The Use of C-MnO 2 as Hybrid Precursor Support for a Pt / CMn x O 1 + x Catalyst with Enhanced Activity for the Methanol Oxidation Reaction ( MOR )

Platinum (Pt) nanoparticles are deposited on a hybrid support (C-MnO2) according to a polyol method. The home-made catalyst, resulted as Pt/C-MnxO1+x, is compared with two different commercial platinum based materials (Pt/C and PtRu/C). The synthesized catalyst is characterized by means of FESEM, XRD, ICP-MS, XPS and μRS analyses. MnO2 is synthesized and deposited over a commercial grade of carbon (Vulcan XC72) by facile reduction of potassium permanganate in acidic solution. Pt nanoparticles are synthesized on the hybrid support by a polyol thermal assisted method (microwave irradiation), followed by an annealing at 600 °C. The obtained catalyst displays a support constituted by a mixture of manganese oxides (Mn2O3 and Mn3O4) with a Pt loading of 19 wt. %. The electro-catalytic activity towards MOR is assessed by RDE in acid conditions (0.5 M H2SO4), evaluating the ability to oxidize methanol in 1 M concentration. The synthesized Pt/C-MnxO1+x catalyst shows good activity as well as good stability compared to the commercial Pt/C based catalyst.


Introduction
Fuel cells are electrochemical devices that produce electricity from the energy of a fuel through a highly efficient conversion process, resulting in low emissions and low environmental impact [1].Between the different types of fuel cell, Direct Alcohol Fuel Cells (DAFC) and more specifically, Direct Methanol Fuel Cells (DMFC), represent a valid alternative for small portable electronic devices and auxiliary power units, due to the high energy density of alcohols, their lightweight and compact nature and their ability for fast recharging [2,3].
Platinum is the most widely used catalyst for both the anodic methanol oxidation reaction (MOR) and the cathodic oxygen reduction reaction (ORR) [4,5].Pt is considered the most suitable electro-catalyst for MOR due to its high activity and stability, especially in acidic media [6].However, one of the main barriers to the commercialization of DMFC technologies is still the high cost of Pt.To reduce the cost, an improvement of the performance of conventional Pt-based catalysts is necessary.This would lead to a reduction of the total Pt loading on the electrode.For this purpose, reaction rates need to be enhanced (i.e., the overvoltage needs to be decreased) by modifying the catalyst composition or structure, to produce a more active electro-catalytic material [7].
A common approach to enhance the activity of Pt involves well dispersed nanoparticle structures, avoiding agglomeration and increasing utilization [7].Further optimization of Pt-based electro-catalysts has been achieved through the formation of bi-metallic alloys such as PtCo and PtNi (for cathodic ORR) and PtRu (for anodic MOR) [8,9].It has also been demonstrated that efficiency can be further improved by promotion of methanol electro-oxidation by means of various metal oxides-, carbidesand nitrides-promoted electro-catalysts.Non-noble metal oxides (M-Ox) such as WO3, CeO2, V2O5, Nb2O5, MoOx, ZrO2, TiO2, MgO and MnO2, exhibit suitable surface properties which can efficiently promote the methanol and ethanol electro-oxidation reactions combined with Pt/C [10].Therefore, a good strategy to improve the catalytic activity of Pt-based catalysts for MOR is to use metal oxides in the catalyst supports, as a hybrid structure (C + M-Ox) [11].Pure Pt, in fact, is readily poisoned by strongly-adsorbed intermediates, of which CO is consistently considered as one of the main poisoning species at low operating temperature [12].
The use of metal oxide-containing Pt/C electro-catalysts has been reported to effectively enhance the electro-oxidation of methanol by the spillover of CO on Pt sites to the adjacent metal oxides.These oxides are supposedly capable of adsorbing large quantities of -OH species, which are then donated to the neighboring Pt sites where stepwise methanol dehydrogenation occurs.Metal oxides also provide suitable functional groups which strongly interact with small Pt crystallites, impeding their random growth and agglomeration during device operation for longer duration.In particular, high surface area metal oxides used as supports or matrices, are capable of physically separating metal particles (to diminish their tendency to undergo degradation by agglomeration) and of interacting mutually with them, thus affecting their chemisorptive and catalytic properties.Oxides are often thought as insulating or semi-conducting materials but certain non-stoichiometric oxides existing in various valance states exhibit conductivity not much lower than that of metals and possess appreciable catalytic activity [7].In electro-catalysis, the reactions occur at the interface, so surface reactivity is very important.Redox reactions of metal oxides involve both ion and electron transfer processes.The electron transfer reactions are influenced by the distribution of electronic states in the electrolyte and within the oxide.When oxides are in contact with aqueous solutions, their surfaces are covered with -OH groups; their actual population depends on the nature of the oxide and its specific crystal face.Some metal oxides are more hydrous than the others.The hydrous behavior, which varies from oxide to oxide, favors proton mobility and affects overall reactivity [7].
MnO2 has been used in a wide range of applications such as catalyst, molecular-sieves, ion-sieves, batteries and magnetic materials due to its excellent physicochemical properties [13].Manganese oxides were widely used as catalyst support for fuel cells due to their promoting effects in the oxidation of small organic molecules, such as the excellent proton conductivity, the increase of catalyst utilization and the synergistic effect between catalysts and manganese oxides [6].In particular, MnO2 possesses good proton-electron intercalation properties and is known to show good electro-chemical properties under various operating conditions [10].Mn possesses a wide range of oxidation states and such oxo-manganese species are generally strong chemical oxidants.Due to the possibility of the Mn 4+ /Mn 3+ redox couple and the presence of labile oxygen, MnO2 shows high promoting and anti-poisoning activities for alcohol electro-oxidation [7].The main reasons for effectiveness of MnO2 as a promoter are attributed to its surface area, tunnel structure and crystal phase.It is known that oxides with one-dimensional structures such as nanorods, nanowires and nanotubes possess distinctive crystalline phase states, as compared to their bulk counterparts [10].It is also known that the interaction between metal crystallites and an oxide surface is influenced by the nature of interfacial contact and the crystalline characteristic of the oxide.MnO2 with smaller and uniform crystalline orientation as well as suitable surface morphology should offer apposite active sites for facile interaction with Pt crystallites, which can provide optimized synergistic effect for alcohol electro-oxidation [14].However, the effect of microstructure/morphology of manganese oxides on the nature of Pt dispersion on MnxO1+x/carbon-based electrocatalysts has not been extensively investigated so far [10].
In this work, α-MnO2 was synthesized and deposited on a commercial carbon black (Vulcan XC-72).Then, Pt nanoparticles were deposited on the formed hybrid support (C-MnO2), called Pt/C-MnxO1+x, by a microwave-assisted polyol method followed by a thermal treatment in inert atmosphere at 600 °C.The synthesized catalyst was compared with two commercial Pt-based catalysts characterized and tested for MOR in acidic medium.

Physical-Chemical Characterization
The XRD pattern of the prepared C-MnO2 is given in Figure 1A.The broad peak at about 23.5° is attributed to the graphitic carbon support.All other peaks are clearly indexed to the pure tetragonal phase of α-MnO2 (JCPDS card #44-0141), with lattice constants of a = 9.73 Å and c = 2.84 Å.No peaks were observed for other types of crystals or amorphous MnO2 which confirmed the purity of the prepared sample.The intensive diffraction peaks appeared at 12.46°, 18.08°, 28.83°, 37.00°, 37.66°, 41.95°, 50.13°, 60.36°, 66.30°, 72.87°, respectively, which are characteristic peaks of α-MnO2 with the major peaks intensity at 18.08° [15,16].α-MnO2 is constructed from the double chains of edge-sharing MnO6 octahedra, which are linked at the corners to form tunnel structures [17].The morphology of prepared C-MnO2 was investigated by FESEM and the corresponding micrographs are shown in Figure 1B,C.MnO2 nanocrystals grow up on the carbon black, forming sphere-like micro-particles with an average diameter of about 1 μm (Figure 1B).At higher magnification (Figure 1C), the outside part of the particles appeared to be urchins, homogeneously composed of densely aligned nanorods with uniform diameter of about 35 nm.The percentage of MnO2 in the hybrid support evaluated by ICP-MS technique is 64.8 wt.%.This value is very close to the theoretical wt.% percentage of MnO2 expected for the adopted synthesis, which is equal to 68.4 wt.%.Thus, the synthesis method adopted allows a very precise control of the mass loading level of nanostructured MnO2 onto the carbon material by controlling the ratio between KMnO4 and Vulcan XC-72 carbon.
XRD patterns were acquired for all catalysts supported on carbon (Figure 2).X-ray spectra exhibited the characteristic peaks corresponding to the Pt face-centered cubic (fcc) polycrystalline structure (111, 200, 220 and 311 reflection planes), consistent with the XRD pattern of JCPDS card #00-4-0802 (2θ = 39.76°,46.24°, 67.45°, 81.28°).A signal near to 25° (2θ) was obtained, which corresponds to the (002) graphite basal planes for Pt/C and PtRu/C [18].This peak is not appreciable on Pt/C-MnxO1+x because of the high manganese oxides content.No metallic Ru diffraction peaks were detected in the commercial PtRu/C which is an indication of alloyed PtRu as reported in the literature [19].As can be seen in Figure 2, Pt diffraction peaks of the commercial PtRu/C shifted to a positive 2θ value compared with that of Pt/C which reveals alloy formation.Formation of solid solution between Pt and Ru by replacing of Pt with smaller Ru atoms in the lattice points of Pt fcc structure results in the reduction of lattice parameter and positive shift of fcc diffraction signals [20,21].It is well known that the alloying of Pt with Ru leads to a decrease in the interatomic bond length because of the smaller Ru atomic radius [22].
Particle diameters were calculated by the Debye-Scherrer equation for all catalyst used.1.7, 4.  The Mn 2p XPS spectrum in Figure 3A exhibited Mn 2p1/2 at 653.52 eV and Mn 2p3/2 at 641.71 eV, in which the spin-energy separation of 11.79 eV which indicates that the element manganese in the sample exists in the chemical state of Mn 2+ and Mn 4+ and therefore the formation of MnO2, Mn2O3 and Mn3O4 [23][24][25].As shown in Figure 3B, the Pt 4f spectrum of the Pt/C-MnxO1+x was deconvoluted into two doublet peaks, corresponding to a spin-orbit splitting of 4f7/2 and 4f5/2 states of ca.3.33 eV.The most intense doublet at 71.45 (4f7/2) and 74.78 eV (4f5/2) was due to the metallic Pt, corresponding to metallic platinum particles (Pt 0 ) [4,6,10,13,17].To assess the chemical structure of the Pt/C-MnxO1+x catalyst, an extra sample of MnO2 annealed at 600 °C (same temperature used to anchor Pt nanoparticles on the C-MnO2 support) was examined by μRS.Raman spectra in different points of the annealed oxide (Figure 4) show the presence of two types of oxides structure, the Mn3O4 hausmannite spinel-like and the Mn2O3 bixbyite.Specifically, five characteristic Raman peaks for the spinel structure [ν1 = 310 cm −1 , ν2 = 357 cm −1 , ν3 = 485 cm −1 , ν4 = 579 cm −1 , ν5 = 653 cm −1 ] and for the bixbyite [ν1 = 263 cm −1 , ν2 = 308 cm −1 , ν3 = 512 cm −1 , ν4 = 631 cm −1 , ν5 = 670 cm −1 ] were detected, suggesting the presence of a mix of oxides [26].In fact, according to the literature [27][28][29], in inert atmosphere at around 500 °C MnO2 is reduced to Mn2O3 and further reduced to Mn3O4 at 900 °C.These results are in line with the presence of the mixture of hausmannite and bixbyite manganese oxides on the final Pt/C-MnxO1+x catalyst, annealed at 600 °C in nitrogen atmosphere, as pointed out by XPS analysis.

Electro-Chemical Characterization
The CV profiles recorded in N2-saturated 0.5 M H2SO4 (Figure 5) exhibit defined regions of hydrogen underpotential, adsorption/desorption and platinum oxide formation/reduction for all the samples.In particular, the hydrogen adsorption/desorption peaks shapes are similar for the Pt/C-MnxO1+x and the commercial Pt/C, with the latter exhibiting a higher hydrogen desorption area.The electrochemical active surface area (ECSA) resulted 44.1 m 2 •g −1 for Pt/C-MnxO1+x and 45.4 m 2 •g −1 for Pt/C, respectively.For the PtRu/C catalyst the peak shape is different from the previous ones, with a sharper hydrogen desorption peak typical for the PtRu based catalysts [30,31] and ECSA of 69.8 m 2 •g −1 .Regarding the Pt oxides reduction peak, for the Pt/C-MnxO1+x it is shifted towards more positive potentials of about 100 mV in comparison with the commercial Pt/C catalyst.This could indicate a lower oxygen reduction overpotential if this catalyst should be used as a cathode catalyst for a PEMFC [32].Otherwise, for the PtRu/C catalyst, the same peak is about 200 mV shifted to more negative potentials.This is also typical for PtRu based catalysts [21].The similar ECSA values for the Pt/C-MnxO1+x and Pt/C catalysts could be due to the similar Pt content of these catalysts, equal to 19 wt.% and 20 wt.%, respectively, according to ICP-MS analysis, whereas the measured Pt content of PtRu/C was almost double compared to the other two catalysts.Moreover, the presence of a high amount of manganese oxides on the surface of Pt/C-MnxO1+x (see previous discussion on XPS and μRS) could result in a low electrical conductivity of the electrode [13,33,34].The onset potential of CO electro-oxidation, taken as the potential at which 5% of the maximum current was reached, was of 0.61, 0.59 and 0.54 V for the commercial Pt/C, the PtRu/C and the Pt/C-MnxO1+x catalysts, respectively (see Table 1).A negative shift of this onset potential indicates an enhanced catalytic activity for CO oxidation.This has been extensively reported for PtRu catalysts [18,20,21].In the case of Pt-transition metal oxide based catalysts this effect can also be observed [14].In particular, for our Pt/C-MnxO1+x catalyst, the onset potential is 70 mV lower than for the commercial Pt/C catalyst.Analyzing more in detail the CO stripping peak's shape, it can be observed that the commercial Pt/C peak has a symmetric shape, while the Pt/C-MnxO1+x catalyst exhibits a second lower and broader peak at higher potentials than the main peak.The presence of the double peak could be due to the presence of both Pt predominant crystal face or Pt agglomerates [37,38].In fact, the oxidation of a monolayer of CO is strongly influenced by the particle size of Pt.Pt agglomerates show a notable activity towards CO oxidation compared to isolated Pt particles.Moreover, the presence of the double peak for Pt/MnO2/C hybrid catalysts has been noticed by other authors as well [10,39].In fact, the CO stripping from the Pt surface in the presence of MnO2 occurs via a kind of synergic effect between the OHads on MnO2 and the COads on Pt [10].The double peak due to CO stripping from the Pt/C-MnxO1+x could be linked with the possible formation of labile OH species on the triple-phase interface between the Pt, the oxide and the electrolyte, which provides electronic suitability for the oxidation of CO species on the Pt surface [39].It has been demonstrated that MnO2 nanorods promoted Pt/C catalysts showed larger negative shift in the CO electro-oxidation peak potential due to OHads species on the MnO2 that tend to electronically weaken the Pt-CO bond and promote the oxidation of CO to CO2 [10].The presence of MnO2 in a MnO2-Pt/C composite electrode primarily plays a catalytic role in the ORR.It enhances the catalytic behavior of Pt for the ORR by substituting for oxygen as an electron-acceptor in the case of oxygen starvation [40].Furthermore, based on studies on Pt/Mn3O4-MWCNT [33], the Mn3O4 leads to uniform and small Pt nanoparticle deposition, with enhanced CO-tolerance and excellent stability in methanol oxidation.In fact, Mn3O4 nanoparticles promote the dissociation of coordinated water and further oxidize COads to release more Pt active sites [33].The hydrous Mn3O4 would use its inherent Mn3O4-OH bonds to directly donate the hydroxide species to the Pt sites and oxidize the adsorbed CO species [41].Mn3O4 is also known for favoring the growth of Pt nanoparticles with high index facets [33,42].Consequently, in our Pt/C-MnxO1+x catalyst, where a mix of manganese oxides is present, both mechanisms could be involved.The promotional CO stripping from the Pt surface in the presence of manganese oxides occurs via a type of synergic effect as reported in the literature [10,39].Overall, the following reaction mechanism can be assumed: The PtRu/C catalyst peak appears to be more asymmetric, with a broadening towards higher overpotentials.Thus, the presence of MnO2 on the surface of the carbon support causes a co-catalytic action which promotes the CO oxidation catalytic effect of Pt.
The electro-catalytic activity toward MOR of the three catalysts was investigated by cyclic voltammetry using a 0.5 M H2SO4 and 1.0 M MeOH solution as electrolyte (Figure 7).For all of the catalysts, the voltammograms exhibit two characteristics oxidation peaks.The first peak is observed during the anodic potential sweep and it is characteristic of the oxidation of methanol adsorbed on the Pt surface.This oxidation occurs in multiple steps, with the production of carboxyl intermediates and strongly adsorbed CO species, as discussed in the literature [43].Mainly formic acid and formaldehyde have been found during methanol oxidation on Pt surface, as intermediate products [44].With the potential increase, after the forward peak, the oxidation current decreases, due to the poisoning effect of the CO species strongly adsorbed on Pt and to the Pt oxides formation, which passivates the Pt surface [45].The second peak appears during the cathodic potential sweep (reverse scan) and it is attributed to the oxidation of adsorbed CO species and/or to the oxidation of further methanol on the Pt oxide surface formed during the anodic scan [10].During electro-oxidation of MeOH, strongly adsorbed carbonaceous species inhibit further adsorption of MeOH on the catalyst surface, which causes a positive shift in the onset potential and a decrease in the current at a specific potential.Therefore, the more the forward scan peak is shifted to negative potentials, the greater the promotion effect of the electro-catalyst [18].The forward peak potentials for the Pt/C-MnxO1+x, Pt/C and PtRu/C catalysts obtained from the CV are shown in Table 1.The value of the ratio between the forward peak maximum current density (If) and the backward peak maximum current density (Ib) is also shown in Table 1.The higher this If/Ib ratio is, the greater the electro-catalyst's resistance to poisoning is [46].Hence, the value of If/Ib can be viewed as an index of the tolerance of a catalyst to poisoning species, i.e., adsorbed CO molecules.From these results, it can be concluded that the Pt/C-MnxO1+x catalyst is a stronger promoter than the commercial Pt/C catalyst for the MOR and this is in agreement with the CO stripping results.In much of the literature, adsorbed CO is considered as a poisoning intermediate for MOR on pure Pt surface.To remove CO from the Pt surface, adsorbed OH species generated from water activation are indispensable.However, a high potential is needed to activate water on the Pt surface.In PtRu catalysts, water activation can occur at lower potential on Ru-sites.Therefore, MOR activity on PtRu catalysts can be enhanced through the bi-functional mechanism [44].
The durability of the electrodes was measured via an accelerated durability test (ADT) at room temperature up to 5000 consecutive cycles for the Pt/C-MnxO1+x catalyst and up to 4000 cycles for the Pt/C one.A noticeable corrosion of carbon nanostructures as Pt supports, confirmed from the reduction of the catalyst thickness from oxidation of carbon, agglomeration and detaching of Pt, had already been reported by other researcher groups, as well [23].Figure 8 compares voltammograms before and after stability tests.The results show that Pt/C-MnxO1+x is more stable compared to Pt/C, showing an increase of ECSA (+29% after 5000 cycles, Figure 8A).In fact, its CV increased progressively up to 1000 cycles, remaining then stable up to the end of the ADT at 5000 cycles.On the contrary, the Pt/C lost continuously stability cycle after cycle, with an overall decrease of ECSA equal to −9% after 4000 cycles (Figure 8B).According to the literature [47], the ECSA increase of Pt/C-MnxO1+x could be due to a re-arrangement of Pt over carbon.This re-arrangement is not a stable condition, but a reversible process.In fact, as observed for Pt/C-MnxO1+x during CO stripping analysis (Figure 6), Pt nanoparticles agglomeration can evolve to more disperse Pt nanoparticles or different Pt nano-shape islands depending on the stress cycling adopted for accelerated degradation procedure [47,48].To better check stability of the Pt/C-MnxO1+x and in particular of the MnxO1+x support, the extra MnxO1+x sample used for μRS analysis (Figure 4) was used to assess its stability in acid conditions.Specifically an RDE prepared with pure MnxO1+x, was subjected to ADT by cycling it 5000 times in the same conditions used for the Pt/C-MnxO1+x (50 mV•s −1 between 0.4 and 0.8 V vs. Ag/AgCl, in a 0.5 M H2SO4 solution).Results from CV degradation (Figure 8C) show very little degradation, sign that MnxO1+x is a stable support in acid environment, as reported in the literature as well [29,40,48,49].Moreover, this RDE was analyzed directly by SEM coupled with EDX detector before and after ADT.Images of this RDE are shown in Figure S1 of the supporting info.From a visual point of view, the MnxO1+x on RDE after cycling showed a rearrangement compared to the fresh configuration: it appears more agglomerated near the edges of the disk (Figure S1C,D), whether in the fresh configuration the electrode appears more homogeneous (Figure S1A,B).EDX elementary analyses on the overall Mn atomic quantity available on the RDE before and after ADT enlightened that after cycling the Mn overall content diminished by 18%.Thus, MnxO1+x, can be considered a stable support in acidic environment.The presence of manganese oxides in a Pt/C composite electrode plays a catalytic role in the ORR by enhancing the catalytic behavior of Pt for the ORR [40].In fact, manganese oxides in the composite electrode can be considered as substitute for oxygen as an electron-acceptor in the case of oxygen starvation.

Synthesis of the Hybrid Support C-MnO2
To prepare the C-MnO2, 3.9 g of KMnO4 and 12.6 g of H2SO4 were added into 130 g of deionized water under magnetic stirring to form the precursor solution.Then, 1.0 g of Vulcan XC-72 was added into this precursor solution.Subsequently, the formed suspension was heated up to 80 °C and kept at 80 °C for 6 h under magnetic stirring.The precipitates were filtered and washed with distilled water.Finally, the obtained powder was dried at 120 °C for 6 h under vacuum.Assuming that all the KMnO4 used in the synthesis can be reduced to MnO2, the theoretical wt.% of MnO2 in the C-MnO2 support is equal to 68.4 wt.%.

Synthesis of the Pt/C-MnxO1+x Catalyst by Thermal Method
For the synthesis of Pt/C-MnxO1+x catalyst, 200 mg of the previously prepared C-MnO2 was added to 50 mL EG and the mixture was stirred for 30 min.Then, H2PtCl6•6H2O was dissolved into the EG solution under stirring.The pH was adjusted to 12, by the addition of 1 M KOH in EG solution.Microwave irradiation was applied to the solution at 700 W for 2 min, in order to reduce the Pt 4+ ions to metallic Pt 0 .The solution was left to cool naturally to room temperature.After cooling, some drops of acetone were added to the solution and the Pt/C-MnxO1+x catalyst was washed thoroughly with abundant water.Finally, the catalyst was annealed under nitrogen atmosphere for 2 h at 600 °C.

Synthesis of the PtRu/C Catalyst
PtRu/C catalyst was prepared by adding 60 wt.% [50] commercial PtRu 1:1 at % on functionalized Vulcan XC72 into a water-isopropyl alcohol solution under stirring for 24 h.Then the PtRu/C catalyst was centrifuged and dried.
The MnO2 and platinum-to-carbon weight percentage in the catalysts was determined by inductively coupled plasma atomic mass spectroscopy (ICP-MS ICAP-Q instrument, ThermoFisher Scientific Inc., Waltham, MA, USA).Prior to analysis, the samples were digested in hot concentrated HCl/HNO3 3:1 mixture with some droplets of H2SO4.
The XRD reflections were recorded on a PANalytical X'Pert PRO diffractomer with a PIXcel detector (PANalytical B.V., Almelo, The Netherlands), using Cu Kα radiation, under the conditions of 2θ = 10°-100° and 2θ step size = 0.03, in order to examine the different polymorphs.
X-ray photoelectron spectroscopy (XPS) was performed to determine the elemental surface composition of the catalysts.The analysis was carried out using a Physical Electronics PHI 5000 Versa Probe electron spectrometer system (Physical Electronics Inc., Chanhassen, MN, USA) with monochromated Al Kα X-ray source (1486.60 eV) run at 15 kV and 1 mA anode current.The survey spectra were collected from 0 to 1200 eV.The narrow Mn 2p spectra were collected from 635 to 665 eV, the narrow Pt 4f spectra from 66 to 86 eV and the narrow C 1s spectra from 280 to 293 eV.All of the spectra were calibrated against a value of the C 1s binding energy of 284.5 eV.Multipak 9.0 software (Physical Electronics Inc., Chanhassen, MN, USA) was used for obtaining semi-quantitative atomic percentage compositions, using Gauss-Lorentz equations with Shirley-type background.A Gaussian/Lorentzian 70%/30% line shape was used to evaluate peak positions and areas of the high resolution Pt 4f and Mn 2p spectra, with a standard deviation in locating the peaks equal to 0.3 eV.
The chemical structure of the support was analyzed by a μ-Raman Spectroscopy (μRS Renishaw InVia spectrometer equipped with a Leica DMLM confocal microscope and a CCD detector with an excitation wavelength of 785 nm, Renishaw plc, Gloucestershire, United Kingdom).The Raman scattered light was collected in the spectral range 100-1000 cm −1 .At least ten scans were accumulated in four different positions of the catalyst to ensure a sufficient signal to noise ratio.

Electro-Chemical Characterization
The prepared electro-catalysts were tested in a conventional three-compartment electrochemical cell using a multi-potentiostat (Bio-Logic SP150, Bio-Logic Science Instruments SAS, Claix, France) and a rotating ring-disk electrode instrument (RRDE-3A ALS Model 2323, ALS Co. Ltd, Tokyo, Japan).The electrolyte was 0.5 M H2SO4 aqueous solution saturated with either N2 or CO 10% v/v in Ar by direct bubbling the gas into the solution.For RDE measurements, the cell was equipped with a glassy carbon (GC) disk working electrode (0.1256 cm 2 geometric area), a Pt helical wire counter electrode and a silver chloride electrode (Ag/AgCl) as reference electrode.Glassy carbon (GC) electrodes were polished with alumina powder, ultrasonic washing and blow drying, before dropping the catalyst ink.Different GC disk electrodes were arranged by preparing the ink using an ionomer-to-catalyst (ITC) mass ratio (mg of Nafion ® over mg of catalyst) equal to 0.1 and catalyst loading of 20 μgPt•cm −2 [51].The working electrode was surface-polished with 1 and 0.06 μm alumina powders to a mirror-like finish its surface and sonicated to remove alumina particles before each experiment.Cyclic voltammograms (CV) with either N2 or CO 10 vol % in Ar were recorded at 10 mV•s −1 and 20 mV•s −1 , respectively.
CO stripping voltammetry was performed in 0.5 M H2SO4 at a scan rate of 20 mV•s −1 .Prior to analysis a flow rate of 10 vol % CO in Ar was pre-adsorbed for 30 min while maintaining the working electrode at the constant potential of −0.19 V (vs.Ag/AgCl) and rotating disk speed of 900 rpm.Afterwards, a flow rate of pure N2 was used for 15 min to remove the CO reversibly adsorbed onto the surface and the excess CO dissolved in the solution.
Cyclic voltammetries for the methanol oxidation reaction in acid conditions were carried out in a 0.5 M H2SO4 solution with 1 M MeOH.The scan rate was 20 mV•s −1 and the potential window was 0.0-1.0V vs. Ag/AgCl.The highest initial activity was usually obtained within ~20 cycles and then the experiment was stopped [52].
The electrocatalyst stability was performed by ADT cycling up catalysts to 5000 times between 0.4 and 0.8 V vs. Ag/AgCl forwards and backwards at a scan rate of 50 mV•s −1 in N2-saturated 0.5 M H2SO4 solution.Such a potential range for accelerated degradation tests should enlighten any problem related to the corrosion of carbon supports as well as the sintering of Pt nanoparticles based on the protocol suggested by DoE [53].

Conclusions
In this work a C-MnO2 hybrid support was coated with platinum nanoparticles followed by a annealing at 600 °C, in order to promote the methanol oxidation reaction.The enhancement of the electrochemical performance of the Pt/C-MnxO1+x was mainly due to the optimized dispersion and smaller particle size of Pt nanoparticles favored by the presence of a mixture of Mn2O3 and Mn3O4, as well as synergistic integration of nanomaterials.Pt/C-MnxO1+x shows better activity than the commercial Pt/C catalyst.However, its performance still falls short of the most commonly used commercial PtRu/C catalyst, due to the presence of some Pt agglomerates.The aspiration that this hybrid support can be optimized and then go on to replace the current PtRu based catalysts can be realized by understanding the real function of this kind of hybrid support and by reducing the presence of Pt agglomerates.All results suggested that the Pt/C-MnxO1+x can act as promising catalysts for fuel cells.
5 and 4 nm were obtained for Pt/C-MnxO1+x, Pt/C and PtRu/C, respectively, with lattice parameter of 3.78, 3.93 and 3.82 Å, respectively.According to ICP-MS analysis, the Pt wt.% loading for the three Pt/C-MnxO1+x, Pt/C and PtRu/C was equal to 19, 20 and 38 wt.%, respectively.

Table 1 .
CO stripping potential, MOR peak potential of the forward scan and If/Ib ratio in the CV curves of Pt/C-MnxO1+x, Pt/C and Pt-Ru/C in 0.5 M H2SO4 and 1 M MeOH.