps: 1) LTE first contacts the leading edge of the spreading droplet, generating a negative voltage peak; 2) LTE second contacts the trailing edge of the retracting droplet, generating a positive voltage peak. In this way, bimodal electrical output is obtained, which exhibits 25% increase in peak-to-peak voltage and 33% increase in average power compared to the traditional DEG with only one voltage peak. These results prove that incorporating the droplet dynamics and morphology control into DEG design uplifts the energy harvesting limit from individual droplet. The proposed LTE-DEG inspires alternative route for DEG power enhancement by maximizing energy utilization of individual droplet from the perspective of droplet dynamic morphology design.