# Bio‐Based Wax Interfaces for Droplet Energy Harvesting at Fluoropolymer‐Like Output Levels

## TL;DR

Researchers developed a sustainable, high-output droplet energy harvester using bio-based waxes instead of harmful fluorinated materials.

## Contribution

Bio-based waxes are shown to achieve fluoropolymer-like energy output while being environmentally sustainable.

## Key findings

- Natural waxes like beeswax generated up to 500 V and 20–40 µA current, matching fluorinated materials.
- A flexible, biodegradable energy harvester was designed using zinc electrodes and wax-coated surfaces.
- Multiple energy harvesting events per droplet were achieved through guided sliding paths.

## Abstract

Droplet impact and rebound on solid surfaces has emerged as a promising method for energy harvesting, typically demonstrated using fluorinated polymers that generate high voltages via liquid–solid contact electrification. However, these materials are non‐degradable and environmentally unsustainable. To address this limitation, bio‐based waxes ‐ selected by their potential role in environmental electrification processes ‐ are explored as sustainable alternatives. Voltage, current, and charge generation are systematically analyzed from water droplets impacting wax‐coated surfaces. Remarkably, natural waxes such as beeswax, operculum wax, and epicuticular plant waxes produced peak voltages up to 500 V and comparable current levels (≈20–40 µA, 10–20 mW peak power) to fluorinated materials under identical conditions. Building on these findings, a flexible, modular, and biodegradable droplet energy harvester is designed using zinc electrodes and wax‐coated electrification sites. By guiding droplets through predefined sliding paths and gates, multiple energy harvesting events per droplet are achieved. These results demonstrate that high‐performance droplet energy harvesting is possible using sustainable materials and tunable harvester design. Additionally, they reveal the need for further investigation of the liquid‐solid electrification mechanism on non‐fluorinated surfaces, both in engineered systems and in nature.

Replacing unsustainable fluorinated polymers in droplet‐based energy harvesters is usually limited by low power outputs, but carefully selected bio‐based polymers are capable of creating fluoropolymer‐like voltage outputs.