English

• Recently, the direct methanol fuel cells (DMFCs) have drawn extensive attention in the field of fuel cells because of their high conversion efficiency and low cost^{[1, 2]}. As well known, platinum (Pt) is widely used as the catalyst in DMFCs for its high activity. However, the high price^{[3, 4]} and low durability^[5-7]of Pt have caused critical problems for their commercialization. Therefore, it is an urgent task to improve the catalytic performance and reduce the consumption of Pt in the electro-catalysts for the application of fuel cells^[8-10].

  Fortunately, Pt-based alloys show great promise. For instance, many Pt-based bimetallic materials have been prepared and applied in fuel cells, such as PtPd^[11], PtCu^[12-15], PtFe^[16], PtCo^[17-19], PtNi^[20], PtMn^[21], PtPb^[22], PtAg^[23-28], etc. These bimetallic alloys exhibited higher catalytic performance than single platinum in the fuel cell reactions, but with much lower cost^[29-31]. Besides, Pt-based alloys are also more stable and corroded much more slowly in alkaline medium than in strong acidic medium^{[32, 33]}, which can enhance the stability of the catalyst and electrode. In addition, the alkaline environment is friendlier to Pt-based alloys, since the methanol electrooxidation reaction (MOR) and oxygen reduction reaction (ORR) are much easier in the alkaline medium^{[34, 35]}.

  It was reported that a proper amount of Ag in PtAg alloy could enhance the resistance of Pt catalyst against CO poisoning and thus greatly improve the catalytic activity^{[36, 37]}. Later, Feng et al^{[38, 39]} also verified the positive role of Ag oxide in promoting the methanol electrooxidation in alkaline electrolyte. Moreover, the catalyst surface cleanness also plays a crucial role in the catalytic performance^[40]. Conventional methods often used the surfactants and capping agents, generating residues on the catalyst surface; these residues were difficult to remove completely and had a great influence on the catalytic performance^[41-43]. Recently, some alternative methods have been employed to prepare the Pt-based alloy nanoparticles (NPs) of controllable shapes and clean surfaces^[44-46]. For example, Pt nanosheets^[47], Pt nanocave^[48], PtCu nanocave^[15], and PtAg nanotube^[23] were obtained with much cleaner surfaces and significantly enhanced MOR and formic acid electrooxidation catalytic performance.

  In this work, a group of Pt_xAg_y alloy NPs with clean surface was prepared in the molten salts system and their performance as anodic catalysts in alkaline media for MOR was then investigated, to explore the important role of Ag in enhancing the catalytic performance of Pt_xAg_y alloy NPs for MOR in alkaline electrolyte.

  1.   Experimental

  1.1   Preparation of the Pt_xAg_y alloy NPs

  The Pt_xAg_y alloy NPs were prepared following the reported procedures^[23]. 6.6 g KNO₃ and 3.4 g LiNO₃ were thoroughly grounded and uniformly mixed in a glass flask and placed in a 170 ℃ salt bath, until the mixture was melted. After that, a designed amount of silver acetate (CH₃COOAg) and tetra-ammine platinum oxalate {Pt(NH₃)₄C₂O₄} (15.6 mg Pt(NH₃)₄C₂O₄ and 0.9 mg CH₃COOAg for Pt₈₆Ag₁₄; 14.1 mg Pt(NH₃)₄C₂O₄ and 1.7 mg CH₃COOAg for Pt₇₉Ag₂₁; 8.8 mg Pt(NH₃)₄C₂O₄ and 4.2 mg CH₃COOAg for Pt₅₂Ag₄₈; 3.5 mg Pt(NH₃)₄C₂O₄ and 6.7 mg CH₃COOAg for Pt₂₁Ag₇₉; 2.0 mg Pt(NH₃)₄C₂O₄ and 7.4 mg CH₃COOAg for Pt₁₁Ag₈₉) and 22.4 mg KOH were added into the mixed molten salt with vigorously stirring for 2 h. After the reaction was complete, the molten salt was cooled to room temperature and washed three times with distilled water to remove the soluble salt.

  1.2   Characterization of the Pt_xAg_y alloy NPs

  Scanning electron microscope (SEM) images were taken on a JEOL 7000F field emission electron microscope; the energy dispersive X-ray (EDX) was used to analyse the average atomic distribution of the Pt_xAg_y NPs. The transmission electron microscopy (TEM) and high-resolution TEM (HRTEM) images were obtained by using a JEOL 3010 with 300 kV acceleration voltages. The Powder X-ray diffraction (XRD) was conducted on a Bruker D8 advance X-ray diffractometer.

  1.3   Electro-catalytic activity of the Pt_xAg_y alloy NPs

  The electro-catalytic performance of the Pt_xAg_y NPs in alkaline electrolytes (0.5 moL/L KOH) media for MOR was evaluated by using cyclic voltammetry (CV) technique with a three-electrode system that consisted of a saturated calomel electrode (SCE) reference electrode, a 1 cm×1 cm platinum plate (99.9%) counter electrode and a glassy carbon (GC) working electrode. The catalyst ink was prepared by dispersing 5 mg Pt_xAg_y catalyst in 5 mL mixed solvent of distilled water, 2-propanol (AR, 99.8%) and 5% Nafion solution (with a volume ratio of 4 :1 :0.025). The working electrode was obtained by dropping 10 μL of catalyst ink onto the GC and dried in air. All potentials in this work were relative to SCE. The stable CV curves were recorded between -1.0 to 0.5 V (vs. SCE) after 50 cycles with the scanning rate of 50 mV/s. CV tests for MOR were carried out in 0.5 moL/L KOH + 2 moL/L CH₃OH (HPLC, 99.9%) solution between -1.0 to 0.5 V (vs. SCE) with the scanning rate of 20 mV/s.

  2.   Results and discussion

  2.1   SEM, TEM, EDX, and XRD analysis of Pt_xAg_y NPs

  Figure 1 shows the SEM and TEM images of the as-prepared Pt_xAg_y alloy NPs with different Pt(NH₃)₄C₂O₄/CH₃COOAg molar ratios (8, 4, 1, 1/4 and 1/8) in the molten salt precursor; on the basis of the EDX results (Table 1), the obtained products are denoted as Pt₈₆Ag₁₄, Pt₇₉Ag₂₁, Pt₅₂Ag₄₈, Pt₂₁Ag₇₉ and Pt₁₁Ag₈₉, respectively.

  Figure 1

  

  Figure 1.  SEM and TEM images of ((a), (f)) Pt₈₆Ag₁₄, ((b), (g)) Pt₇₉Ag₂₁, ((c), (h)) Pt₅₂Ag₄₈, ((d), (i)) Pt₂₁Ag₇₉, and ((e), (j)) Pt₁₁Ag₈₉

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  Table 1

  

  Table 1.  Pt_xAg_y atomic molar ratios in the alloy NPs prepared with different Pt(NH₃)₄C₂O₄/CH₃COOAg ratios in the molten salt precursor, analyzed by EDX

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  PtxAgy sample	Pt(NH3)4C2O4/CH3COOAg	Pt/Ag, by EDX
  Pt86Ag14	8:1	6.09
  Pt79Ag21	4:1	3.89:1
  Pt52Ag48	1:1	1.10:1
  Pt21Ag79	1:4	1:3.88
  Pt11Ag89	1:8	1:8.51

  The as-prepared Pt_xAg_y alloy NPs have a very clean surface, since the preparation process was operated in the system of molten salts without using any organic surfactant or solvent^[23]. As shown in Figure 1(a)-(e), (f)-(j), with a decrease in the content of Pt, the morphology of products changes gradually from NPs to nanotubes (NTs) and to mixture of NPs and NTs. A proper content of silver in the molten salt can promote the change in the product shape from NPs to NTs; in particular, NT becomes the main products with a Pt/Ag ratio of 1 in the molten salt precursor. The average size displays a great decrease from (82.5±12.1) nm for Pt₈₆Ag₁₄ to (32.1±5.9) nm for Pt₅₂Ag₄₈, as shown in Figure 2.

  Figure 2

  

  Figure 2.  Particle size distribution histogram for Pt₈₆Ag₁₄ (a) and nanotube diameter distribution histogram for Pt₅₂Ag₄₈ (b), estimated from the SEM images

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  2.2   TEM and HRTEM analysis of Pt₅₂Ag₄₈ NTs

  Figure 3 displays the TEM and HRTEM images of Pt₅₂Ag₄₈ NTs. The Pt₅₂Ag₄₈ NTs shows a worm-like morphology with hollow or solid interior (Figure 3(a), (b)); the tube diameter and wall thickness are about 25.6 and 6.5 nm, respectively. It seems that the Pt₅₂Ag₄₈ NTs are aggregated with several NPs with or without hollow interiors. Meanwhile, the HRTEM images shown in Figure 3(c), (d) indicate that the lattice spacing of Pt₅₂Ag₄₈ NTs was about 0.230 and 0.198 nm, which could be indexed to the (111) and (200) crystal planes of Pt_xAg_y alloy, respectively^[40].

  Figure 3

  

  Figure 3.  TEM images ((a), (b)) of the Pt₅₂Ag₄₈; HRTEM images ((c), (d)) of the local sites of Pt₅₂Ag₄₈ labelled in (b)

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  Furthermore, the peaks in the XRD patterns of Pt_xAg_y NPs can be labelled as (111), (200), (220), (311), and (222) planes of a face-centred-cubic (fcc) structure, as shown in Figure 4. With a high content of Pt (or Ag), the diffraction peak is very close to pure metallic Pt (or Ag), indicating a Pt-rich (or Ag-rich) alloy phase^[49]. The redundant diffraction peaks appear in the XRD patterns of Pt₇₉Ag₂₁ and Pt₅₂Ag₄₈, probably due to the formation of trace amounts of Ag-rich alloy or pure Ag.

  Figure 4

  

  Figure 4.  XRD patterns of the Pt, Pt₈₆Ag₁₄, Pt₇₉Ag₂₁, Pt₅₂Ag₄₈, Pt₂₁Ag₇₉, Pt₁₁Ag₈₉, and Ag

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  2.3   Cyclic voltammograms analysis of Pt_xAg_y NPs

  Figure 5 shows the typical cyclic voltammograms (CVs) of Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ electrodes with the same loading in the electrolyte of N₂-saturated 0.5 moL/L KOH.

  Figure 5

  

  Figure 5.  Cyclic voltammograms of Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ NPs performed in the electrolyte of N₂-saturated 0.5 moL/L KOH. the inset is the enlarge image of CV between -1.0 and -0.7 V

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  Two anode peaks appear in the forward sweep, one shoulder at low potential (about 0.20 V) and another strong peak at higher potential (about 0.25 V). These two anodization peaks were generally attributed to the oxidation of Ag to AgO^- and Ag₂O, respectively^[50]. In the backward sweep, an obvious cathodic peak appears at about 0.0 V, which could be assigned to the reduction of Ag₂O to metallic Ag^[51]. With a decrease in the Ag content in Pt_xAg_y, the redox peak current of Ag decreases gradually, indicating that the number of Ag atoms exposed on the surface is declining. In the low-potential region of the CVs curve, the peaks appeared at -1.0 to -0.7 V are attributed to the hydrogen adsorption-desorption characteristics of Pt surface, as shown in the inset of Figure 5^[52]. In addition, in the backward sweep, the broad cathode peak at -0.2 to -0.7 V can be assigned to the reduction of Pt oxide during the anodization process at high potential^[53].

  As shown in Figure 6, when the cyclic voltammetry is applied to Pt₅₂Ag₄₈ NTs, the Ag atoms in the alloy are de-alloyed, which will expose more Pt surface (about -0.5 V) and gave a larger electrochemical surface area (ECSA) for the hydrogen adsorption-desorption (-1.0 to -0.7 V). Furthermore, the intensity of Ag redox peaks increases with an increase in the number of CV cycles and tends to stabilize after 50 cycles, suggesting that Ag element exists in the surface layer of the Pt_xAg_y alloys.

  Figure 6

  

  Figure 6.  Cyclic voltammograms of Pt₅₂Ag₄₈ in N₂-saturated 0.5 moL/L KOH electrolyte

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  2.4   Effect of positive potential limit to the cyclic voltammograms of Pt₅₂Ag₄₈ NTs

  Figure 7 shows the CV curves of Pt black (JM) and Pt₅₂Ag₄₈ catalysts performed with different positive potential limits (-1.0 to 0.5 V and -1.0 to 0.1 V). The commercial Pt black displays a classical H adsorption-desorption region (-1.0 to -0.7 V) and a Pt oxides formation and reduction region (-0.2 to -0.5 V). The potential limit has almost no effect on the Pt oxide reduction peaks position; however, a decrease in the positive potential limit leads to a slight decline of the peak current. In contrast, the CV feature of the Pt₅₂Ag₄₈ NTs is greatly dependent on the potential limit. With the positive potential limit of -1.0 to 0.5 V, the Ag redox peak and the H adsorption-desorption characteristics are observed. However, if the positive potential is limited in -1.0 to 0.1 V, the features of Ag redox and hydrogen adsorption-desorption disappear.

  Figure 7

  

  Figure 7.  Cyclic voltammograms of Pt black and Pt₅₂Ag₄₈ performed with different positive potential limits (-1.0 to 0.5 V and -1.0 to 0.1 V) in the electrolyte of N₂-saturated 0.5 mol/L KOH

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  It is well known that the adsorption and desorption of hydrogen on silver atoms are inactive^[54]. When the potential is applied in the range of -1.0 to 0.1 V, Ag atoms cannot be de-alloyed from the catalyst surface and it is then difficult to reflect the hydrogen adsorption-desorption characteristics. In addition, the electric double layer for Pt₅₂Ag₄₈ NTs subjected to 0.5 V is much broader than that at 0.1 V, suggesting that the surface of Pt₅₂Ag₄₈ NTs can be roughened by the Ag redox process^{[55, 56]}.

  2.5   Evaluation of the activity of Pt_xAg_y NPs in MOR

  Figure 8 a shows the CV and linear polarization curves of MOR over the Pt black, Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁, and Pt₈₆Ag₁₄ catalysts in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH. During the forward scanning process, substantially no current can be detected when the potential is lower than -0.6 V. If the scan is moved to more positive potential, a very distinct symmetrical anodic peak appears at around -0.2 V. The peak potential and peak current density are important indicators to evaluate the catalyst performance. As given in the Tbale 2, in the forward scanning, the peak current densities (I_f) for the MOR are 1.43 and 1.61 mA/ μg_Pt for the Pt black and Pt₅₂Ag₄₈ catalysts, respectively. Meanwhile, the mass current densities of the Pt₅₂Ag₄₈ NTs measured at -0.25 V is about 1.19 times higher than that of Pt black (insert in Figure 8(a)). Furthermore, all Pt_xAg_y catalysts presents a more negative peak potential (E_p), in comparison with the Pt black, suggesting a higher activity of Pt_xAg_y in CO_ads oxidation, as given in Table 2. For example, E_p of Pt₅₂Ag₄₈ NTs is -0.12 V, which shifts negatively by 50 mV compared with that of the Pt black (-0.07 V).

  Figure 8

  

  Figure 8.  Cyclic voltammograms (a) and linear polarization curves (b) for MOR on the Pt black (JM), Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ catalysts in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH, the insets in (a) and (b) show the corresponding activities at -0.25 V and the dependence between the onset potential of MOR and the catalysts composition, respectively (the scan rate is 20 mV/s)

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  Table 2

  

  Table 2.  MOR performance of Pt black, Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ catalysts in 0.5 moL/L KOH + 2 moL/L CH₃OH

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  Sample	E0 /V	Ep /V	If /(mA·μgPt-1)	Ib /(mA·μgPt-1)	If/Ib	I@-0.25V /(mA·μgPt-1)
  Pt black	-0.77	-0.07	1.43	0.56	2.55	0.86
  Pt11Ag89	-0.51	-0.28	0.02	-	-	0.02
  Pt21Ag79	-0.71	-0.25	0.34	0.03	11.33	0.33
  Pt52Ag48	-0.91	-0.20	1.61	0.19	8.47	1.02
  Pt79Ag21	-0.82	-0.21	0.43	0.06	7.17	0.39
  Pt86Ag14	-0.66	-0.24	0.25	0.02	12.50	0.26

  In the backward scanning process, another anodic peak is observed at about -0.4 V for the catalysts of Pt black and Pt_xAg_y NPs. The tolerance ability of the catalyst to the accumulation of carbonaceous species can be evaluated by the ratio of the value of forward peak current (I_f) to the backward peak current (I_b); a higher I_f/I_b ratio means a higher capacity in the oxidation of methanol and the carbonaceous residues accumulated on the catalyst surface to CO₂ during the forward scan^[22]. The I_f/I_b values for the Pt black, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁, and Pt₈₆Ag₁₄ catalyst are 2.55, 11.33, 8.47, 7.17 and 12.50, respectively, as given in Table 2, indicating that the Pt_xAg_y alloy NPs are more active to directly oxidize methanol to CO₂ than Pt black.

  To investigate the electrocatalytic performance of the catalysts at low potential, the onset potential (E₀) of MOR was measured based on the CV curve. As shown in Figure 8(b), among all the Pt_xAg_y and Pt black catalysts, the Pt₅₂Ag₄₈ NPs shows the most negative E₀ and highest I_f values (Table 2), which indicates that the Pt₅₂Ag₄₈ NTs catalyst has a much better MOR activity than that the Pt black. That is, the presence of Ag can remarkably improve the catalytic performance of Pt-Ag alloy in MOR. In view of the extremely limited catalytic activity of Ag compared to Pt in alkaline media^[57], the enhancement in the catalytic performance of the Pt_xAg_y alloy in MOR is mainly ascribed to the promoting effect of Ag.

  2.6   Promoting effect of Ag on the catalytic activity of Pt₅₂Ag₄₈ NTs in MOR

  In addition to the catalyst composition, the positive potential limit of CV also has a great effect on the catalytic activity of Pt_xAg_y alloys in MOR. For comparison, the catalytic activity of Pt black in MOR with the different potential limits was also tested. Figures 9(a) and 9(b) show the CVs of Pt black and Pt₅₂Ag₄₈, in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH, with the potential limit of -1.0 to 0.5 V and -1.0 to 0.1 V, respectively. For the Pt black, the MOR performance is approximately the same when the positive potential limits are changed from 0.1 to 0.5 V (Figure 9(a)). In contrast, for the Pt₅₂Ag₄₈ catalyst, the catalytic characteristics have a large discrepancy among different positive potential limits (Figure 9(b)).

  Figure 9

  

  Figure 9.  Cyclic voltammograms of (a) Pt black and (b) Pt₅₂Ag₄₈ in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH with different potential limits at a scan rate of 20 mV/s

  black solid line: -1.0 to 0.5 V; red dotted line: -1.0 to 0.1 V

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  With a relatively lower potential limit of 0.1 V, the Pt₅₂Ag₄₈ catalyst shows a mass peak current density of 0.84 mA/μg_Pt. As the potential limit increases to 0.5 V, the peak current density of the Pt₅₂Ag₄₈ catalyst increases to 1.61 mA/μg_Pt, which is 1.92 times higher than that subjected to the 0.1 V potential limit. The catalytic activity of Pt-Ag alloy is improved significantly, as the redox reaction of Ag can be initiated with the positive potential limit of -1.0 to 0.5 V. Moreover, the Ag oxide formed in the redox reaction can greatly enhance the catalytic activity of the Pt_xAg_y alloy in MOR^[38]. The promoting effect of Ag oxide for MOR can be ascribed to the trace Ag oxide wrapped around the active Pt atoms in the Pt_xAg_y alloy NPs, which may play an important role in the reaction to remove the CO-like intermediate species adsorbed on Pt atoms, to release the the active Pt sites; in this way, the bifunctional effect between Pt and Ag oxide leads to a significant improvement of MOR activity^[38].

  To further verify the promoting effect of Ag on the methanol oxidation performance of Pt_xAg_y alloy, the sequential cyclic voltammogram technique was used to identify the MOR activity of Pt₅₂Ag₄₈ catalyst in different potential limits. For the potential limit of -1.0 to 0.5 V, the Pt₅₂Ag₄₈ catalyst was subjected to CV in 0.5 moL/L KOH solution for 50 cycles until the electrode was stable, and the sequential CV was then tested in 0.5 moL/L KOH + 2 moL/L CH₃OH. A parallel operation was conducted with the same process in the solution of 0.5 moL/L KOH for 50 cycles with the potential limit of -1.0 to 0.1 V.

  As shown in Figure 10(a), the values of peak current for the Pt₅₂Ag₄₈ NTs shows a rapid increase from the first to the fifth cycle, when the potential is applied within the range -1.0 to 0.5 V. After the tenth cycle, the peak current tends to be stable and increases no longer. On the contrary, the peak current decreases continuously when the positive potential is limited in the range of -1.0 to 0.1 V (Figure 10(b)). The value of peak current at the 50th cycle (0.84 mA/μg_Pt) is only 67.2% of that at the first cycle (1.25 mA/ μg_Pt). With the potential limit of -1.0 to 0.1 V, it is difficult to perform the redox reaction of Ag during the oxidation of methanol and the CO-like intermediate species adsorbed on the surfaces of Pt atoms cannot be removed immediately. As a result, the catalytic performance of Pt-Ag alloy in MOR degrades gradually, suggesting that the promoting effect of Ag on the MOR activityof Pt_xAg_y alloy is in effect mainly in the redox reaction process.

  Figure 10

  

  Figure 10.  Sequential cyclic voltammograms of Pt₅₂Ag₄₈ in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH with the potential ranges of (a) -1.0 to 0.5 V and (b) -1.0 to 0.1 V (scan rate 20 mV/s)

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  3.   Conclusions

  A series of platinum-silver alloy nanoparticles (Pt_xAg_y NPs) were synthesized in a molten salt system without using any organic surfactants or solvents; the catalytic role of Ag in the methanol electrooxidation reaction (MOR) in alkaline electrolyte over Pt_xAg_y NPs was investigated.

  The results indicate that Pt₅₂Ag₄₈ nanotubes (NTs) can be obtained when the Pt/Ag ratio in the molten salt precursor reaches 1. The catalytic performance of Pt_xAg_y alloy in MOR in alkaline electrolyte is greatly enhanced by the Ag element. The Pt₅₂Ag₄₈ NTs with a clean surface exhibits a much better catalytic performance than the conventional Pt black in MOR. Meanwhile, the catalytic activity of the Pt₅₂Ag₄₈ NTs is greatly related to the positive potential limit; the peak current of MOR reaches 1.61 mA/ μg_Pt with a positive potential limit from -1.0 to 0.5 V (vs. SCE), which is 1.92 times higher than that with a positive potential limit from -1.0 to 0.1 V (vs. SCE). The Ag element in the surface layer of Pt_xAg_y alloy may promote the MOR through a redox process during the electrochemical cycle. The findings in this work are valuable in explaining the mechanism of Ag in promoting catalytic performance of Pt-Ag alloy and designing bimetallic catalysts in MOR, which should be beneficial to the application of Pt_xAg_y alloy in the direct methanol fuel cells (DMFCs).

  
  
• 1. [1]

     SAXENA N, PRANEETH N, RAO K, PARIA S. Organization of palladium nanoparticles into fractal patterns for highly enhanced catalytic activity and anode material for direct borohydride fuel cells applications[J]. ACS Appl Energy Mater, 2018, 1(5):  2164-2175. doi: 10.1021/acsaem.8b00211 doi: 10.1021/acsaem.8b00211
     

  2. [2]

     SHARAF O Z, ORHAN M F. An overview of fuel cell technology:Fundamentals and applications[J]. Renewable Sustainable Energ Rev, 2014, 32:  810-853. doi: 10.1016/j.rser.2014.01.012 doi: 10.1016/j.rser.2014.01.012
     

  3. [3]

     STAMENKOVIC V R, FOWLER B, MUN B S, WANG G, ROSS P N, LUCAS C A, MARKOVIĆ N M. Improved oxygen reduction activity on Pt₃Ni (111) via increased surface site availability[J]. Science, 2007, 5811:  493-497.  
     

  4. [4]

     GASTEIGER H A, MARKOVIĆ N M. Just a dream-or future reality?[J]. Science, 2009, 324(5923):  48-49. doi: 10.1126/science.1172083 doi: 10.1126/science.1172083
     

  5. [5]

     GASTEIGER H A, KOCHA S S, SOMPALLI B, WAGNER F T. Activity benchmarks and requirements for Pt, Pt-alloy, and non-Pt oxygen reduction catalysts for PEMFCs[J]. Appl Catal B:Environ, 2005, 56(1):  9-35.  
     

  6. [6]

     YANG H, DAI L, XU D, FANG J, ZOU S. Electrooxidation of methanol and formic acid on PtCu nanoparticles[J]. Electrochim Acta, 2010, 55(27):  8000-8004. doi: 10.1016/j.electacta.2010.03.026 doi: 10.1016/j.electacta.2010.03.026
     

  7. [7]

     CHEN J, LIM B, LEE E P, XIA Y. Shape-controlled synthesis of platinum nanocrystals for catalytic and electrocatalytic applications[J]. Nano Today, 2009, 4(1):  81-95. doi: 10.1016/j.nantod.2008.09.002 doi: 10.1016/j.nantod.2008.09.002
     

  8. [8]

     TIAN N, ZHOU Z Y, SUN S G, DING Y, WANG Z L. Synthesis of tetrahexahedral platinum nanocrystals with high-index facets and high electro-oxidation activity[J]. Science, 2007, 316(5825):  732-735. doi: 10.1126/science.1140484 doi: 10.1126/science.1140484
     

  9. [9]

     HUANG X, ZHAO Z, FAN J, TAN Y, ZHENG N. Amine-assisted synthesis of concave polyhedral platinum nanocrystals having {411} high-index facets[J]. J Am Chem Soc, 2011, 133(13):  4718-4721. doi: 10.1021/ja1117528 doi: 10.1021/ja1117528
     

  10. [10]

      TIAN N, ZHOU Z Y, SUN S G. Platinum metal catalysts of high-index surfaces:From single-crystal planes to electrochemically shape-controlled nanoparticles[J]. J Phys Chem C, 2008, 112(50):  19801-19817. doi: 10.1021/jp804051e doi: 10.1021/jp804051e
      

  11. [11]

      LIM B, JIANG M, CAMARGO P H C, CHO E C, TAO J, LU X, ZHU Y, XIA Y. Pd-Pt bimetallic nanodendrites with high activity for oxygen reduction[J]. Science, 2009, 324(5932):  1302-1305. doi: 10.1126/science.1170377 doi: 10.1126/science.1170377
      

  12. [12]

      XU D, LIU Z, YANG H, LIU Q, ZHANG J, FANG J, ZOU S, SUN K. Solution-based evolution and enhanced methanol oxidation activity of monodisperse platinum-copper nanocubes[J]. Angew Chem Int Ed, 2009, 48(23):  4217-4221. doi: 10.1002/anie.200900293 doi: 10.1002/anie.200900293
      

  13. [13]

      HONG F, SUN S, YOU H, YANG S, FANG J, GUO S, YANG Z, DING B, SONG X. Cu₂O template strategy for the synthesis of structure-definable noble metal alloy mesocages[J]. Cryst Growth Des, 2011, 11(9):  3694-3697. doi: 10.1021/cg2001893 doi: 10.1021/cg2001893
      

  14. [14]

      XU H, SONG P, WANG J, DU Y. Shape-controlled synthesis of platinum-copper nanocrystals for efficient liquid fuel electrocatalysis[J]. Langmuir, 2018, 34(27):  7981-7988. doi: 10.1021/acs.langmuir.8b01729 doi: 10.1021/acs.langmuir.8b01729
      

  15. [15]

      ZHAO H, YU C, YOU H, YANG S, GUO Y, DING B, SONG X. A green chemical approach for preparation of Pt_xCu_y nanoparticles with a concave surface in molten salt for methanol and formic acid oxidation reactions[J]. J Mater Chem, 2012, 22(11):  4780-4789. doi: 10.1039/c2jm15792f doi: 10.1039/c2jm15792f
      

  16. [16]

      ZHANG J, FANG J. A general strategy for preparation of Pt 3d-transition metal (Co, Fe, Ni) nanocubes[J]. J Am Chem Soc, 2009, 131(51):  18543-18547. doi: 10.1021/ja908245r doi: 10.1021/ja908245r
      

  17. [17]

      WANG X X, HWANG S, PAN Y T, CHEN K, HE Y, KARAKALOS S, ZHANG H, SPENDELOW J S, SU D, WU G. Ordered Pt₃Co intermetallic nanoparticles derived from metal-organic frameworks for oxygen reduction[J]. Nano Lett, 2018, 18(7):  4163-4171. doi: 10.1021/acs.nanolett.8b00978 doi: 10.1021/acs.nanolett.8b00978
      

  18. [18]

      ZHANG L, FISCHER J, JIA Y, YAN X, XU W, WANG X, CHEN J, YANG D, LIU H, ZHUANG L, HANKEL M, SEARLES D J, HUANG K, FENG S, BROWN C L, YAO X. Coordination of atomic Co-Pt coupling species at carbon defects as active sites for oxygen reduction reaction[J]. J Am Chem Soc, 2018, 140(34):  10757-10763. doi: 10.1021/jacs.8b04647 doi: 10.1021/jacs.8b04647
      

  19. [19]

      YANG D, YAN Z, LI B, HIGGINS D C, WANG J, LV H, CHEN Z, ZHANG C. Highly active and durable Pt-Co nanowire networks catalyst for the oxygen reduction reaction in PEMFCs[J]. Int J Hydrog Energy, 2016, 41(41):  18592-18601. doi: 10.1016/j.ijhydene.2016.08.159 doi: 10.1016/j.ijhydene.2016.08.159
      

  20. [20]

      DING J, BU L, GUO S, ZHAO Z, ZHU E, HUANG Y, HUANG X. Morphology and phase controlled construction of Pt-Ni nanostructures for efficient electrocatalysis[J]. Nano Lett, 2016, 16(4):  2762-2767. doi: 10.1021/acs.nanolett.6b00471 doi: 10.1021/acs.nanolett.6b00471
      

  21. [21]

      MATIN M A, JANG J H, KWON Y U. PdM nanoparticles (M=Ni, Co, Fe, Mn) with high activity and stability in formic acid oxidation synthesized by sonochemical reactions[J]. J Power Sources, 2014, 262:  356-363. doi: 10.1016/j.jpowsour.2014.03.109 doi: 10.1016/j.jpowsour.2014.03.109
      

  22. [22]

      YANG S, PENG Z, YANG H. Platinum lead nanostructures:Formation, phase behavior, and electrocatalytic properties[J]. Adv Funct Mater, 2008, 18(18):  2745-2753. doi: 10.1002/adfm.200800266 doi: 10.1002/adfm.200800266
      

  23. [23]

      ZHAO H, LIU R, GUO Y, YANG S. Molten salt medium synthesis of wormlike platinum silver nanotubes without any organic surfactant or solvent for methanol and formic acid oxidation[J]. Phys Chem Chem Phys, 2015, 17(46):  31170-31176. doi: 10.1039/C5CP05641A doi: 10.1039/C5CP05641A
      

  24. [24]

      CAO X, WANG N, HAN Y, GAO C, XU Y, LI M, SHAO Y. PtAg bimetallic nanowires:Facile synthesis and their use as excellent electrocatalysts toward low-cost fuel cells[J]. Nano Energy, 2015, 12:  105-114. doi: 10.1016/j.nanoen.2014.12.020 doi: 10.1016/j.nanoen.2014.12.020
      

  25. [25]

      WISNIEWSKA J, YANG C, ZIOLEK M. Changes in bimetallic silver-platinum catalysts during activation and oxidation of methanol and propene[J]. Catal Today, 2019, 333:  89-96. doi: 10.1016/j.cattod.2018.03.001 doi: 10.1016/j.cattod.2018.03.001
      

  26. [26]

      LV J J, LI S S, ZHENG J N, WANG A J, CHEN J R, FENG J J. Facile synthesis of reduced graphene oxide supported PtAg nanoflowers and their enhanced electrocatalytic activity[J]. Int J Hydrog Energy, 2014, 39(7):  3211-3218. doi: 10.1016/j.ijhydene.2013.12.112 doi: 10.1016/j.ijhydene.2013.12.112
      

  27. [27]

      LI J, RONG H, TONG X, WANG P, CHEN T, WANG Z. Platinum-silver alloyed octahedral nanocrystals as electrocatalyst for methanol oxidation reaction[J]. J Colloid Interface Sci, 2018, 513:  251-257. doi: 10.1016/j.jcis.2017.11.039 doi: 10.1016/j.jcis.2017.11.039
      

  28. [28]

      LIU Q, HE Y M, WENG X, WANG A J, YUAN P X, FANG K M, FENG J J. One-pot aqueous fabrication of reduced graphene oxide supported porous PtAg alloy nanoflowers to greatly boost catalytic performances for oxygen reduction and hydrogen evolution[J]. J Colloid Interface Sci, 2018, 513:  455-463. doi: 10.1016/j.jcis.2017.11.026 doi: 10.1016/j.jcis.2017.11.026
      

  29. [29]

      STAMENKOVIC V R, MUN B S, ARENZ M, MAYRHOFER K J J, LUCAS C A, WANG G, ROSS P N, MARKOVIC N M. Trends in electrocatalysis on extended and nanoscale Pt-bimetallic alloy surfaces[J]. Nat Mater, 2007, 6:  241. doi: 10.1038/nmat1840 doi: 10.1038/nmat1840
      

  30. [30]

      LIN R, CHE L, SHEN D, CAI X. High durability of Pt-Ni-Ir/C ternary catalyst of PEMFC by stepwise reduction synthesis[J]. Electrochim Acta, 2020, 330:  135251. doi: 10.1016/j.electacta.2019.135251 doi: 10.1016/j.electacta.2019.135251
      

  31. [31]

      LIN R, CAI X, HAO Z, PU H, YAN H. Rapid microwave-assisted solvothermal synthesis of shape-controlled Pt-Ni alloy nanoparticles for PEMFC[J]. Electrochim Acta, 2018, 283:  764-771. doi: 10.1016/j.electacta.2018.03.190 doi: 10.1016/j.electacta.2018.03.190
      

  32. [32]

      JIANG Q, JIANG L, HOU H, QI J, WANG S, SUN G. Promoting effect of Ni in PtNi bimetallic electrocatalysts for the methanol oxidation reaction in alkaline media:Experimental and density functional theory studies[J]. J Phys Chem C, 2010, 114(46):  19714-19722. doi: 10.1021/jp1039755 doi: 10.1021/jp1039755
      

  33. [33]

      WU F, ZHANG Z, ZHANG F, DUAN D, LI Y, WEI G, LIU S, YUAN Q, WANG E, HAO X. Exploring the role of cobalt in promoting the electroactivity of amorphous Ni-B nanoparticles toward methanol oxidation[J]. Electrochim Acta, 2018, 287:  115-123. doi: 10.1016/j.electacta.2018.07.106 doi: 10.1016/j.electacta.2018.07.106
      

  34. [34]

      PRABHURAM J, MANOHARAN R. Investigation of methanol oxidation on unsupported platinum electrodes in strong alkali and strong acid[J]. J Power Sources, 1998, 74(1):  54-61. doi: 10.1016/S0378-7753(98)00012-3 doi: 10.1016/S0378-7753(98)00012-3
      

  35. [35]

      BLIZANAC B B, ROSS P N, MARKOVIC N M. Oxygen electroreduction on Ag(111):The pH effect[J]. Electrochim Acta, 2007, 52(6):  2264-2271. doi: 10.1016/j.electacta.2006.06.047 doi: 10.1016/j.electacta.2006.06.047
      

  36. [36]

      FENG L, GAO G, HUANG P, WANG X, ZHANG C, ZHANG J, GUO S, CUI D. Preparation of Pt Ag alloy nanoisland/graphene hybrid composites and its high stability and catalytic activity in methanol electro-oxidation[J]. Nanoscale Res Lett, 2011, 6:  551. doi: 10.1186/1556-276X-6-551 doi: 10.1186/1556-276X-6-551
      

  37. [37]

      HE W, WU X, LIU J, ZHANG K, CHU W, FENG L, HU X, ZHOU W, XIE S. Formation of AgPt alloy nanoislands via chemical etching with tunable optical and catalytic properties[J]. Langmuir, 2010, 26:  4443-4448. doi: 10.1021/la9034968 doi: 10.1021/la9034968
      

  38. [38]

      FENG Y Y, BI L X, LIU Z H, KONG D S, YU Z Y. Significantly enhanced electrocatalytic activity for methanol electro-oxidation on Ag oxide-promoted PtAg/C catalysts in alkaline electrolyte[J]. J Catal, 2012, 290:  18-25. doi: 10.1016/j.jcat.2012.02.013 doi: 10.1016/j.jcat.2012.02.013
      

  39. [39]

      FENG Y Y, LIU Z H, KONG W Q, YIN Q Y, DU L X. Promotion of palladium catalysis by silver for ethanol electro-oxidation in alkaline electrolyte[J]. Int J Hydrog Energy, 2014, 39(6):  2497-2504. doi: 10.1016/j.ijhydene.2013.12.004 doi: 10.1016/j.ijhydene.2013.12.004
      

  40. [40]

      XU J B, ZHAO T S, LIANG Z X. Synthesis of active platinum-silver alloy electrocatalyst toward the formic acid oxidation reaction[J]. J Phys Chem C, 2008, 112(44):  17362-17367. doi: 10.1021/jp8063933 doi: 10.1021/jp8063933
      

  41. [41]

      WU J, ZHANG J, PENG Z, YANG S, WAGNER F T, YANG H. Truncated octahedral Pt₃Ni oxygen reduction reaction electrocatalysts[J]. J Am Chem Soc, 2010, 132(14):  4984-4985. doi: 10.1021/ja100571h doi: 10.1021/ja100571h
      

  42. [42]

      CHEN X, WU G, CHEN J, CHEN X, XIE Z, WANG X. Synthesis of "clean" and well-dispersive Pd nanoparticles with excellent electrocatalytic property on graphene oxide[J]. J Am Chem Soc, 2011, 133(11):  3693-3695. doi: 10.1021/ja110313d doi: 10.1021/ja110313d
      

  43. [43]

      MERGA G, SAUCEDO N, CASS L C, PUTHUSSERY J, MEISEL D. "Naked" gold nanoparticles:Synthesis, characterization, catalytic hydrogen evolution, and SERS[J]. J Phys Chem C, 2010, 114(35):  14811-14818. doi: 10.1021/jp104922a doi: 10.1021/jp104922a
      

  44. [44]

      CASWELL K K, BENDER C M, MURPHY C J. Seedless, surfactantless wet chemical synthesis of silver nanowires[J]. Nano Lett, 2003, 3(5):  667-669. doi: 10.1021/nl0341178 doi: 10.1021/nl0341178
      

  45. [45]

      SUN S H, YANG D Q, VILLERS D, ZHANG G X, SACHER E, DODELET J P. Template-and surfactant-free room temperature synthesis of self-assembled 3D Pt nanoflowers from single-crystal nanowires[J]. Adv Mater, 2008, 20(3):  571-574. doi: 10.1002/adma.200701408 doi: 10.1002/adma.200701408
      

  46. [46]

      HUANG C, JIANG J, LU M, SUN L, MELETIS E I, HAO Y. Capturing electrochemically evolved nanobubbles by electroless deposition. A facile route to the synthesis of hollow nanoparticles[J]. Nano Lett, 2009, 9(12):  4297-4301. doi: 10.1021/nl902529y doi: 10.1021/nl902529y
      

  47. [47]

      ZHAO H, WU J, YOU H, YANG S, DING B, YANG Z, SONG X, YANG H. In situ chemical vapor reaction in molten salts for preparation of platinum nanosheets via bubble breakage[J]. J Mater Chem, 2012, 22(24):  12046-12052. doi: 10.1039/c2jm31422c doi: 10.1039/c2jm31422c
      

  48. [48]

      ZHAO H, YANG S, YOU H, WU Y, DING B. Synthesis of surfactant-free Pt concave nanoparticles in a freshly-made or recycled molten salt[J]. Green Chem, 2012, 14(11):  3197-3203. doi: 10.1039/c2gc35995b doi: 10.1039/c2gc35995b
      

  49. [49]

      PENG Z, YANG H. Ag-Pt alloy nanoparticles with the compositions in the miscibility gap[J]. J Solid State Chem, 2008, 181(7):  1546-1551. doi: 10.1016/j.jssc.2008.03.013 doi: 10.1016/j.jssc.2008.03.013
      

  50. [50]

      POUND B G, MACDONALD D D, TOMLINSON J W. The electrochemistry of silver in KOH at elevated temperatures-II. Cyclic voltammetry and galvanostatic charging studies[J]. Electrochim Acta, 1980, 25(5):  563-573. doi: 10.1016/0013-4686(80)87058-7 doi: 10.1016/0013-4686(80)87058-7
      

  51. [51]

      LIMA F, SANCHES C D, TICIANELLI E A. Physical characterization and electrochemical activity of bimetallic platinum-silver particles for oxygen reduction in alkaline electrolyte[J]. J Electrochem Soc, 2005, 152(7):  1466-1473. doi: 10.1149/1.1933514 doi: 10.1149/1.1933514
      

  52. [52]

      XU C W, WANG H, SHEN P K, JIANG S P. Highly ordered Pd nanowire arrays as effective electrocatalysts for ethanol oxidation in direct alcohol fuel cells[J]. Adv Mater, 2007, 19(23):  4256-4259. doi: 10.1002/adma.200602911 doi: 10.1002/adma.200602911
      

  53. [53]

      FENG Y Y, ZHANG G R, MA J H, LIU G, XU B Q. Carbon-supported Pt/Ag nanostructures as cathode catalysts for oxygen reduction reaction[J]. Phys Chem Chem Phys, 2011, 13(9):  3863-3872. doi: 10.1039/c0cp01612h doi: 10.1039/c0cp01612h
      

  54. [54]

      CHATENET M, GENIES B L, AUROUSSEAU M, DURAND R, ANDOLFATTO F. Oxygen reduction on silver catalysts in solutions containing various concentrations of sodium hydroxide-comparison with platinum[J]. J Appl Electrochem, 2002, 32(10):  1131-1140. doi: 10.1023/A:1021231503922 doi: 10.1023/A:1021231503922
      

  55. [55]

      NAGLE L C, AHERN A J, BURKE D L. Some unusual features of the electrochemistry of silver in aqueous base[J]. J Solid State Electr, 2002, 6(5):  320-330. doi: 10.1007/s100080100233 doi: 10.1007/s100080100233
      

  56. [56]

      JOVIC B M, JOVIC V D, STAFFORD G R. Cyclic voltammetry on Ag(111) and Ag(100) faces in sodium hydroxide solutions[J]. Electrochem Commun, 1999, 1(6):  247-251. doi: 10.1016/S1388-2481(99)00049-1 doi: 10.1016/S1388-2481(99)00049-1
      

  57. [57]

      OROZCO G, PÉREZ M C, RINCÓ N A, GUTIÉRREZ C. Electrooxidation of methanol on silver in alkaline medium[J]. J Electroanal Chem, 2000, 495(1):  71-78.  
      

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  Figure 1  SEM and TEM images of ((a), (f)) Pt₈₆Ag₁₄, ((b), (g)) Pt₇₉Ag₂₁, ((c), (h)) Pt₅₂Ag₄₈, ((d), (i)) Pt₂₁Ag₇₉, and ((e), (j)) Pt₁₁Ag₈₉

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  Figure 2  Particle size distribution histogram for Pt₈₆Ag₁₄ (a) and nanotube diameter distribution histogram for Pt₅₂Ag₄₈ (b), estimated from the SEM images

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  Figure 3  TEM images ((a), (b)) of the Pt₅₂Ag₄₈; HRTEM images ((c), (d)) of the local sites of Pt₅₂Ag₄₈ labelled in (b)

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  Figure 4  XRD patterns of the Pt, Pt₈₆Ag₁₄, Pt₇₉Ag₂₁, Pt₅₂Ag₄₈, Pt₂₁Ag₇₉, Pt₁₁Ag₈₉, and Ag

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  Figure 5  Cyclic voltammograms of Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ NPs performed in the electrolyte of N₂-saturated 0.5 moL/L KOH. the inset is the enlarge image of CV between -1.0 and -0.7 V

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  Figure 6  Cyclic voltammograms of Pt₅₂Ag₄₈ in N₂-saturated 0.5 moL/L KOH electrolyte

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  Figure 7  Cyclic voltammograms of Pt black and Pt₅₂Ag₄₈ performed with different positive potential limits (-1.0 to 0.5 V and -1.0 to 0.1 V) in the electrolyte of N₂-saturated 0.5 mol/L KOH

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  Figure 8  Cyclic voltammograms (a) and linear polarization curves (b) for MOR on the Pt black (JM), Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ catalysts in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH, the insets in (a) and (b) show the corresponding activities at -0.25 V and the dependence between the onset potential of MOR and the catalysts composition, respectively (the scan rate is 20 mV/s)

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  Figure 9  Cyclic voltammograms of (a) Pt black and (b) Pt₅₂Ag₄₈ in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH with different potential limits at a scan rate of 20 mV/s

  black solid line: -1.0 to 0.5 V; red dotted line: -1.0 to 0.1 V

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  Figure 10  Sequential cyclic voltammograms of Pt₅₂Ag₄₈ in the electrolyte of 0.5 moL/L KOH + 2 moL/L CH₃OH with the potential ranges of (a) -1.0 to 0.5 V and (b) -1.0 to 0.1 V (scan rate 20 mV/s)

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  Table 1.  Pt_xAg_y atomic molar ratios in the alloy NPs prepared with different Pt(NH₃)₄C₂O₄/CH₃COOAg ratios in the molten salt precursor, analyzed by EDX

  PtxAgy sample	Pt(NH3)4C2O4/CH3COOAg	Pt/Ag, by EDX
  Pt86Ag14	8:1	6.09
  Pt79Ag21	4:1	3.89:1
  Pt52Ag48	1:1	1.10:1
  Pt21Ag79	1:4	1:3.88
  Pt11Ag89	1:8	1:8.51

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  Table 2.  MOR performance of Pt black, Pt₁₁Ag₈₉, Pt₂₁Ag₇₉, Pt₅₂Ag₄₈, Pt₇₉Ag₂₁ and Pt₈₆Ag₁₄ catalysts in 0.5 moL/L KOH + 2 moL/L CH₃OH

  Sample	E0 /V	Ep /V	If /(mA·μgPt-1)	Ib /(mA·μgPt-1)	If/Ib	I@-0.25V /(mA·μgPt-1)
  Pt black	-0.77	-0.07	1.43	0.56	2.55	0.86
  Pt11Ag89	-0.51	-0.28	0.02	-	-	0.02
  Pt21Ag79	-0.71	-0.25	0.34	0.03	11.33	0.33
  Pt52Ag48	-0.91	-0.20	1.61	0.19	8.47	1.02
  Pt79Ag21	-0.82	-0.21	0.43	0.06	7.17	0.39
  Pt86Ag14	-0.66	-0.24	0.25	0.02	12.50	0.26

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