New method can generate electricity from footsteps

Move over solar energy! Researchers have developed a novel, inexpensive and simple method that can convert footsteps into usable electricity.

The method developed by researchers at University of Wisconsin-Madison in the US puts to good use a common waste material: wood pulp.

The pulp, which is already a common component of flooring, is partly made of cellulose nanofibres - tiny fibres that, when chemically treated, produce an electrical charge when they come into contact with untreated nanofibers.

When the nanofibres are embedded within flooring, they are able to produce electricity that can be harnessed to power lights or charge batteries, said Xudong Wang, an associate professor of materials science and engineering at UW–Madison.

Because wood pulp is a cheap, abundant and renewable waste product of several industries, flooring that incorporates the new technology could be as affordable as conventional materials, Wang said.

While there are existing similar materials for harnessing footstep energy, they are costly, nonrecyclable, and impractical at a large scale.

Wang's research centres around using vibration to generate electricity. For years, he has been testing different materials in an effort to maximise the merits of a technology called a triboelectric nanogenerator (TENG).

Triboelectricity is the same phenomenon that produces static electricity on clothing. Chemically treated cellulose nanofibers are a simple, low-cost and effective alternative for harnessing this broadly existing mechanical energy source, Wang says.

Heavy traffic floors in hallways and places like stadiums and malls that incorporate the technology could produce significant amounts of energy, Wang said.

Each functional portion inside such flooring has two differently charged materials - including the cellulose nanofibres, and would be a millimetre or less thick.

The floor could include several layers of the functional unit for higher energy output.
"So once we put these two materials together, electrons move from one to another based on their different electron affinity," Wang said.

The electron transfer creates a charge imbalance that naturally wants to right itself but as the electrons return, they pass through an external circuit. The energy that process creates is the end result of TENGs.

Wang said the TENG technology could be easily incorporated into all kinds of flooring once it is ready for the market.The study was published in the journal Nano Energy.