Alternative Electrolytes
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@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!
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thanks for this info! FYI I forked your post into a separate topic into the "Electrolyte Development" category just to keep the intro thread relevant.
I am a big fan of Savinell's and Wainright's work at Case! Savinell was on on the all-iron RFB development quite a long time ago... this is one of my highlights from one of his papers in 1981 (!):
Source:
Hruska, L.W. and Savinell, R.F. (1981). Investigation of Factors Affecting Performance of the Iron‐Redox Battery. Journal of The Electrochemical Society. https://doi.org/10.1149/1.2127366.Showing quite clearly the issue of iron kinetics, even at 60 C...
@muntasirms said in Alternative Electrolytes:
In flow batteries, any time you have plating you end up re-tying power density and energy density through that half cell.
Yes, unfortunately, would love to have an all-liquid configuration that plays well with porous separators but asides from iron-chromium (which also has its own set of cons, like HER/high purity req's) there isn't much out there that's easy to start with, which is why we're starting with zinc to get things going.
@muntasirms said in Alternative Electrolytes:
They attempted to scale but really struggled with having a performant enough slurry electrode that wasn't too viscous.
I saw this, I think I skimmed their ARPA-E report (https://www.osti.gov/biblio/1506426) and they also had issues with the cell plugging. IIRC they also licensed the tech to an Australian company?
@muntasirms said in Alternative Electrolytes:
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.
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!@muntasirms said in Alternative Electrolytes:
I did a little study collecting the centralization/governance of various metals and ranked aqueous battery chemistries by cost and "criticality".
Definitely of interest, 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).
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@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!
@muntasirms Thanks for sharing. This is all very interesting. I have made several experiments with Zn/Fe fully symmetric cells (since Zn plates preferably over Fe), using glycine as a chelating agent to make sure Fe stays soluble at mildly acidic pH on the catholyte side. It hasn't really worked very well, 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).
I have never tried WISE electrolytes in flow batteries, and had actually never read the Fe+MgCl2 paper you mentioned. I just ordered MgCl2 and CaCl2, so I'll give that a try as soon as I have those salts! If we can get 1M FeCl2 work with MgCl2, then that would be amazing as a demonstration for the kit at both small and large scales.
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thanks for this info! FYI I forked your post into a separate topic into the "Electrolyte Development" category just to keep the intro thread relevant.
I am a big fan of Savinell's and Wainright's work at Case! Savinell was on on the all-iron RFB development quite a long time ago... this is one of my highlights from one of his papers in 1981 (!):
Source:
Hruska, L.W. and Savinell, R.F. (1981). Investigation of Factors Affecting Performance of the Iron‐Redox Battery. Journal of The Electrochemical Society. https://doi.org/10.1149/1.2127366.Showing quite clearly the issue of iron kinetics, even at 60 C...
@muntasirms said in Alternative Electrolytes:
In flow batteries, any time you have plating you end up re-tying power density and energy density through that half cell.
Yes, unfortunately, would love to have an all-liquid configuration that plays well with porous separators but asides from iron-chromium (which also has its own set of cons, like HER/high purity req's) there isn't much out there that's easy to start with, which is why we're starting with zinc to get things going.
@muntasirms said in Alternative Electrolytes:
They attempted to scale but really struggled with having a performant enough slurry electrode that wasn't too viscous.
I saw this, I think I skimmed their ARPA-E report (https://www.osti.gov/biblio/1506426) and they also had issues with the cell plugging. IIRC they also licensed the tech to an Australian company?
@muntasirms said in Alternative Electrolytes:
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.
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!@muntasirms said in Alternative Electrolytes:
I did a little study collecting the centralization/governance of various metals and ranked aqueous battery chemistries by cost and "criticality".
Definitely of interest, 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).
@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.
