All-2D Transition Metal Dichalcogenide Nanosheets Enhance Raindrop Energy Harvesting.

Harvesting energy from the natural world presents a compelling solution to sustainable power generation, and now researchers are exploring the potential of raindrops as a viable source. Foad Ghasemi, Jonas Heirich, and Dimitri Sharikow, from Kassel University, alongside colleagues including Georg Duesberg from the University of the Bundeswehr Munich and Jonathan Coleman from Trinity College, demonstrate a significant step forward in this field with the development of all-2D-material-based raindrop triboelectric nanogenerators. This work addresses the need for efficient materials capable of converting the mechanical energy of raindrops into electricity, utilising nanosheets of molybdenum disulfide and other layered materials. The team’s innovative approach, involving a rapid and low-cost fabrication technique, reveals that medium-sized molybdenum disulfide nanosheets exhibit particularly high performance, paving the way for scalable and sustainable energy harvesting technologies that could one day power small devices from rainfall alone.

Harvesting Energy from Raindrops with 2D Materials

The world’s increasing energy demands drive research into innovative and sustainable power sources, and harvesting energy from everyday occurrences like rainfall is a promising, yet largely untapped, area. Researchers are exploring triboelectric nanogenerators – devices that convert mechanical motion into electrical energy – to capture power from raindrops. This work pioneers the use of entirely two-dimensional (2D) materials to build these devices, moving beyond the limitations of conventional polymer-based designs.

Materials like graphene and transition metal dichalcogenides possess exceptional mechanical flexibility, high surface area, and tunable electrical properties, making them ideally suited for these applications. A key challenge in utilizing 2D materials is producing large, uniform films. The team overcame this hurdle by employing a two-step process beginning with liquid phase exfoliation.

This technique gently separates individual layers from bulk materials, creating a stable suspension of nanosheets in liquid. Researchers refined this process to control the size and thickness of the nanosheets, recognizing that these properties dramatically impact performance. Following liquid phase exfoliation, they further refined nanosheet size using centrifugation, ensuring a consistent starting material for device fabrication.

The innovative core of their methodology lies in liquid-liquid interface deposition. This technique builds films by carefully spreading a suspension of nanosheets across a liquid surface, then transferring them onto a conductive substrate. This method allows for precise control over film thickness and coverage, maximizing the potential for efficient charge transfer.

Researchers systematically varied the number of deposition cycles to fine-tune the film’s properties and optimize performance. Detailed analysis revealed that medium-sized nanosheets consistently outperformed both larger and smaller flakes, striking an optimal balance between surface coverage and effective charge transfer. Larger flakes tended to leave gaps, reducing the active area, while smaller flakes didn’t generate as strong a signal.

Testing various materials revealed that medium-sized molybdenum disulfide nanosheets consistently generated the highest electrical output when exposed to raindrops, due to its favourable electronic properties and surface characteristics. The study highlights the importance of surface oxidation in influencing charge transfer and decay within the materials, providing insight into the underlying mechanisms driving the energy generation process. Importantly, the liquid phase exfoliation and deposition techniques are relatively inexpensive and can be adapted for large-scale production, opening the door to integrating these raindrop-powered generators into a variety of applications, from self-powered environmental sensors to portable electronics.