0
\$\begingroup\$

I am running a half-cell battery configuration. I am using carbon paste (graphite) as a trace (jumper) because my solution contains bio-materials and carbon is bio-friendly. The carbon paste is coated around the paper as a substrate to solidify the paste. Furthermore, I use commercial alligator clips to connect the other end of the carbon trace to a digital platform. Usually, my open-circuit voltage (OCV) is about 0.3 V. When the alligator clips touch the bio-materials in the solution the OCV goes to 0.7.

What is causing this:

  1. The alligator clips are better conductors than carbon since they are metal. (Does conductivity impact voltage measurement?)
  2. The clips react with the water content in the solution causing ion-transfer and false readings.
\$\endgroup\$
2
  • \$\begingroup\$ A drawing could be useful. The ion-transfer seems plausible however. AFAIK graphite is quite neutral (100% carbon ideally) \$\endgroup\$
    – Lorenzo Marcantonio
    Commented Oct 4, 2021 at 11:04
  • \$\begingroup\$ I was more referring to the Ion transfer from metals in the alligator clips! \$\endgroup\$
    – Anwar Elhadad
    Commented Oct 4, 2021 at 11:12

1 Answer 1

Reset to default
3
\$\begingroup\$

Any metal connected to your biological system can create a "battery" - assuming your system includes an electrolyte solution that dissolves some small amount of the metals in your setup. Your alligator clips may be made of copper wires and chrome or nickel plated clips.
As an example "battery", you can wet a piece of paper (20mm x 50mm) with saliva (or a 1% to 10% salt water solution), then set a copper coin (US penny) on one side and a coin made of nickel metal (US 5cent) on the other half. Then measure the voltage across the the copper coin and nickel coin.
Now, look for similar connections in your setup to see if this exposure to metal to electrolyte "salt bridges" might be adding a battery effect to your measurements.

\$\endgroup\$
3
  • \$\begingroup\$ any metal connected to your biological system can create a "battery" ! Are those electrons coming from the metallic clips or from the bio-system? \$\endgroup\$
    – Anwar Elhadad
    Commented Oct 4, 2021 at 12:19
  • \$\begingroup\$ @AnwarElhadad The electrons are all the same...nothing in your system is creating electrons. The correct question is "Where is the voltage coming from?" and I think this answer sums it up pretty well. \$\endgroup\$
    – Elliot Alderson
    Commented Oct 4, 2021 at 12:38
  • \$\begingroup\$ The electrons are coming from the "reduction and oxidation "half cells" created as the metallic form ionizes and dissolves into the electrolyte and a very small amount of chloride ion in the salt is reduced to chlorine (Cl2) which likely is some small it stays dissolved in your electrolyte so you don't readily smell or see it as a gas. You can get a general chemistry test book and look up electrochemical batteries and a table of "reduction potentials". From there you can calculate the voltage produced by various half-cell pairs (a reduction and an oxidation). \$\endgroup\$
    – GT Electronics
    Commented Oct 4, 2021 at 20:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.