Methanol Electro-Oxidation on PtâCarbon Vulcan Catalyst Modified

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Methanol electro-oxidation on Pt-carbon Vulcan catalyst modified with WOx nanostructures: an approach to the reaction sequence using DEMS Jesus Mateos Santiago, Martha Leticia Hernández-Pichardo, Luis Lartundo-Rojas, and Arturo Manzo-Robledo Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b02420 • Publication Date (Web): 28 Nov 2016 Downloaded from http://pubs.acs.org on December 3, 2016

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Industrial & Engineering Chemistry Research

Methanol electro-oxidation on Pt-carbon Vulcan catalyst modified with WOx nanostructures: an approach to the reaction sequence using DEMS

J. Mateos-Santiago1, M. L. Hernández-Pichardo2, L. Lartundo-Rojas3, A. ManzoRobledo1* 1

Instituto Politecnico Nacional. Laboratorio de Electroquímica y Corrosión. 2Instituto Politecnico Nacional.

Laboratorio de Nanomateriales Sustentables. Departamento de Ingeniería Química Industrial (DIQI), Sección de Estudios de Posgrado e Investigación (SEPI), Escuela Superior de Ingeniería Química e Industrias Extractivas (ESIQIE). 3Instituto Politécnico Nacional, Centro de Nanociencias y Micro y Nanotecnologías. UPALM 07738 México, D.F., México. *corresponding author: [email protected]

ABSTRACT The oxidation of methanol was carried out on platinum nanoparticles supported on carbon Vulcan (10% wt. Pt/C), as well as on the tungsten oxide modified material (Pt/WO3-C; WO3 5% wt.). The Pt/C samples were synthesized by the impregnation method and the tungsten oxide was added by an in-situ reflux approach. It was found, by using on-line differential electrochemical mass spectrometry (DEMS), that the route for methanol oxidation on the Pt/C surface is quite different from the Pt/WO3-C sample. When the support matrix is modified with tungsten-oxide species, the reaction pathway is also modified, producing some traces of formic acid and increasing the direct-methanol oxidation toward CO2 (m/z = 44). HRTEM and X-ray photoelectron spectroscopy analysis showed the interaction between platinum and tungsten. This fact is associated to the redox process of WO3 to form hydrogen tungsten-oxide-bronzes or lower tungsten-oxide oxidation states, and it might explain the role of tungsten in the interfacial electrochemistry included at WO3-OH-Pt complex. Keywords: Fuel cells, reaction mechanism, methanol electro-oxidation, electro-catalysis, DEMS, WOx nanostructures.

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1. Introduction Direct methanol fuel cells are an important alternative for electricity generation since alcohols are easier to control compared with gas-based fuel cells, using hydrogen, for example1–4. Unfortunately, in the oxidation of methanol, COx-based compounds are normally produced5–7. The active sites of the catalyst are blocked when carbon monoxide is adsorbed in the catalyst surface; whereas pollution is evident when CO2 is produced. In addition, a crossover effect could be observed when methanol is used as a fuel, reducing the catalyst performance8,9. Depending on the catalyst used, carbon monoxide, carbon dioxide, or both, can be generated. Therefore, a challenge for the materials science is to find a COtolerant catalyst for the anode side, and a methanol tolerant catalyst (including the support to avoid corrosion), in order to increase the efficiency in the generation of the electricity. In this context, the development of improved catalysts would have an important impact on the fuel cell efficiency10–12. The discovery of new nano-scaled materials with unique surface structures and geometric architectures often provide unexpected surface properties, as well as an enhanced electrocatalytic performance. Recently, it has been found that PtWO3 materials show an enhancement in the catalytic activity for the electro-oxidation of methanol in direct methanol fuel cells (DMFC); as well as in the oxygen reduction reaction high-CO-tolerance for polymer electrolyte fuel cells (PEFC)13–16. The main advantages of the Pt-WO3 solids are: (i) H-spillover effect from Pt to WO3 providing free sites to accelerate methanol de-hydrogenation, (ii) when intercalated with ions M+ (M = H, Li, Na, K, etc.), it would form tungsten-oxide-bronzes (MxWO3) with high conductivity, (iii) acid resistance, good stability and outstanding CO tolerance, and (iv) much cheaper than highloading noble metals required in DMFC17. However, despite the considerable number of studies that have provided a good description of the physicochemical and catalytic properties of WO3-Pt/C materials, further work is needed to better understand the inﬂuence of the addition of this oxide on the reaction sequence of Pt/WO3-C solids in the electro-oxidation of methanol. Thus, the oxidation of methanol (MOR) in acid conditions was studied at the interface of Pt/WO3-C electrodes. The formed species during the MOR were monitored using differential electrochemical


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mass spectrometry (DEMS) in order to stablish, in a direct way, the oxidation products during the interfacial interaction methanol-electrolyte-catalyst.

2. Experimental section

2.1. Synthesis of the catalysts and electrode preparation

The Pt/C electro-catalyst (Pt 10% wt.) was prepared by impregnation method using hexachloroplatinic acid (H2PtCl6·6H2O; Aldrich 99.9%), and carbon Vulcan XC-72R as a support. Briefly, a suspension of 360 mg of carbon Vulcan, 50 mL of ethanol and 5 mL of aqueous solution of hexachloroplatinic acid (41 mM) was prepared. Then, the obtained suspension was stirred during 6 h at 40 ˚C. After the induced reaction, the product was dried at 70 ˚C for 12 h and then subject to heat-treatment at 200 ˚C for 2 h in hydrogen atmosphere. For the catalyst modified with tungsten oxide (WO3, labeled as Pt/WO3-C) metatungstate ammonium ((NH4)6W12O39·xH2O; Aldrich 99.9%) was used as precursor in order to obtain WO3 5% wt. on the Pt/C matrix (Pt/C, prepared as previously described). For this synthesis, 380 mg of Pt/C were mixed with 21.1 mg of ammonium metatungstate and 50 mL of ethanol. The obtained suspension was stirred during 3 h at 70 ˚C in reflux conditions in argon atmosphere. Afterward, the product was dried at 40 ˚C for 6 h. All the solutions were prepared with Millipore water (> 18 MΩ). The supporting electrolyte was 0.5 M H2SO4. Argon was used to deaerate the solutions. A reversible hydrogen electrode was employed as reference electrode in all experiments, and the potentials reported therein refer to this electrode. Electrodes were prepared according to a modification of the procedure described by Garsany18,19. For this analysis, an ink with 4 mg of the catalyst was prepared using 2 mL of a solution composed of 20% isopropanol, 79.08% of Millipore water (> 18 MΩ) and 0.02% Nafion (5% wt.). An aliquot of 9.5 µL of this ink was deposited onto a mirror-finished glassy carbon electrode (0.196 cm2). The Pt loading on the



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glassy carbon was 9.7 µgPt cm-2 having concentrations of 10 wt% Pt on the support. Afterwards, the electrode was dried in argon atmosphere during rotation at 300 rpm.

2.2. Material Characterization

The XPS General spectra were obtained with a K-Alpha from Thermo Scientific (Al Kα monochromator), using a pass energy of 160 eV and 60 eV for high-resolution profiles. The X-ray diffraction (XRD) patterns were obtained in a Siemens D-500 diffractometer fitted with a Cu tube (35 kV, 25 mA) and a graphite monochromator, for eliminating the Kβ lines. The Pt phases were identified by JCPDS database. Also, the samples were studied by highresolution transmission electron microscopy (HRTEM). The micrographs were obtained in a TITAN 80-300 with Schottky type field emission source operating at 300 kV. The pointresolution and the information limit were better than 0.085 nm.

2.3. Electrochemical measurements

The electrochemical measurements were performed potentiostatically (Versastat 3) in a three-electrode standard electrochemical cell. A carbon rod and a hydrogen electrode (RHE) were used as counter (CE) and reference electrode, respectively. The i-E characteristics of the catalysts using cyclic voltammetry (CV) was performed in a solution of H2SO4 0.5 M at scan rate of 100 mV/s in a potential window from 0.05 to 1.2 V/RHE, starting at open circuit potential. For experiments as a function of methanol concentration (0.001, 0.01, 0.1 and 1.0 M), the catalyst was deposited onto a glass carbon surface of 5 mm in diameter. The solutions were purged with argon prior to electrochemical analysis for 15 min. All reagents were of analytical grade without further purification.


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2.4. DEMS experiments

A homemade differential electrochemical mass spectrometer (DEMS) apparatus was employed for the detection of generated species during methanol electro-oxidation. A carbon rod served as counter-electrode and a reversible hydrogen electrode (RHE) was used as reference; the scheme of the DEMS setup and further experimental details can be found in reference20. For this case, 3.4 µL ink was deposited onto a glassy carbon electrode (0.0707 cm2) with a Pt loading of ca 9.7 µgPt cm-2 having concentrations of 10 wt% Pt on the support. The scan rate was fixed at 1 mV/s starting at 0.05 V/RHE. The interface between the cell and the vacuum system consists of a PTFE porous membrane (thickness 60 µm, 0.1 µm pore size, 50% porosity). Mass spectrometric profiles (ionic current (Ii) versus potential (E)) and faradic current (IF) versus potential (E) for selected mass to charge ratios (m/z) were recorded simultaneously. The working pressure at the quadrupole-mass spectrometer chamber for all set of experiments described therein was maintaining at ca. 7x10-5 mbar.

3. Results and discussions

3.1. Characterization of the nanostructure: XRD, HRTEM and XPS results

The nanostructure of the Pt/C and Pt/WO3-C samples was studied by XRD, HRTEM and XPS techniques. Figure 1 shows the XRD patterns obtained in the 2θ-interval from 20 to 80 degrees for both catalysts. It is observed the diffraction signals corresponding to metallic platinum (39.8˚, 67.5˚ and 46.2˚), and they were assigned to the cubic face centered phase (JCPDS 4-802). The peaks for tungsten oxides were not observed, due to the overlapping with the amorphous carbon signals at the 2θ-interval (from 23 to 25 degree) and the low content of WO3 (5% wt.) compared to the carbon content. It has been found that by using



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this synthesis method, WO3 crystallites could be present as small clusters of mono and/or poly-tungstates, probably with a size lower than 2 nm16. The crystallite size of platinum was calculated using the Debye-Scherrer formula. According to this equation, the crystallite size was ca. 5.7 and 8.5 nm for Pt/C and Pt/WO3-C, respectively, which is an expected result coming from the same Pt/C precursor. The increment of crystallite size of platinum in Pt/ WO3-C is probably during the reflux procedure, due the incorporation of tungsten oxide. Following with this analysis, in the images obtained by HRTEM (Figure 2) it is observed the presence of particles at nano-metric scale corresponding to platinum in the range of ca. 2 to 10 nm. The insets in these figures show the particle size-distribution and the FFT pattern for platinum (Figure 2A). In the case of the modified composite, the presence of tungsten oxide species (as WO3) and platinum nanoparticles is shown from Figure 2B, through the inter-planar distances measurements of about 2.2 and 2.37 nm, respectively. In addition, the particle size-distribution of Pt is in agreement with those obtained by XRD. Surface chemistry of platinum nanoparticles and WOx clusters were characterized by X-ray photoelectron spectroscopy, XPS (Figures 3 and 4). The XPS spectra in the 4f region of Pt for Pt/C and Pt/WO3-C is shown in Figure 3a and 3b, respectively. The results of deconvolution indicated a phase composition for the Pt/C catalysts of 59.4% of Pt in metallic Pt0, 21.7% in Pt2+ (as PtO), 12.3% in Pt2+ (as PtCl2), and 6.7% in Pt4+ (as PtCl4). Similar deconvolution for the Pt/WO3-C sample was: 61.4% of Pt in metallic Pt0, 19.4% in Pt2+ (as PtO), 12.5% in Pt2+ (as PtCl2) and 6.7% in Pt4+ (as PtCl4). We observe a slight reduction of oxidized species with the presence of tungsten. Moreover, the intensity of the Pt4f spectra decreases with the addition of the WOx more likely due to the synthesis method, since the WOx is incorporated over the Pt/C sample and it may be located preferentially on the surface, diminishing the quantity of Pt detected on the catalyst surface. On the other hand, in the case of tungsten (Figure 4a and 4b), the comparison between pure tungsten oxide and the Pt/WO3-C catalyst, as well as the deconvolution of the Pt/WO3-C sample are presented in Figure 4. Figure 4a shows the XPS spectral in the 4f region of W for pure WO3 and the Pt/WO3-C catalyst. It is observed that the WOx species grown in the


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Pt/WO3-C catalysts are different from those in the pure tungsten oxide. The spectrum for the pure WO3 presents the typical W4f signals at binding energies of ca. 38.5 and 36.4 eV assigned to the oxidation state W(VI), corresponding to the WO3; while in the spectrum for the Pt/WO3-C sample the binding energy of W4f peak shifted slightly towards lower binding energies, indicating the presence of reduced species, most likely due to the electronic interactions between platinum and tungsten oxide species. This interaction has been also observed in platinum catalysts supported on tungsten21,22. In addition, it is evident the W4f peak asymmetry produced for the presence of the reduced species. The results of the deconvolution of the high-resolution spectral bands for the Pt/WO3-C sample (Figure 4b) shows the presence of the 4f7/2-4f5/2 doublets and the doublet and the 5p3/2 line associated with formation of the W(IV) and W(VI) oxidation states21,23. It has been suggested that the role of this WO3/WO2 system is to perform as a redox surface mediator for the oxidation of adsorbed CO-like species from methanol eletro-oxidation23. Moreover, Kulesza et al. have showed that the efficient use of Pt-W materials requires the oxide to be in the reduced state to provide high conductivity21. On the other hand, it has been found that the WO3 go through reversible redox processes, which produce hydrogen tungsten oxide bronzes (HxWO3, 0 < x < 1) or lower tungsten oxides (WO3-y, 0 < y < 1)21. Thus, a synergistic mechanism along with Pt might occurs by the dissociation of molecular hydrogen on platinum, followed by hydrogen spillover and migration of H-atoms to the WO3 lattice to form hydrogen tungsten bronzes (HxWO3)13. These bronzes play an important role during the methanol oxidation reaction, since they may improve the rates of charge (electron and proton) propagation.

3.2. Electrochemical evaluation

a) Catalyst characterization and ex-situ methanol oxidation



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Figure 5 shows the electrochemical characteristics of the Pt/C and Pt/WO3-C electrodes in cyclic voltammetry using H2SO4 0.5 M at scan rate of 100 mV/s in a potential window from 0.05 to 1.2 V/RHE. It is observed that the obtained shape during the scan corresponds to redox process assigned to platinum for both materials. Nevertheless, when tungstenoxide was added such signal presents a better faradaic-current performance. In addition, at the potential of ca. 0.35 V/RHE a typical peak assigned with the formation of bronze sites (Hx-WO3) is evident13, having better conductive properties that might promote different electrochemical activity and reaction-mechanisms in the methanol oxidation. For example, the activity for the oxidation of this alcohol as a function of concentration on Pt/C and Pt/WO3-C-synthesized-nanoparticles is presented in Figure 6 at scan rate of 5 mV/s and starting at 0.05 V/RHE. From these current-versus-potential signals, typical shapes of methanol oxidation are evident, with a major charge (Q/C, calculated during the anodic scan from 0.5 to 1.0 V/RHE) in presence of tungsten in the matrix (inset in Figure 6b), in agreement with bronze-sites formation, as mentioned from Figure 5. Then, as suggested by Shim13 tungsten-oxide sites can serve as proton acceptors (protonation) according with equation 1 and then leaving platinum-free sites (de-protonation) for subsequent adsorbedpromoted redox reactions, equation 2.

Pt-H + WOx → Pt + H-WOx

(1)

Pt + CH3OH → Pt-(CH3OH)ads

(2)

In this context, the relationship between the current-density peak in the positive-going scan (If) and the current-density peak during the negative-going scan (Ib) can be related with the tolerance to accumulation of carbonaceous species at the electrode interface24. For example, for the case of the commercial catalyst Pt/C (E-TEK) and the commercial bi-metallic PtRu/C (E-TEK) the calculated ratio (If/Ib) was ca. 1.025 and 1.8824, respectively; whereas for the synthesized Pt/3D-graphene the ratio was 2.2525. In the case of our materials, the calculated relationship (If/Ib) was 1.3 and 1.2 for Pt/C and Pt/WO3-C, respectively; indicating a better performance that the mono-metallic from commercial source. Also, the


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observed difference in this ratio might be related with the selectivity and conversion of the materials, as discussed in the next section. On the other hand, concerning with the support matrix, Maiyalagan et al.26 reported a

platinum loading of 20 µgPt cm-2 and specific activity of 62.0 mA cm-2 in their synthesized Pt/WO3 catalyst. Conversely, for Pt/WO3-C (this work) the Pt loading was 9.7 µgPt cm-2 (10% wt. Pt and 5% wt. WO3) with a specific activity of 28 mA cm-2 and mass-specific activity of ca. 207.1 mA mg-1Pt (calculated from the current-versus potential peak in the positive-going scan (IF) at 50mV/s). Therefore, from a point of view of specific activity, both catalysts present similar performance even though our material has been prepared with less charge of tungsten oxide. For the case of the mono-metallic of platinum free of tungsten oxide (Pt/C, this work) the metal-noble loading was of 9.7 µgPt cm-2, giving a specific activity and mass-specific activity of 16.3 mA cm-2 and 118.6 mA mg-1Pt, respectively. Then, as a manner of comparison, the Pt-Ru/C (E-TEK, with a mass-specific activity of 375.0 mA mg-1Pt)24 is the best catalyst, followed by Pt/WO3-C (this work) and Pt/C (this work). This significant improvement in the catalytic performance of the Pt/WO3-C catalysts might be attributed to WO3 as it is able to form a hydrogen tungsten bronze (Hx-WO3) sites in acid solution, facilitating the dehydrogenation during methanol oxidation reaction (equation 1)13,26. However, the impact in the reaction performance and selectivity-conversion is more marked when in-situ mass spectrometry technique was used during MOR, see next section.

b) in-situ methanol oxidation using DEMS

The MOR was studied in the acid conditions using DEMS. Volatile and gaseous species were monitored in a solution of 1 M CH3OH and 0.5 M H2SO4 at a scan rate of 1 mV/s. The modification in the matrix support (i.e. Vulcan and/or Vulcan + WOx) plays an important role during the oxidation process. Figure 7a and 8a showed that during the faradaic-current scan in presence of methanol the process is similar for both materials. Nevertheless, taking into account the mass signals recorded using DEMS, the interfacial



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modification promotes some changes. For the faradic current in the MOR at the interface of Pt/C electrode (Figure 7a), the mass signal observed using mass spectrometry was assigned to carbon dioxide (CO2, m/z=44), Figure 7c. However, the mass signal assigned to formic acid via methyl-formate (m/z=60, Figure 7b) was not observed. On the other hand, m/z=60 and CO2 ionic-current signals were detected at the modified electrode with tungsten oxidespecies (Figure 8b and 8c). Therefore, the alteration in the material (support) also modifies the performance toward the oxidation of the alcohol. For example, at Pt/C electrode, the adsorption of methanol is carried out (equation 2), inducing the production of CO2, equation 4, with adsorbed hydroxyl species (OHads) at platinum-active sites27, equation 3. Pt + H2O → Pt-(OH)ads + H+ + e-

(3) +

-

Pt-(CO)ads + Pt-(OH)ads → CO2↑ + 2Pt + H + 2e

(4)

In contrast, the oxidation of the alcohol on the Pt/WO3-C electrode presents a different behavior. The presence of tungsten-oxide-species modifies the activation and the entirely selectivity-conversion of methanol toward methyl-formate (produced via a chemical reaction, equation 8) and CO2 (produced via methyl-formate and/or direct methanol oxidation), as it can be seen from the mass signals obtained by DEMS, Figure 8.

Pt-(OH) ads + WO3 → WO3-(OH) ads + Pt

(5)

Pt-(CH3OH)ads + WO3-(OH) ads → Pt-(HCOOH)ads + WO3 + 3H+ + 3e-

(6)

Pt-(HCOOH)ads → CO2↑ + Pt + 2H+ + 2e-

(7)

Pt-(HCOOH)ads + CH3OH → HCOO-CH3↑ + H2O + Pt

(8)

Therefore, the presence of tungsten might modify the interaction of (OHads) at Pt sites (equation 5). It is possible that WO3 particles functions in the same way as Ru and TiO2 does in Pt-Ru/C and Pt/WO3, respectively, catalysts because OHads species could easily form on the surface of the WO3 particles28, promoting a major interaction of the probe molecule (methanol for this case) as is proposed in equations 6 and 7.


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In addition, the interfacial reaction corresponding with WO3-OH-Pt could be the main mechanism-alteration causing the modification in the reaction-selectivity and then increasing the relative production of CO2 when compared with Pt/C, as stated by DEMS. Also, another parallel route promoting the generation of CO2 at Pt/ WO3-C might be related with the formation of formic acid (equation 7) that has been detected by DEMS from the proposed chemical reaction presented in equation 8. Linked with this last assumption, formic acid in the form of methyl-formate (Figure 8b) is produced (one order of magnitude less intense), simultaneously with carbon dioxide (Figure 8c).

Therefore, the ionic current magnitude for CO2 is more marked at the modified catalyst with tungsten oxide, altering also the reaction mechanism, indicating a major performance in the oxidation reaction for fuel cell applications, as has been also presented and discussed in other reports concerning methanol-oxidation pathways29.

4. Conclusions Electrochemical interactions during methanol oxidation at the interface of Pt/C and Pt/WO3-C materials have been discussed. Such alteration in the Pt/C electrocatalyst promotes modifications in its matrix-intrinsic structure. Two well-defined reaction routes were obtained in the MOR using differential electrochemical mass spectroscopy (DEMS). For the case of the modified material with tungsten, the reaction sequence is from methanol to CO2 in a practically direct-oxidation with formic acid as a by-product. Conversely, the blocked-sites interference at carbon Vulcan free of tungsten promotes a less efficiency for the MOR. This behavior can be explained by increased conductivity produced by the formation of the tungsten oxide bronze sites, as well as the interaction of these bronzes with the platinum nanoparticles which favors the weakening of hydrogen, and the CO-adsorbed species, on the electrode surface. The analysis using HRTEM, XRD and XPS indicated that the reaction selectivity-conversion and performance is highly linked with the electrode nature via WO3-OH-Pt interactions.



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Acknowledgements The authors thank the financial support giving through the projects ESIQIE-SIP-IPN20160434, 20160157 as well as COFAA and CONACyT (project DEMS 160333 and 247208). JMS thanks the financial support from CONACyT within Doctor Fellowship.


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Figure captions

Figure 1. XRD patterns of Pt/C and Pt/WO3-C electrocatalysts. Figure 2. HRTEM details for Pt/C (A) and Pt/WO3-C (B) electrocatalysts, with the particles-size-distribution and inter-planar contributions from the lattice, with the planes and directions (insets) Figure 3. XPS high-resolution spectra of Pt4f for a) Pt/C and b) Pt/WO3-C catalysts. Figure 4. XPS high-resolution spectra of W4f for: a) Pt/WO3-C catalyst and pure tungsten oxide, and b) Deconvolution for the W4f spectrum for the Pt/WO3-C catalyst. Figure 5. Current versus potential characteristics for the electrocatalysts, scan rate of 100 mV/s. Figure 6. i-E characteristic for methanol electro-oxidation depending on the concentration of methanol for a) Pt/C and b) Pt/WO3-C. Scan rate of 5 mV/s. Inset: variation of charge with concentration. Figure 7. (a) Current versus potential characteristic obtained at Pt/C for the electrooxidation of methanol in 0.5 M H2SO4 + 1 M CH3OH; and ion current (mass signal) versus potential obtained using DEMS for the production of (b) methyl-formate [HCO2CH3]+ (m/z=60) and (c) carbon dioxide CO2 (m/z=44). Scan rate of 1 mV/s. Figure 8. (a) Current versus potential characteristic obtained at Pt/WO3-C for the electrooxidation of methanol in 0.5 M H2SO4 + 1 M CH3OH; and ion current (mass signal) versus potential obtained using DEMS for the production of (b) methyl-formate [HCO2CH3]+ (m/z=60) and (c) carbon dioxide CO2 (m/z=44). Scan rate of 1 mV/s.


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Graphical Abstract



Figures 111

Intensity (a. u.)

200

220

Pt/WO3-C Pt/C

20

30

40

50

60

70

80

2degree

Figure 1.

180 160 140 120 100 80 60 40 20 0

WO3

2.2 nm 2

3

4

5

6

7

8

9 10

Particle size of Pt (nm)

120

Frequency

Frequency

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 21

100 80 60 40 20 0

2

3

4

5

6

7

8

9

Pt

A

5

n

2.37 nm

m

B

5

Figure 2.


10

Particles size of Pt (nm)

n

m

Page 19 of 21

a)

4f5/2(Pt)

b)

4f7/2(Pt)

4f5/2(PtCl2)

4f7/2(Pt-O)

4f5/2(PtCl4)

80

Intensity (a. u.)

Intensity (a. u.)

4f7/2(PtCl2)

4f5/2(Pt-O)

82

4f5/2(Pt)

4f7/2(Pt)

4f7/2(PtCl4)

4f7/2(PtCl4)

5p1/2(Pt)

78 76 74 72 70 Binding Energy [eV]

4f5/2(PtCl2)

4f7/2(Pt-O)

4f5/2(PtCl4)

82

68

4f7/2(PtCl2)

4f5/2(Pt-O)

80

5p1/2(Pt)

78 76 74 72 70 Binding Energy [eV]

68

Figure 3. W4f7/2 35.78 W4f5/2

b)

Pt/WO3-C WO3

44

42

4f5/2

37.88

Intensity (a. u.)

a) Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 38 36 Binding Energy [eV]

34

32

4f7/2

WO3 5p3/2

44

42

40 38 36 Binding Energy [eV]

Figure 4.


WO2

34

32


0.4 0.3

HxWO3

0.2

i / mA

0.1 0.0 -0.1 -0.2 -0.3

Pt/C WPt/C

-0.4 -0.5 -0.6 0.0

0.2

0.4

0.6 0.8 E / V(RHE)

1.0

1.2

Figure 5. 1.8

0.07

1.6

1.2 1.0 0.8

Q/C

1.4

Pt/C

0.04 0.03 0.02 0.01

(b)

1M 0.1 M 0.01 M 0.001 M

0.00 1E-3

0.6 0.4

(a)

Pt/WO3-C

0.06 0.05

i / mA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 21

0.01 0.1 -1 [CH3OH] / mol L

1

Pt/WO3-C

Pt/C

0.2 0.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3

E / V(RHE)

E / V(RHE)

Figure 6.


Page 21 of 21

(c)

1x10-11 A

Mass signal

m/z=44 (CO2)

(b)

2x10-12 A

m/z=60 (a)

i / mA

0.04 0.02 0.00

-0.02

0.0

0.2

0.4 0.6 0.8 E / V (RHE)

1.0

1.2

Figure 7. -11

Mass signal

2x10

i / mA

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(c)

A

m/z=44 (CO2)

-12

5x10

(b)

A

m/z=60

0.10 0.08 0.06 0.04 0.02 0.00 -0.02

(a)

0.0

0.2

0.4 0.6 0.8 E / V (RHE)

1.0

Figure 8.


1.2

Methanol Electro-Oxidation on PtâCarbon Vulcan Catalyst Modified

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