Flow Battery Research Collective

@kirk So my thesis is specifically on slurry/suspension electrodes (instead of using a graphite felt/porous electrode, you suspend conductive carbons with the electrolyte - which also allow you to run solid-phase chemistries in flow) in a way that's sort of chemistry-agnostic. Basically applying chemical reactor design principles to designing slurry electrodes. But here are some salient idiosyncrasies of all-iron cells:

• iron plating in porous electrodes is annoying (acidic = HER, basic = whole host of nasty iron oxides, many of which are quite stable. Plating on carbon substrates is also a pain - most studies I've seen plate onto copper. Also volume expansion is a big pain in static cells. In flow batteries, any time you have plating you end up re-tying power density and energy density through that half cell. Iron plating kinetics are also quite slow, especially in relation to zinc plating.
• Bunch of folks (Savinell and Wainright groups) at case western used slurry electrodes and plated iron onto the slurry particles (ostensibly). They attempted to scale but really struggled with having a performant enough slurry electrode that wasn't too viscous. But plating on suspended particles re-de-couples power and energy density.
• Have you guys looked into water-in-salt electrolytes? They involve dissolving a ton of a supporting electrolyte to the point where they lower the activity of water and suppress HER. I've seen some work using acetate salts and this one using magnesium chloride to support even iron plating - and I've replicated it successfully. The study plates on copper like I mentioned earlier, but I also got it to plate on grafoil.

Solving that performance/viscosity tradeoff in slurry electrodes is part of my thesis! And so is improving the power density of otherwise crappy flow battery chemistries. I'm still working on getting some of it out, but I'd love to share soon or help in any other way.

Material choice from the perspective of mineral centralization and cost is another problem I think regularly about - I did a little study collecting the centralization/governance of various metals and ranked aqueous battery chemistries by cost and "criticality". If that's of interest let me know too!

Hi all, I'm Muntasir, a doctoral student in chemical engineering at Worcester Polytechnic Institute in Massachusetts the USA. I just started perusing your work - I found it on an Autodesk Research lecture you guys did.

I'm a doctoral student in chemical engineering focusing specifically on scaleup and electrode design of flow batteries (the general idea is - if you start from absolutely nothing, can we get a general idea of electrode properties, dimensions, etc. that would lead to specific power/capacity/cost benchmarks, agnostic to chemistry?) Most of my expertise is tying very parsimonious models to practical performance metrics/experimental data, specifically for all-iron and iron-air chemistries. I'm happy to lend some of my experience (if not at least point folks toward useful resources)!

Hey @sepi take a look at Bert Neyhouse's spreadsheet cycling models (https://www.bertrand-neyhouse.com/rfb-models). They might not include stack-scale calculations you're looking for though. If you're interested in more of an economic analysis vs. nitty gritty engineering design let me know.

@kirk said in Alternative Electrolytes:

I am a big fan of this type of electrolyte engineering! The viscosity can also become an issue with this sort of approach too, no? (You are from now the FBRC viscosity expert ) I see in that paper though they only cycle up to 0.5 M [Fe], which is quite low in terms of energy density (~8 Wh/L if I'm not mistaken). But it seems solid enough to at least test in the development kit as an exercise. Also a huge confidence boost that you were able to reproduce it and make it plate on grafoil!

Haha I certainly don't feel like much of an expert. Viscosity does become an issue, especially with WISE electrolytes. Actually @danielfp248 if you end up trying out the MgCl2 work, you'll notice that the electrolyte is almost oily. The slurries Savinell and Wainright were working with are even more viscous - something like mayo. I don't remember the exact numbers but I'm happy to point you to more papers if you're interested!

@danielfp248 said in Alternative Electrolytes:

I see big increases in ohmic resistance as a function of time, but I don't see any iron oxides forming on the cathode or on the membrane. I don't see full dissolution of the plated metal though, so I bet it has something to do with the oxidation of that metallic deposit (since probably some Fe+Zn alloy is depositing anyway).

Luckily the oxides don't tend to form in acidic conditions (see the Pourbaix diagram - the phase diagram of stable iron species under varying pH and potential). But HER is more prevalent under acidic conditions. I'm interested in the Zn/Fe half cells though - do you notice any galvanic corrosion/passive loss after you charge the cells? Pourbaix diagrams are an excellent tool for designing thermodynamically possible redox couples. Which leads me to...

@kirk said in Alternative Electrolytes:

would love to see it if you're able to share - it's one of my concerns with iodine chemistries at scale (avoiding artisanal iodine production from seaweed).

I'll let you know when I actually churn out the draft! Might be a bit, but in a nutshell, the low cost (redox active materials under ~$3/kWh) and low criticality (generally abundant and decentralized) aren't too surprising: mostly cells using Fe/Mn/Zn and/or air redox couples meet these criteria. Exact redox couples + electrolyte conditions vary but are based on Pourbaix diagrams.

@quinnale said in Towards a working system:

I got excellent prints with high impact polystyrene (HIPS) and have been flowing DI water through the system without leaks. Admittedly, I used a Bambu system for this one while I am trying to get reasonable prints on my Ender3.

Thanks for documenting this! Looks awesome so far. Open question to you and others, especially about alkaline electrolytes. All of the easily printable polymers I've worked with have pretty poor resistance to highly basic solutions. PP has been the best of both worlds but it's hard to say it's easy to print with. Is HIPS working well? Is it easier to print with and still able to handle ~20wt% hydroxide solutions?

Hey! This is incredible work. I noticed you guys are exploring the shunt current/pressure drop/residence time distribution issue of manifold design. This is well outside my expertise, but I did run into this paper a while back from Kyle Smith, who offered a manifold design (and methodology) to resolve at least the pressure drop/residence time issue. Here's the paper - let me know if you have trouble accessing it and I'm happy to send it along.

They use a tapered header channel with straight diffuser channels and achieve very even flow rate distributions (at Reynolds numbers < 10)

Not sure how well this prevents shunt currents but I hope this helps.