Testing Mg-Cu and Zn-Cu Galvanic Cells

A project log for Stomach Acid Powered Smart Pill

Zn-Cu stomach acid based bio-galvanic cell powers a hacked activity tracker small enough to swallow and reconfigured as a 'smart pill'.

curt-whiteCurt White 07/17/2018 at 00:570 Comments

I'm testing Magnesium-Copper (Mg-Cu) and Zinc-Copper (Zn-Cu) galvanic cells in a 0.16M solution of Hydrochloric acid (HCL). This solution of HCL approximately matches the PH and HCL concentration in the human stomach (though conditions in the stomach can vary). The Mg-Cu cell initially produces a voltage (electric potential) of 1.46V, however, the surfaces of the Mg strips rapidly corrode and the voltage plateaus at 1.28V after one minute. 

The Zn-Cu test is a little more complex. I had already tested the Zn-Cu cell before I started shooting this video. The residual HCL in the thread and plastic mesh surrounding the Zn and Cu is functioning as an electrolyte. This is why there is a significant electric potential before the cell is even submerged in HCL. When the cell is submerged, the electric potential drops to about 0.5V. Why? This particular Zn-Cu cell is actually three Zn-Cu cells in series. I have separated the cells with plastic flaps which are supposed to act as ion barriers (essentially they insulate the cells from one another). The plastic flaps function well enough when the cell has residual HCL on it, but when the cells are submerged they short across one another.

Electric potential of Zn-Cu cell bank at various functional levels:

1.45V: Ion barriers working, three Zn-Cu cells in series.

0.76V: Center cells shorted, combined cells acting as a single cell.

0.5V: Significant short across all cells.