• Maher El-Kady

Electronic Design: Printable Nanogenerator Harvests Falling Snow

A research team has developed and tested an energy-harvesting transducer and sensor that uses triboelectric current developed by snow falling on their unique layered material.

:::Source: Electronic Design:::

By Bill Schweber

DEC 30, 2019

There’s apparently little limit to the imaginative ways to explore and exploit the “something for almost nothing” potential of energy harvesting. Researchers at UCLA working with participants at other institutions devised a triboelectric-based energy harvester that creates electricity from falling snow. Their snow-based triboelectric nanogenerator (TENG) uses the fact that falling snow is positively charged and seeks to give up electrons (Fig. 1).

1. The working mechanisms and FEM simulations of a snow-TENG: Schematic illustration showing the working mechanism of a snow-TENG utilizing three different operating modes including tapping, sliding, and snowfall (a, b, c); FEM simulation results for the corresponding operational modes (d, e, f). Finally, triboelectric charges can also be generated when snow falls on the silicone film. (Source: UCLA)

Co-author Maher El-Kady, a UCLA assistant researcher of chemistry and biochemistry, said “Snow is already charged, so we thought, why not bring another material with the opposite charge and extract the charge to create electricity?”

To pair with the falling snow and create the required electron transfer, they needed a suitable negatively charged material. “After testing a large number of materials including aluminum foils and Teflon, we found that silicone produces more charge than any other material,” said El-Kady. They then used 3D printing to construct the device, which has a layer of silicone and an electrode (Fig. 2). This allowed them to precisely control the design and deposition of the electrode and triboelectric layer, leading to a flexible, stretchable, and metal-free TENG.

2. The 3D-printing process and architecture along with the optical and mechanical properties of a snow-TENG. Shown is a schematic illustration of the printing process of a snow-TENG (a): printing of a conductive polymer electrode (a-i); inset shows the chemical composition of the ink, (a-ii). On the right is printing of the triboelectrification layer based on UV curable silicone ink; inset reveals the chemical composition of the silicone ink. Next is a schematic illustration of the structure of the device, featuring a micropatterned surface of the UV curable silicone; SEM images on the left are showing the micropattern at different magnifications (scale bars are 100 µm and 50 µm, respectively) (b). The working principle of the device based on snow triboelectrification is shown in (c). In (d) is a photograph showing the high transparency of the silicone layer; the logo of McMaster University in the background can be recognized through the silicone layer. Exposure of the snow-TENG to different stretching conditions is given in (e). (Source: UCLA)

Based on the single electrode mode, the device can generate an instantaneous output power density as high as 0.2 mW/m2 (50-MΩ load), open-circuit voltage up to 8 V, and a current density of 40 μA/m2 under defined conditions (Figs. 3 and 4).

3. Evaluation of the electrical performance of a snow-TENG for harvesting energy from falling snow: Voc and Jsc define the triboelectrification performance of a snow-TENG using different positive and negative triboelectric materials (a); influence of the UV light intensity and curing time of the triboelectrification layer (silicone) on the electrical output of the device (b, c). The plots compare the open-circuit voltage, short-circuit current, and short-circuit charge under different conditions. (Source: UCLA)

4. Characterization of the electrical properties of a snow-TENG in tapping and sliding scenarios: The testing setup showing a vertical linear motor, snow layer, and the fabricated snow-TENG (a). Open-circuit voltage, Voc; short-circuit current Jsc; and external load dependent peak power in the tapping scenario (b, c, and d, respectively). The charging behavior of a 1-µF capacitor using the output from the snow-TENG; results show that the capacitor can charge to 2 V in almost four minutes (e). There’s no apparent degradation in voltage profiles for the snow-TENG even after about 8000 cycles of repeated loading and unloading at 3-Hz rate (f). This confirms that the snow-TENG is a durable and stable device, even with long-term usage. (Source: UCLA)

The team did more than merely build an energy-harvesting transducer and power source. The snow-TENG can function as a self-powered sensor and weather station to monitor the weather in real time to provide accurate information about the snowfall rate, snow accumulation depth, wind direction, and speed in snowy and/or icy environments. In addition, it can be used as a wearable power source and biomechanical sensor to detect human body motions.

The team believes the device could be produced at low cost given “the ease of fabrication and the availability of silicone,” added the project leader Richard Kaner, professor of chemistry and biochemistry, as well as materials science and engineering, and who holds UCLA’s Dr. Myung Ki Hong Endowed Chair in Materials Innovation.

Full details of theory, fabrication, and test are in their paper “All printable snow-based triboelectric nanogenerator” published in Elsevier’s Nano Energy.

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