Canadian researchers say that their device could find multiple uses in snowy environments

Snow electrification – the natural phenomenon by which snow particles carry an electric charge – has been known by meteorologists since the early 1960s. The exact nature of the charge depends on temperature; snow layers tend to be positively charged between −5 °C and −10 °C, and negatively between −15 °C and −20 °C. The effect has been attributed mainly to the ordering of dipoles that occurs within water molecules as they crystallise, but it can also be caused by friction between snow and sliding surfaces.

And it’s this contact electrification aspect that first caught the attention of researchers at Canada’s McMaster University. They wondered if they could use snow’s inherent charge to build a triboelectric device to generate electricity in harsh winter conditions. They’ve reported their findings – and their design – in a new Nano Energy paper [DOI: 10.1016/j.nanoen.2019.03.032].

Triboelectric generators harvest electrical energy through contact/separation and sliding friction, so finding the optimal combination of materials is key to their performance. The authors set out to test a range of materials across the triboelectric series, and found that the most tribo-negative materials provided the best electrical performance. Based on this, they fabricated a snow-triboelectric nanogenerator (snow-TENG) using 3D extrusion printing. They deposited successive thin films of PEDOT:PSS, which acted as the electrode, and UV-curable silicone (the triboelectrification layer). The silicone layer was patterned with an array of 25 µm squares, to further enhance the contact surface area. The resulting structure was transparent, mechanically strong, metal-free and flexible. The device could also be stretched, reaching a maximum of 125% of its original length.

The team tested their device under three different modes of operation – tapping, sliding and snowfall. In ‘tapping mode’, the device was briefly and repeatedly brought into contact with a snow surface, and its output used to charge a 1 μF capacitor. Even after 8000 cycles, the snow-TENG continued to operate, charging the capacitor to 2 V in four minutes. To test its performance in ‘sliding mode’, the device was attached onto a rubber bicycle wheel which was then ridden across a snow-covered surface. This is where the TENG reached its optimal energy harvesting performance – an open-circuit voltage of 8 V and a current density of 40 μA/m2 were obtained. In ‘snowfall mode’ the device could be used to detect snowfall angles, and its electrical output was found to vary with the falling rate of the snow.

This led the authors to conclude that the snow-TENG could be used as “…a self-powered, sensitive snow-related meteorological monitoring station to measure critical weather parameters.” The authors also suggest that, with further work, this device might even be suitable for direct printing onto solar panels, “…to create electricity during snow seasons without compromising the efficiency of the solar cells.” They also suggest that the snow-TENG could be a power source for wearable electronic devices. Work is ongoing.

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Abdelsalam Ahmed, Islam Hassan, Islam M. Mosa, Esraa Elsanadidy, Gayatri S. Phadke, Maher F. El-Kady, James F. Rusling, Ponnambalam Ravi Selvaganapathy, Richard B. Kaner. “All printable snow-based triboelectric nanogenerator” Nano Energy 60 (2019) 17–25. DOI: 10.1016/j.nanoen.2019.03.032