Evaluating platinized electrodes for electrolysis

[gerrit]

I decided to run an experiment to test two different platinized electrodes for the in-situ electrolysis, and thought I’d write up the results.

I bought a platinized titanium mesh electrode on Ebay for £8.72 and like @Martin I cut out a smaller piece using a hacksaw to be able to fit it inside the Pioreactor’s 20mL vial.

I 3D printed the vial cap for eIetrolysis and CO2 sparging and attached ring terminals to two female Dupont wires. I then used a short 10mm bolt and two nuts to attached the electrode and wire to the vial cap. I also attached an M4 stainless steel bolt and nut to the other ring terminal through the vial cap.

I made up some macro nutrient solution (with no micronutrients and distilled water) and added it to the vial. I connected the platinized mesh electrode to channel D positive on the Pioreactor, connected the stainless steel electrode to channel D negative and set the LED channel D intensity to 10%:

I then placed the vial inside the Pioreactor and measured the change in optical density over 6 hours:

That’s a big OD increase considering that there was nothing growing in the nutrient solution:

I suspect the platinized titanium electrode is maybe not platinized and/or made of titanium, as it was looking worse for wear, while the stainless steel electrode looked fine:

Next up I wanted to repeat the experiment with a short platinum electrode I bought for £28.60 (including shipping). It was significantly more expensive than the mesh version, but is just the right size to fit inside the vial and would provide a good baseline as I’m more convinced that this electrode was platinized and made of actual titanium.

I designed a vial cap that would fit the short platinum electrode and wired it up using a crocodile clip instead of a ring terminal. I used the same stainless steel electrode from the previous experiment and refreshed the nutrient solution:

Again, I set the channel D intensity to 10% and waited another 6 hours:

As you can see there was very little variation in the overall optical density. The variations can probably be accounted for by the hydrogen and oxygen bubbles in the solution.

The solution was also still clear:

There was some discolouration on the platinum electrode, so maybe we should decrease the channel intensity even further to prolong the lifespan of the electrode:

From these two experiments, I think it’s safe to assume the mesh electrode is not fit for purpose. Maybe someone knows of a more reputable source of the platinized mesh electrodes that would like to repeat this experiment?

[Martin]

That’s brilliant, well done.

The first was similar to the experiment that killed my YouTube series. I was doing it with microbes and a crazy orange vitamin pill micronutrient attempt. It did something similar but took me ages to find out, because I let it run much longer before looking at it. I then decided on a number of experiments I needed to run to determine exactly what was happening, but ran out of cash & needed to focus on both paid work to feed the family and grant applications so we can make the effort sustainable.

I think I agree with your conclusions. I also think a longer platinum electrode would fare better, with a larger surface area to reduce current density while maximising electrolysis.

What about using the platinum electroplating mesh (or a more reputable one) to electroplate our own titanium bolt anodes within a pioreactor vial?

[Martin]

@gerrit - is your new cap design published anywhere? Goldn have confirmed that they don’t offer customised versions. I might try one of their 85mm long 6mm diameter electrodes if I can’t find a way to tap a bolt into the titanium, or otherwise attach it to a vial cap.

[gerrit]

@Martin Just published it on Printables:

https://www.printables.com/model/974845-pioreactor-vial-cap-with-hole-for-6mm-electrode

[Martin]

Brilliant, thanks for this Gerrit. Richard at Spa Plating (goldn.co.uk) has also agreed to do a couple of 60mm long specials for us. He also recommended that if we’re going to require regular large quantities, we might consider fabricating them ourselves & mentioned that they have some videos outlining the platinising process.

I presume these are the most relevant ones:

How To make platinum electrodes with Spa Plating's Platinum Tank Plating Solution

Platinum tank plating

[gerrit]

@Martin Nice!

Have you tried testing if your mesh electrode is fake? (I need to buy some hydrogen peroxide first):

Testing a Platinum Electrode

[gerrit]

@Martin I was watching a video of someone the same guy from my previous post building a hydrogen generator this morning, and interestingly enough he was using nickel electrodes:

Building a Hydrogen Generator

Looks like they’ve got through quite a few design iterations, shown towards the end of the video. Now I’m wondering if we should try it out, or whether it’s only suitable when you’re using sodium hydroxide?

[Martin]

I think it works fine for hydrolysis, but believe the Ni²⁺ ions that would most likely leach off may kill the HOB. Surviving HOB would likely do so either by efflux or intracellular sequestration. The latter would make them inedible.

I don’t think there’s anything special about the sodium hydroxide, he’s just not wanting to produce chlorine or other gasses, hence avoiding chlorides, sulphates, etc.

This chap’s using potassium hydroxide as the electrolyte and stainless steel for both electrodes - although you can see the rust formation around the anode around the midway point:

DIY Hydrogen/Oxygen Generators From Grocery Store Items (HHO Fuel Cells & Split Cell Electrolysis)

Carbon could be our best value anode. I thought I’d find a video on it, and was really interested to see here that it does a better job in a magnetic field:

1696 Low Cost Hydrogen With the Help Of Magnets And Carbon Felt

[gerrit]

Replaced my M4 stainless steel bolt with a 316 stainless steel rod - looks much cleaner:

I got it in the same 6mm diameter as the platinized anode, but thinking I may go a bit smaller next time as it doesn’t leave much room for other things - they need to be that close together to fit straight through the top part of the vial.

[Martin]

Cool, when you say cleaner, do you mean the overall appearance or the solution?

I guess surface area is a limitation - I’m wondering if, given that 2x as much H2 is produced than O2, we need 2x the surface area on the cathode?

Also what does an optimised electrode look like, and how do we balance that with the competing needs of the pioreactor & it’s space for light paths, CO2 tubes etc.

[gerrit]

The overall appearance. Having it the same diameter as the anode means you can use the same o-rings for both.

There are probably hundreds of different designs to try - I just wanted a simple solution that doesn’t involve machining them myself and works/looks better than a M4 bolt.

[Martin]

Crazy idea – do threaded bolts give us greater surface area than rods? If so, might we be able to find titanium bolts that we can platinize and then get matching SS bolts.

I haven’t been using o-rings on my rods (but then I’m not yet using an aseptic electroPioreactor). I imagine the need for o-rings would be even less if we could have a tight fitting thread in the caps. If that meant that o-rings and stainless steel rods were no longer required, I imagine there could be a reasonable BoM and assembly cost reduction.

Conversely, threaded titanium is likely significantly more expensive than titanium rods, and threaded graphite is unlikely to even exist.

If we ignore the anode and just look at the cathode, ChatGPT5 suggests switching from an M4 SS bolt to an SS rod would almost certainly increase cost – stainless rod stock is more expensive per mm³ than common stainless fasteners due to manufacturing scale.
The rod also has a larger diameter (e.g., 6 mm vs ~4 mm core for an M4), which gives a greater surface area: a smooth 6 mm rod has ~50 % more surface area than a smooth M4 bolt shank of the same length, so @gerrit’s move from an M4 bolt to a 6 mm rod already increased cathode area significantly.

That still only takes us up to parity between cathode and anode surface area, and doesn’t take the 2× H₂ vs O₂ disparity into account, on reflection the stoichiometry difference isn’t giving us practical issues – only the platinum anode is discolouring.

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GPT5 suggests:

Although H₂ is produced at twice the molar rate of O₂ during electrolysis, this does not necessitate twice the cathode surface area.
What fundamentally matters is current density and reaction kinetics.
The oxygen evolution reaction (OER) is kinetically slower and more energy-demanding (higher overpotential) than the hydrogen evolution reaction (HER), so HER often proceeds faster at the same current density (nature.com, en.wikipedia.org).

If the platinum anode is showing discolouration or fouling, the priority should be to reduce its current density (e.g., by increasing its surface area or improving bubble release) and minimise chloride contamination, because chloride ions substantially accelerate platinum dissolution (researchgate.net).

Therefore, if the SS cathode is performing well, you may not need to increase its area at all – focus instead on mitigating stress and degradation at the anode. (90 % certain)

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Context (assumptions for quick maths): both electrodes modelled as smooth rods or ISO coarse-thread bolts; triangular thread profile with depth = 0.325 × pitch (standard approximation). Results are % surface area vs a smooth rod of the same OD over the same length. (75 % certain)

Implications:

1. Threading both electrodes modestly increases area, improves wetting, but adds crevices that trap bubbles/biofilm and complicate cleaning. (85 % certain)
2. O-ring-free, threaded seals in CF-PC caps are possible but risk leaks from thermal expansion and will abrade platinised Ti during repeated install/removal. (75 % certain)

Threading impact by size

Thread size	OD (mm)	Pitch (mm)	Assumed depth (mm)	Estimated surface area gain vs smooth
M4 (coarse)	4.0	0.70	0.2275	≈ +24 % (70 % certain)
M5 (coarse)	5.0	0.80	0.2600	≈ +23 % (70 % certain)
M6 (coarse)	6.0	1.00	0.3250	≈ +23 % (70 % certain)

Notes: Exact gain varies with crest/root truncation, plating thickness, finish roughness and helix angle. Expect ±5–10 % swing. (70 % certain)

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Options summary

Option	Surface area gain vs smooth	Durability	Seal reliability without O-ring	Cost impact	Notes
Smooth rod (Ti/Pt-Ti/SS/graphite)	Baseline	High (except graphite brittle)	Needs O-ring	Low	Easiest to clean
Threaded Ti rod/bolt (platinised)	~ +20–30 %	Moderate (plating abrasion risk)	Possible but riskier	Higher	Modest electrochemical benefit; harder to sterilise
Threaded graphite	~ +20–30 % (geometric)	Low–moderate (chips, brittle)	Poor	Higher	Area gain exists but handling/cleaning are problematic
Deep-profile thread	Up to ~ +50 %	Lower (strength loss)	Poor	Higher	More crevices; bubble-trapping risk

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Better cathode-area paths than threading:
• Expanded/platinised mesh inserts
• Multi-rod bundles (same OD envelope)
• Short fins or perforated sleeves aligned to avoid light/CO₂ paths (design-dependent)
(85 % certain)

On seals: O-rings are cheap and robust; removing them rarely saves money overall once machining, rejects, and maintenance are counted. (80 % certain)

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Conclusion:
For aseptic electroPioreactors, Gerrit’s matched 6 mm rods (for O-ring compatibility) are a good, simple standard.
For non-aseptic, low-cost builds where sealing isn’t critical, you could use cheaper stainless bolts or rods without O-rings, but focus anode changes on increasing surface area and improving durability rather than chasing cathode area parity.