Electrocatalysts for ethanol and ethylene glycol ...

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Electrocatalysts for ethanol and ethylene glycol oxidation reactions. Part II: Effects of the polyol synthesis conditions on the characteristics and catalytic activity of PteRu/C anodes lez-Quijano a, W.J. Pech-Rodrı´guez a, J.A. Gonza lez-Quijano b, D. Gonza J.I. Escalante-Garcıá a,c, G. Vargas-Gutierrez a,c, I. Alonso-Lemus c, F.J. Rodrı´guez-Varela c,* mica, Cinvestav Unidad Saltillo, Av. Industria Metalu´rgica 1062, Parque Ingenierıá Metalu´rgica e Ingenierıá Cera Industrial Ramos Arizpe, Ramos Arizpe, Coahuila, C.P. 25900, Mexico b n, Programa de Energıás Renovables, ITSP, Boulevard Vıćtor Manuel Cervera Pacheco S/N, Progreso, Yucata C.P. 97320, Mexico c Sustentabilidad de los Recursos Naturales y Energıá, Cinvestav Unidad Saltillo, Av. Industria Metalu´rgica 1062, Parque Industrial Ramos Arizpe, Ramos Arizpe, Coahuila, C.P. 25900, Mexico a

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abstract

Article history:

This paper presents a continuation about the effects of polyol synthesis conditions on the

Received 17 March 2015

physicochemical and electrocatalytic characteristics of Pt-based alloys. PteRu/C alloys

Received in revised form

with nominal Pt:Ru atomic ratio of 1:1 were synthesized by a polyol process with different

24 May 2015

ethylene glycol:ethanol:water volume ratios. The PteRu/C catalysts were tested as anodes

Accepted 26 June 2015

for the Ethanol and the Ethylene Glycol Oxidation Reactions. X-ray diffraction showed that

Available online 17 July 2015

the PteRu/C catalysts have low crystallinity, which limited the analysis of some important factors such as average particle size, degree of alloying and lattice parameter. Such

Keywords:

structural feature was attributed to a very small particle size, as confirmed by TEM anal-

Polyol method

ysis. The chemical composition by EDS indicated that the Pt:Ru 1:1 ratio can be achieved

PteRu/C alloys

under most of the synthesis conditions. Moreover, the formation of oxides was a constant

Ethanol oxidation reaction

characteristic, whether water was present or absent during the synthesis. The electro-

Ethylene glycol oxidation reaction

chemical characterization showed that the synthesis conditions have an important effect

DAFCs

on the electrocatalytic activity of the PteRu/C alloys for both oxidation reactions. Compared to a Pt/C catalyst, all of the alloys showed lower onset potentials for the oxidation reactions, but several of them delivered smaller oxidation current densities. Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

* Corresponding author. E-mail address: [email protected] (F.J. Rodrı´guez-Varela). http://dx.doi.org/10.1016/j.ijhydene.2015.06.154 0360-3199/Copyright © 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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Introduction The use of liquid fuels, like alcohols, to feed Direct Alcohol Fuel Cells (DAFCs), has been widely investigated worldwide [1,2]. One of the main challenges has been the low performance of Pt-alone (Pt/C) catalysts when used as anodes for the oxidation of organic molecules [1,2]. The complete oxidation of liquid fuels to CO2 is a complex pathway that involves the breaking of CeC bonds in the initial steps of the dissociative adsorption of the molecules. Additionally, the specific reaction mechanism of molecules like methanol, ethanol or ethylene glycol produces different varieties of intermediates that depolarize the monometallic Pt/C [1,2]. Even though, it is recognized that the oxidation of the three fuels form CO-like species that strongly adsorb on Pt active sites, which have a negative effect on the capability of Pt/C catalysts to carry out the oxidation reaction [1e8]. Several Pt-based alloys, such as PteRu/C, PteSn/C, and PteMo, have shown higher catalytic activity than Pt-alone when evaluated as anodes, i.e. the onset potential is more negative and the oxidation current density is higher during the Methanol, Ethanol, and Ethylene Glycol Oxidation Reactions (MOR, EOR, and EGOR, respectively) [9e19]. The alloys become more tolerant to the poisoning effect of CO, as the presence of the co-catalyst modifies the Pt atomic structure and d-band valence [11,12,20]; the latter weakens the adsorption energy of CO and facilitates the CeC bond cleavage of adsorbed alcohols [1,2,21]. Moreover, the alloying element provides eOH species that facilitate the alcohol oxidation at lower potentials than Pt/C catalysts [1,2,13,22]. However, the preparation of Pt-based alloyed catalysts is complex. Their physicochemical characteristics vary depending on the synthesis procedure and conditions, which in turn will have an effect on their electrocatalytic behavior. For example, it has been reported that the presence of oxides on the catalytic surface influences their catalytic activity. Datta et al. synthesized PteRu/C alloys by an electrodeposition process and found that Ru-oxides participate in the effective electro-oxidation of carbonaceous species formed during the EOR [23]. They also concluded that the chemical state of the oxide species strongly influences the reaction, with the formation of a low-valent RuO2 which facilitates the oxygen transfer at lower potentials. Neto et al. developed PteSn/C and PteRu/C catalysts, and pointed that the reaction mechanism of the EGOR in the presence of Pt-alloys needs more investigation [14]. Moreover, the role of the solvent used for dispersion of the reactants has been studied by Chen et al. [24]. This group evaluated the effect of the chemical nature of the solvent on PteRu/C alloys and concluded that the use of H2O produces catalysts with large particle size and low degree of alloying, which decreased their catalytic activity for the MOR. In contrast, catalysts synthesized in the presence of tetrahydrofuran displayed higher degree of alloying and lower onset and peak potential for the reaction. In a previous communication, we reported the first part of the study regarding the effects of the polyol synthesis conditions on the properties and electrochemical behavior of PteSn/C alloys [9]. The results have shown that the EG:EtOH:H2O ratios have an important effect on the

physicochemical characteristics and thus on the electrocatalytic activity of the alloys for the electro-oxidation of ethanol and ethylene glycol. As a result, the PteSn/C alloys synthesized in the absence of H2O showed smaller particle size, higher degree of alloying and larger lattice parameters, delivering higher performance as anodes for the EOR and the EGOR in acid electrolyte compared to other PteSn/C and Pt/C catalysts [9]. Considering the importance of developing high performance anode catalysts for DAFC applications, this work aims to extend the previously published study on the effects of the synthesis conditions to PteRu/C alloys obtained by the polyol method. The influence of the EG:EtOH:H2O ratios (v/o) on the characteristics and catalytic activity of the alloys for the EOR and EGOR in acid media is systematically evaluated.

Experimental Reactants and gases Analytical grade chemicals were purchased from Aldrich and used as received in this investigation: H2PtCl6$6H2O, RuCl3 as metallic precursors, ethanol (EtOH), ethylene glycol (EG) and H2SO4. Vulcan XC-72 (Cabot Corp) was used as the catalysts support. Ultra high purity nitrogen gas purchased from Infra gas (purity > 99.999%) was used to control the atmosphere of the electrochemical cell.

Synthesis of PteSn/C catalysts PteRu/C alloys with 20 wt. % metal loading and Pt:Ru atomic ratio of 1:1, were synthesized by the polyol method. For that purpose, a methodology was used varying the EG:EtOH:H2O volume ratio (v/o) in the dispersing solution. The temperature was kept at 130 C. The experiments also included a set of syntheses without H2O, resulting in 12 PteRu/C catalysts, as in our previous report [9]. The synthesis was carried out as follows (e.g. BX0 sample): the appropriate amount of Vulcan was dissolved in a mixture of 25 mL EG and 21 mL EtOH. The metal precursors were dissolved separately in 2 mL of pure ethanol. The solutions were sonicated for 30 min at room temperature, mixed and stirred for 1 h. Afterwards, a solution of 1 mol L1 NaOH was added to the mixture to adjust the pH to 12, the temperature was then increased to 130 C and soaked for 3 h. The solution was then left to cool down to room temperature under stirring conditions for 3 h. Then, 1 mol L1 H2SO4 was added to set the pH ¼ 2 and the mixture was stirred for another 3 h. The obtained powder was filtered, washed, and dried. The other catalysts were similarly synthesized with the EG:EtOH:H2O ratios listed in Table 1. For comparison purposes, a Pt/C catalyst (labeled as D1) was synthesized as reference. The H2PtCl6$6H2O precursor was dissolved in 2 mL of H2O and the Vulcan support in 48 mL EG. The solutions were sonicated separately for 30 min followed by mixing and stirring for 1 h. The following steps were as described above.


Table 1 e Synthesis parameters used for the preparation of PteRu/C alloys, sort by ethanol content during the synthesis process. Group 1

2

3

4

Sample

Temp ( C)

EG (v/o)

Ethanol (v/o)

Water (v/o)

BX0 BX1 BX2 B0 B1 B2 B3 B4 B5 B6 B7 B8

130 130 130 130 130 130 130 130 130 130 130 130

50 90 96 92 86 46 92 86 46 92 86 46

50 10 4 4 4 4 2 2 2 0.4 0.4 0.4

0 0 0 4 10 50 6 12 52 7.6 13.6 53.6

Physicochemical characterization X-ray diffraction (XRD) patterns of the catalysts were obtained using an X'pert Philips diffractometer, with a Cu Ka radiation ˚ ), over a range of 10e100 (2q). The chemical source (l ¼ 1.54 A composition of the catalysts was obtained by Energy Dispersive Spectroscopy (EDS) analyses (Philips XL30 SEM) using an accelerating voltage of 20 keV. The morphology of the PteRu/C BX0 was evaluated by transmission electron microscopy (TEM) in a JEOL JEM-ARM200F microscope operating at 200 keV.

Electrochemical set-up and characterization The preparation of the catalytic inks has been described elsewhere [9]. Briefly, 10 mg of the catalysts were dispersed in a mixture of 1 ml propanol and 5 ml Nafion®, with a subsequent sonication for 30 min. The electrochemical measurements were performed with a VoltaLab PGZ 301 potentiostat/galvanostat in a standard three-electrode cell. The working electrode was a glassy carbon disk (5 mm diameter) containing 10 ml of each catalytic ink. A Pt foil was the counter-electrode and an Ag/AgCl was the reference electrode, even though all potentials have been referred in this work to the Standard Hydrogen Electrode (SHE). Cyclic voltammograms (CVs) in N2-saturated 0.5 M H2SO4 electrolyte were obtained at a scan rate of 20 mV s1. The potential scan was between 50 and 800 mV/SHE, in order to avoid the formation of irreversible oxides and the Ru particle growth. Afterwards, CVs of the EOR and EGOR were acquired in the same electrolyte containing 0.5 mol L1 C2H5OH or C2H6O2, in the potential interval 50e1200 mV/SHE, maintaining the N2 atmosphere. Chronoamperometric curves of the EOR and EGOR were acquired in fresh acid electrolyte containing C2H5OH or C2H6O2 under a static potential of 600 mV/ SHE for 30 min.

Results and discussion Physicochemical characterization Fig. 1 shows the XRD patterns of Pt/C (D1) and the series of PteRu/C alloys, organized in the groups as given in Table 1. All

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samples show the peak located at around 26 (2q) which corresponds to the hexagonal structure of graphite (002) plane, due to the presence of Vulcan. The D1 catalyst shows the planes (111), (200), (220), and (311), corresponding to the facecentered-cubic (fcc) structure of Pt (JCPDS # 040802). In general, the XRD patterns of the PteRu/C catalysts reveal materials with low crystallinity, which suggests the formation of quasi-amorphous structures, or alloyed materials with particle sizes that may be difficult to detect by the technique. A reflection seems to form at ca. 34 (2q) on some of the patterns that can be due to a RuO2 phase. This conclusion is in good agreement with the report by Arriaga et al. showing the formation of the (101) peak of tetragonal RuO2 after calcination treatment [25]. However, a clear correlation between the peak in Fig. 1 and the EG:EtOH:H2O ratio used during the synthesis of the PteRu/C alloys could not be established. The low crystallinity limited the calculation of several relevant factors such as lattice parameters, crystallite sizes and degrees of alloying. Fig. 2 shows characteristic TEM images of the PteRu/C BX0 alloy. In Fig. 2(a), the catalyst has a highly homogeneous dispersion of the metallic nanoparticles on the support. The insert shows a narrow particle size distribution and a mean diameter of around 1.65 nm. This confirms the small particle size of the alloy and correlates well with the XRD results. In Fig. 2(b), small nanoparticles having a diameter of around 1.8 nm could be measured, in good agreement with the above. Fig. 2(c) shows a HR-TEM image of BX0, where several small particles can be seen. The insert is an electron diffraction (SAED) pattern of the region indicated by the red square, from which distances between fringes d ¼ 0.201 and 0.233 nm have been determined. These values can be ascribed to the Ru (101) and Pt (111) planes, respectively [26e28], confirming the presence of both alloyed metals in the catalyst. The small average particle size of the BX0 catalyst demonstrates the capacity of the polyol method to produce materials having very small particles. Table 2 shows the EDS results of the samples. The carbon content in the different catalysts is ca. 80 wt. %, which correlates well with the amount of carbon theoretically expected. The presence of Ox species has been detected for all PteRu/C catalysts, irrespective of the changes in volume ratios of the solvent used (i.e. the EG:EtOH:H2O mixture, see Table 1). The formation of Ox is believed to be in part due to the presence of RuOx phases, although this could not be confirmed by XRD. Meanwhile, the EDS analysis of Pt/C did not show the formation of Pt-Ox species, despite the fact that the Pt alone catalyst has been synthesized in the presence of relatively large amounts of water (4 v/o). This result seems to confirm that RuOx phases are responsible for the Ox species detected. However, the presence of Pt-Ox phases should not be discarded at the PteRu/C structures. The formation of Ox species has also been observed from the polyol synthesis of related PteSn/C alloys [9]. On the other hand, the Pt:Ru ratio on almost all alloys approaches fairly close to the 1:1 nominal value, indicating that the chemical composition can be controlled and is not considerably affected by the solvent, except for the B2 and B5 samples.

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Fig. 1 e XRD Patterns of a) PteRu/C BX0, BX1, BX2, and Pt/C; b) PteRu/C B0, B1, and B2; c) PteRu/C B3, B4, and B5; d) PteRu/C B6, B7, and B8. For the synthesis conditions details of the PteRu/C catalysts, see Table 1.

Electrochemical characterization Catalytic activity for the EOR Fig. 3 shows the CVs of Pt/C and the PteRu/C alloys in 0.5 M H2SO4. The PteRu/C catalysts show characteristics of relatively low current densities associated to the H2 adsorption/desorption region and large double layers. The shape of these CVs and the fact that Ru atoms may participate in the adsorption/desorption reaction, constrained the determination of ECSA values by calculation of the charge QH from the area under the curve in the H2 desorption region. Fig. 4 shows the evaluation of the catalytic activity of Pt/C and the PteRu/C alloys for the EOR. The current densities in the figure have been normalized with respect to the Pt mass content in the catalysts using the chemical composition obtained by EDS. Fig. 4(a) depicts a direct comparison of the polarization curves of D1 and the PteRu/C catalysts BX0, BX1 and BX2. The performance of the alloys clearly surpasses that of the monometallic by showing: i) a lower onset potential of the EOR, and ii) a higher current density in the forward scan with a maximum peak current density at more negative potentials. Fig. 4(bed) show the polarization curves of the rest of the PteRu/C samples. The electrocatalytic parameters of the EOR at all the catalysts are specified in Table 3. The results indicate that the most active catalyst for the EOR is B0, which shows an onset potential of 235 mV with a peak current density of 434.22 mA mg1 Pt at 879 mV. Even more, considering the peak current densities in the forward (jf) and backward (jb) scans, this alloy has a jf/jb ratio of 1.72 (Table 3). It is acknowledged that a high jf/jb ratio is an indication of a high efficiency for the oxidation of an organic molecule.

Overall, the B1 and B2 alloys also show a high catalytic activity for the EOR. As a comparison, D1 has an onset potential of 450 mV and a peak current density of 427.57 mA mg1 Pt at 1002 mV, with a jf/jb ratio of 0.81. The PteRu/C B3 and B4 samples have a lower onset potential than B0, but a significantly smaller peak current density. In Fig. 4(d), B6 shows an onset potential of 250 mV and a current density of 333.76 mA mg1 Pt, outperforming the other two catalysts synthesized with low ethanol content (0.4 v/o); however, its catalytic activity falls behind those of B0, B1 and even B2. The analysis of results from Fig. 4 and Table 3 demonstrate that the B0, B1, and B2 samples, synthesized using relatively large amounts of H2O (4, 10, and 50 v/o, respectively, Table 1) and a fixed amount of ethanol (4 v/o), have higher catalytic activity for the EOR than those obtained without water (i.e., BX0, BX1, and BX2). This trend in catalytic activity of the PteRu/C series differs from that of the PteSn/C catalysts previously reported [9], for which the alloys with higher catalytic activity for the EOR were those synthesized without water. However, attention must be paid to the amount of water during the synthesis of PteRu/C by the polyol method, because B8 (53.6 v/o H2O during synthesis), shows a very low performance for the reaction (Fig. 4(d)).

Catalytic activity for the EGOR Fig. 5 shows the CVs of the EGOR at the Pt/C and PteRu/C catalysts. In the positive scan, most of the catalysts show the emerging of two current density peaks (see for example the D1 sample in Fig. 5(a)), or in some cases the formation of a wide shoulder (e.g. samples B7 and B8 in Fig. 5(d)). This behavior is characteristic of the electro-catalytic oxidation of EG at Pt-


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Fig. 2 e TEM (a) and HR-TEM (bec) micrographs of the PteRu/C BX0 catalyst.

Table 2 e Chemical Composition of PteRu/C alloys and Pt/ C. Sample

Chemical composition, (wt. %) Pt

Ru

C

Ox

D1 BX0 BX1 BX2 B0 B1 B2 B3 B4 B5 B6 B7 B8

19.2 11.96 8.6 8.76 10.01 10.19 11.76 8.92 13.02 12.61 9.07 8.4 12.39

e 5.19 3.81 4.46 4.16 4.07 3.68 3.44 5.02 3.89 3.92 3.33 5.3

80.8 79.23 82.46 81.35 81.11 79.59 79.66 81.23 77.92 78.89 80.84 83.12 77.6

e 3.63 5.13 5.43 5.72 6.15 4.90 6.41 4.03 4.60 6.17 5.15 4.71

Pt:Ru atomic ratio e 1.2:1 1.2:1 1:1 1.2:1 1.3:1 1.7:1 1.3:1 1.3:1 1.7:1 1.2:1 1.3:1 1.2:1

catalysts that has been attributed to the partial oxidation of ethylene glycol to C2 by-products and/or ethylene glycol dissociation to CO [10,15,16]. In Fig. 5(a), the D1 catalyst shows an onset potential of ca. 565 mV and a peak current density of 201.23 mA mg1 Pt at 883 mV. The jf/jb ratio is of 0.75, indicating its low efficiency for the electrocatalytic oxidation of EG. On the other hand and similar to the EOR, B0, B1, and B2 show a higher catalytic activity for the EGOR. As an example, the B2 sample (Fig. 5(b)) has an onset potential of 293 mV and a peak current density of 190.4 mA mg1 Pt at 814 mV. Its jf/jb ratio is of 1.94 (Table 4). Thus, contrary to the behavior of D1, the PteRu/C B2 catalyst is highly efficient for the oxidation of EG. In contrast, the B8 sample generated a significantly low current density from the anodic reaction, similar to its poor performance for the EOR. Table 4 enlists the electrochemical parameters of the catalysts for the EGOR. The chronoamperometric behavior of D1, BX0, B0, B1, and B8 during the EOR is shown in Fig. 6(a). Within the first few

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Fig. 3 e CVs of a) Pt/C-D1 and PteRu/C (BX0, BX1, and BX2), b) PteRu/C (B0, B1, and B2), c) PteRu/C (B3, B4, and B5), d) PteRu/C (B6, B7, and B8). Electrolyte: N2-satured, 0.5 M H2SO4. Scan rate 20 mV s¡1. minutes, BX0, B0, and B1 demonstrate a slower current density decay compared to D1, in good agreement with their higher catalytic activity in Fig. 4. However, after ca. 2.5 min for B0 and B1, and 7 min for BX0, the current density at the Pt/C catalyst is above those of the alloys. It is also shown that the stability of the B8 sample is poor in the chronoamperometric tests, as it has a sharp current density drop within the first few

seconds of polarization. This catalyst delivered the smaller current density with a relatively high onset potential for the EOR (Table 3). The chronoamperometric curves corresponding to the EGOR of D1, B0, B1, B2, and B8 are depicted in Fig. 6(b). Clearly, the Pt/C catalyst has a higher stability for the reaction compared to the alloys. A detailed analysis of the performance of the PteRu/C catalysts during the measurements in Fig. 6

Fig. 4 e CVs of the EOR at a) Pt/C-D1 and PteRu/C (BX0, BX1, and BX2), b) PteRu/C (B0, B1, and B2), c) PteRu/C (B3, B4, and B5), d) PteRu/C (B6, B7, and B8). Electrolyte: N2-satured 0.5 M C2H5OH þ 0.5 M H2SO4. Scan rate 20 mV s¡1.


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Table 3 e Electrocatalytic parameters of the EOR at the PteRu/C alloys and Pt/C. Catalyst D1 BX0 BX1 BX2 B0 B1 B2 B3 B4 B5 B6 B7 B8

Onset potential (mV) 450 266 362 367 235 235 245 217 209 286 250 252 288

jf (mA mg1 Pt) 427.57 405.37 248.96 379.35 434.22 380.61 341.84 250.15 240.22 223.16 333.76 209.98 136.08

(aeb), demonstrates that their behavior is analogous to that of PteSn/C alloys as previously described [9]. In both cases, the alloys with higher catalytic activity for the EOR have shown higher stability during the first few minutes at a given static potential, followed by a decreased performance compared to Pt/C. Also, in Ref. [9] and this study, the Pt/C catalyst has shown a higher stability for the EGOR than the alloys. The results in Fig. 6 indicate that, as in the case of PteSn/C, the stability of the PteRu/C catalyst needs to be improved.

Conclusions A series of PteRu/C nanocatalysts was synthesized by the polyol procedure using different EG:EtOH:H2O solution ratios.

@ 1002 mV @ 899 mV @ 858 mV @ 876 mV @ 879 mV @ 887 mV @ 913 mV @ 861 mV @ 868 mV @ 853 mV @ 869 mV @ 882 mV @ 886 mV

jb (mA mg1 Pt)

jf/jb Ratio

529.28 @ 822 mV 258.80 @ 612 mV 228.59 @ 585 mV 151.10 @ 535 mV 252.12 @ 569 mV 215.76 @ 579 mV 240.18 @ 608 mV 154.19 @ 550 mV 142.23 @ 558 mV 200.38 @ 579 mV 216.96 @ 573 mV 128.03 @ 5515 mV 92.20 @ 541 mV

0.81 1.57 1.09 2.51 1.72 1.76 1.42 1.62 1.69 1.11 1.54 1.64 1.48

X-ray diffraction demonstrated the formation of materials of low crystallinity, suggesting a small particle size. This structural characteristic did not allow the calculation of crystallite size, degree of alloying, and lattice parameter of the alloys, thus restraining the study of the effects of the polyol synthesis conditions on those parameters. Nevertheless, transmission electron microscopy of the BX0 sample confirmed a catalyst with homogeneously dispersed metallic nanoparticles with an average particle size of around 1.65 nm. The chemical composition of the catalysts correlated well with the values expected from theoretical calculations. The expected Pt:Ru atomic ratio was 1:1 and fairly close values were obtained for most of the alloys. It was interesting to see that significant amounts of Ox species formed under the experimental conditions implemented, which appeared

Fig. 5 e CVs of the EGOR at a) Pt/C-D1 and PteRu/C (BX0, BX1, and BX2), b) PteRu/C (B0, B1, and B2), c) PteRu/C (B3, B4, and B5), d) PteRu/C (B6, B7, and B8). Electrolyte: N2-satured, 0.5 M C2H6O2 þ 0.5 M H2SO4. Scan rate 20 mV s¡1.

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Table 4 e Electrocatalytic parameters of the EGOR at the PteRu/C alloys and Pt/C. Sample D1 BX0 BX1 BX2 B0 B1 B2 B3 B4 B5 B6 B7 B8

Onset potential (mV)

jf (mA mg1 Pt)

jb (mA mg1 Pt)

jf/jb Ratio

565 310 323 311 290 293 294 286 313 330 300 291 296



0.75 1.65 1.67 1.56 1.94 1.27 1.06 1.01 1.49 0.95 1.25 4.29 1.86

Fig. 6 e Chronoamperometric curves of (a) EOR at D1, BX0, B0, B1, and B8; (b) EGOR at D1, B0, B1, B2, and B8. Electrolyte: N2satured, 0.5 M H2SO4. Static potential: 600 mV.

regardless of the presence or absence of water during the synthesis. The electrochemical characterization of the catalysts demonstrated that the PteRu/C B0 sample has the higher catalytic activity for the EOR, promoting the reaction at a significantly low onset potential and sustaining a higher jf, than the rest of the samples. Meanwhile, the PteRu/C B2 alloy showed the higher performance for the EGOR, in terms of onset potential and delivering a higher jf compared to the other alloys. Overall, the B0, B1, and B2 samples, synthesized in the presence of water, showed the best performance for both reactions. However, the chronoamperometric curves demonstrated that the electrochemical stability of the alloys must be improved. The multi-effect of parameters on the catalytic activity of the PteRu/C alloys could not be clearly established as in the case of the PteSn/C catalysts in our previous work. However, the polyol synthesis conditions had an effect on their performance for the EOR and EGOR.

Acknowledgments The authors wish to thank the Mexican National Council for Science and Technology (CONACyT) for financial support of this work through grants 252079, 241526 and 252003. Also, for

Doctoral scholarships granted to DGQ and WJPR. IAL acknowledges the support from CONACyT through the Programa tedras para Jovenes Investigadores. de Ca

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