This New Device Can Generate Electricity from Human Motion

July 24, 2017

You may never need to carry a charger again, instead, your phone will draw energy from your clothes and the environment. This is the potential of a new device developed at Vanderbilt University’s Nanomaterials and Energy Devices Laboratory.

Using battery technology and layers of black phosphorus, the new device generates small amounts of electricity when bent or pressed. The phosphorus which is only a few atoms thick can generate the electricity even at extremely low frequencies in line with human movement.

[Image Source: John Russell/Vanderbilt]

Assistant Professor of Mechanical Engineering, Cary Pint, who directed the research said“In the future, I expect that we will all become charging depots for our personal devices by pulling energy directly from our motions and the environment.”

[Image Source: John Russell/Vanderbilt]

The findings were published in a paper titled, “Ultralow Frequency Electrochemical Mechanical Strain Energy Harvester using 2D Black Phosphorus Nanosheets”  in the online journal ACS Energy Letters.

Effectively harvesting energy from ambient sources, is a growing field of science. The field includes devices that can pull energy from temperature variation, radiant energy devices that capture energy from light and electrochemical devices that tap biochemical reactions.

The work published by Pint and his team have two distinct advantages, Pint explains, “Compared to the other approaches designed to harvest energy from human motion, our method has two fundamental advantages.The materials are atomically thin and small enough to be impregnated into textiles without affecting the fabric look or feel and it can extract energy from movements that are slower than 10 Hertz—10 cycles per second—over the whole low-frequency window of movements corresponding to human motion.”

[Image Source: Nanomaterials and Energy Devices Laboratory / Vanderbilt]

Capturing energy at low frequency is hugely challenging.  Many other experiments have been unable to create devices that work effectively below 100 hertz, making their efficiency rates between 5-10 percent even under optimal conditions.  

The black phosphorus device, on the other hand, can operate with more than twice that efficiency. “Our harvester is calculated to operate at over 25 percent efficiency in an ideal device configuration, and most importantly harvest energy through the whole duration of even slow human motions, such as sitting or standing,” Pint said.

[Image Source: John Russell/Vanderbilt]

The research team has spent the last three years exploring advanced battery systems and specifically the capabilities of batteries to bend and stretch. The group was the first to present research demonstrating the voltage changes in batteries when placed under stress. Under tension, the voltage rises and under compression, the voltage drops again. From here the team started to reconstruct batteries with both positive and negative electrodes made from the same material. While this prevents the device from storing energy, it can fully engage with the voltage changes caused by the stresses of bending and twisting applied to it.

This idea was then transformed into the current device being tested that is constructed from the ultra thin black phosphorus. This material is perfect due to its attractive electrical, optical and electrochemical properties.

The researchers admit they are some way off mobile phone charging material, the latest breakthroughs provide the building blocks for such applications. The technology could also power low voltage LCD screens.  

Sources: TechExplore, NewElectronicsVanderbilt

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