*2.2. Characterisation*

A Fourier transform infrared spectrophotometer (Shimadzu FTIR-8400 S- Japan) was used to monitor the functional groups of PO4TiO2 nanotubes and composite membranes, while an X-ray diffractometer was used to analyze the structures (Schi-madzu7000-Japan). A thermo-gravimetric analyser (Shimadzu TGA-50, Tokyo, Japan) was used to track SPVA/PEO/PO4TiO2 membranes; the temperature range was 25–800 ◦C, with the heating rate was 10 ◦C/min under nitrogen environment. The membranes were also evaluated using differential scanning calorimetry (DSC) (Shimadzu DSC-60, Japan) at temperatures ranging from 25 to 300 ◦C. The SPVA/PEO/PO4-TiO2-1 membrane's morphological structure was revealed using a scanning electron microscope (SEM). Transmission electron microscopy (TEM, JEM 2100 electron microscope) and energy-dispersive X-ray (EDX) were used to visualise the PO4-TiO2 nanotube (Joel Jsm 6360LA-Japan).

The hydrophilicity of membranes was determined by measuring the contact angles between membrane surfaces and water drops. a Rame-Hart Instrument Co. model 500-FI contact-angle analyser was used to analyse the measurements. To determine swelling ratio (SR) and water uptake, a certain weight of membrane with actual dimensions was soaked in deionised water for 24 h then gently dried on tissue paper to remove surface water before analysis again. Finally, the composite membranes' SR and WU were calculated using Equations (1) and (2).

$$\text{SR}(\%) = \frac{\text{L}\_{\text{wet}} - \text{L}\_{\text{dry}}}{\text{L}\_{\text{dry}}} \times 100 \tag{1}$$

$$\text{WU}(\%) = \frac{\text{W}\_{\text{wet}} - \text{W}\_{\text{dry}}}{\text{W}\_{\text{dry}}} \times 100 \tag{2}$$

where Ldry and Lwet denote the length of dry and wet of tested membranes, respectively, and Wdry and Wwet denote the weight of dry and wet tested sample.

The nanocomposite membranes' ion exchange capacity (IEC) was estimated by acidbase titration [32]. The weighted membranes were submerged in a 50 cm3 2M NaCl solution for two days before titrating with a 0.01 N NaOH solution. The IEC was calculated using Equation (3) below:

$$IEC\left(\frac{meq}{\mathcal{g}}\right) = \frac{V\_{NaOH} \times C\_{NaOH}}{W\_d} \tag{3}$$

The volume of sodium hydroxide consumed in titration, the concentration of sodium hydroxide solution, and the dry sample weight, respectively, are represented by *VNaOH*, *CNaOH* and *Wd*.

To investigate the proton conductivity of formulated films, the electrochemical impedance spectroscopy (EIS) will be utilised using PAR 273A potentiostat (Princeton Applied Research, Inc., Oak Ridge, TN, USA) and a SI 1255 HF frequency response analyser (FRA, Schlumberger Solartron). according to the published method in the literature with modification [1]. the ionic conductivity of the membranes was estimated using Equation (4),

$$
\sigma = \frac{\text{d}}{\text{RA}} \tag{4}
$$

where σ (S cm<sup>−</sup>1) is the membrane's ionic conductivity, R (Ω) is its resistance, A (cm2) is its area and d (cm) is its thickness.

To estimate the methanol permeability, The tested membrane was seated within two vessels in a glass diffusion chamber to assess its methanol permeability. The receptor vessel (B) was charged with water, while the other vessel (A) was filled with 2 M methanol [29]. the crossing of methanol through membrane as a function of time was calculated according to Equation (5),

$$\mathbf{C}\_{\rm B}(\mathbf{t}) = \frac{\rm A}{V\_{\rm B}} \frac{P}{L} \mathbf{C}\_{\rm A}(\mathbf{t} - \mathbf{t}\_{0}) \tag{5}$$

where A (cm2) is the active membrane area, VB (cm3) is the capacity of the receptor vessel, L (cm) is the crosssection film thickness, CB and CA (mol L<sup>−</sup>1) are the concentrations of methanol in vessels B and A, respectively, and the period (t–t0) is the time of the methanol crossover (cm2 s<sup>−</sup>1). The selectivity of the membranes (the ratio of ionic conductivity to methanol permeability) was determined since it can provide vital information about the fuel cell's performance.

The oxidative stability of tested membranes was measured gravimetrically as a function of membrane weight soaked in oxidative solution [Fenton's reagent (3 wt.% H2O2 containing 2 ppm FeSO4)] at 68 ◦C for 24 h [19].

The dry nano-composite membranes were put through a tensile strength test at room temperature until they broke, using Lloyd Instruments LR10k [32].

#### **3. Results**
