*3.1. Effect of Adding Ionic Compounds on Nanofluids*

To explore the effect of adding different concentrations of sodium hydroxide (NaOH) on the particle size and suspension of the polymeric nanofluids, this study appended a better concentration of NaOH to the 2 wt.% titanium dioxide (TiO2) nanofluid to improve the electrical properties of the novel TEP device. NaOH is an ionic compound that will completely dissociate into sodium ions (Na+) and hydroxide ions (OH- ) in an aqueous solution, which increases the number of ions that react with the cathode of aluminum in the solution to raise the amount of current. Figure 5a exhibits the effect of adding 0.1 to 0.5 wt.% NaOH on the particle size of nanofluid in 2 wt.% TiO2 nanofluid. The average size of nanoparticle of polymeric nanofluids was less than 100 nm when adding lower concentrations of 0.1 to 0.2 wt.% NaOH. When 0.3 wt.% NaOH was appended, the particle size was 211 nm, and the particle sizes were 488 and 1050 nm respectively, when 0.4 to 0.5 wt.% NaOH was added. NaOH will erode the surface of nanoparticles inside the metallic nanofluids as it reaches a certain concentration, resulting in an agglomeration phenomenon. Therefore, for the stability and suspension of polymeric nanofluids, we chose to add a lower concentration of NaOH to reduce the impact on nanoparticles. In Figure 5b, comparing the effect of adding 0.2 wt.% NaOH on the particle size, the overall increase in the particle size of the TiO2 nanofluid with 0.2 wt.% NaOH was about 39%. Adding ionic compounds into the titanium dioxide nanofluids in this experiment, 0.2 wt.% NaOH has tiny effects on the stability of nanoparticles and suspension by detecting particle size and concentration of the polymeric nanofluids, resulting in improving the electrical properties of the present novel TEP.

**Figure 5.** The effect of sodium hydroxide (NaOH) on titanium dioxide (TiO2) nanofluid. (**a**) Different concentrations of NaOH, (**b**) particle size.
