I tested a cell which had aluminum sulfate as its anode electrolyte (12 grams aluminum in 50 mL water and a pH of 3.2), and potassium hydroxide as the cathode electrolyte (5 grams of KOH in 200 g of water, pH of 12.3). The anode electrode was aluminum foil and the cathode was platinum. The OCV of the cell was 0.9V and when connected to a 1 kΩ resistor, the voltage was 0.324V

When I increased the concentration of KOH from 5 grams to 10 grams, and all other material concentrations were kept constant, the OCV decreased from 0.9V to 0.7V, but when I attached the 1kΩ resistor, the voltage increased to 0.42V.

I do not understand why increasing pH is causing the OCV to decrease, but increase the voltage under a load to increase.

I am guessing for the voltage under the load that maybe the higher concentration of KOH leads to more ions in solution thus increasing the current flow. But if this assumption/hypothesis were true, shouldn't the OCV also increase?

Can someone please help?

P.S. OCV is open circuit voltage

  • $\begingroup$ Did you clean/change the aluminum foil in the mean time? It is possible that the aluminum surface is changing/passivating. $\endgroup$ – Burak Ulgut Mar 27 '17 at 13:53
  • $\begingroup$ i cleaned the aluminum, yet the observation was the same $\endgroup$ – user510 Mar 27 '17 at 22:04

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