4 ms·

I was wondering about that too but they did show a difference between the different circuit types presumably with the same electrodes.

zdragnar 3y ago
The open circuit and control having a similar effect show that it likely isn't ions from the anode or cathode. The other two are more interesting- presuming the short circuit had a lower effect than the one with some resistive load (labelled closed circuit), I presume there's something changing in the soil chemistry itself once sufficient potential is reached by microbe activity. Ions being knocked loose from the dirt itself, rather than the anode or cathode, which wouldn't happen when there's a direct short / no load other than the wire.
- amluto 3y ago
  I don’t have access to the full paper, but this doesn’t follow: > The open circuit and control having a similar effect show that it likely isn't ions from the anode or cathode. When you apply current between two electrodes in an electrolyte, you do a few things: 1. Create an electric field between them. 2. Create an ionic current through bulk electrolyte. 3. Cause chemical reactions at the surfaces. This has to happen: the current in the electrode is made up of electrons (or, equivalently, holes), but the electrolyte doesn’t conduct electrons — it conducts ions. [0]. So, for charge balance to be maintained, every electron that exits the anode into the medium needs to somehow turn into an ion, which happens by chemically adding an electron to something, thus reducing it. Similarly, the cathode pulls electrons from the electrolyte, and they come from something in the electrolyte, which is oxidized as it loses the electrons. If the cathode in particular is not inert at the voltage used, the cathode itself can be oxidized. A copper cathode can, for example, produce copper ions much faster than it it would naturally leach them without an applied voltage. [0] I’m sure that exceptions exist. Solvated electrons are a thing. And you could use an electrically conductive substance as your medium, e.g. carbon or metal powder.
  - smaddox 3y ago
    Yeah, seems like they would need to use gold or platinum electrodes to rule out copper (or whatever) leaching. But even if it's copper leaching that boosts growth, that seems interesting in and of itself---just not really due to electric current.
  - tagawa 3y ago
    But according to the article, the researchers did not apply any current.
    - zwieback 3y ago
      Right, the soil makes a battery.

zdragnar 3y ago

The open circuit and control having a similar effect show that it likely isn't ions from the anode or cathode. The other two are more interesting- presuming the short circuit had a lower effect than the one with some resistive load (labelled closed circuit), I presume there's something changing in the soil chemistry itself once sufficient potential is reached by microbe activity. Ions being knocked loose from the dirt itself, rather than the anode or cathode, which wouldn't happen when there's a direct short / no load other than the wire.

amluto 3y ago
I don’t have access to the full paper, but this doesn’t follow: > The open circuit and control having a similar effect show that it likely isn't ions from the anode or cathode. When you apply current between two electrodes in an electrolyte, you do a few things: 1. Create an electric field between them. 2. Create an ionic current through bulk electrolyte. 3. Cause chemical reactions at the surfaces. This has to happen: the current in the electrode is made up of electrons (or, equivalently, holes), but the electrolyte doesn’t conduct electrons — it conducts ions. [0]. So, for charge balance to be maintained, every electron that exits the anode into the medium needs to somehow turn into an ion, which happens by chemically adding an electron to something, thus reducing it. Similarly, the cathode pulls electrons from the electrolyte, and they come from something in the electrolyte, which is oxidized as it loses the electrons. If the cathode in particular is not inert at the voltage used, the cathode itself can be oxidized. A copper cathode can, for example, produce copper ions much faster than it it would naturally leach them without an applied voltage. [0] I’m sure that exceptions exist. Solvated electrons are a thing. And you could use an electrically conductive substance as your medium, e.g. carbon or metal powder.
- smaddox 3y ago
  Yeah, seems like they would need to use gold or platinum electrodes to rule out copper (or whatever) leaching. But even if it's copper leaching that boosts growth, that seems interesting in and of itself---just not really due to electric current.
- tagawa 3y ago
  But according to the article, the researchers did not apply any current.
  - zwieback 3y ago
    Right, the soil makes a battery.