Power from sweat for wearable electronics

July 22, 2020 by
Filed under: News 

Researchers at the University of Bath in the UK have developed the first fuel cell that can be stacked in a printed circuit board for wearable designs.

Glucose Fuel Cells (GFCs) generate power from any body fluid at room temperature, including sweat for wearables and blood for embedded medical devices

The team led by Carla Gonzalez-Solino at the Centre for Biosensors, Bioelectronics and Biodevices (C3Bio) at the  University of Bath developed an integrated arrays of GFCs and successfully demonstrate their operation at physiological concentrations of glucose.

Each GFC consists of a porous gold anode and a Pt/Au cathode in a single layer, and generates a maximum power of 14.3 μW/cm2 (in 6 mM of glucose) a 297mV, with a linear response to glucose within a concentration range that includes both low and high glucose levels.

The challenge for individual GFCs is the low voltage output. So the team also connected four GFCs in parallel in a stack on a PCB. This generated between 1.4V and 0.9V.

Each board measures 42.5 mm x 34.5 mm consisted of four rows that include a circular electrode (geometric area: 1.54 mm2) used as the anode, and a crescent electrode, used as the cathode (geometric area: 7.22 mm2).

To demonstrate meaningful energy harvesting, the four GFC stack was connected to a commercial off-the-shelf power management system using a BQ25504 PMIC from Texas Instruments that can handle the low output voltage. The BQ25504 system is designed to operate with input voltages as low as 100 mV, a range that covers most fuel cells. It has a built-in Maximum Power Point Tracking (MPPT) function that finds the open circuit potential (OCP) of the fuel cell and sets the operating point by varying the effective load impedance seen by the fuel cell to  around 80 percent of this voltage.

The OCP is sampled for 256 ms, which, for the GFCs proposed in this work, is sufficient for the cells to reach full OCP. The BQ25504 system also includes a battery management system, which was connected to a storage capacitor. Both the 4-GFC voltage and the voltage over the energy storage element were continually logged using a Pico datalogger to record the voltage over time.




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