Preparation of platinum-silver alloy nanoparticles and their catalytic performance in methanol electro-oxidation

Hai-dong ZHAO Zhen LU Rui LIU Zuo-peng LI Yong GUO

Citation:  ZHAO Hai-dong, LU Zhen, LIU Rui, LI Zuo-peng, GUO Yong. Preparation of platinum-silver alloy nanoparticles and their catalytic performance in methanol electro-oxidation[J]. Journal of Fuel Chemistry and Technology, 2020, 48(8): 1015-1024. shu

铂银合金的制备及其对甲醇电氧化反应的催化性能

    通讯作者: 卢珍, luzhen0313@aliyun.com
    李作鹏, lizuopeng@126.com
  • 基金项目:

     201701D121016

     201901D211433

     2013-B-16

     2019L0737

     2017119

     2019L0749

     201819

     MMIA2019106

     201801D121073

摘要: 采用一种无需使用任何有机表面活性剂或溶剂的方法,在熔融盐体系中制备了铂银纳米合金颗粒,考察了合金中元素银对碱性电解质中甲醇电氧化反应(MOR)的催化作用。透射电子显微镜表征结果显示,当前躯体铂银物质的量比为1时,可以得到组成为Pt52Ag48的合金纳米管。甲醇电氧化反应测试结果表明,具有干净表面的Pt52Ag48纳米管比常规的Pt黑具有更好的催化性能。Pt52Ag48合金纳米管的催化活性与其最大正扫电位密切相关,正扫电位从-1.0到0.5 V(vs.SCE),MOR峰值电流达到1.61 mA/μgPt,是从-1.0到0.1 V(vs.SCE)正扫电位的1.92倍。铂银合金表面层中的Ag元素主要通过在电化学循环中发生氧化还原反应来促进合金的MOR活性。研究结果可以为铂银合金在直接甲醇燃料电池(DMFC)中的应用提供理论支持。

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 PtxAgy 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 PtxAgy alloy NPs for MOR in alkaline electrolyte.

    The PtxAgy 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.

    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 PtxAgy 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.

    The electro-catalytic performance of the PtxAgy 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 PtxAgy 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.

    Figure 1 shows the SEM and TEM images of the as-prepared PtxAgy 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

    Table 1

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

    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 PtxAgy 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)

    Furthermore, the peaks in the XRD patterns of PtxAgy 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

    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

    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 PtxAgy, 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 PtxAgy alloys.

    Figure 6

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

    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

    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].

    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 (If) for the MOR are 1.43 and 1.61 mA/ μgPt 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 PtxAgy catalysts presents a more negative peak potential (Ep), in comparison with the Pt black, suggesting a higher activity of PtxAgy in COads oxidation, as given in Table 2. For example, Ep 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)

    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
    下载: 导出CSV
    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 PtxAgy 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 (If) to the backward peak current (Ib); a higher If/Ib 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 If/Ib 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 PtxAgy 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 PtxAgy and Pt black catalysts, the Pt52Ag48 NPs shows the most negative E0 and highest If 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 PtxAgy alloy in MOR is mainly ascribed to the promoting effect of Ag.

    In addition to the catalyst composition, the positive potential limit of CV also has a great effect on the catalytic activity of PtxAgy 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

    With a relatively lower potential limit of 0.1 V, the Pt52Ag48 catalyst shows a mass peak current density of 0.84 mA/μgPt. As the potential limit increases to 0.5 V, the peak current density of the Pt52Ag48 catalyst increases to 1.61 mA/μgPt, 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 PtxAgy 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 PtxAgy 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 PtxAgy 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/μgPt) is only 67.2% of that at the first cycle (1.25 mA/ μgPt). 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 PtxAgy 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)

    A series of platinum-silver alloy nanoparticles (PtxAgy 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 PtxAgy 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 PtxAgy 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/ μgPt 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 PtxAgy 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 PtxAgy 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 PtxCuy 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.  

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

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

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

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

    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

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

    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

    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)

    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

    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)

    Table 1.  PtxAgy 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
    下载: 导出CSV

    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
    下载: 导出CSV
  • 加载中
计量
  • PDF下载量:  0
  • 文章访问数:  118
  • HTML全文浏览量:  10
文章相关
  • 发布日期:  2020-08-01
  • 收稿日期:  2020-07-14
  • 修回日期:  2020-07-24
通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索

/

返回文章