@kirk said in Following your documentation – feedback & questions:
In the CAD files we have specified a 2D endplate (https://codeberg.org/FBRC/RFB-dev-kit/src/branch/main/CAD/exports/Metal Endplate.step), that could be laser cut or milled from aluminum. @danielfp@chemisting.com has received endplate versions of this in aluminum, the only catch is then you need insulating washers so as to not short them. Another rigid polymer could work too.
I found a pic of this setup: 
@gus said in Following your documentation – feedback & questions:
The cell itself doesn’t leak. I used a torque of 3 Nm for now, but it already looks slightly distorted. Have you considered using more bolts?
In our meeting today, @quinnale mentioned that in their lab they use 1.5-2 Nm max to tighten a similar size of flow cell. @danielfp@chemisting.com also builds his FBRC cells without a torque wrench, by tightening them only as much as he can holding the short end of the allen key.
@gus, awesome work! This is so exciting to see you've independently replicated the setup. Apologies on the delay for the pump wiring, I have recorded the raw video of me setting it all up as well as the pin numbers and I am in the process of editing it and updating the docs to match.
@gus said in Following your documentation – feedback & questions:
The new reservoirs seem fine now.
Did you encounter this problem too? How did you solve it?
Our best strategy against leaking in PP prints has been 100% infill, 5 perimeters. I know some have success with slight overextrusion / flowrate multiplier of up to, say, 1.02 times. We have had reservoirs leak there before but tuning print settings usually leads to a tight reservoir. Could you share the file you modified? It looks like you added a big cylinder.
@gus said in Following your documentation – feedback & questions:
The cell itself doesn’t leak. I used a torque of 3 Nm for now, but it already looks slightly distorted. Have you considered using more bolts?
I think we need a stiffer endplate - similar hole pattern geometry, just thicker. This is an area to improve for sure, it's not ideal as-is. In the CAD files we have specified a 2D endplate (https://codeberg.org/FBRC/RFB-dev-kit/src/branch/main/CAD/exports/Metal Endplate.step), that could be laser cut or milled from aluminum. @danielfp@chemisting.com has received endplate versions of this in aluminum, the only catch is then you need insulating washers so as to not short them. Another rigid polymer could work too.
@gus said in Following your documentation – feedback & questions:
I also wanted to ask: is silicone resistant to this type of chemistry? Since it’s used for gaskets, maybe silicone tubing could be used as well?
We've tested and silicone tubing doesn't work for zinc-iodide, unfortunately. The gasket application of silicone is forgiving enough that it seems to work for this purpose, however, but we may be pushing our luck.
@gus said in Following your documentation – feedback & questions:
Regarding the Arduino program: it seems there are four defined pins — In1 (pin 9), In2 (pin 8), In3 (pin 7), and In4 (pin 6) — but they don't appear to serve any purpose.
These are legacy pins from when we used to use an H-bridge driver for different motors, before we got these stepper motors with built-in drivers.
This code is outdated, I have the new code but it's on my lab PC which is offline right now 
I am going to upload it soon.
@gus said in Following your documentation – feedback & questions:
As for the main Python program — should it work with no issues once the Arduino and MYSTAT are connected to the computer?
The program here * should * work on linux when run as root (in order to have proper USB access). You can control the pump speeds via the Arduino with the software, even without the MYSTAT connected (under the "charge/discharge" tab) (this will all hopefully be in a video soon!)
I'll have some more info soon (tomorrow hopefully?)
@kirk said in Following your documentation – feedback & questions:
We have used the Membrane Frame on-and-off through some of our testing as we tested different separator materials and thicknesses. I just went back and checked some old notes, we did a lot of testing with three layers of photopaper in the end, so go ahead and just use three layers for now! I see one section of the docs said four layers and another said three, as well as the old photo.
*use three-layers of photopaper and the membrane frame, I meant to say!
We have used the Membrane Frame on-and-off through some of our testing as we tested different separator materials and thicknesses. I just went back and checked some old notes, we did a lot of testing with three layers of photopaper in the end, so go ahead and just use three layers for now! I see one section of the docs said four layers and another said three, as well as the old photo.
@gus said in Following your documentation – feedback & questions:
I'm attaching a photo of my 3.2 x 6.4 mm tubing—hopefully it's the correct one.
You will be able to make connections and leak test using water with this! Also, this tubing can stand up to Zn-I testing, but not within the pumps themselves - see below.
@gus said in Following your documentation – feedback & questions:
It seems that the default tubes in the Kamoer KPK200 pumps are already Pharmed BPT, so I assume there's no need to replace them - is that correct?
Regrettably, for the Zn-I testing, you need to replace the stock tubing in the KPK200 pumps with this tubing: https://fbrc.codeberg.page/rfb-dev-kit/tubing.html , it can also be ordered directly from Kamoer on Alibaba (may be hectic right now with tariffs in case you are based in the US). Warning, the process is annoying, but doable. I haven't documented it yet, only thrown the tubing in the BOM so that people can get it.
However we hope that an all-copper chemistry will play well with the stock BPT tubing, so hang tight on that. That chemistry operates using the exact same principle/hardware as we use for Zn-I and could be more forgiving in terms of chemical compatability.
@gus said in Following your documentation – feedback & questions:
Oh, you mentioned a barbed fitting adapter now, but it wasn’t listed in the bill of materials - do I actually need it, or can I manage without it?
Shoot, I will add this to the BOM - the ones we have leftover from our various pumps we've tested - I need to find a supplier link for just the fitting. For a leak test, you can get by without it, it just makes removing the cell from the jig much more ergonomic. The FDM-printed barbs can be difficult to install the tubing onto, the adapter allows you to break the connection from the cell and the reservoir without removing an FDM-printed barb connection. That way, rebuilding cells goes faster.
@gus said in Following your documentation – feedback & questions:
A guide showing how to connect all the cables between the pumps, Arduino, MYSTAT, and the power supply would be really helpful for me.
Got it, I'm on it!
Updates from @danielfp@chemisting.com during today's meeting:
I started a test with 2M KI, 1M ZnCl2, 2M NH4Cl, 5% Trieg with Daramic and felt on both sides. Going to charge to 1.6V at 10mA/cm2, see if it makes any difference regarding stability with Trieg on subsequent cycles.
I did one cycle at 10mA/cm2, charged to around 240mAh (noticed a dip indicating start of solid I2 buildup, so cut it there), discharged 180mAh. I am now charging to 150mAh at 30mA/cm2, normally I would see drops in capacity with cycling with Trieg at this level, we'll see if they happen.
Seems to be stable now at 30mA/cm2. I will leave it cycling here longer, see if it starts decaying.
ok, went for 9 cycles with no issues at all. I am now going to cycle it to 1.65V, to the Nernst limit, see if it continues working equally well.
Charging to 1.65V showed the weird start for the discharge curve, although with no apparent deterioration of the cycle characteristics after the first cycle. No evidence for solid iodine formation was present, so the solution is very well behaved.
Test at 15mA/cm2 of the same cell. Some deterioration is now evident, charging to 1.55 V
From Roth et al., Aalto University built a (sizable!) stack for all-copper and used ABS for their flow frames - I'd imagine it would play better with BPT tubing than the Zn-I chemistry also.
@gus @SamAuc ABS may work with an all-copper chemistry!
Making a thread for a potential all-copper chemistry, which came up in discussion during our regular meeting today as a potential safe chemistry for testing, particularly as we scale to larger electrolyte volumes/cell areas. H/t to @danielfp@chemisting.com !
The voltage is too low to be of major commercial interest (~ 0.6 V), but in the charged state it's not volatile like iodine-containing complexes.
It also fulfills our emerging criteria:
From Roth et al. chapter 38 on all-copper [1]:
The CuFB is a novel aqueous system based on the three oxidation states of copper, achieved by stabilizing the Cu(I) complexes (CuCl2−, CuCl32−) in concentrated chloride solutions. The resulting cell has a hybrid configuration with the chemical reactions shown in Eqs. (38.1) and (38.2).
And the self-discharge reaction for completeness:
We are considering testing this in the dev kit and then in our first large-format cells, as it could be cheaper and safer on the 100-1,000 mL scale than zinc-iodide.
[1] Roth, C. et al. (eds.) (2023). Flow Batteries: From Fundamentals to Applications, Wiley.
