On my last post, I showed the results of charging/discharging a flow battery using a ZnCl₂+NH₄Cl+KI electrolyte using 4 layers of Daramic as a membrane. However, while Daramic is a low cost material, it is not easily accessible for DIY testing at this moment. For this reason, I wanted to run some tests on materials that are easier to source than Daramic.

I looked for materials around my house that had similar porosity (0.1-5um). I tested several different papers that I had around but none of them worked very well. The porosity of most traditional printer papers is high, with most having 10-20um pore sizes. This means that you need many layers to prevent fast self-discharge from migration of the triiodide across the membrane. Additionally, the papers lost structural integrity quite easily.

Finally, I stumbled upon matte photo paper as a potential solution. This paper has much lower porosity with <5um pore sizes. Some of these papers might even have pore sizes that are below 1um. This is important for printing photographs, as low pore sizes implies that there is less bleeding of ink when it is applied to the paper, although ink needs to be applied much more slowly to the material (reason why printing with these papers is really slow).

For my initial test, I used 4 layers of matte photo paper. The paper does have a substantially higher ohmic resistance compared to Daramic, so I had to lower the current density to 20mA/cm². I did 4 cycles of charge/discharge that you can see above (I only did 4 because the lower current meant cycling was quite slow). The CE of 87.54% and EE of 75.72% with a capacity of 33.8 Ah/L shows that photo paper is definitely a good choice for at least the short term cycling of these devices.

On inspection, the photo paper did not show any evident degradation although dendrite penetration happened just as much as it did with the Daramic separator. The separator was also completely black, fully permeated by the catholyte solution which contains triiodide in solution when charged.