All-copper

[kirk]

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:

1. Safe (in comparison to vanadium or lead-based aqueous systems)
2. Accessible (low-cost and available to amateur chemists)
3. Compatible with porous separators (no requirement for ion-exchange membrane)

---

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.

[kirk]

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.