*3.3. Oxidative Stability*

The chemical stability parameters of the formulated nanocomposite membranes were described in Table 1. The SPVA/PEO membrane has the lowest stability against the oxidation condition; however, adding PO4TiO2 as a dopant improves polymeric composite protection against OOH and OH radical. The PVA/PEO/PO4TiO2-3 membrane was the most chemically stable, with weight retention of nearly 100%, suggesting that adding a doping agent such as TiO2 or functionalising TiO2 improves the oxidation chemical stability of formulated membranes [20,48].

#### *3.4. Ionic Conductivity, IEC and Methanol Crossover*

As the composite membrane contains further acidic exchangeable groups from PO4TiO2, the IEC values increase as PO4TiO2 in the composite membranes increases. This is due to the acidic (phosphate) sites of PO4TiO2 increasing the charges in the membranes, which promotes ionic conduction [19,20]. This is due to the SPVA/PEO/ PO4TiO2- 3 membrane's superior ionic conductivity (28 mS cm<sup>−</sup>1) when compared to an undoped membrane (12 mS cm<sup>−</sup>1). Adding PO4TiO2 to the polymeric matrix avoids methanol crossing when it comes to the fuel permeability of composite membranes. The undoped polymeric membrane exhibited a methanol permeability of 4.5 × 10−<sup>7</sup> cm<sup>2</sup> s<sup>−</sup>1, but the SPVA/PEO/PO4TiO2-3 membrane permeability of 0.42 × 10−<sup>7</sup> cm<sup>2</sup> s−<sup>1</sup> when PO4TiO2 was added to the membrane matrix, as indicated in Table 2. The capacity of the doping

agent to restrict the polymeric matrix channels, reducing water uptake and hence fuel permeability, may be the cause of the membrane containing the doping agent's decreased methanol permeability [19,20,49,50]. When compared to undoped SPVA/PEO membrane (0.26 × 10<sup>5</sup> S cm−<sup>3</sup> s) and Nafion 117 (0.24 × 10<sup>5</sup> S cm−<sup>3</sup> s), SPVA/PEO/ PO4TiO2-3 (6.66 × 10<sup>5</sup> S cm−<sup>3</sup> s) showed higher selectivity, indicating that the nanocomposite membranes produced are suitable for use in DMFCs [49].

**Table 2.** Ionic conductivity, methanol permeability, IEC and selectivity of the fabricated membranes and Nafion 117 [1].


#### **4. Conclusions**

Using eco-friendly and readily available polymers, a simple blending and solution casting approach created a more economical nanocomposite membrane. Furthermore, incorporating PO4TiO2 nanotubes into the polymeric blend improves the membrane's physicochemical parameters, such as ionic conductivity, mechanical properties, oxidative stability, reducing water sorption and limiting methanol permeability, especially in the composite membrane with 3 percent PO4TiO2. that also demonstrate the most suitable oxidative chemical stability and methanol crossover limiting. Finally, the manufactured membrane with the best characteristics (PVA/PEO/PO4TiO2-3) could be used as a cation exchange composite membrane to construct environmentally friendly and low-cost DMFCs.

**Author Contributions:** M.H.G. performed the experiments; M.H.G. and M.S.M.E. analysed the data; M.H.G., T.M.T. and M.S.M.E. wrote the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to express their grateful thanks to the City of Scientific Research and Technological Applications (SRTA-City) for its support in preparation and characterization and evaluation.

**Conflicts of Interest:** The authors declare no conflict of interest.

#### **References**

