In conjunction with the recent redesign, we decided to look into alternative solutions to use in our fuel cell.  Specifically, we are looking to compare sodium carbonate, sodium chloride, and sodium borate with the currently used urea borate. 

This is because urea borate must be very concentrated to shift the Ph appreciably, and the expected concentration gradient across the membrane is small. Moreover there were questions about the degree of reversibility once the urea adsorbed to an active site on the ionomer: could it stay ionized? If so, the ionomer membranes could become saturated, and this kills the effect because there must be unoccupied active sites to form the nonequilibrium steady state. Moreover there was a remote possibility that the urea could oxidize under ambient conditions and get used up as a fuel, and the borate ions being trivalent seem to get chelated by the ionomers and remain stuck there over time. The hope with sodium carbonate is that although it is a multivalent acid, it is such a weak acid that it tends not to get chelated when in the presence of sodium ions. Perhaps this could add nonlinear behaviors which improve the output of the devices.

As when initially determining the suitability of materials for this device, we needed to confirm the solutions would not interact with any of the materials used. To do this, we soaked the materials in each of the three solutions. The process was similar to that used in testing materials described in parts 2-1 to 2-5 of the instructions. Unlike when first testing the materials, in this instance we only looked for changes in pH.

As shown in the table above, most of the materials did not react significantly to the different solutions. The only material that showed a significant pattern in changing the pH was silicone, which raised the pH slightly. This is not unexpected, as we did not use silicone in the pervious iteration of the fuel cell because it raised the pH in the initial materials testing as well. We chose to retest because we switched to an aquarium grade silicone to see if that would reduce the reaction, which it seems to have done. Additional testing should be done before we introduce silicone into the fuel cell. We expect aquarium-grade silicone will perform better, because it is designed not to leach chemicals into water.

None of the potential solutions show significant reactivity to the main materials used in the fuel cell, with sodium chloride having the smallest change in pH for the materials overall. In a followup experiment it would be good to collect repeat testing data to perform statistical analysis on these data and get an idea of the standard deviation of each result, but for now this gives us a sense of what works and what doesn't.