We have a quick update for you, to show an interesting result we had with one of our proof-of-concept devices. 

The bipolar membranes in these devices need to be soaked in a dilute solution of sodium hydroxide because the anion membranes have a quaternary ammonium ion, and they use chloride ions for shipping the membrane. This would make them acidic in our experiments if they are not neutralized.

We ran the experiment without pre-soaking the device and got measurements that were extremely acidic, though there was still a pH difference. There were two devices, one with the anion membrane facing the outer cylinder and one with it facing the inner cylinder. For the device with the anion membrane facing the outer cylinder, the outer measurement was a pH of 2.471 and the inner measurement was 3.264. For the one with the anion membrane facing the inner cylinder, the outer measurement was 3.382 and the inner measurement was 2.475.

All these were much more acidic than the 6.776 pH of the solution used, due to the HCl forming from the chloride in the membrane. We do see a much larger pH gradient than what is expected for this device, which should have fully equalized. We're not sure if the chamber directly exposed to the anion membrane had a lower pH because the membrane was not neutralized, or if the pH gradient we are trying to demonstrate is exaggerated at a lower pH. We plan on exploring this idea at a later date, but wanted to share the interesting results.

Keep an eye out for a much larger update, including a complete overhaul of the bipolar membrane flow cell.