I've compiled a list of design / operating suggestions from the comment section of Robert's video, and from what I've learned from reading the research papers, and other sources. I also explain how to create a carbon foam electrode (CFE), and point out the cost for materials in order to reach the projected levelized cost of storage (LCOS).
Cell Design Suggestions
a. Space top and bottom electrodes 0.4 cm apart. This was determined to be optimal spacing, according to Princeton's research.
b. Use 1.0 M ZnBr2 electrolyte. Despite Robert's comment of 1.75 M ZnBr2 electrolyte, 1.0 M was in factdetermined to beoptimal in terms of the lowest LCOS, according to Princeton's research.
c.DoNOTuse a supporting salt to reduce resistivity, despite Robert using 1 M ofsodium sulfate. Princeton tested supporting salts (includingsodium sulfate), and found that the best supporting salt (sodium chloride) decreased performance significantly as it created high levels of hydrogen.
d. Use a carbon foam electrode (positive), opposed to the carbon feltelectrode in Robert's cell. Doing so produces greater coulombic efficiencies, resulting in as much as 10% greater energy efficiency, according to Princeton's research. Note that a carbon foam electrode which is hollow on the inside (shell) will hypothetically increase cell capacity, according to Princeton. However, this makes the production of CFEs more complex, opposed to a solid foam piece.
e. Use a carbon cloth electrode (negative). Both zinc and titanium (having good resistance to the electrolyte) negative electrodeswere tested, however, their outputs were unstable opposed to the carbon cloth. Princeton also stated that to improve cell performance that they began"double-bussing" the[size=medium]carbon cloth. I think that means doubling up on the carbon cloth..?[/size]
f. Both carbon electrodes should have aluminium (affordable) current collectors coated in carbonto protect them from the electrolyte. This is just my opinion.
g. Invert electrodes (positive on top, negative on bottom), opposed to Robert's design. Princeton's exemplary battery design inverted the electrodes. By doing this, the top carbon foam electrode reacts with the hydrogen as it bubbles to the top, and redissolves it back into the solution, "thus recapturing any potential losses."
h. For a 48V battery, 30 cells in series may be optimal. The Redflow ZBM2 Battery (a zinc-bromine flow battery) has a operating range of 40-57V, and has 30 cells in series. I imagine this is for good reason [size=medium](for inverters/charge controllers?).[/size]
i. Shorter charge/discharge times (e.g., 4-hours, 8-hours, 12-hours) offer the lowest LCOS because shorter cycles allow more cycles during its lifetime, and there are lower self-discharge rates per cycle, according to P[size=medium]rinceton's research.[/size]
How to make a carbon foam electrode (general information)
To make 1 kg of carbon foam material, combine 425 g of carbon black (powder?) with 425 g of graphite[size=medium](powder?). Next, create asolution of polyvinylidene difluoride (PVDF) in N-Methyl-2-pyrrolidone (NMP). NPM can be found on ebay. It used to be a common paint stripper. Properly mix a solution of 150 g of PVDF with 2.85 kg of NPM with a magnetic hotplate with a lid on the glass beaker. Pour the solution in with the carbon mixture, and mix to create a carbon slurry. Pour the slurry into a mold(s) to create your desired shape and sizeCFE.[/size]
Princeton's CFE was cylindrical. They created a 3D printed retractable piston to compress the slurry down in the mold using a hydraulic press to ~1 psig. With a littleingenuity,you should be able to compact the slurry @ ~1 psig without a hydraulic press.
Finally, put the mold(s) in a vacuum oven, and baked for 8 hr at 130 C, evaporating the NMP and leaving behind a porous but rigid carbon foam.Time and temperature may vary depending on the size and shape of your CFE.I estimate the weight of the large cylindrical CFEwhich Princeton created to be around ~24.5 g when calculating your oven temperature and time.
[size=medium]Warning:[size=medium]N-Methyl-2-pyrrolidone (NMP) is not safe. Research it first. Never allow NPM to contact your skin or eyes, and avoidinhalation, using excellent ventilation.[/size][/size]
**Cost of materials to reach the projected LCOS (according to Princeton)
Plastic (HDPE or PTFE) cell case: $0.22 - $0.37 per liter (volume within case)
Zinc bromide (anhydrous): $2.30 - $3.10 per kilogram
Carbon foam electrode: $5.70 - $11.20 per kilogram
*Carbon cloth and Titanium current collector: $13.10 - $19.10 per square meter
* Note that this cost is bundled, and the the titanium current collector was used on the positive electrode. A more affordable solution may be to use aluminium current collectors coated in carbon to protect it from the electrolyte. Although, maybe titanium alone is the more affordable solution, as it has good chemical resistance to the electrolyte, and therefor may not need to be coated in carbon (or plastic).
** Note that to reach these figures you're most likely looking for technical (industrial) grade materials, or battery grade. Avoid expensive laboratory and reagent grades.