Test electrolysis

Safety

Drive the electrodes from the electroPioreactor job, never by setting LED channel D by hand: only the job clamps electrolysis power to 10%.

The electrodes were fitted, and their polarity and depth checked, in Set up electrolysis.

1. Weigh the dry empty vial and record its weight.
2. Fill it to 14 ml, the working volume, with nutrient solution or 2 M bicarbonate solution.
3. Screw the vial cap fully onto the vial.
4. Connect the electrodes to LED channel DOne of the HAT's four LED outputs, A to D. The electroPioreactor job drives the electrodes from channel D, clamped to 10% power., catch upwards.
5. Start electroPioreactor from Activities on the Manage screen, with electrolysisSplitting water with an electric current: hydrogen at the cathode, oxygen at the anode. It supplies the hydrogen the HOB grow on. power at 2.5% in the job’s Settings panel. Set a long spargeBubbling gas through the culture. Here, CO₂ from the cylinder flows down the anode on a timer set in the electroPioreactor job. interval until CO₂ is set up.
6. Check bubbles form on both electrodes within 30 seconds, roughly twice as many on the cathodeThe negative electrode: a stainless steel rod. Hydrogen forms on it, so it shows about twice the bubbles of the anode. It must never be wired as the anode. as on the anodeThe positive electrode: a titanium tube coated with mixed metal oxide (IrO₂-Ta₂O₅). Oxygen forms on it, and CO₂ flows down its bore into the vial.: the 2:1 ratio of H₂ to O₂.
7. Measure the voltage across the electrodes with a multimeter on DC volts, probes on the two ring terminals, and record it.
8. Measure the current: break into one electrode lead, put the multimeter in line on the DC mA range, reconnect, and record it.
9. Stop the job, and seat the vial in the Pioreactor.

Notes

• Check the voltage and current again before and after each experiment. A significant change means recalibrating.
• Graphite electrodes are for testing only. Run them in bicarbonate solution, not nutrient solution, which corrodes them faster.
• Record any loose connection at an ElectrodeTopStopThe printed block that sits on top of the MEP's O-ring vial cap. It holds both electrodes parallel and clamps each cable's ring terminal to its electrode with an M3 bolt through a captive nut. bolt, a change in bubble rate or anode discolouration with the run.

Parts

• 1×O-ring vial capearlier step
• 1×Pioreactor 20 ml glass vialearlier step
• 1×Pioreactor 20 ml v1.1earlier step

Tools

• 1×Analytical balancetool
• 1×Multimetertool

Check your work

1. Within 30 seconds of starting the job, where do the bubbles form?

   • On both, about twice as fast on the anode
   • On neither: no bubbles after 30 seconds
   • On both, about twice as fast on the cathode
   Show the answer

   Answer: On both, about twice as fast on the cathode

   • If you see On both, about twice as fast on the anode: The cables are swapped. Stop the job and swap them as in the first check of Set up electrolysisSplitting water with an electric current: hydrogen at the cathode, oxygen at the anode. It supplies the hydrogen the HOB grow on..
   • If you see On neither: no bubbles after 30 seconds: Check the cables are tight under the ElectrodeTopStopThe printed block that sits on top of the MEP's O-ring vial cap. It holds both electrodes parallel and clamps each cable's ring terminal to its electrode with an M3 bolt through a captive nut. bolts and plugged into LED channel DOne of the HAT's four LED outputs, A to D. The electroPioreactor job drives the electrodes from channel D, clamped to 10% power., and the job is running.

≈ 0.02 g CO₂e per view