Improved electrocatalytic activity and stability of PtPd/graphene nanoplates using sulfated zirconia for methanol electro-oxidation in DMFCs: An experimental and computational study

Improved electrocatalytic activity and stability of PtPd/graphene nanoplates using sulfated zirconia for methanol electro-oxidation in DMFCs: An experimental and computational study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Improved electrocatalytic activity and stability of PtPd/graphene nanoplates using sulfated zirconia for methanol electro-oxidation in DMFCs: An experimental and computational study Maryam Yaldagard, Mina Sedighi, Hassan Sabzyan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7637410/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract In this study, graphene nanoplates (GNPs) are coated with sulfated zirconia (S-ZrO₂) to enhance the proton conductivity of the support and improve the electrochemical activity and stability of the platinum-palladium (PtPd) catalyst. The carbon monoxide (CO) tolerance and electrocatalytic activity of the prepared PtPd/S-ZrO₂-GNP electrocatalyst are evaluated for the methanol oxidation reaction (MOR). The electrocatalyst shows a reduction in the CO oxidation peak voltage (0.71 V vs. 0.93 V for Pt/C). PtPd/S-ZrO₂-GNPs exhibit higher catalytic activity for MOR compared to Pt/ZrO₂-GNPs and Pt/C, with electrochemical surface area (ECSA) values of 87.24, 69.36, and 54.91 m²·g_pt⁻¹, respectively. This enhancement is attributed to Pt/Pd alloying, the high surface area of GNPs, and sulfated ZrO₂. Tafel slope analysis also indicates higher MOR activity for PtPd/S-ZrO₂-GNPs. First-principles computations reveal that the magnetic nature of PtPd, the increased cell volume of S-ZrO₂, and improved charge transfer efficiency are responsible for boosting the electrocatalytic activity of PtPd/S-ZrO₂-GNPs towards MOR. Physical sciences/Chemistry Physical sciences/Energy science and technology Physical sciences/Materials science Physical sciences/Nanoscience and technology Methanol electro-oxidation PtPd graphene nanoplate (GNP) sulfated-ZrO2 (S-ZrO2) direct methanol fuel cell (DMFC) Density functional theory (DFT) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1. Introduction Direct methanol fuel cells (DMFCs) use liquid methanol and have a simple system setup, and are thus ideal choices for portable devices. However, one major obstacle preventing their widespread application is the insufficient activity of their anode electrocatalyst 1 , 2 . To enhance the catalytic performance of DMFCs, platinum-metal alloys (PtM) are commonly applied 3 – 6 . Platinum dissociates methanol to the H₃CO and H adsorbed species, while the metal M forms oxy-hydroxide and oxidizes the H₃CO adsorbate to CO₂ 3–5 . Another significant challenge in the commercialization of DMFCs is the instability of the support materials. Carbon supports, such as carbon blacks, have high electronic conductivity and surface area, making them ideal for use as nanosized catalyst particles. However, recent studies have shown that electrocatalysts, including carbon supports, degrade under cell conditions, leading to performance loss over prolonged operation 7 . To counteract the corrosion of carbon supports by acids, non-precious metal oxides such as titania (TiO 2 ) 8 – 12 , Ti 4 O 7 13 , tungsten trioxide WO 3 14,15 , cerium oxide (CeO 2 ) 16 – 18 , aluminum oxide (Al 2 O 3 ) 19 , tin (IV) oxide (SnO 2 ) 20 – 22 , ruthenium oxide ( RuO 2 ) 23 , 24 , indium tin oxide (ITO) 25 , and molybdenum oxide (MoO 3 ) 26 have been used as the secondary supports. Valve metals such as titanium, zirconium, tantalum, and niobium prevent high corrosion of carbon supports through passivation in strong acidic solutions 27 . The aforementioned metal oxides can serve as support materials for DMFCs anode electrode. Zirconium dioxide (ZrO₂) nanoparticles have desirable properties, including a high dielectric constant, fast electron transfer, and superior CO adsorption. They also exhibit remarkable stability in fuel cell environments due to their hydrophilic nature, which helps to prevent oxidation, especially at higher pH levels 28 . ZrO₂ also has the ability to remove the poisoning species CO from the catalyst surface through a bifunctional mechanism. At its surface, water is dissociated into OH species, which react with adsorbed CO to produce CO₂. Additionally, ZrO₂ supplies oxygen to react with CO-like compounds, cleaning the catalyst surface for the subsequent methanol oxidation cycle 29 – 31 . However, metal oxides, including ZrO₂, generally have low electrical conductivity, and it is challenging to achieve highly dispersed platinum on their surfaces due to low surface area, which may decrease Pt utilization in the electrocatalyst structure. To solve the former drawback, metal oxides can be combined with conductive supports like carbon-based materials 32 – 34 , and to solve the latter, it would be beneficial to use mixed electron-proton conducting materials as electrocatalyst supports for DMFCs. Graphene nanoplates (GNPs) are being studied as potential electrocatalyst supports for DMFCs due to their unique electrical and mechanical properties 35 , 36 . It has been reported that Pt and Pt-Ruthenium (Ru) nanoparticles supported by graphene exhibit considerable catalytic activity for the electrooxidation of ethanol and methanol 35 – 40 . Oxygen functional groups are responsible for the anti-poisoning effect of reduced graphene oxide (GO) due to their ability to further oxidize and remove CO-like intermediates in electrooxidation reactions 41 . These findings have resulted in growing interest in the application of GNPs as a favorable support for DMFCs. Sulfate-treated ZrO₂ (abbreviated as S-ZrO₂ or SO₄²⁻-ZrO₂) is a proton-conducting solid superacid with high electrical conductivity and improved surface hydrophilicity 42 , 43 . The sulfate-treated ZrO₂ is a superacid with a Hammett acid strength of H₀ = −16.03, while Nafion has a Hammett acid strength of about − 12 44 . Studies have shown that S-ZrO₂ remains highly active up to 300°C in the presence of methanol and water 45 . In addition, it is easier to form smaller nanoparticles with larger surface area using S-ZrO₂ instead of untreated ZrO₂, which improves the utilization and dispersion of the Pt catalyst 42 . There are several reports regarding the application of S-ZrO₂ on carbon and carbon nanostructures as support materials in the direct electro-oxidation of methanol and ethanol in DMFCs/DEFCs (E refers to ethanol) 46 – 49 . Our study introduces a new electrocatalyst which is a combination of S-ZrO 2 nanocrystals with GNPs support and PtPd nanoparticles, resulting in a composite electrocatalyst with enhanced proton and electron conductivities. The active superacid S-ZrO 2 (SO 4 –2 -ZrO 2 ) component is supported on the GNPs surface via chemical links of the proton-conducting sulfonic acid groups onto the GNPs surface, which serves as a new S-ZrO 2 -GNPs support for the PtPd catalyst in DMFCs. The resulting PtPd/S-ZrO 2 -GNPs electrocatalysts are characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) equipped with an energy-dispersive X-ray (EDX) analyzer, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) methods. The impact of sulfation on the characteristics and performance of the prepared electrocatalysts is also investigated. The electrode containing the prepared PtPd/S-ZrO₂-GNPs electrocatalysts significantly outperforms the electrocatalyst PtPd/ZrO₂-GNPs prepared with untreated ZrO₂. 2. Material and Methods 2.1. Materials All materials used in this study, along with their suppliers, are provided in Text S1 of the supplementary information. 2.2. Experimental Methods 2.2.1. Preparation of GO and GNPs A detailed step-by-step description of the synthesis of GNPs from graphite is presented in Text S2 of the Supplementary Information. 2.2.2. Preparation of S-ZrO 2 -GNPs support The process of preparing sulfated zirconia on graphene support (S-ZrO₂-GNPs) is described in Text S3 of the Supplementary Information. 2.2.3 Polyol synthesis of PtPd/S-ZrO 2 -GNPs nanocomposites PtPd nanoparticles were loaded onto the S-ZrO₂-GNPs using the polyol method [55, 56]. To synthesize PtPd/S-ZrO₂-GNPs with a catalyst loading of 20 wt% PtPd, 25 mg of H₂PtCl₆·6H₂O + PdCl₂ (with a weight ratio of H₂PtCl₆ : PdCl₂ = 1:1) were dissolved in 25 mL ethylene glycol. The pH was adjusted to ~ 10 using an aqueous NaOH solution. The resulting solution was refluxed at 160°C for 6 h with rigorous stirring. The mixture was then cooled down to room temperature. Once the polyol reaction was completed, the S-ZrO₂-GNPs support material was added to the solution, and the mixture was stirred for 20 h to load the PtPd nanoparticles. The mixture was filtered, washed with sufficient double-distilled water, and dried under vacuum at 160°C for 50 min. This process was also repeated to prepare the sulfate-free ZrO₂-GNPs mixture. The experimental methodology used in this study to synthesize PtPd/S-ZrO₂-GNPs is illustrated in Fig. 1 . 2.2.4. Electrode construction After preparing the catalyst powder, a solution (ink) was made by adding 2 mL of isopropanol and 0.05 g of Nafion to 5 mg of the catalyst, and ultrasonicated for 30 min [57]. Next, 10 microliters of ink were pipetted and spread onto a glassy carbon electrode with an area of 0.196 cm², then dried in a vacuum oven at 80°C. To firmly fix the catalyst layer onto the electrode, a Nafion ionomer solution (0.05%) was dropped on the top surface of the catalyst layer. This electrode, acting as the working electrode, was then introduced into the electrolyte. The catalyst loading on the working electrode was set to 0.04 mg cm⁻². 2.2.5 Characterization analyses and instrumentation Characterization analyses, including physical, chemical, and electrochemical measurements, along with the corresponding instruments, are described in Text S4 of the Supplementary Information. 2.3. First principal computations To examine the origin of the electrocatalytic performance of the PtPd/S-ZrO₂-GNPs nanocomposites, the lattice structures of the S-ZrO₂ and PtPd components were optimized, and their electronic structure characteristics, i.e., band structure, total, and partial density of states (PDOS), were computed using first-principles density functional theory (DFT) computations. The computed characteristics were compared with those of the corresponding pure ZrO₂ and Pt lattices. The band structure and density of states of graphene were also calculated for validation. Detailed description of DFT computations and structures of simulated supercells are provided, respectively, in Text S5 and Fig. S1 of the Supplementary Information. 3. Results and Discussion 3.1 Physical characterization 3.1.1 Topography and textural characteristics of pure and zirconia-doped GNPs The AFM results shown in Fig. S2 of the Supplementary Information reveal the surface topography of both pure and zirconia-doped GNPs. A comparison between Figs. S2(a) and S2(b) clearly shows the presence of S-ZrO₂ nanoparticles on the surface of the doped GNPs. According to Fig. S2(b), the GNPs are layered with variable thicknesses ranging from 30 to 80 nm. The histogram presented in this figure shows that ~ 23% of the synthesized GNPs have pore size distributions, reflecting inter-sheet voids, below 6 nm, and the rest have pore size distributions of about 6–110 nm. The phase charts of GNPs resulting from the chemical reduction of exfoliated GO, along with the pore size distribution, are presented in Fig. S2(c). The specific surface areas of the pure and ZrO₂-doped GNPs were measured using N₂ adsorption/desorption based on BET theory. Details are given in Text S6 and Fig. S3 of the Supplementary Information. 3.1.2. Morphology and composition The morphology and microstructures of GNPs and the PtPd/S-ZrO₂-GNPs nanocomposite were analyzed by FESEM and TEM characterization methods (Fig. 2 ). According to these figures, the entire surface of the GNPs is uniformly covered by well-distributed spherical PtPd and S-ZrO₂ particles. A typical EDX pattern of the PtPd/S-ZrO₂-GNP electrocatalyst is demonstrated in Fig. 2 (d). According to this figure, the primary components corresponding to the most intense peaks are Pt, Pd, Zr, S, and C. The carbon signal comes from the GNPs. The EDX analyzer software also detects the presence of small amounts of silicon, gold, and potassium. The intense silicon peak is due to the Si substrate used in SEM analysis, and the gold peak comes from the sputtering layer. The potassium peak observed in the EDX diagram may be caused by the KMnO₄ used in the GO synthesis. The elemental composition of the prepared electrocatalyst, derived from the EDX pattern, is presented in Table 1 . The PtPd loading on the prepared composite is calculated to be 19.25% based on EDX analysis, which is a semi-quantitative technique and may not provide fully accurate metal loading values, however, it gives a reasonable estimation of the composition in this study. The particle size distribution of PtPd/S-ZrO₂-GNPs, extracted from the FESEM images, is also plotted in Fig. 2 (e). Table 1 Composition of the prepared PtPd/S-ZrO 2 -GNP sample (quantitative results) derived from EDX spectrum Element C O Na Al Si S Cl K Zr Pt Pd Au Total Line Kα Kα Kα Kα Kα Kα Kα Kα Lα Lα Lα Lα - Wt % 59.65 10.29 0.95 2.43 1.77 0.30 0.28 0.57 1.35 10.40 9.21 2.80 100.00 3.1.3. FTIR and Raman structural specifications The FTIR spectra of different synthesized materials, including GO, ZrO₂-GNPs, and S-ZrO₂-GNPs, are illustrated in Fig. S4(a) of the Supplementary Information. In the FTIR spectrum of GO, the vibrational bands appearing at 1643 and 2989 cm⁻¹ correspond, respectively, to the C = C and C–H stretching modes. Also, the two peaks observed around 1750 cm⁻¹ are assigned to the stretching mode of the C = O bonds of the carbonyl and carboxylic groups, and the peak at 1045 cm⁻¹ can be assigned to the stretching mode of the C–O bonds of the epoxy groups, indicating the presence of oxygen-containing functional groups in GO. In the FTIR spectrum of GNPs, the peak located at 1631 cm⁻¹ corresponds to the C = C bond stretching and reflects the sp² hybrid reconstruction. In the IR spectrum of ZrO₂-GNPs, the successful removal of the C = O bond is confirmed by the absence of its corresponding peak located at 1758 cm⁻¹ for GO. The appearance of new peaks at 2379 and 2372 cm⁻¹ related to the CH and CH₂ bond vibrations in the GNPs IR spectrum (Fig. S4(a)) suggests a reduction in GO content. In the S-ZrO₂-GNPs FTIR spectra, the bands observed at 1040, 1130, and 1220–1235 cm⁻¹ can be assigned to the symmetric and asymmetric stretching of the double bond S = O and single bond S–O chelated to Zr atoms 50 , 51 . The FTIR spectra of the S-ZrO₂/GNP composite show a broad band between 1300 and 990 cm⁻¹, which corresponds to the vibrational modes of the sulfate. The Raman spectra (Fig. S4(b)) were also obtained to determine the vibrational modes of GNPs and ZrO₂-GNPs after sulfation treatment. A detailed analysis of the G, D, and 2D bands, as well as the I_D/I_G intensity ratio for GNPs and S-ZrO₂/GNPs, is provided in Text S7 of the Supplementary Information. The results indicate that the overall structure of the graphene sheet remains intact after doping with S-ZrO₂, and the addition of zirconia does not introduce any specific functional groups to the surface of GNPs. 3.1.4. PXRD pattern The PXRD diffractogram obtained for the powder of the PtPd/S-ZrO₂-GNP electrocatalyst is shown in Fig. 3 . This diffractogram contains strong peaks corresponding to the crystalline lattice patterns of the PtPd and carbon components. The most intense diffraction peaks at 2θ = 26.65° and 54.48° correspond, respectively, to the [002] and [004] planes of graphite, indicating the presence of highly graphitic and well-ordered GNP layers in the nanocomposite. A detailed description of the PXRD peaks shown in Fig. 3 is provided in Text S8 of the Supplementary Information. 3.2. Electrochemical assessments 3.2.1. Electrochemical active surface area of the electrocatalyst To determine the electrochemical active surface area (ECSA) of the electrocatalyst, CV experiment is conducted in a three-electrode cell by a working electrode coated with an ionomer-blended electrocatalyst ink. The voltage is swept between − 0.24 and 1.2 V versus Ag/AgCl at a scan rate of 50 mV/s in a 0.5 M H₂SO₄ solution saturated with N₂. Using the obtained CV voltammogram (Fig. 4 ), the ECSA of the electrocatalysts is evaluated by computing the hydrogen adsorption/desorption area, using a conversion factor of 210 µC cm⁻² for polycrystalline Pt. The ECSA is then calculated using 52 : $$\:ECSA\left({m}^{2}{{g}_{metal}}^{-1}\right)=\:⌈\frac{{Q}_{H-adsorption}\left(C\right)}{{210\:\mu\:C{cm}^{-2}\times\:L}_{Pt}\left(mg{cm}^{-2}\right)\times\:{A}_{s}\left({cm}^{-2}\right)}⌉{10}^{5}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(7\right)$$ where \(\:{L}_{Pt}\) is the Pt loading (mg cm − 2 ) on the surface of an electrode, \(\:{Q}_{H}\) is the hydrogen adsorption charge (mC cm − 2 ), the 210 factor is the required charge for oxidizing a monolayer of H 2 on brilliant Pt, and \(\:{A}_{s}\) is the electrode surface area. According to the CV voltammogram shown in Fig. 4 , the adsorption/desorption peaks are visible in the range of − 0.2 to 0.04 V versus Ag/AgCl, and the surface oxidation and reduction peaks are clearly observable. The electrochemical measurements showed that the electrocatalytic activity of PtPd/S-ZrO₂-GNPs and PtPd/ZrO₂-GNPs composite electrocatalysts is higher than that of the commercial Pt/C electrocatalyst. The ECSA values evaluated for these electrocatalysts (respectively 87.24, 69.36, and 54.91 m² g⁻¹) follow the order PtPd/S-ZrO₂-GNPs > PtPd/ZrO₂-GNPs > commercial Pt/C. This indicates that more active sites are available for the hydrogen adsorption and desorption reactions on the PtPd/S-ZrO₂-GNPs electrode. The reason behind this could be the structural changes due to alloying and the high specific surface area of the graphene nanoplate (GNP) catalyst support resulting from the presence of S-ZrO₂. The catalyst layer containing the S-ZrO₂-GNPs support can accommodate a significant quantity of PtPd, indicating that the presence of S-ZrO₂ enhances the efficiency of DMFCs. 3.2.2. Performance of the electrode in the methanol oxidation reaction (MOR) and carbon monoxide (CO) tolerance The potential of the electrocatalyst PtPd/S-ZrO₂-GNP electrode is scanned at a speed of 50 mV s⁻¹ for oxidation in a solution of 0.5 M H₂SO₄ and 1 M CH₃OH. The obtained CV is shown in Fig. 5 (a), where the CVs of the PtPd/ZrO₂-GNPs and Pt/C electrodes under the same conditions are also presented for comparison. The activities of the electrocatalysts are analyzed using the peak potentials, onset potentials, and peak current densities. During the anodic forward scan in the voltammogram, methanol oxidation occurs, which leads to the generation of Pt-adsorbed carbonaceous intermediates such as CO_ads and CH_ads. The backward oxidation peak causes further electrooxidation of these adsorbed carbonaceous species to CO₂. Electrooxidation of CH₃OH on the PtPd/S-ZrO₂-GNPs electrode surface starts at around 0.52 V, with its peak current density occurring at ~ 0.64 V. The next step of the oxidation of methanol begins at approximately 0.57 V on the reverse half-cycle of the CV scan and reaches its peak current density at ~ 0.36 V, after which the strongly bonded surface intermediates start blocking the electrocatalyst surface. According to Fig. 5 (a), the peak current density of PtPd/S-ZrO 2 -GNPs (14 𝑚𝐴𝑚 \(\:{g}_{PtPd}^{-1}\) ) is considerably higher than those of PtPd/ZrO 2 -GNPs and Pt/C (6.62 𝑚𝐴 \(\:{mg}_{PtPd}^{-1}\) and 4.37 𝑚𝐴 \(\:{mg}_{Pt}^{-1}\) , respectively). In addition, the onset voltage of MOR on PtPd/S-ZrO 2 -GNPs is 0.36 V, while on PtPd/ZrO 2 -GNPs and Pt/C it is increased 0.46 and 0.54 V, respectively, in the positive (forward) half cycle of the scan. This indicates that sulfating ZrO 2 results in increased electrocatalytic activity and stability for MOR on PtPd/S-ZrO 2 -GNPs compared to the other two electrocatalysts. The relatively larger \(\:{I}_{forward}/{I}_{backward}\:\) ratio obtained for MOR on PtPd/S-ZrO₂-GNPs, i.e., 1.78 vs. 1.24 and 1.11 on PtPd/ZrO₂-GNPs and Pt/C, respectively, suggests that methanol molecules undergo efficient oxidation on PtPd/S-ZrO₂-GNPs during the positive (forward) half-cycle of the CV, producing relatively fewer poisoning species than those on PtPd/ZrO₂-GNPs and Pt/C. This improved performance can be attributed to the synergistic effects of the PtPd and ZrO₂ nanoparticles, as well as the mixed-conducting nature of PtPd/S-ZrO₂-GNP, which enhances electron and proton transport in the anode catalyst layer. As a result, the MOR performance of the PtPd/S-ZrO₂-GNP electrode is superior to those of the PtPd/ZrO₂-GNP and Pt/C electrodes. Additionally, the larger ECSA value of PtPd/S-ZrO₂-GNP is attributed to its increased hydrophilic character and proton conductivity. The transport behavior of methanol in the solution in the vicinity of the nanocomposite electrocatalyst is investigated by carrying out CV at various scan rates (Fig. 5 (b)). It can be observed in this figure that as the scan rate increases, the peak current density of methanol oxidation increases significantly, from ~ 4.6 mA/cm² at 10 mV/s to 9.8 mA/cm² at 100 mV/s, while the peak potentials increase more slightly, i.e., from 0.64 V at 10 mV/s to 0.7 V at 100 mV/s. The inset in Fig. 5 (b) indicates that the anodic peak current densities have a more or less proportional relationship with the square root of the scan rate, which reveals, according to the Randles–Ševčík equation, that the electrocatalytic oxidation of methanol is predominantly a diffusion-controlled process 53 . Throughout the MOR, the main intermediate causing poisoning of the electrode surface is CO. Therefore, an excellent electrocatalyst for MOR should have a high capability for CO electrooxidation with increased tolerance, as determined by the voltammetry of CO stripping. An electrocatalyst with a greater ability to oxidize CO and greater tolerance to CO poisoning can oxidize it more efficiently at lower potentials. The voltammograms of CO stripping on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes, obtained through the electrooxidation of pre-adsorbed CO, are illustrated in Fig. 6 . It can be seen in this figure that the peak and onset potentials for CO electrooxidation on the two electrocatalysts containing ZrO₂ are significantly different from those of the original PtPd electrocatalyst. The CO stripping analysis also indicates that the onset potential of CO electrooxidation on PtPd/S-ZrO₂-GNPs is 0.54 V, which is about 0.03 and 0.28 V lower than those observed for the PtPd/ZrO₂-GNP and Pt/C electrodes, respectively. This denotes the efficient performance of the sulfated ZrO₂-GNPs component for CO electrooxidation. The peak potential of CO electrooxidation on PtPd/S-ZrO₂-GNPs is 0.71 V, which is 0.02 and 0.22 V lower than those of PtPd/ZrO₂-GNPs and Pt/C, respectively. Furthermore, the electrooxidation peak current of the CO_ads species on PtPd/S-ZrO₂-GNPs is ~ 0.84 mA, which is significantly higher than those of PtPd/ZrO₂-GNPs and Pt/C (i.e., 0.67 and 0.64 mA). This indicates that the PtPd/S-ZrO₂-GNP electrode is relatively more tolerant to CO poisoning than the PtPd/ZrO₂-GNPs and Pt/C electrodes. The peak charge density \(\:{Q}_{CO}\) (mC cm − 2 ) is used to calculate the electroactive surface area (ESA) of the electrocatalyst, via: $$\:{ESA}_{CO}=\frac{{Q}_{CO}}{0.484\times\:{L}_{Pt}}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(1\right)$$ In this equation, the factor 0.484 (mC cm⁻²) is the charge density required to oxidize a monolayer of CO on bright Pt 54,55 . The peak charge density \(\:{Q}_{CO}\) corresponds to the following CO oxidation reaction: $$\:Pt-CO+{H}_{2}O\to\:Pt+{CO}_{2}+2{H}^{+}+\:2{e}^{-}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(2\right)$$ The ESA CO values of the PtPd/S-ZrO₂-GNP, PtPd/ZrO₂-GNPs, and Pt/C electrodes are calculated to be 42.56, 35.50, and 12.99 m² g⁻¹, respectively. Due to its greater ESA CO , the PtPd/S-ZrO₂-GNP electrocatalyst utilizes the Pt component more efficiently and exhibits higher activity in CO oxidation. The presence of SO₄²⁻ groups on the ZrO₂ surface increases its hydrophilicity and facilitates the adsorption of additional dissociative hydroxyl groups of H₂O on the solid superacid, which in turn enhances the conversion of CO_ads to CO₂ via a bifunctional mechanism 11 , 46 . This allows easier and faster regeneration of active sites on PtPd for further electrochemical reactions. Furthermore, the improved CO tolerance observed for PtPd/S-ZrO₂-GNP and PtPd/ZrO₂-GNP electrodes, compared to the Pt/C electrode, is attributed to various structural changes caused by alloying, as well as electronic (increased Pt d-band vacancy) and geometric (decreased Pt–Pt bond distance) factors 56 , 57 . 3.2.3. Linear sweep voltammetry analysis Linear sweep voltammograms and corresponding Tafel plots are obtained for methanol oxidation on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes in a 1 M KOH + 1 M CH₃OH solution at a scan rate of 5 mV s⁻¹ (Figs. 7 (a) and 7(b)). It is observed that the activity of the PtPd/S-ZrO₂-GNPs electrode is higher than that of the PtPd/ZrO₂-GNPs and Pt/C electrodes for methanol electro-oxidation. The electrocatalytic activity of the PtPd/ZrO₂-GNPs electrode is improved by sulfating the ZrO₂. Anodic electrooxidation reactions carried out on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes show Tafel slopes (Fig. 7 (b)) of approximately 251, 192, and 117 mV/dec, respectively, which are consistent with literature. 47,58 . In addition, similar shapes of the linear sweep voltammograms and Tafel plots obtained for the two catalysts, shown in Fig. 7 , may suggest comparable electrochemical kinetics, as indicated in 47,58 . 3.2.4. Reaction mechanism It is well established that incorporating Pd into Pt catalysts significantly reduces the overpotential for methanol electro-oxidation by enabling a bifunctional mechanism as described by the following reactions 59 – 61 : \(\:Pt+\left(C{H}_{3}OH\right)bulk\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt-{\left(C{H}_{3}OH\right)}_{ad}\) (3) \(\:Pt-{\left(C{H}_{3}OH\right)}_{ad}\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt-C{O}_{ad}+\:{4H}^{+}+4{e}^{-}\:\) (4) \(\:Pd+{H}_{2}O\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pd-({H}_{2}{O)}_{ad}\:\) (5) \(\:Pd-({H}_{2}{O)}_{ad}\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pd-({OH)}_{ad}+\:{H}^{+}+{e}^{-}\) (6) \(\:Pt-{CO}_{ad}+Pd-({OH)}_{ad}\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt+Pd+C{O}_{2}+\:{H}^{+}+{e}^{-}\:\:\) (7) In this mechanism, Pt primarily adsorbs methanol molecules, which undergo dehydrogenation to form strongly adsorbed CO intermediates that tend to poison the catalyst surface (Reactions 3 and 4). Meanwhile, Pd sites promote the adsorption and dissociation of water at lower potentials, generating reactive hydroxyl (OH) species (Reactions 5 and 6). These Pd-bound hydroxyl species subsequently oxidize the CO adsorbed on neighboring Pt sites to CO₂ (Reaction 7), thereby removing poisoning intermediates and maintaining catalytic activity. The close spatial proximity of Pt and Pd active sites is essential, as it facilitates efficient transfer of OH species from Pd to Pt-bound CO, improving CO oxidation kinetics and reducing the overall overpotential for methanol oxidation. The role of S-ZrO₂ in promoting the activity of the PtPd/S-ZrO₂-GNP electrocatalyst can be explained by the mechanism previously proposed for the MOR on Pt/ZrO₂-GNPs, summarized in the following reactions 62 : \(\:Pt+C{H}_{3}OH\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt-{CO}_{ad}+4\:{H}^{+}+4{e}^{-}\) (8) \(\:Pt+{H}_{2}O\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt-{OH}_{ad}+\:{H}^{+}+{e}^{-}\:\) (9) \(\:Zr{O}_{2}+{H}_{2}O\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Zr{O}_{2}-{OH}_{ad}+\:{H}^{+}+{e}^{-}\:\) (10) \(\:Pt-{CO}_{ad}+Pt-{OH}_{ad}\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:2Pt+C{O}_{2}+\:{H}^{+}+{e}^{-}\) (11) \(\:Pt-{CO}_{ad}+Zr{O}_{2}-{OH}_{ad}\:\underrightarrow{\:\:\:\:\:\:\:\:\:\:\:\:\:\:}\:Pt+Zr{O}_{2}+C{O}_{2}+\:{H}^{+}+{e}^{-}\:\:\) (12) It is well known that a catalyst for methanol oxidation must be capable of breaking both C–H and O–H bonds and facilitating the reaction of the resulting intermediates with oxygen-containing species to form CO₂ 63 . In this mechanism, the initially adsorbed methanol molecules are dehydrogenated on Pt sites, resulting in the formation of strongly adsorbed CO intermediates that poison the Pt surface and inhibit its catalytic activity (Reaction 8). To remove these intermediates, hydroxyl (OH) species are essential. These can be generated on Pt (Reaction 9) and also on the ZrO₂ support (Reaction 10), which, due to its reducible nature, surface oxygen vacancies, and Brønsted acidity, can dissociate water even at relatively low potentials 64 . The generated OH species are then involved in the oxidative removal of CO. The reaction between Pt–CO ads and Pt–OH ads results in CO₂ formation and regeneration of the active Pt sites (Reaction 11). Additionally, OH groups formed on ZrO₂ can directly oxidize adjacent Pt–CO species at the Pt–ZrO₂ interface (Reaction 12). The importance of surface oxygen species for effective CO oxidation at lower potentials in DMFC electrocatalysts has been well established, particularly in the case of cobalt oxides [65] and other supports 64 . ZrO₂ is a widely studied reducible oxide that exhibits a high oxygen storage capacity and strong metal–support interaction with noble metals such as Pt 29–31,48 . These properties make it an effective promoter in electrocatalysis. Accordingly, the following interfacial reaction can be proposed for the methanol electro-oxidation on the PtPd/S-ZrO₂-GNP electrode: $$\:PtPd\bullet\:\bullet\:\bullet\:S-Zr{O}_{2}\left(interface\right)+xCO\to\:PtPd\bullet\:\bullet\:\bullet\:S-Zr{O}_{2-x}\left(interface\right)+xC{O}_{2}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(13\right)$$ The enhancement of methanol oxidation activity can be primarily attributed to the catalytic synergy at the PtPd‧‧‧S-ZrO₂ interface. The presence of S-ZrO₂ facilitates water adsorption and dissociation at lower potentials, generating reactive oxygen species directly at the metal–support boundary. These oxygen species participate in the oxidation of CO intermediates adsorbed on PtPd, effectively removing poisoning species and regenerating active sites 64 . This interfacial reactivity reduces the anodic overpotential and enhances the overall electrocatalytic performance of the PtPd/S-ZrO₂-GNP catalyst. 3.2.5. Short term stability CV analysis was also used to examine the stability of each electrode in 0.5 M H₂SO₄ saturated with N₂. The potential sweep was performed at a scan rate of 50 mV s⁻¹ from − 0.24 to 1.2 V vs. Ag/AgCl (saturated). Figures 8 (a) to 8(c) display the CV curves obtained for all three electrodes after 1500 continuous potential scan cycles. ECSA loss was observed for both catalysts during potential cycling, likely due to Pt dissolution or agglomeration. The results indicate that the PtPd/S-ZrO₂-GNPs electrode is more electrochemically stable than the PtPd/ZrO₂-GNPs and Pt/C electrodes. Chronoamperometric measurements are also conducted to evaluate stability and possible poisoning of the nanocomposite electrocatalysts during short-term continuous operation in 0.5 M H₂SO₄ and 1 M CH₃OH at 0.4 V (Fig. S5). According to this figure, the current density of the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and commercial Pt/C electrodes decays rapidly at the beginning of the operation. This may be due to the formation of intermediate species such as CO_ads and CH_ads during the methanol oxidation process. After a short transient period, the current gradually stabilizes. Also, the current density of the PtPd/S-ZrO₂-GNPs electrode is significantly higher than that of the PtPd/ZrO₂-GNPs and Pt/C electrodes over a longer period of time, indicating that the application of sulfated ZrO₂ (S-ZrO₂) on the graphene support enhances the electrocatalytic activity and stability of the nanocomposite. These results, once again, demonstrate the high tolerance for intermediate species and superior electrocatalytic performance of the prepared PtPd/S-ZrO₂-GNPs composite catalyst in the MOR. 3.3. First-principal computations 3.3.1. Structural characteristics The optimized crystal structures of ZrO₁.₃₃S₀.₆₇ and PtPd₁.₆₇ are shown along different lattice planes in Figs. 9 (a) to 9(c). The DFT-optimized cell volumes, lattice parameters, and interatomic distances of the pristine and modified structures are reported in Table 2 . The DFT computational data obtained for the pristine materials (i.e., ZrO₂ and Pt) agree with those reported in the literature 65 , 66 . As a result of structural modifications, the cell parameters and interatomic distances of the modified materials differ from those of the pristine lattices. The equilibrium cell volume of the ZrO₂ supercell increases from 404.0 to 540.5 ų by replacing 8 oxygen atoms in the ZrO₂ lattice with S atoms. This partial replacement results in an increase in the Zr–O interatomic distance, which expands the lattice parameters and consequently the surface area of the nanostructure. This facilitates the accommodation of the PtPd catalyst on the S-ZrO₂ surface. Conversely, by partially replacing Pt with Pd in the Pt lattice, the Pt–Pt interatomic distance decreases, reducing the cell volume from 148.54 to 137.04 ų. Table 2 The DFT-optimized equilibrium lattice parameters, cell volumes, and inter-atomic distances of the S-ZrO2 (ZrO1.33S0.67), ZrO2, PtPd1.67, Pt, and graphene lattices for their supercells of 1×1×3, 1×1×3, 1×1×2, 1×1×2, and 2×1×1 unit cells, respectively. Lattice Lattice parameters Cell volume (Å 3 ) Inter-atomic distances (Å) a b c α β γ S-ZrO 2 (ZrO 1.33 S 0.67 ) 5.6881 5.7644 17.1787 90 90 73.65 540.50 Zr-O Zr-S 2.27 2.63 ZrO 2 5.1257 5.1257 15.3773 90 90 90 404.02 Zr-O 2.22 PtPd 1.67 4.0911 4.0926 8.1846 90 90 90 137.04 Pt-Pt 2.91 Pt 4.2034 4.2034 8.4068 90 90 90 148.54 Pt-Pt 2.98 Graphene 4.9502 2.4748 - 90 90 120 210.98 C-C 1.43 3.3.2. Electronic properties The total DOS and band structure of graphene obtained by DFT computations are plotted in Fig. S6 of the Supplementary Information for validation. The calculated electronic properties of graphene are in agreement with the results reported in the literature 67 , 68 . The apparently extra bands appearing in the calculated band structure diagram of Fig. S6 are due to the use of the 2×1×1 supercell in this work (instead of the 1×1×1 unit cell used for obtaining the band structure diagrams reported in the literature). The band structures and the total and partial DOSs calculated for the pristine (pure) Pt and PtPd₁.₆₇ alloy lattices are shown in Figs. 10 (a) and 10(b). According to Fig. 10 , the valence and conduction bands overlap at the Fermi level for both the PtPd₁.₆₇ alloy and Pt, implying that both structures are electrical conductors, i.e., metals. The band structures of Pt and PtPd₁.₆₇ are similar in some aspects. The band structure of PtPd₁.₆₇ is denser, especially near the Fermi level, due to the shift in the local (core) Pt levels and the splitting of the bonding electronic levels caused by the introduction of Pd into the Pt lattice. It can be seen in the DOS diagram of Pt (Fig. 10 (a)) that the density of states of the spin-up and spin-down channels are equal over the entire energy range. This denotes the non-magnetic nature of pure Pt. In contrast, for the PtPd₁.₆₇ alloy, the spin-up and spin-down densities of states are not symmetric, especially near the Fermi level. This asymmetry denotes the magnetic nature of this alloy. Also, the asymmetry of the calculated elemental PDOSs shows that both Pt and Pd contribute to the magnetic properties of this alloy. As reported for the magnetic CoPt alloy, the magnetic field can lower the activation barrier and facilitate the dehydrogenation of methanol, resulting in enhanced MOR electrocatalytic performance 69 , It can be expected that the application of a magnetic field may improve the performance of the prepared PtPd/S-ZrO₂-GNP electrocatalyst due to the magnetic nature of the Pt/Pd alloy. Electronic band structures and the corresponding total and partial DOSs for the pristine and sulfur-treated ZrO₂ (i.e., ZrO₂ and S-ZrO₂) are also calculated by DFT computations, and the results are illustrated in Figs. 11 (a) and 11(b), respectively. According to Fig. 11 , the band structures of these two materials are distinctly different. For example, the ZrO₂ band structure shows a direct band gap value of 2.28 eV at the B point, indicating the semiconductor character of ZrO₂. In contrast, this band gap is reduced to 0.91 eV for the S-ZrO₂ (ZrO₁.₃₃S₀.₆₇). This discrepancy can be attributed to the distinctly different natures of the Zr-S and Zr-O bonds 70 , 71 . Furthermore, Idrissi et al. 71 reported that sulfur doping of the ZrO₂ structure decreases the band gap of pure ZrO₂. The perfect symmetry of the spin-up and spin-down states in the PDOS diagrams of both pristine ZrO₂ and sulfur-treated ZrO₂ implies their non-magnetic nature. Analysis of the total DOS and elemental partial DOS (contributions of the orbitals of Zr, O, and S to the total DOS) indicates that the O-p and S-p orbitals contribute to the valence band, while the Zr-d orbitals mainly contribute to the conduction band. Overall, it is observed that introducing sulfur into the ZrO₂ structure changes its charge transfer efficiency, which boosts the catalytic activity of ZrO₂ towards MOR. 4. Conclusions High-density GNPs were prepared by modifying the Hummers and Offeman method. Additionally, a chemical method was used to introduce sulfonic acid groups onto the surface of ZrO₂-GNPs, resulting in the successful preparation of S-ZrO₂-GNPs. A PtPd/S-ZrO₂-GNP-modified GC electrode was successfully constructed using the polyol synthesis method, exhibiting superior physical and electrochemical properties relative to the pure PtPd alloy and the unsulfated electrocatalyst PtPd/ZrO₂-GNP. These properties include successful dispersion of catalyst nanoparticles on the support, a lower CO electro-oxidation peak potential (0.71 V vs. 0.74 V and 0.93 V), and a much higher methanol electro-oxidation current density compared to the PtPd/ZrO₂-GNPs and commercial Pt/C electrodes. The onset and peak potentials of methanol electro-oxidation were significantly reduced, respectively, from 0.54 V and 0.81 V for Pt/C to 0.36 V and 0.67 V for the PtPd/S-ZrO₂-GNP electrode. In addition, a considerable increase is observed in the anodic Tafel slope, from 117 mV to 251 mV, indicating an increase in MOR activity due to PtPd alloying and the replacement of C/ZrO₂-GNPs with S-ZrO₂-GNPs. The higher electrochemical activity of the prepared PtPd/S-ZrO₂-GNPs electrode can be attributed to the reduced CO poisoning of the platinum-palladium surface by sulfated ZrO₂-GNP. Analyses of the DFT-optimized structures and their corresponding band structures and DOSs obtained for the pristine and partly S/O replaced bulk ZrO₂ indicate that the inter-atomic distances increase and the band gap is reduced as a result of S/O replacement. These findings suggest that PtPd/S-ZrO₂-GNPs is a promising electrocatalyst to be applied as an anode material, providing greater MOR activity and elevated CO tolerance in higher-performance DMFCs. Declarations Conflict of Interest There are no conflicts of interest to declare. Supplementary Information This article included a supplementary Information file. Funding information There was a no funding for this research. Author Contribution Maryam Yaldagard: Conceptualization, Methodology, Validation, Investigation, Formal analysis, Data curation, Writing-original draft. Mina Sedighi: Methodology, Software, Investigation, Formal analysis, Data curation, Writing - original draft, Writing - review & editing. Hassan Sabzyan: Investigation, Formal analysis, Validation, Writing - review & editing. Acknowledgement: This work was supported by Hydrogen and Fuel Cell Research Institute, Urmia University, Urmia, Iran, which is acknowledged here by the authors. 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1","display":"","copyAsset":false,"role":"figure","size":366178,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic presentation of the experimental methodology used in this work for the synthesis of PtPd/S-ZrO₂-GNPs.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/dda86ec7c11df2353ff97c23.png"},{"id":95109843,"identity":"e4fd11b2-8eae-4e49-ad1c-ea332a2de146","added_by":"auto","created_at":"2025-11-04 11:40:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":503344,"visible":true,"origin":"","legend":"\u003cp\u003e(a) FESEM image of GNPs, (b,c) FESEM and TEM images of PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs electrocatalyst, (d) the EDX pattern and (e) the size distribution (histogram) of the PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs electrocatalyst.\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/f8bf54871863a1c10f90baa4.png"},{"id":95109841,"identity":"4cd44f8d-5ef9-449c-9f8e-0ed556b5507f","added_by":"auto","created_at":"2025-11-04 11:40:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":80911,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray diffractogram of PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNP electrocatalyst.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/7076f694e4db250e6ca485ff.png"},{"id":95225086,"identity":"f52d2cd9-9ace-4960-98ff-eb65e0db0757","added_by":"auto","created_at":"2025-11-05 16:24:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":155949,"visible":true,"origin":"","legend":"\u003cp\u003eCyclic voltammograms obtained for the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrocatalysts in 0.5 M H₂SO₄ solution at a scan rate of 50 mV s⁻¹ at 25 °C under N₂ flux.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/6e1acf60e93efb1ce88df683.png"},{"id":95109845,"identity":"e6be0a6e-7c86-4816-bbb4-da407d79156a","added_by":"auto","created_at":"2025-11-04 11:40:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":246113,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Cyclic voltammograms of methanol oxidation on the PtPd/S-ZrO2-GNPs, PtPd/ZrO2-GNP, and Pt/C electrodes in 0.5M H\u003csub\u003e2\u003c/sub\u003e SO\u003csub\u003e4\u003c/sub\u003e+1 MCH\u003csub\u003e3\u003c/sub\u003e OH solution at a scan rate of 50mV s\u003csup\u003e-1\u003c/sup\u003e at 25 °C under N2 flux. (b) The anodic peak current densities of PtPd/S-ZrO2-GNP in the 0.5 M H2SO4 + 1 M CH3OH solution at different scan rates.\u0026nbsp;\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/6f9b2fe8fdc19d2f167f9f7b.png"},{"id":95109848,"identity":"e812d694-c1e8-4790-8b7f-59a35f23e11c","added_by":"auto","created_at":"2025-11-04 11:40:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":165664,"visible":true,"origin":"","legend":"\u003cp\u003eThe cyclic voltammograms displaying the CO stripping from the surface PtPd/S-ZrO2-GNPs, PtPd/ZrO2-GNPs, and Pt/C electrodes in 0.5M H\u003csub\u003e2\u003c/sub\u003e SO\u003csub\u003e4\u003c/sub\u003e+1 MCH3 OH solution at a scan rate of 50mV s\u003csup\u003e-1\u003c/sup\u003e at 25 °C under N2 flux.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/2e606f71ebc46153b782e0f8.png"},{"id":95225483,"identity":"6dfb32ba-a7d9-4216-be9d-ad7723ac4e12","added_by":"auto","created_at":"2025-11-05 16:25:07","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":108939,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Linear sweep voltammetry of methanol oxidation on the PtPd/S-ZrO2-GNPs, PtPd/ ZrO2-GNPs and Pt/C electrodes in 1 M KOH +1 M CH\u003csub\u003e3\u003c/sub\u003e OH solution at a scan rate of 5 mVs- 1, and (b) the corresponding Tafel plots.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/70aba800a1ade23e0edd5f76.png"},{"id":95224611,"identity":"14b84a9a-4511-4b7e-aef3-cefe1171e7cd","added_by":"auto","created_at":"2025-11-05 16:24:01","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":298701,"visible":true,"origin":"","legend":"\u003cp\u003eThe CV curves obtained after 1500 cycles of continuous potential scanning for the (a) PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs, (b) PtPd/ ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs and (c) Pt/C electrodes in 0.5 M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e solution at a scan rate of 50 mVs\u003csup\u003e-1\u003c/sup\u003e under the N\u003csub\u003e2\u003c/sub\u003e flux.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/932b6d9a7603d2fbf2f5bcb6.png"},{"id":95109860,"identity":"426d17d6-4ffa-4078-aeba-71efc8be4c8d","added_by":"auto","created_at":"2025-11-04 11:40:18","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":330547,"visible":true,"origin":"","legend":"\u003cp\u003eThe DFT-optimized structure of the of ZrO\u003csub\u003e1.33\u003c/sub\u003eS\u003csub\u003e0.67\u003c/sub\u003e lattice along the (a) [100] and (b) [001] planes, and (c) the DFT-optimized structure of the PtPd\u003csub\u003e1.67 \u003c/sub\u003ealloy lattice along the [100] plane. \u0026nbsp;Red, yellow, cyan, orange and gray spheres represent O, S, Zr, Pt, and Pd elements, respectively.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/69d8cf39b9b1a8f6dd0b4566.png"},{"id":95224921,"identity":"c5f61c78-ca94-4f2d-95b0-3de8b6c385f5","added_by":"auto","created_at":"2025-11-05 16:24:27","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":402107,"visible":true,"origin":"","legend":"\u003cp\u003eThe DFT-calculated band structures along high symmetry path of the first Brillouin zone (left) and corresponding DOS and PDOS (right) obtained for 1×1×2 supercells of (a) pure Pt and (b) PtPd\u003csub\u003e1.67\u003c/sub\u003e alloy lattices\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/d1314401c135d98dd52423e4.png"},{"id":95224771,"identity":"f77bf06e-31cd-4925-84e5-4659d94a1e61","added_by":"auto","created_at":"2025-11-05 16:24:16","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":513315,"visible":true,"origin":"","legend":"\u003cp\u003eThe DFT-calculated band structure along the high symmetry path of the first Brillouin zone (left) and corresponding total DOS and elemental PDOS (right) obtained for a 1×1×3 supercells of (a) pristine ZrO\u003csub\u003e2\u003c/sub\u003e and (b) sulfur-treated ZrO\u003csub\u003e2 \u003c/sub\u003e(ZrO\u003csub\u003e1.33\u003c/sub\u003eS\u003csub\u003e0.67\u003c/sub\u003e) lattices.\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/74a8b642809ec8d5eed30bd1.png"},{"id":96894071,"identity":"8f59c55b-9314-42f3-8e93-192209d6fa20","added_by":"auto","created_at":"2025-11-27 09:53:37","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4251514,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/7c5b4008-8930-456e-a919-c061090859ee.pdf"},{"id":95224573,"identity":"822398a1-aad8-498d-8762-984032d16e5b","added_by":"auto","created_at":"2025-11-05 16:23:56","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":4750276,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7637410/v1/b0fa701905cae1d1a4501145.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Improved electrocatalytic activity and stability of PtPd/graphene nanoplates using sulfated zirconia for methanol electro-oxidation in DMFCs: An experimental and computational study","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003e\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003eDirect methanol fuel cells (DMFCs) use liquid methanol and have a simple system setup, and are thus ideal choices for portable devices. However, one major obstacle preventing their widespread application is the insufficient activity of their anode electrocatalyst \u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e,\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e. To enhance the catalytic performance of DMFCs, platinum-metal alloys (PtM) are commonly applied \u003csup\u003e\u003cspan additionalcitationids=\"CR4 CR5\" citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e. Platinum dissociates methanol to the H₃CO and H adsorbed species, while the metal M forms oxy-hydroxide and oxidizes the H₃CO adsorbate to CO₂ \u003csup\u003e3\u0026ndash;5\u003c/sup\u003e. Another significant challenge in the commercialization of DMFCs is the instability of the support materials. Carbon supports, such as carbon blacks, have high electronic conductivity and surface area, making them ideal for use as nanosized catalyst particles. However, recent studies have shown that electrocatalysts, including carbon supports, degrade under cell conditions, leading to performance loss over prolonged operation \u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e. To counteract the corrosion of carbon supports by acids, non-precious metal oxides such as titania (TiO\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e\u003cspan additionalcitationids=\"CR9 CR10 CR11\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e, Ti\u003csub\u003e4\u003c/sub\u003eO\u003csub\u003e7\u003c/sub\u003e \u003csup\u003e13\u003c/sup\u003e, tungsten trioxide WO\u003csub\u003e3\u003c/sub\u003e \u003csup\u003e14,15\u003c/sup\u003e, cerium oxide (CeO\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, aluminum oxide (Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) \u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, tin (IV) oxide (SnO\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e, ruthenium oxide ( RuO\u003csub\u003e2\u003c/sub\u003e) \u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e,\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, indium tin oxide (ITO) \u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e, and molybdenum oxide (MoO\u003csub\u003e3\u003c/sub\u003e) \u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e have been used as the secondary supports. Valve metals such as titanium, zirconium, tantalum, and niobium prevent high corrosion of carbon supports through passivation in strong acidic solutions \u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e. The aforementioned metal oxides can serve as support materials for DMFCs anode electrode.\u003c/p\u003e\u003cp\u003eZirconium dioxide (ZrO₂) nanoparticles have desirable properties, including a high dielectric constant, fast electron transfer, and superior CO adsorption. They also exhibit remarkable stability in fuel cell environments due to their hydrophilic nature, which helps to prevent oxidation, especially at higher pH levels \u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. ZrO₂ also has the ability to remove the poisoning species CO from the catalyst surface through a bifunctional mechanism. At its surface, water is dissociated into OH species, which react with adsorbed CO to produce CO₂. Additionally, ZrO₂ supplies oxygen to react with CO-like compounds, cleaning the catalyst surface for the subsequent methanol oxidation cycle \u003csup\u003e\u003cspan additionalcitationids=\"CR30\" citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. However, metal oxides, including ZrO₂, generally have low electrical conductivity, and it is challenging to achieve highly dispersed platinum on their surfaces due to low surface area, which may decrease Pt utilization in the electrocatalyst structure. To solve the former drawback, metal oxides can be combined with conductive supports like carbon-based materials \u003csup\u003e\u003cspan additionalcitationids=\"CR33\" citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e, and to solve the latter, it would be beneficial to use mixed electron-proton conducting materials as electrocatalyst supports for DMFCs.\u003c/p\u003e\u003cp\u003eGraphene nanoplates (GNPs) are being studied as potential electrocatalyst supports for DMFCs due to their unique electrical and mechanical properties \u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. It has been reported that Pt and Pt-Ruthenium (Ru) nanoparticles supported by graphene exhibit considerable catalytic activity for the electrooxidation of ethanol and methanol \u003csup\u003e\u003cspan additionalcitationids=\"CR36 CR37 CR38 CR39\" citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e. Oxygen functional groups are responsible for the anti-poisoning effect of reduced graphene oxide (GO) due to their ability to further oxidize and remove CO-like intermediates in electrooxidation reactions \u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. These findings have resulted in growing interest in the application of GNPs as a favorable support for DMFCs.\u003c/p\u003e\u003cp\u003eSulfate-treated ZrO₂ (abbreviated as S-ZrO₂ or SO₄\u0026sup2;⁻-ZrO₂) is a proton-conducting solid superacid with high electrical conductivity and improved surface hydrophilicity \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. The sulfate-treated ZrO₂ is a superacid with a Hammett acid strength of H₀ = \u0026minus;16.03, while Nafion has a Hammett acid strength of about \u0026minus;\u0026thinsp;12 \u003csup\u003e44\u003c/sup\u003e. Studies have shown that S-ZrO₂ remains highly active up to 300\u0026deg;C in the presence of methanol and water \u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e. In addition, it is easier to form smaller nanoparticles with larger surface area using S-ZrO₂ instead of untreated ZrO₂, which improves the utilization and dispersion of the Pt catalyst \u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThere are several reports regarding the application of S-ZrO₂ on carbon and carbon nanostructures as support materials in the direct electro-oxidation of methanol and ethanol in DMFCs/DEFCs (E refers to ethanol) \u003csup\u003e\u003cspan additionalcitationids=\"CR47 CR48\" citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e. Our study introduces a new electrocatalyst which is a combination of S-ZrO\u003csub\u003e2\u003c/sub\u003e nanocrystals with GNPs support and PtPd nanoparticles, resulting in a composite electrocatalyst with enhanced proton and electron conductivities. The active superacid S-ZrO\u003csub\u003e2\u003c/sub\u003e (SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026ndash;2\u003c/sup\u003e-ZrO\u003csub\u003e2\u003c/sub\u003e) component is supported on the GNPs surface via chemical links of the proton-conducting sulfonic acid groups onto the GNPs surface, which serves as a new S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs support for the PtPd catalyst in DMFCs. The resulting PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs electrocatalysts are characterized by Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) equipped with an energy-dispersive X-ray (EDX) analyzer, transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) methods. The impact of sulfation on the characteristics and performance of the prepared electrocatalysts is also investigated. The electrode containing the prepared PtPd/S-ZrO₂-GNPs electrocatalysts significantly outperforms the electrocatalyst PtPd/ZrO₂-GNPs prepared with untreated ZrO₂.\u003c/p\u003e"},{"header":"2. Material and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1. Materials\u003c/h2\u003e\u003cp\u003eAll materials used in this study, along with their suppliers, are provided in Text S1 of the supplementary information.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2. Experimental Methods\u003c/h2\u003e\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\u003ch2\u003e2.2.1. Preparation of GO and GNPs\u003c/h2\u003e\u003cp\u003eA detailed step-by-step description of the synthesis of GNPs from graphite is presented in Text S2 of the Supplementary Information.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\u003ch2\u003e2.2.2. Preparation of S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs support\u003c/h2\u003e\u003cp\u003eThe process of preparing sulfated zirconia on graphene support (S-ZrO₂-GNPs) is described in Text S3 of the Supplementary Information.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\u003ch2\u003e2.2.3 Polyol synthesis of PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs nanocomposites\u003c/h2\u003e\u003cp\u003ePtPd nanoparticles were loaded onto the S-ZrO₂-GNPs using the polyol method [55, 56]. To synthesize PtPd/S-ZrO₂-GNPs with a catalyst loading of 20 wt% PtPd, 25 mg of H₂PtCl₆\u0026middot;6H₂O\u0026thinsp;+\u0026thinsp;PdCl₂ (with a weight ratio of H₂PtCl₆ : PdCl₂ = 1:1) were dissolved in 25 mL ethylene glycol. The pH was adjusted to ~\u0026thinsp;10 using an aqueous NaOH solution. The resulting solution was refluxed at 160\u0026deg;C for 6 h with rigorous stirring. The mixture was then cooled down to room temperature. Once the polyol reaction was completed, the S-ZrO₂-GNPs support material was added to the solution, and the mixture was stirred for 20 h to load the PtPd nanoparticles. The mixture was filtered, washed with sufficient double-distilled water, and dried under vacuum at 160\u0026deg;C for 50 min. This process was also repeated to prepare the sulfate-free ZrO₂-GNPs mixture. The experimental methodology used in this study to synthesize PtPd/S-ZrO₂-GNPs is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\u003ch2\u003e2.2.4. Electrode construction\u003c/h2\u003e\u003cp\u003eAfter preparing the catalyst powder, a solution (ink) was made by adding 2 mL of isopropanol and 0.05 g of Nafion to 5 mg of the catalyst, and ultrasonicated for 30 min [57]. Next, 10 microliters of ink were pipetted and spread onto a glassy carbon electrode with an area of 0.196 cm\u0026sup2;, then dried in a vacuum oven at 80\u0026deg;C. To firmly fix the catalyst layer onto the electrode, a Nafion ionomer solution (0.05%) was dropped on the top surface of the catalyst layer. This electrode, acting as the working electrode, was then introduced into the electrolyte. The catalyst loading on the working electrode was set to 0.04 mg cm⁻\u0026sup2;.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec9\" class=\"Section3\"\u003e\u003ch2\u003e2.2.5 Characterization analyses and instrumentation\u003c/h2\u003e\u003cp\u003eCharacterization analyses, including physical, chemical, and electrochemical measurements, along with the corresponding instruments, are described in Text S4 of the Supplementary Information.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\u003ch2\u003e2.3. First principal computations\u003c/h2\u003e\u003cp\u003eTo examine the origin of the electrocatalytic performance of the PtPd/S-ZrO₂-GNPs nanocomposites, the lattice structures of the S-ZrO₂ and PtPd components were optimized, and their electronic structure characteristics, i.e., band structure, total, and partial density of states (PDOS), were computed using first-principles density functional theory (DFT) computations. The computed characteristics were compared with those of the corresponding pure ZrO₂ and Pt lattices. The band structure and density of states of graphene were also calculated for validation. Detailed description of DFT computations and structures of simulated supercells are provided, respectively, in Text S5 and Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e of the Supplementary Information.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec12\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Physical characterization\u003c/h2\u003e\u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\u003ch2\u003e3.1.1 Topography and textural characteristics of pure and zirconia-doped GNPs\u003c/h2\u003e\u003cp\u003eThe AFM results shown in Fig. S2 of the Supplementary Information reveal the surface topography of both pure and zirconia-doped GNPs. A comparison between Figs. S2(a) and S2(b) clearly shows the presence of S-ZrO₂ nanoparticles on the surface of the doped GNPs. According to Fig. S2(b), the GNPs are layered with variable thicknesses ranging from 30 to 80 nm. The histogram presented in this figure shows that ~\u0026thinsp;23% of the synthesized GNPs have pore size distributions, reflecting inter-sheet voids, below 6 nm, and the rest have pore size distributions of about 6\u0026ndash;110 nm. The phase charts of GNPs resulting from the chemical reduction of exfoliated GO, along with the pore size distribution, are presented in Fig. S2(c).\u003c/p\u003e\u003cp\u003eThe specific surface areas of the pure and ZrO₂-doped GNPs were measured using N₂ adsorption/desorption based on BET theory. Details are given in Text S6 and Fig. S3 of the Supplementary Information.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\u003ch2\u003e3.1.2. Morphology and composition\u003c/h2\u003e\u003cp\u003eThe morphology and microstructures of GNPs and the PtPd/S-ZrO₂-GNPs nanocomposite were analyzed by FESEM and TEM characterization methods (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). According to these figures, the entire surface of the GNPs is uniformly covered by well-distributed spherical PtPd and S-ZrO₂ particles.\u003c/p\u003e\u003cp\u003eA typical EDX pattern of the PtPd/S-ZrO₂-GNP electrocatalyst is demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d). According to this figure, the primary components corresponding to the most intense peaks are Pt, Pd, Zr, S, and C. The carbon signal comes from the GNPs. The EDX analyzer software also detects the presence of small amounts of silicon, gold, and potassium. The intense silicon peak is due to the Si substrate used in SEM analysis, and the gold peak comes from the sputtering layer. The potassium peak observed in the EDX diagram may be caused by the KMnO₄ used in the GO synthesis. The elemental composition of the prepared electrocatalyst, derived from the EDX pattern, is presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The PtPd loading on the prepared composite is calculated to be 19.25% based on EDX analysis, which is a semi-quantitative technique and may not provide fully accurate metal loading values, however, it gives a reasonable estimation of the composition in this study. The particle size distribution of PtPd/S-ZrO₂-GNPs, extracted from the FESEM images, is also plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(e).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eComposition of the prepared PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNP sample (quantitative results) derived from EDX spectrum\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"14\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003eElement\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003eC\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eO\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003eNa\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eAl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eSi\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eS\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\"\u003e\u003cp\u003eCl\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c9\"\u003e\u003cp\u003eK\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c10\"\u003e\u003cp\u003eZr\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c11\"\u003e\u003cp\u003ePt\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c12\"\u003e\u003cp\u003ePd\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c13\"\u003e\u003cp\u003eAu\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c14\"\u003e\u003cp\u003eTotal\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eLine\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e\u003cem\u003eKα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e\u003cem\u003eLα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e\u003cem\u003eLα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e\u003cem\u003eLα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e\u003cem\u003eLα\u003c/em\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eWt %\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e59.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e10.29\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e0.95\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e2.43\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e1.77\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e0.30\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e0.28\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003e0.57\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c10\"\u003e\u003cp\u003e1.35\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c11\"\u003e\u003cp\u003e10.40\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c12\"\u003e\u003cp\u003e9.21\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c13\"\u003e\u003cp\u003e2.80\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c14\"\u003e\u003cp\u003e100.00\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec15\" class=\"Section3\"\u003e\u003ch2\u003e3.1.3. FTIR and Raman structural specifications\u003c/h2\u003e\u003cp\u003eThe FTIR spectra of different synthesized materials, including GO, ZrO₂-GNPs, and S-ZrO₂-GNPs, are illustrated in Fig. S4(a) of the Supplementary Information. In the FTIR spectrum of GO, the vibrational bands appearing at 1643 and 2989 cm⁻\u0026sup1; correspond, respectively, to the C\u0026thinsp;=\u0026thinsp;C and C\u0026ndash;H stretching modes. Also, the two peaks observed around 1750 cm⁻\u0026sup1; are assigned to the stretching mode of the C\u0026thinsp;=\u0026thinsp;O bonds of the carbonyl and carboxylic groups, and the peak at 1045 cm⁻\u0026sup1; can be assigned to the stretching mode of the C\u0026ndash;O bonds of the epoxy groups, indicating the presence of oxygen-containing functional groups in GO. In the FTIR spectrum of GNPs, the peak located at 1631 cm⁻\u0026sup1; corresponds to the C\u0026thinsp;=\u0026thinsp;C bond stretching and reflects the sp\u0026sup2; hybrid reconstruction. In the IR spectrum of ZrO₂-GNPs, the successful removal of the C\u0026thinsp;=\u0026thinsp;O bond is confirmed by the absence of its corresponding peak located at 1758 cm⁻\u0026sup1; for GO. The appearance of new peaks at 2379 and 2372 cm⁻\u0026sup1; related to the CH and CH₂ bond vibrations in the GNPs IR spectrum (Fig. S4(a)) suggests a reduction in GO content. In the S-ZrO₂-GNPs FTIR spectra, the bands observed at 1040, 1130, and 1220\u0026ndash;1235 cm⁻\u0026sup1; can be assigned to the symmetric and asymmetric stretching of the double bond S\u0026thinsp;=\u0026thinsp;O and single bond S\u0026ndash;O chelated to Zr atoms \u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e. The FTIR spectra of the S-ZrO₂/GNP composite show a broad band between 1300 and 990 cm⁻\u0026sup1;, which corresponds to the vibrational modes of the sulfate.\u003c/p\u003e\u003cp\u003eThe Raman spectra (Fig. S4(b)) were also obtained to determine the vibrational modes of GNPs and ZrO₂-GNPs after sulfation treatment. A detailed analysis of the G, D, and 2D bands, as well as the I_D/I_G intensity ratio for GNPs and S-ZrO₂/GNPs, is provided in Text S7 of the Supplementary Information. The results indicate that the overall structure of the graphene sheet remains intact after doping with S-ZrO₂, and the addition of zirconia does not introduce any specific functional groups to the surface of GNPs.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\u003ch2\u003e3.1.4. PXRD pattern\u003c/h2\u003e\u003cp\u003eThe PXRD diffractogram obtained for the powder of the PtPd/S-ZrO₂-GNP electrocatalyst is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. This diffractogram contains strong peaks corresponding to the crystalline lattice patterns of the PtPd and carbon components. The most intense diffraction peaks at 2θ\u0026thinsp;=\u0026thinsp;26.65\u0026deg; and 54.48\u0026deg; correspond, respectively, to the [002] and [004] planes of graphite, indicating the presence of highly graphitic and well-ordered GNP layers in the nanocomposite. A detailed description of the PXRD peaks shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e is provided in Text S8 of the Supplementary Information.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec17\" class=\"Section2\"\u003e\u003ch2\u003e3.2. Electrochemical assessments\u003c/h2\u003e\u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\u003ch2\u003e3.2.1. Electrochemical active surface area of the electrocatalyst\u003c/h2\u003e\u003cp\u003eTo determine the electrochemical active surface area (ECSA) of the electrocatalyst, CV experiment is conducted in a three-electrode cell by a working electrode coated with an ionomer-blended electrocatalyst ink. The voltage is swept between \u0026minus;\u0026thinsp;0.24 and 1.2 V versus Ag/AgCl at a scan rate of 50 mV/s in a 0.5 M H₂SO₄ solution saturated with N₂. Using the obtained CV voltammogram (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), the ECSA of the electrocatalysts is evaluated by computing the hydrogen adsorption/desorption area, using a conversion factor of 210 \u0026micro;C cm⁻\u0026sup2; for polycrystalline Pt. The ECSA is then calculated using \u003csup\u003e\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:ECSA\\left({m}^{2}{{g}_{metal}}^{-1}\\right)=\\:\u0026lceil;\\frac{{Q}_{H-adsorption}\\left(C\\right)}{{210\\:\\mu\\:C{cm}^{-2}\\times\\:L}_{Pt}\\left(mg{cm}^{-2}\\right)\\times\\:{A}_{s}\\left({cm}^{-2}\\right)}\u0026rceil;{10}^{5}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(7\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{L}_{Pt}\\)\u003c/span\u003e\u003c/span\u003e is the Pt loading (mg cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) on the surface of an electrode, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{Q}_{H}\\)\u003c/span\u003e\u003c/span\u003e is the hydrogen adsorption charge (mC cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e), the 210 factor is the required charge for oxidizing a monolayer of H\u003csub\u003e2\u003c/sub\u003e on brilliant Pt, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{A}_{s}\\)\u003c/span\u003e\u003c/span\u003e is the electrode surface area.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAccording to the CV voltammogram shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, the adsorption/desorption peaks are visible in the range of \u0026minus;\u0026thinsp;0.2 to 0.04 V versus Ag/AgCl, and the surface oxidation and reduction peaks are clearly observable. The electrochemical measurements showed that the electrocatalytic activity of PtPd/S-ZrO₂-GNPs and PtPd/ZrO₂-GNPs composite electrocatalysts is higher than that of the commercial Pt/C electrocatalyst. The ECSA values evaluated for these electrocatalysts (respectively 87.24, 69.36, and 54.91 m\u0026sup2; g⁻\u0026sup1;) follow the order PtPd/S-ZrO₂-GNPs\u0026thinsp;\u0026gt;\u0026thinsp;PtPd/ZrO₂-GNPs\u0026thinsp;\u0026gt;\u0026thinsp;commercial Pt/C. This indicates that more active sites are available for the hydrogen adsorption and desorption reactions on the PtPd/S-ZrO₂-GNPs electrode. The reason behind this could be the structural changes due to alloying and the high specific surface area of the graphene nanoplate (GNP) catalyst support resulting from the presence of S-ZrO₂. The catalyst layer containing the S-ZrO₂-GNPs support can accommodate a significant quantity of PtPd, indicating that the presence of S-ZrO₂ enhances the efficiency of DMFCs.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec19\" class=\"Section3\"\u003e\u003ch2\u003e3.2.2. Performance of the electrode in the methanol oxidation reaction (MOR) and carbon monoxide (CO) tolerance\u003c/h2\u003e\u003cp\u003eThe potential of the electrocatalyst PtPd/S-ZrO₂-GNP electrode is scanned at a speed of 50 mV s⁻\u0026sup1; for oxidation in a solution of 0.5 M H₂SO₄ and 1 M CH₃OH. The obtained CV is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), where the CVs of the PtPd/ZrO₂-GNPs and Pt/C electrodes under the same conditions are also presented for comparison. The activities of the electrocatalysts are analyzed using the peak potentials, onset potentials, and peak current densities. During the anodic forward scan in the voltammogram, methanol oxidation occurs, which leads to the generation of Pt-adsorbed carbonaceous intermediates such as CO_ads and CH_ads. The backward oxidation peak causes further electrooxidation of these adsorbed carbonaceous species to CO₂. Electrooxidation of CH₃OH on the PtPd/S-ZrO₂-GNPs electrode surface starts at around 0.52 V, with its peak current density occurring at ~\u0026thinsp;0.64 V. The next step of the oxidation of methanol begins at approximately 0.57 V on the reverse half-cycle of the CV scan and reaches its peak current density at ~\u0026thinsp;0.36 V, after which the strongly bonded surface intermediates start blocking the electrocatalyst surface.\u003c/p\u003e\u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), the peak current density of PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs (14 \u0026#119898;\u0026#119860;\u0026#119898;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{g}_{PtPd}^{-1}\\)\u003c/span\u003e\u003c/span\u003e) is considerably higher than those of PtPd/ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs and Pt/C (6.62 \u0026#119898;\u0026#119860;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{mg}_{PtPd}^{-1}\\)\u003c/span\u003e\u003c/span\u003e and 4.37 \u0026#119898;\u0026#119860;\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{mg}_{Pt}^{-1}\\)\u003c/span\u003e\u003c/span\u003e, respectively). In addition, the onset voltage of MOR on PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs is 0.36 V, while on PtPd/ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs and Pt/C it is increased 0.46 and 0.54 V, respectively, in the positive (forward) half cycle of the scan. This indicates that sulfating ZrO\u003csub\u003e2\u003c/sub\u003e results in increased electrocatalytic activity and stability for MOR on PtPd/S-ZrO\u003csub\u003e2\u003c/sub\u003e-GNPs compared to the other two electrocatalysts.\u003c/p\u003e\u003cp\u003eThe relatively larger \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{I}_{forward}/{I}_{backward}\\:\\)\u003c/span\u003e\u003c/span\u003e ratio obtained for MOR on PtPd/S-ZrO₂-GNPs, i.e., 1.78 vs. 1.24 and 1.11 on PtPd/ZrO₂-GNPs and Pt/C, respectively, suggests that methanol molecules undergo efficient oxidation on PtPd/S-ZrO₂-GNPs during the positive (forward) half-cycle of the CV, producing relatively fewer poisoning species than those on PtPd/ZrO₂-GNPs and Pt/C. This improved performance can be attributed to the synergistic effects of the PtPd and ZrO₂ nanoparticles, as well as the mixed-conducting nature of PtPd/S-ZrO₂-GNP, which enhances electron and proton transport in the anode catalyst layer. As a result, the MOR performance of the PtPd/S-ZrO₂-GNP electrode is superior to those of the PtPd/ZrO₂-GNP and Pt/C electrodes. Additionally, the larger ECSA value of PtPd/S-ZrO₂-GNP is attributed to its increased hydrophilic character and proton conductivity.\u003c/p\u003e\u003cp\u003eThe transport behavior of methanol in the solution in the vicinity of the nanocomposite electrocatalyst is investigated by carrying out CV at various scan rates (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b)). It can be observed in this figure that as the scan rate increases, the peak current density of methanol oxidation increases significantly, from ~\u0026thinsp;4.6 mA/cm\u0026sup2; at 10 mV/s to 9.8 mA/cm\u0026sup2; at 100 mV/s, while the peak potentials increase more slightly, i.e., from 0.64 V at 10 mV/s to 0.7 V at 100 mV/s. The inset in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b) indicates that the anodic peak current densities have a more or less proportional relationship with the square root of the scan rate, which reveals, according to the Randles\u0026ndash;Ševč\u0026iacute;k equation, that the electrocatalytic oxidation of methanol is predominantly a diffusion-controlled process \u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThroughout the MOR, the main intermediate causing poisoning of the electrode surface is CO. Therefore, an excellent electrocatalyst for MOR should have a high capability for CO electrooxidation with increased tolerance, as determined by the voltammetry of CO stripping. An electrocatalyst with a greater ability to oxidize CO and greater tolerance to CO poisoning can oxidize it more efficiently at lower potentials.\u003c/p\u003e\u003cp\u003eThe voltammograms of CO stripping on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes, obtained through the electrooxidation of pre-adsorbed CO, are illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. It can be seen in this figure that the peak and onset potentials for CO electrooxidation on the two electrocatalysts containing ZrO₂ are significantly different from those of the original PtPd electrocatalyst. The CO stripping analysis also indicates that the onset potential of CO electrooxidation on PtPd/S-ZrO₂-GNPs is 0.54 V, which is about 0.03 and 0.28 V lower than those observed for the PtPd/ZrO₂-GNP and Pt/C electrodes, respectively. This denotes the efficient performance of the sulfated ZrO₂-GNPs component for CO electrooxidation. The peak potential of CO electrooxidation on PtPd/S-ZrO₂-GNPs is 0.71 V, which is 0.02 and 0.22 V lower than those of PtPd/ZrO₂-GNPs and Pt/C, respectively. Furthermore, the electrooxidation peak current of the CO_ads species on PtPd/S-ZrO₂-GNPs is ~\u0026thinsp;0.84 mA, which is significantly higher than those of PtPd/ZrO₂-GNPs and Pt/C (i.e., 0.67 and 0.64 mA). This indicates that the PtPd/S-ZrO₂-GNP electrode is relatively more tolerant to CO poisoning than the PtPd/ZrO₂-GNPs and Pt/C electrodes.\u003c/p\u003e\u003cp\u003eThe peak charge density \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{Q}_{CO}\\)\u003c/span\u003e\u003c/span\u003e (mC cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) is used to calculate the electroactive surface area (ESA) of the electrocatalyst, via:\u003cdiv id=\"Equb\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equb\" name=\"EquationSource\"\u003e\n$$\\:{ESA}_{CO}=\\frac{{Q}_{CO}}{0.484\\times\\:{L}_{Pt}}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(1\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn this equation, the factor 0.484 (mC cm⁻\u0026sup2;) is the charge density required to oxidize a monolayer of CO on bright Pt \u003csup\u003e54,55\u003c/sup\u003e. The peak charge density \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{Q}_{CO}\\)\u003c/span\u003e\u003c/span\u003e corresponds to the following CO oxidation reaction:\u003cdiv id=\"Equc\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equc\" name=\"EquationSource\"\u003e\n$$\\:Pt-CO+{H}_{2}O\\to\\:Pt+{CO}_{2}+2{H}^{+}+\\:2{e}^{-}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(2\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe ESA\u003csub\u003eCO\u003c/sub\u003e values of the PtPd/S-ZrO₂-GNP, PtPd/ZrO₂-GNPs, and Pt/C electrodes are calculated to be 42.56, 35.50, and 12.99 m\u0026sup2; g⁻\u0026sup1;, respectively. Due to its greater ESA\u003csub\u003eCO\u003c/sub\u003e, the PtPd/S-ZrO₂-GNP electrocatalyst utilizes the Pt component more efficiently and exhibits higher activity in CO oxidation. The presence of SO₄\u0026sup2;⁻ groups on the ZrO₂ surface increases its hydrophilicity and facilitates the adsorption of additional dissociative hydroxyl groups of H₂O on the solid superacid, which in turn enhances the conversion of CO_ads to CO₂ via a bifunctional mechanism \u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e,\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. This allows easier and faster regeneration of active sites on PtPd for further electrochemical reactions. Furthermore, the improved CO tolerance observed for PtPd/S-ZrO₂-GNP and PtPd/ZrO₂-GNP electrodes, compared to the Pt/C electrode, is attributed to various structural changes caused by alloying, as well as electronic (increased Pt d-band vacancy) and geometric (decreased Pt\u0026ndash;Pt bond distance) factors \u003csup\u003e\u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e,\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec20\" class=\"Section3\"\u003e\u003ch2\u003e3.2.3. Linear sweep voltammetry analysis\u003c/h2\u003e\u003cp\u003eLinear sweep voltammograms and corresponding Tafel plots are obtained for methanol oxidation on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes in a 1 M KOH\u0026thinsp;+\u0026thinsp;1 M CH₃OH solution at a scan rate of 5 mV s⁻\u0026sup1; (Figs.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a) and 7(b)). It is observed that the activity of the PtPd/S-ZrO₂-GNPs electrode is higher than that of the PtPd/ZrO₂-GNPs and Pt/C electrodes for methanol electro-oxidation. The electrocatalytic activity of the PtPd/ZrO₂-GNPs electrode is improved by sulfating the ZrO₂. Anodic electrooxidation reactions carried out on the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and Pt/C electrodes show Tafel slopes (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b)) of approximately 251, 192, and 117 mV/dec, respectively, which are consistent with literature. \u003csup\u003e47,58\u003c/sup\u003e. In addition, similar shapes of the linear sweep voltammograms and Tafel plots obtained for the two catalysts, shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, may suggest comparable electrochemical kinetics, as indicated in \u003csup\u003e47,58\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec21\" class=\"Section3\"\u003e\u003ch2\u003e3.2.4. Reaction mechanism\u003c/h2\u003e\u003cp\u003eIt is well established that incorporating Pd into Pt catalysts significantly reduces the overpotential for methanol electro-oxidation by enabling a bifunctional mechanism as described by the following reactions \u003csup\u003e\u003cspan additionalcitationids=\"CR60\" citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e:\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt+\\left(C{H}_{3}OH\\right)bulk\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt-{\\left(C{H}_{3}OH\\right)}_{ad}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(3)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt-{\\left(C{H}_{3}OH\\right)}_{ad}\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt-C{O}_{ad}+\\:{4H}^{+}+4{e}^{-}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(4)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pd+{H}_{2}O\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pd-({H}_{2}{O)}_{ad}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(5)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pd-({H}_{2}{O)}_{ad}\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pd-({OH)}_{ad}+\\:{H}^{+}+{e}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(6)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt-{CO}_{ad}+Pd-({OH)}_{ad}\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt+Pd+C{O}_{2}+\\:{H}^{+}+{e}^{-}\\:\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(7)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIn this mechanism, Pt primarily adsorbs methanol molecules, which undergo dehydrogenation to form strongly adsorbed CO intermediates that tend to poison the catalyst surface (Reactions 3 and 4). Meanwhile, Pd sites promote the adsorption and dissociation of water at lower potentials, generating reactive hydroxyl (OH) species (Reactions 5 and 6). These Pd-bound hydroxyl species subsequently oxidize the CO adsorbed on neighboring Pt sites to CO₂ (Reaction 7), thereby removing poisoning intermediates and maintaining catalytic activity. The close spatial proximity of Pt and Pd active sites is essential, as it facilitates efficient transfer of OH species from Pd to Pt-bound CO, improving CO oxidation kinetics and reducing the overall overpotential for methanol oxidation.\u003c/p\u003e\u003cp\u003eThe role of S-ZrO₂ in promoting the activity of the PtPd/S-ZrO₂-GNP electrocatalyst can be explained by the mechanism previously proposed for the MOR on Pt/ZrO₂-GNPs, summarized in the following reactions \u003csup\u003e\u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e:\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e\u003ccolgroup cols=\"2\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt+C{H}_{3}OH\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt-{CO}_{ad}+4\\:{H}^{+}+4{e}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(8)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt+{H}_{2}O\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt-{OH}_{ad}+\\:{H}^{+}+{e}^{-}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(9)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Zr{O}_{2}+{H}_{2}O\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Zr{O}_{2}-{OH}_{ad}+\\:{H}^{+}+{e}^{-}\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(10)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt-{CO}_{ad}+Pt-{OH}_{ad}\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:2Pt+C{O}_{2}+\\:{H}^{+}+{e}^{-}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(11)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:Pt-{CO}_{ad}+Zr{O}_{2}-{OH}_{ad}\\:\\underrightarrow{\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:}\\:Pt+Zr{O}_{2}+C{O}_{2}+\\:{H}^{+}+{e}^{-}\\:\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e(12)\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eIt is well known that a catalyst for methanol oxidation must be capable of breaking both C\u0026ndash;H and O\u0026ndash;H bonds and facilitating the reaction of the resulting intermediates with oxygen-containing species to form CO₂ \u003csup\u003e63\u003c/sup\u003e. In this mechanism, the initially adsorbed methanol molecules are dehydrogenated on Pt sites, resulting in the formation of strongly adsorbed CO intermediates that poison the Pt surface and inhibit its catalytic activity (Reaction 8). To remove these intermediates, hydroxyl (OH) species are essential. These can be generated on Pt (Reaction 9) and also on the ZrO₂ support (Reaction 10), which, due to its reducible nature, surface oxygen vacancies, and Br\u0026oslash;nsted acidity, can dissociate water even at relatively low potentials \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e. The generated OH species are then involved in the oxidative removal of CO. The reaction between Pt\u0026ndash;CO\u003csub\u003eads\u003c/sub\u003e and Pt\u0026ndash;OH\u003csub\u003eads\u003c/sub\u003e results in CO₂ formation and regeneration of the active Pt sites (Reaction 11). Additionally, OH groups formed on ZrO₂ can directly oxidize adjacent Pt\u0026ndash;CO species at the Pt\u0026ndash;ZrO₂ interface (Reaction 12).\u003c/p\u003e\u003cp\u003eThe importance of surface oxygen species for effective CO oxidation at lower potentials in DMFC electrocatalysts has been well established, particularly in the case of cobalt oxides [65] and other supports \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e. ZrO₂ is a widely studied reducible oxide that exhibits a high oxygen storage capacity and strong metal\u0026ndash;support interaction with noble metals such as Pt \u003csup\u003e29\u0026ndash;31,48\u003c/sup\u003e. These properties make it an effective promoter in electrocatalysis.\u003c/p\u003e\u003cp\u003eAccordingly, the following interfacial reaction can be proposed for the methanol electro-oxidation on the PtPd/S-ZrO₂-GNP electrode:\u003cdiv id=\"Equd\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equd\" name=\"EquationSource\"\u003e\n$$\\:PtPd\\bullet\\:\\bullet\\:\\bullet\\:S-Zr{O}_{2}\\left(interface\\right)+xCO\\to\\:PtPd\\bullet\\:\\bullet\\:\\bullet\\:S-Zr{O}_{2-x}\\left(interface\\right)+xC{O}_{2}\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\:\\left(13\\right)$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e\u003cp\u003eThe enhancement of methanol oxidation activity can be primarily attributed to the catalytic synergy at the PtPd‧‧‧S-ZrO₂ interface. The presence of S-ZrO₂ facilitates water adsorption and dissociation at lower potentials, generating reactive oxygen species directly at the metal\u0026ndash;support boundary. These oxygen species participate in the oxidation of CO intermediates adsorbed on PtPd, effectively removing poisoning species and regenerating active sites \u003csup\u003e\u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e\u003c/sup\u003e. This interfacial reactivity reduces the anodic overpotential and enhances the overall electrocatalytic performance of the PtPd/S-ZrO₂-GNP catalyst.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec22\" class=\"Section3\"\u003e\u003ch2\u003e3.2.5. Short term stability\u003c/h2\u003e\u003cp\u003eCV analysis was also used to examine the stability of each electrode in 0.5 M H₂SO₄ saturated with N₂. The potential sweep was performed at a scan rate of 50 mV s⁻\u0026sup1; from \u0026minus;\u0026thinsp;0.24 to 1.2 V vs. Ag/AgCl (saturated). Figures\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a) to 8(c) display the CV curves obtained for all three electrodes after 1500 continuous potential scan cycles. ECSA loss was observed for both catalysts during potential cycling, likely due to Pt dissolution or agglomeration. The results indicate that the PtPd/S-ZrO₂-GNPs electrode is more electrochemically stable than the PtPd/ZrO₂-GNPs and Pt/C electrodes.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eChronoamperometric measurements are also conducted to evaluate stability and possible poisoning of the nanocomposite electrocatalysts during short-term continuous operation in 0.5 M H₂SO₄ and 1 M CH₃OH at 0.4 V (Fig. S5). According to this figure, the current density of the PtPd/S-ZrO₂-GNPs, PtPd/ZrO₂-GNPs, and commercial Pt/C electrodes decays rapidly at the beginning of the operation. This may be due to the formation of intermediate species such as CO_ads and CH_ads during the methanol oxidation process. After a short transient period, the current gradually stabilizes. Also, the current density of the PtPd/S-ZrO₂-GNPs electrode is significantly higher than that of the PtPd/ZrO₂-GNPs and Pt/C electrodes over a longer period of time, indicating that the application of sulfated ZrO₂ (S-ZrO₂) on the graphene support enhances the electrocatalytic activity and stability of the nanocomposite. These results, once again, demonstrate the high tolerance for intermediate species and superior electrocatalytic performance of the prepared PtPd/S-ZrO₂-GNPs composite catalyst in the MOR.\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Sec23\" class=\"Section2\"\u003e\u003ch2\u003e3.3. First-principal computations\u003c/h2\u003e\u003cdiv id=\"Sec24\" class=\"Section3\"\u003e\u003ch2\u003e3.3.1. Structural characteristics\u003c/h2\u003e\u003cp\u003eThe optimized crystal structures of ZrO₁.₃₃S₀.₆₇ and PtPd₁.₆₇ are shown along different lattice planes in Figs.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a) to 9(c). The DFT-optimized cell volumes, lattice parameters, and interatomic distances of the pristine and modified structures are reported in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e. The DFT computational data obtained for the pristine materials (i.e., ZrO₂ and Pt) agree with those reported in the literature \u003csup\u003e\u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e,\u003cspan citationid=\"CR66\" class=\"CitationRef\"\u003e66\u003c/span\u003e\u003c/sup\u003e. As a result of structural modifications, the cell parameters and interatomic distances of the modified materials differ from those of the pristine lattices. The equilibrium cell volume of the ZrO₂ supercell increases from 404.0 to 540.5 \u0026Aring;\u0026sup3; by replacing 8 oxygen atoms in the ZrO₂ lattice with S atoms. This partial replacement results in an increase in the Zr\u0026ndash;O interatomic distance, which expands the lattice parameters and consequently the surface area of the nanostructure. This facilitates the accommodation of the PtPd catalyst on the S-ZrO₂ surface. Conversely, by partially replacing Pt with Pd in the Pt lattice, the Pt\u0026ndash;Pt interatomic distance decreases, reducing the cell volume from 148.54 to 137.04 \u0026Aring;\u0026sup3;.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e\u003ccaption language=\"En\"\u003e\u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\u003cdiv class=\"CaptionContent\"\u003e\u003cp\u003eThe DFT-optimized equilibrium lattice parameters, cell volumes, and inter-atomic distances of the S-ZrO2 (ZrO1.33S0.67), ZrO2, PtPd1.67, Pt, and graphene lattices for their supercells of 1\u0026times;1\u0026times;3, 1\u0026times;1\u0026times;3, 1\u0026times;1\u0026times;2, 1\u0026times;1\u0026times;2, and 2\u0026times;1\u0026times;1 unit cells, respectively.\u003c/p\u003e\u003c/div\u003e\u003c/caption\u003e\u003ccolgroup cols=\"11\"\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e\u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e\u003cthead\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eLattice\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"6\" nameend=\"c7\" namest=\"c2\"\u003e\u003cp\u003eLattice parameters\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e\u003cp\u003eCell volume (\u0026Aring;\u003csup\u003e3\u003c/sup\u003e)\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"3\" nameend=\"c11\" namest=\"c9\"\u003e\u003cp\u003eInter-atomic distances (\u0026Aring;)\u003c/p\u003e\u003c/th\u003e\u003c/tr\u003e\u003ctr\u003e\u003cth align=\"left\" colname=\"c2\"\u003e\u003cp\u003ea\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c3\"\u003e\u003cp\u003eb\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c4\"\u003e\u003cp\u003ec\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c5\"\u003e\u003cp\u003eα\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c6\"\u003e\u003cp\u003eβ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colname=\"c7\"\u003e\u003cp\u003eγ\u003c/p\u003e\u003c/th\u003e\u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e\u0026nbsp;\u003c/th\u003e\u003cth align=\"left\" colspan=\"1\" nameend=\"c11\" namest=\"c11\"\u003e\u0026nbsp;\u003c/th\u003e\u003c/tr\u003e\u003c/thead\u003e\u003ctbody\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eS-ZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003cp\u003e(ZrO\u003csub\u003e1.33\u003c/sub\u003eS\u003csub\u003e0.67\u003c/sub\u003e)\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.6881\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.7644\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e17.1787\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e73.65\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e540.50\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eZr-O\u003c/p\u003e\u003cp\u003eZr-S\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2.27\u003c/p\u003e\u003cp\u003e2.63\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eZrO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e5.1257\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e5.1257\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e15.3773\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e404.02\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eZr-O\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2.22\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePtPd\u003csub\u003e1.67\u003c/sub\u003e\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.0911\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4.0926\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8.1846\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e137.04\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003ePt-Pt\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2.91\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003ePt\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.2034\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e4.2034\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e8.4068\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e148.54\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003ePt-Pt\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e2.98\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003ctr\u003e\u003ctd align=\"left\" colname=\"c1\"\u003e\u003cp\u003eGraphene\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c2\"\u003e\u003cp\u003e4.9502\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c3\"\u003e\u003cp\u003e2.4748\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c4\"\u003e\u003cp\u003e-\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c5\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c6\"\u003e\u003cp\u003e90\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c7\"\u003e\u003cp\u003e120\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c8\"\u003e\u003cp\u003e210.98\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colname=\"c9\"\u003e\u003cp\u003eC-C\u003c/p\u003e\u003c/td\u003e\u003ctd align=\"left\" colspan=\"2\" nameend=\"c11\" namest=\"c10\"\u003e\u003cp\u003e1.43\u003c/p\u003e\u003c/td\u003e\u003c/tr\u003e\u003c/tbody\u003e\u003c/colgroup\u003e\u003c/table\u003e\u003c/div\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec25\" class=\"Section3\"\u003e\u003ch2\u003e3.3.2. Electronic properties\u003c/h2\u003e\u003cp\u003eThe total DOS and band structure of graphene obtained by DFT computations are plotted in Fig. S6 of the Supplementary Information for validation. The calculated electronic properties of graphene are in agreement with the results reported in the literature \u003csup\u003e\u003cspan citationid=\"CR67\" class=\"CitationRef\"\u003e67\u003c/span\u003e,\u003cspan citationid=\"CR68\" class=\"CitationRef\"\u003e68\u003c/span\u003e\u003c/sup\u003e. The apparently extra bands appearing in the calculated band structure diagram of Fig. S6 are due to the use of the 2\u0026times;1\u0026times;1 supercell in this work (instead of the 1\u0026times;1\u0026times;1 unit cell used for obtaining the band structure diagrams reported in the literature).\u003c/p\u003e\u003cp\u003eThe band structures and the total and partial DOSs calculated for the pristine (pure) Pt and PtPd₁.₆₇ alloy lattices are shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a) and 10(b).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAccording to Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the valence and conduction bands overlap at the Fermi level for both the PtPd₁.₆₇ alloy and Pt, implying that both structures are electrical conductors, i.e., metals. The band structures of Pt and PtPd₁.₆₇ are similar in some aspects. The band structure of PtPd₁.₆₇ is denser, especially near the Fermi level, due to the shift in the local (core) Pt levels and the splitting of the bonding electronic levels caused by the introduction of Pd into the Pt lattice. It can be seen in the DOS diagram of Pt (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a)) that the density of states of the spin-up and spin-down channels are equal over the entire energy range. This denotes the non-magnetic nature of pure Pt. In contrast, for the PtPd₁.₆₇ alloy, the spin-up and spin-down densities of states are not symmetric, especially near the Fermi level. This asymmetry denotes the magnetic nature of this alloy. Also, the asymmetry of the calculated elemental PDOSs shows that both Pt and Pd contribute to the magnetic properties of this alloy. As reported for the magnetic CoPt alloy, the magnetic field can lower the activation barrier and facilitate the dehydrogenation of methanol, resulting in enhanced MOR electrocatalytic performance \u003csup\u003e\u003cspan citationid=\"CR69\" class=\"CitationRef\"\u003e69\u003c/span\u003e\u003c/sup\u003e, It can be expected that the application of a magnetic field may improve the performance of the prepared PtPd/S-ZrO₂-GNP electrocatalyst due to the magnetic nature of the Pt/Pd alloy.\u003c/p\u003e\u003cp\u003eElectronic band structures and the corresponding total and partial DOSs for the pristine and sulfur-treated ZrO₂ (i.e., ZrO₂ and S-ZrO₂) are also calculated by DFT computations, and the results are illustrated in Figs.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e(a) and 11(b), respectively. According to Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, the band structures of these two materials are distinctly different. For example, the ZrO₂ band structure shows a direct band gap value of 2.28 eV at the B point, indicating the semiconductor character of ZrO₂. In contrast, this band gap is reduced to 0.91 eV for the S-ZrO₂ (ZrO₁.₃₃S₀.₆₇). This discrepancy can be attributed to the distinctly different natures of the Zr-S and Zr-O bonds \u003csup\u003e\u003cspan citationid=\"CR70\" class=\"CitationRef\"\u003e70\u003c/span\u003e,\u003cspan citationid=\"CR71\" class=\"CitationRef\"\u003e71\u003c/span\u003e\u003c/sup\u003e. Furthermore, Idrissi et al. \u003csup\u003e71\u003c/sup\u003e reported that sulfur doping of the ZrO₂ structure decreases the band gap of pure ZrO₂. The perfect symmetry of the spin-up and spin-down states in the PDOS diagrams of both pristine ZrO₂ and sulfur-treated ZrO₂ implies their non-magnetic nature. Analysis of the total DOS and elemental partial DOS (contributions of the orbitals of Zr, O, and S to the total DOS) indicates that the O-p and S-p orbitals contribute to the valence band, while the Zr-d orbitals mainly contribute to the conduction band. Overall, it is observed that introducing sulfur into the ZrO₂ structure changes its charge transfer efficiency, which boosts the catalytic activity of ZrO₂ towards MOR.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eHigh-density GNPs were prepared by modifying the Hummers and Offeman method. Additionally, a chemical method was used to introduce sulfonic acid groups onto the surface of ZrO₂-GNPs, resulting in the successful preparation of S-ZrO₂-GNPs. A PtPd/S-ZrO₂-GNP-modified GC electrode was successfully constructed using the polyol synthesis method, exhibiting superior physical and electrochemical properties relative to the pure PtPd alloy and the unsulfated electrocatalyst PtPd/ZrO₂-GNP. These properties include successful dispersion of catalyst nanoparticles on the support, a lower CO electro-oxidation peak potential (0.71 V vs. 0.74 V and 0.93 V), and a much higher methanol electro-oxidation current density compared to the PtPd/ZrO₂-GNPs and commercial Pt/C electrodes. The onset and peak potentials of methanol electro-oxidation were significantly reduced, respectively, from 0.54 V and 0.81 V for Pt/C to 0.36 V and 0.67 V for the PtPd/S-ZrO₂-GNP electrode. In addition, a considerable increase is observed in the anodic Tafel slope, from 117 mV to 251 mV, indicating an increase in MOR activity due to PtPd alloying and the replacement of C/ZrO₂-GNPs with S-ZrO₂-GNPs. The higher electrochemical activity of the prepared PtPd/S-ZrO₂-GNPs electrode can be attributed to the reduced CO poisoning of the platinum-palladium surface by sulfated ZrO₂-GNP. Analyses of the DFT-optimized structures and their corresponding band structures and DOSs obtained for the pristine and partly S/O replaced bulk ZrO₂ indicate that the inter-atomic distances increase and the band gap is reduced as a result of S/O replacement. These findings suggest that PtPd/S-ZrO₂-GNPs is a promising electrocatalyst to be applied as an anode material, providing greater MOR activity and elevated CO tolerance in higher-performance DMFCs.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eConflict of Interest\u003c/h2\u003e\u003cp\u003eThere are no conflicts of interest to declare.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eSupplementary Information\u003c/h2\u003e\u003cp\u003eThis article included a supplementary Information file.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding information\u003c/h2\u003e\u003cp\u003eThere was a no funding for this research.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eMaryam Yaldagard: Conceptualization, Methodology, Validation, Investigation, Formal analysis, Data curation, Writing-original draft. Mina Sedighi: Methodology, Software, Investigation, Formal analysis, Data curation, Writing - original draft, Writing - review \u0026amp; editing. Hassan Sabzyan: Investigation, Formal analysis, Validation, Writing - review \u0026amp; editing.\u003c/p\u003e\u003ch2\u003eAcknowledgement:\u003c/h2\u003e\u003cp\u003eThis work was supported by Hydrogen and Fuel Cell Research Institute, Urmia University, Urmia, Iran, which is acknowledged here by the authors.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003e\"The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.\"\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHogarth, M. \u0026amp; Hards, G. Direct methanol fuel cells. \u003cem\u003ePlatinum Met. 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Sulfur doping effect on the electronic properties of zirconium dioxide ZrO2. \u003cem\u003eMater. Sci. Engineering: B\u003c/em\u003e. \u003cb\u003e270\u003c/b\u003e, 115200. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.mseb.2021.115200\u003c/span\u003e\u003cspan address=\"10.1016/j.mseb.2021.115200\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e (2021).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e "}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Methanol electro-oxidation, PtPd, graphene nanoplate (GNP), sulfated-ZrO2 (S-ZrO2), direct methanol fuel cell (DMFC), Density functional theory (DFT)","lastPublishedDoi":"10.21203/rs.3.rs-7637410/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7637410/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this study, graphene nanoplates (GNPs) are coated with sulfated zirconia (S-ZrO₂) to enhance the proton conductivity of the support and improve the electrochemical activity and stability of the platinum-palladium (PtPd) catalyst. The carbon monoxide (CO) tolerance and electrocatalytic activity of the prepared PtPd/S-ZrO₂-GNP electrocatalyst are evaluated for the methanol oxidation reaction (MOR). The electrocatalyst shows a reduction in the CO oxidation peak voltage (0.71 V vs. 0.93 V for Pt/C). PtPd/S-ZrO₂-GNPs exhibit higher catalytic activity for MOR compared to Pt/ZrO₂-GNPs and Pt/C, with electrochemical surface area (ECSA) values of 87.24, 69.36, and 54.91 m\u0026sup2;\u0026middot;g_pt⁻\u0026sup1;, respectively. This enhancement is attributed to Pt/Pd alloying, the high surface area of GNPs, and sulfated ZrO₂. Tafel slope analysis also indicates higher MOR activity for PtPd/S-ZrO₂-GNPs. First-principles computations reveal that the magnetic nature of PtPd, the increased cell volume of S-ZrO₂, and improved charge transfer efficiency are responsible for boosting the electrocatalytic activity of PtPd/S-ZrO₂-GNPs towards MOR.\u003c/p\u003e","manuscriptTitle":"Improved electrocatalytic activity and stability of PtPd/graphene nanoplates using sulfated zirconia for methanol electro-oxidation in DMFCs: An experimental and computational study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-04 11:40:12","doi":"10.21203/rs.3.rs-7637410/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"53aff586-a60d-45e4-b989-ac00075745c0","owner":[],"postedDate":"November 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":56816321,"name":"Physical sciences/Chemistry"},{"id":56816322,"name":"Physical sciences/Energy science and technology"},{"id":56816323,"name":"Physical sciences/Materials science"},{"id":56816324,"name":"Physical sciences/Nanoscience and technology"}],"tags":[],"updatedAt":"2025-11-27T09:53:15+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-04 11:40:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7637410","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7637410","identity":"rs-7637410","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}