Introduction

Direct methanol fuel cells (DMFCs) have attracted considerable scientific interest as one of the next-generation power sources for small and portable applications, due to their high energy density, near zero toxic emission, easy refueling, and fuel security [1]. However, commercialization of DMFCs still confronts major challenges including poor catalytic activity, high-cost materials, and short-term durability [2, 3], which have mostly arisen from the Pt catalyst. These problems may be minimized using the carbonaceous materials and metal oxides as the appropriate Pt supports in methanol oxidation reactions (MORs) [4, 5]. Zinc oxide (ZnO) has received great attention due to its low cost, non-toxicity, environmentally friendly feature and low resistivity [6, 7]. Moreover, ZnO is a transparent conducting oxide (TCO) with outstanding features, which can be considered as a co catalyst. The chemical and thermal stability of metal oxide in the acidic and oxidative media is related to its large band gap (~3.23 eV) [8, 9]. It can promote the catalytic activity and stability of Pt catalysts for MOR, which is the main anodic reaction in the DMFCs. ZnO is able to remove intermediate carbonaceous species (like CO) and prevent CO poisoning during the MOR by the formation of the hydroxyl radicals (OHads) on the catalyst surface. These hydroxyl groups are produced via the activation of water discharge at low overpotentials [10]. Oxygen vacancy (VO) plays an important role in determining the special properties of ZnO [11, 12]. It was reported that the VO is the electrical charge of Zn2+ and the origin of n-type conductivity in ZnO [13]. ZnO has found its place in solar cells [14,15,16], solid oxide fuel cells (SOFCs) [17,18,19], semiconductor electronics [20,21,22], and batteries [23,24,25]. Huang et al. [26] added ZnO to the catalyst layer as water adsorbent to improve the hydration of electrode surface. Metal doped ZnO films such as Al [27,28,29], Ga [30, 31], Si [32], Zr [33], and Ti [34, 35] increase the band gap to 3.26 eV and promote the corrosion and oxidation resistant [36, 37]. Doping ZnO with elements of group III, i.e., Al, Ga, and In, as donor atoms can improve the electrical conductivity and charge transfer process [38]. Co-doping ZnO with Ti and Al as the new trioxide for TCO applications has been reported [38,39,40].

Doping quantity affects the structure, morphology, and chemical nature of metal oxides. In low concentration, the electrode surface is smooth and uniform [41]. The physical characterizations of doping ZnO with Ti and Al have been reported in the literature [8,9,10,11]. However, the practical applications of this nanocomposite could be furthermore investigated. As a result, modified carbonaceous materials and use of Al and Ti nanoparticles in ZnO matrix (ATZO: aluminum titanium-doped zinc oxide) may be considered as the ideal supports for the Pt catalysts in the acidic and oxidative environments of fuel cells.

Based on our knowledge, the electrochemical activity of Pt@Al-Ti-ZnO-CC electrodes for the methanol oxidation in the DMFCs has not been reported yet. So, the aim of this study is to promote the catalytic activity and stability of Pt catalysts and introduce a promising anode for DMFCs. ATZO thin films on carbon cloth (CC) were prepared using the sol–gel and co-precipitation methods. These processes are preferred due to the direct film deposition on the support materials. Besides, they are inexpensive methods in low temperatures with no need of special atmosphere. Pt catalysts were deposited on these supports via airbrushing technique. The prepared electrodes were investigated and compared with Pt@CC electrode. Physical characterizations including scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), and X-ray diffraction technique (XRD) were used. The electrochemical surface area (ECSA) and methanol oxidation of the prepared electrodes were determined by cyclic voltammetry (CV) in the acidic media. The stability of the prepared electrodes and the tolerance ability toward CO were investigated via chronoamperometry measurements. The electron transfer resistance of the synthesized electrodes was determined via the electrochemical impedance spectroscopy (EIS). The catalytic activity of the Pt@Al-Ti-ZnO-CC anode was investigated in the active DMFCs.

Experimental

Materials

All chemical materials were purchased from Merck. Pt black with average particle size of below 20 µm was obtained from Sigma-Aldrich. Carbon cloth and Pt/C commercial electrode (0.5 mg cm−2, 60 wt.% Pt on Vulcan-Carbon Cloth) were obtained from Fuel Cell Store. Nafion 117 was bought from Chemours, USA. Deionized (DI) water was used.

Preparation of catalyst support materials

Pt support materials were prepared by the sol–gel and co-precipitation methods according to the scheduled prescription (Table 1). Initially, the CC substrate (1 × 1 cm2) was cleaned with acetone, distilled water, and ethanol several times to remove any contaminations [42]. TiCl4 was completely dissolved in the ethanol. The CC was immersed in the solution and was refluxed at 80 °C for 30 min. The CC was dried at 100 °C for 1 h to form Ti layer. Then, ZnSO4.7H2O and Al2 (SO4)3.18 H2O were dissolved in the DI water to form a 0.1 M solution and stirred until a clear solution was observed. The CC was immersed in the solution and NH4OH (1 M) as precipitator was added dropwise to adjust the pH to 10. The mixture was stirred rapidly at 80 °C for 30 min. The CC was dried at 100 °C for 1 h and finally annealed at 350 °C for 2 h to give ZnO and Al nanoparticles. The proposed reaction mechanism for the synthesis of catalyst supports is shown in Fig. 1.

Table 1 Composition of the electrodes
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Fig. 1
figure 1

The proposed reaction mechanism for the synthesis of catalyst supports

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Preparation of Pt nanoparticles

Pt black was stirred by ultrasound (Sounopuls, HD2200) for 30 min in DI water with loading of 2 mg cm−2. This slurry was coated upon the prepared supports using the spray apparatus (see Fig. 1) and dried for 24 h in the air and then for 2 h in N2 (99.99%) at 100 °C [43].

Preparation of membrane electrode assembly (MEA)

The effective area of the MEA was 5 cm2. Pt/C commercial electrode and the prepared Pt@Al-Ti-ZnO-CC electrode were used as the cathode and anode, respectively. Nafion 117 membrane was pretreated for 1 h by 3 wt.% H2O2 solution and then rehydrated in the near-boiling 0.5 M H2SO4 for about 1 h to reach the protonated form. The membrane was washed by boiling DI water several times and was stored in DI water before use. The MEA was finally fabricated by uniaxially hot-pressing of the electrodes and membrane at temperature of 130 °C and pressure of 120 atm for 3 min [43]. The MEA was placed in a gold-plated fuel cell hardware (AHNS Co.) and then connected to the fuel cell test station (Scribner-Associates, USA).

Physical analysis

SEM, SERON technology, AIS2100 was used to observe the surface morphology of the prepared electrodes. To recognize the elemental composition, the EDX technique with an accelerating voltage of 15 kV was applied. The crystal structures of the prepared electrodes were examined by X-ray diffractometry (XRD-Rigakuultima iv, Japan).

Electrochemical measurement

Electrochemical tests were performed in Autolab potentiostat instrument (PGSTAT302N). Three-electrode cell was used including the prepared electrodes, Pt rod (Metrohm, d = 2 mm) and the standard calomel electrode (SCE; Metrohm 6.07.29.100) as working, the counter and the reference electrodes, respectively. Before testing, the degasification of solution was performed by high purity nitrogen bubbling. The ECSA was determined by hydrogen under potential deposition (Hupd) region measured by the CV recorded between -0.4 and + 1.3 V vs SCE in 0.5 M H2SO4 at a scan rate of 50 mV s−1. Electrooxidation of methanol was examined by the CV between 0 and 1.3 V at a scan rate of 50 mV s−1 in 0.5 M H2SO4 containing 1 M methanol. The chronoamperometry was measured by polarization of electrodes at the peak potential of CV for 1200 s in 0.5 M H2SO4 containing 1 M methanol. EIS was carried out in 0.5 M H2SO4 containing 1 M methanol. The Nyquist plots were obtained at a near peak potential of MOR at a frequency range of 100 kHz to 100 mHz with 10 mV as the amplitude of the sine wave. All experiments were performed at room temperature (~25 °C).

MEA activation

Initially, the MEA was activated by off-line and on-line preconditioning procedures [44], respectively. In the off-line method, electrodes were exposed to the water steam for 1 h. In the on-line method, the MEA was activated by a constant voltage at 0.6 V for 6 h. By these activations, the electrodes were hydrated, the contaminants were eliminated, and the active sites of the catalyst layer were readied for reaction with methanol. The performance of the MEA was investigated in the active DMFC. Methanol solution in the concentrations from 1 to 5 M and the flowrate of 1 mL min−1 at 60 °C (near its boiling point) were used. Pure oxygen was fed to the cathode by the flowrate of 100 mL min−1. Current/voltage curves were obtained by scanning the cell voltage in the range of open-circuit voltage up to 100 mV with a scan rate of 20 mV s−1 at 40, 50, and 60 °C. Meanwhile, the EIS investigation was carried out in the ranges of 100 kHz -10 mHz and the optimum operations (3 M methanol, 60 °C) at 0.2 and 0.3 V. The AC signal amplitude was 5% of the DC current.

Results and discussion

Characterization of synthesized electrodes

The surface of Al-Ti doped ZnO on the CC electrodes is shown in Fig. 2. The nonporous and interconnected structure is seen. The average particles size of the nanoparticles was between 30 and 60 nm. Al and Ti doped ZnO nanoparticles improved the dispersion of Pt nanoparticles and increased the electrochemical surface area. In other words, Al-Ti nanoparticles caused more homogeneous dispersion of Pt nanoparticles, which created more active catalytic sites for MORs.

Fig. 2
figure 2

SEM image of Al and Ti doped ZnO on carbon cloth electrode

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The shape of Pt nanoparticle is spherical granule (Fig. 3). The average particle size of Pt on CC, ZnO-CC, Al-ZnO-CC, Ti-ZnO-CC, and Al-Ti-ZnO-CC was about 70, 100, 80, 90, and 95 nm, respectively. As shown in Fig. 3, the use of Al and Ti nanoparticles in the electrode composition decreased the average particles size of Pt.

Fig. 3
figure 3

SEM images of the (a) Pt@CC, (b) Pt@ZnO-CC, (c) Pt@Al-ZnO-CC, (d) Pt@Ti- ZnO-CC, and (e) Pt@Al-Ti-ZnO-CC electrodes

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EDX analysis of prepared electrodes is shown in Fig. 4. The peaks attributed to Zn, Al, Ti, C, and Pt are presented in the EDX spectrum. The results confirmed that Pt and metal oxides were successfully deposited on CC.

Fig. 4
figure 4figure 4

EDX analysis of (a) Pt@CC, (b) Pt@ZnO-CC, (c) Pt@Al-ZnO-CC, (d) Pt@Ti- ZnO-CC, and (e) Pt@Al-Ti-ZnO-CC electrodes

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The XRD of prepared electrodes is displayed in Fig. 5. As seen, the diffraction peaks at 26 and 43.5° corresponded to the (002) and (100) planes of graphitic carbon (JCPDS card no. 08–0415), indicating the amorphous nature of CC [45]. The diffraction peeks around 32.06, 34.71, 36.51, 47.79, and 56.84° can be indexed to the (100), (002), (101), (102), and (110) planes of the hexagonal wurtzite structure of ZnO (JCPDS no. 36–1451) [46]. Doping Al and Ti nanoparticles with ZnO kept the crystal structure of ZnO as reported in the literature [40]. The relatively sharp XRD patterns demonstrated the crystallinity of prepared Pt@Al-Ti-ZnO nanoparticles. Al, Ti, and Pt have been incorporated into the crystal structure of ZnO [47]. There were no characteristic peaks of impurities in the pattern. It is concluded that the preparation method used in this study is very reliable to synthesize ATZO thin films.

Fig. 5
figure 5figure 5

X-ray patterns of (a) Pt@ZnO-CC, (b) Pt@Al-ZnO-CC, (c) Pt@Ti- ZnO-CC, and (d) Pt@Al-Ti-ZnO-CC electrodes

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Electrochemical characterization

ECSA

Figure 6a indicates the cyclic voltammograms of prepared electrodes in N2-saturated 0.5 M H2SO4 solution. The electrochemically active surface area of the electrodes was also estimated from the integrated charge in the hydrogen adsorption and deposition region from the electrode surface of CVs. The potential ranges from -0.25 to 0.15 V represent the hydrogen adsorption/deposition region. The Coulombic charge (QH) of monolayer of H2 adsorbed on Pt between -0.25 and + 0.15 V vs. SCE in CV was then obtained. The ECSA of electrodes was calculated using Eq. (1):

$$\textit{ECSA}\,=\frac{Q_H}{210\,\times L_{Pt}}$$
(1)
Fig. 6
figure 6

(a) Cyclic voltammograms of the electrocatalysts in H2SO4 solution (0.5 M) and (b) ECSA data for the electrocatalysts

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In this equation, \(Q_{H}\) is the Coulombic charge for hydrogen adsorption on Pt sites, \(L_{Pt}\) is the loading of Pt in the working electrode, and the number of 210 is the electrical charge required to oxidize a monolayer of hydrogen on Pt surface [48].

The ECSA values of Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC were 21.1, 66.7, 79.4, 92.3, and 98.6 m2 g−1, respectively (Fig. 6b). These results showed that the ECSA of electrodes increased by doping of ZnO with Al and Ti. The support modification and the use of ATZO improved the Pt catalyst dispersion and enhanced the electrochemical surface area which affected the stability and lowering the cost. The highest ECSA value was measured for Pt@Al-Ti-ZnO-CC electrode, which indicated the most accessible active sites toward the MOR. As a result, the high ECSA of Pt may be due to high electrical conductivity and surface area of ATZO, suggesting a relation between ECSA and electronic conductivity of the support materials.

Alcohol electrooxidation

Figure 7 shows the CV measurements of the prepared electrodes for methanol oxidation. The electrochemical parameters obtained from the CV have been tabulated in Table 2. In this table, Ep, If, Ir, and If /Ir are the peak potential, the current density of forwarding peak, the current density of reverse peak, and the ratio of forwarding peak current to reverse peak current, respectively [48]. The CV values displayed well-defined peaks in the anodic scan, which confirmed the good Pt catalyst activation for MOR [49]. The current density of Pt@Al-Ti-ZnO-CC electrode at the peak potential of 0.82 V was 107 mA cm−2. The identical Pt loading on the prepared electrodes increased the current density by 1.6 times compared to Pt@CC electrode, which may be attributed to the higher electrochemical surface area of Pt@Al-Ti-ZnO-CC electrode compared to Pt@CC electrode. The increase in the surface area may be attributed to the coverage of CC surface with Al and Ti doped ZnO nanoparticles (see SEM images).

Fig. 7
figure 7

Cyclic voltammograms of the electrocatalysts in H2SO4 solution (0.5 M) + CH3OH solution (1 M)

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Table 2 Electrochemical characterization of methanol oxidation
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If /Ir values for Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC were 1.7, 2, 2.1, 2.4 m and 3.4, respectively. Since the large If /Ir ratio indicated high CO tolerance ability and stability of electrodes [48], doping ZnO with Al and Ti increased If /Ir values for the prepared electrodes and improved the Pt catalyst activity toward CO poisoning [50].

The peak potential, Ep on Pt@Al-Ti-ZnO-CC electrode was located at a lower potential and a reduction of about 0.05 V in the overpotential reaction was found when compared to Pt@CC electrode. As the lower amount of Ep means more oxidizing ability [51], doping Al and Ti with ZnO promoted the catalytic activity of the Pt catalysts.

Generally, the high electrical conductivity, the high electrochemical surface area, and the high CO tolerance are three essential properties that should be considered for the supporting materials in MORs [51, 52]. Among the prepared electrodes, Pt@Al-Ti-ZnO-CC exhibited the highest electrical conductivity, electrochemical surface area, and CO tolerance, as described, below.

Pt nanoparticles on the relatively stable nanocomposite and interaction between the Pt and the ATZO nanocomposite and the high levels of electrical conductivity due to the efficient existence of the dopant atoms are two main reasons for this phenomena. As the results showed, doping ZnO with Al and Ti led to the appropriate formation of active catalytic sites for MORs.

Chronoamperometry test

Chronoamperometry measurement of the prepared electrodes for the methanol oxidation is indicated in Fig. 8. Methanol can be oxidized continuously on the catalyst surface at the peak potential [48]. As seen, the current density decreased rapidly at the first and then reached a steady-state due to the formation of Pt oxide or the adsorbed intermediate species such as COads on the Pt catalyst surface [53]. When the electrocatalyst has good physical–chemical stability and poisoning-resistance, this decreasing slope is mild and gradual. The initial current densities of Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC were 67, 78, 84, 92, and 107 mA cm−2, respectively. Pt@Al-Ti-ZnO-CC electrode had the most ECSA value and the most available catalytic active sites for methanol oxidation and showed the highest initial current density. After 1200 s, the current densities of Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC dropped to 8.1, 16.4, 17.4, 32, and 40.8 mA cm−2, respectively. The final current density for Pt@Al-Ti-ZnO-CC electrode was fivefold greater compared to the Pt@CC electrode. It may be attributed to the larger ECSA value and higher oxidation ability toward CO-like intermediate. Intermediate species could be strongly adsorbed on Pt@CC electrode during MOR and blocked the catalytic reaction active sites [51]. Synergistic effect of advanced oxidation process of ZnO in removal of COads from the catalyst surface is illustrated in Fig. 9. In ZnO semiconductor, the electron (e−) can be conducted from its valence band (VB) to the conduction band (CB) at low overpotentials. The outcome of this phenomenon is formation of holes in VB (h+) that will act as oxidizing sites as described in Fig. 9. In h+ of ZnO surface, H2O acts as electron donor and generates \(OH^{ \circ }\). Hydroxyl radicals can oxidize COads and prevent Pt from poisoning. Poisoning rate (\(\delta\)) and stability of prepared catalysts are calculated from the chronoamperograms using Eq. (2) [54]:

$$\delta = {\raise0.7ex\hbox{${100}$} \!\mathord{\left/ {\vphantom {{100} {i_{0} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${i_{0} }$}} \times \left( {{{di} \mathord{\left/ {\vphantom {{di} {dt}}} \right. \kern-0pt} {dt}}} \right)_{t\rangle 200s}\,(\%\;\mathrm{per}\;\mathrm{second})$$
(2)

where, \(i_{0}\) is the current obtained by the extrapolating the linear current decay and \(\left( {{{di} \mathord{\left/ {\vphantom {{di} {dt}}} \right. \kern-0pt} {dt}}} \right)_{t\rangle 200s}\) is the slope of linear current at \(t > 200\,s\). The long-term poisoning values for Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC catalysts were calculated 0.16, 0.1, 0.07, 0.05, and 0.03% per second in the methanol, respectively. As results show, Al-Ti co-doped ZnO support material enhanced CO tolerance of Pt catalyst, which may be attributed to the high electrical conductivity and interaction between the Pt catalyst and ATZO support material. Similarly, the electronic effect between Pt and ATZO led to the proper adsorption of \(OH^{ \circ }\) on Pt sites and removal of the carbonaceous intermediate species during the MOR. Furthermore, the strong metal oxide interaction could hinder the aggregation of Pt nanoparticles. It is important to note that the prepared electrodes keep their alcohol oxidation activity even after 1200 s despite a rapid activity loss at the initial stage.

Fig. 8
figure 8

Chronoamperometric curves of the electrocatalysts for the methanol oxidation in H2SO4 solution (0.5 M) + CH3OH solution (1 M)

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Fig. 9
figure 9

Synergistic effect of ZnO advanced oxidation process

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EIS

Figure 10 displays the EIS Nyquist plots and the equivalent circuit for prepared electrodes. The equivalent circuit was obtained by fitting the impedance data using Autolab NOVA software. In this circuit, Zw, Rs, Rct, and Cdl are the Warburg impedance, the solution resistance, the charge transfer resistance, and the double layer capacitance, respectively. The faster oxidation reaction rate of alcohol led to lower Rct value and higher electrocatalytic activity [51]. Based on the obtained results, the Rct values of Pt@CC, Pt@ZnO-CC, Pt@Al-ZnO-CC, Pt@Ti-ZnO-CC, and Pt@Al-Ti-ZnO-CC were 38.5, 26.8, 24.9, 18.1, and 14 Ω cm2 in methanol, respectively. The minimum amount of Rct was obtained for Pt@Al-Ti-ZnO-CC electrode. These results confirmed the other findings. Al-Ti doped ZnO can produce hydroxyl radicals and oxidize the intermediate carbonaceous species on the Pt catalyst surface. Likewise, ATZO increased the electrical conductivity that improved the catalytic activity of Pt.

Fig. 10
figure 10

EIS Nyquist plots (dots) and equivalent circuit for the electrocatalysts in H2SO4 solution (0.5 M) + CH3OH solution (1 M)

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Active DMFC

Figure 11 shows the polarization and power density curves of the MEA by changing the methanol concentration. It is clear that the cell activity increased after increasing methanol concentration from 1 to 3 M. The lower methanol concentration, i.e., 1 M, was associated with a severe rate of polarization during the high-current operation, due to the difficulty in absorbing sufficient amount of methanol. In contrast, the cell performance declined at concentrations of 4 and 5 M. The use of higher methanol concentrations, e.g., 4 and 5 M, inevitably induced the methanol crossover (MCO) from the anode to the cathode [55]. The highest power densities and potential values at all current densities were observed in 3 M methanol concentration. In this concentration, the current densities of 28.6, 45.4, 66.6, 74.8, 96.5, and 108.8 mA cm−2 were achieved at 0.3, 0.26, 0.22, 0.2, 0.14, and 0.1 V, respectively.

Fig. 11
figure 11

Polarization and power density for the MEA at different methanol concentrations at 60 °C

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The peak power density of the MEA was 15.1 mW cm−2 and a current density of 83.4 mA cm−2 at a cell voltage of 0.2 V was obtained in 3 M methanol concentration.

The polarization and power density curves of the MEA by changing the operating temperature are shown in Fig. 12. As expected, the cell performance improved with increasing the temperature due to the increment in the rates of MOR and ORR (oxygen reduction reaction) at the anode and cathode, respectively [56]. However, an increase in the rate of MCO and a decrease in the membrane quality function are inevitable [57]. As previously reported [58, 59], at higher temperatures than 80 °C, membrane drying increased MCO values and then catalyst deterioration occurred. The current densities of 14.2, 21, 31.4, 44.5, 54, and 66.1 mA cm−2 were obtained at 0.3, 0.26, 0.22, 0.2, 0.14, and 0.1 V, respectively, at 40 °C. Similarly, the current densities of 22.9, 32.1, 44.5, 51.4, 65, and 79 mA cm−2 were taken at 0.3, 0.26, 0.22, 0.2, 0.14, and 0.1 V, respectively, at 50 °C. The peak power densities were 8.4, 10.4, and 15.1 mW cm−2 at 40, 50, and 60 °C, respectively.

Fig. 12
figure 12

Polarization and power density for the MEA at different temperatures by consuming methanol solution (3 M)

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The EIS Nyquist plots at 0.3 and 0.2 V for the MEA in 3 M methanol at 60 °C were measured and showed in Fig. 13. The equivalent circuit was determined by fitting the impedance data using Zview software (Fig. 13). Two arcs in the high and low frequency areas of the impedance spectrum were observed due to the low rate of MOR and ORR in DMFCs, respectively [60, 61]. The equivalent circuit parameters are tabulated in Table 3. Rct,a is the charge transfer resistance at the anode, Rct,c is the charge transfer resistance at the cathode, CPE-a and CPE-c are the double layer capacitances at the anode and cathode, respectively. Rohm is the bulk resistance and is attributed to the proton exchange membrane. In this case, Rohm values are close to each other in 0.2 and 0.3 V potentials due to the same MEA with the similar hydration level. By reducing the cell voltage from 0.3 to 0.2 V, Rct,a and Rct,c values decreased by 11.6 and 26.6%, respectively. As a result, the reduction of the cell voltage provided the reactions activation energy and the resistance to the charge transfer at the electrode surface decreased.

Fig. 13
figure 13

EIS Nyquist plots (dots) and equivalent circuit for the MEA at 0.2 V and 0.3 V

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Table 3 The obtained fitting EIS data of prepared MEA in the fuel cell
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Conclusion

The catalyst Pt@Al-Ti-ZnO-CC was synthesized by the sol–gel and co-precipitation methods. Physical analysis and electrochemical measurements of the prepared electrocatalyst were investigated in half and whole cell of MOR by the electrochemical techniques.

SEM images confirmed the nonporous and interconnected structure for the synthesized ATZO. The average particle size of Pt decreased by the use of Al and Ti nanoparticles in the electrode composition. XRD patterns revealed the purity and crystallinity of the synthesized Pt@Al-Ti-ZnO nanoparticles on CC.

Electrochemical characterization results showed the higher catalytic activity of Pt@Al-Ti-ZnO-CC in terms of stability, electrical conductivity, electrochemical surface area, and If compared to Pt@CC for MOR in the acidic media.

Finally, the highest peak power density for the MEA was obtained in 3 M methanol and 60 °C. Pt@Al-Ti-ZnO-CC as the anode revealed excellent activity for DMFCs.