The biofuel cell can stretch and flex, conforming to the human body.
Credit: University of California San Diego





Islands and bridges


To be compatible with wearable devices, the biofuel cell needs to be flexible and stretchable. So engineers decided to use what they call a “bridge and island” structure developed in Xu’s research group. Essentially, the cell is made up of rows of dots that are each connected by spring-shaped structures. Half of the dots make up the cell’s anode; the other half are the cathode. The spring-like structures can stretch and bend, making the cell flexible without deforming the anode and cathode.


Increasing energy density

The researchers’ biggest challenge was increasing the biofuel cell’s energy density, meaning the amount of energy it can generate per surface area. Increasing energy density is key to increasing performance for the biofuel cells. The more energy the cells can generate, the more powerful they can be.

“We needed to figure out the best combination of materials to use and in what ratio to use them,” said Amay Bandodkar, one of the paper’s first authors, who was then a Ph.D. student in Wang’s research group. He is now a postdoctoral researcher at Northwestern University.


Testing applications

The biofuel cell was connected to a custom-made circuit board manufactured in Mercier’s research group. The board is a DC/DC converter that evens out the power generated by the fuel cells, which fluctuates with the amount of sweat produced by a user, and turns it into constant power with a constant voltage.


Next steps


Also, the concentration of lactic acid in a person’s sweat gets diluted over time. That is why subjects were able to light up an LED for only four minutes while biking. The team is exploring a way to store the energy produced while the concentration of lactate is high enough and then release it gradually.

Story Source: Materials provided by University of California – San Diego Original written by Whitney Clavin.Note: Content may be edited for style and length.
Journal Reference:
Amay J. Bandodkar, Jung-Min You, Nam-Heon Kim, Yue Gu, Rajan Kumar, A. M. Vinu Mohan, Jonas Kurniawan, Somayeh Imani, Tatsuo Nakagawa, Brianna Parish, Mukunth Parthasarathy, Patrick P. Mercier, Sheng Xu, Joseph Wang. Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat. Energy Environ. Sci., 2017; 10 (7): 1581 DOI: 10.1039/c7ee00865a