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Article

Size-Dependence of the Electrochemical Activity of Platinum Particles in the 1 to 2 Nanometer Range

by
Hiroshi Yano
* and
Kouta Iwasaki
New Field Pioneering Division, Toyota Boshoku Corporation, 1-1, Toyoda-cho, Kariya 448-8651, Aichi, Japan
*
Author to whom correspondence should be addressed.
Surfaces 2024, 7(3), 472-481; https://doi.org/10.3390/surfaces7030030
Submission received: 27 May 2024 / Revised: 20 June 2024 / Accepted: 1 July 2024 / Published: 2 July 2024
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Abstract

:
Monodisperse Pt nanoparticles supported on carbon (Pt/C) were prepared via an impregnation method. By changing the concentration of the platinum precursor in the initial reagent mixture, the average particle size (d) could be controlled to within a narrow range of less than 2 nm. The specific activity (SA) of these materials, when applied to the oxygen reduction reaction (ORR), increased rapidly with d in the range below 1.8 nm, with a maximum SA at d = 1.3 nm. This value is approximately four times that of a commercial Pt/CB catalyst. The electrochemical active area, ECAA (electrochemical surface area (ECSA)/specific surface area (SSA) × 100), decreased drastically from 100% with decreases in d below 1.3 nm. In this study, we present a correlation between SA and ECAA as a means of determining the appropriate d for polymer electrolyte fuel cells (PEFCs) and propose an optimal size.

Graphical Abstract

1. Introduction

Polymer electrolyte fuel cells (PEFCs), which typically incorporate platinum nanoparticles as catalysts, may serve as next-generation primary power sources for vehicles and residences. To allow for large-scale commercialization of this technology, it will be critical to reduce the amount of platinum used in PEFCs due to cost and supply constraints. In particular, the overvoltage of the cathode (at which the oxygen reduction reaction (ORR) proceeds) is higher than that of the anode (at which the hydrogen oxidation reaction (HOR) proceeds) and so requires a large amount of platinum. The most effective approach to minimizing the Pt loading in PEFCs is to increase the electrochemical surface area (ECSA). Therefore, the average particle sizes (d) of Pt catalysts have been gradually reduced to the nanometer range. Currently, d values can be as small as 2–5 nm. As an example, a commercial Pt/C catalyst (TEC10E50E, TKK) that is often used as a standard for comparison has an ECSA of ca. 100 m2 g−1. The catalytic performance of aggregates of atoms (referred to as clusters) has also been investigated [1,2,3,4]. However, many studies of cluster-type catalysts have shown that the ECSA is considerably lower than the specific surface area (SSA) predicted from particle geometry. As a result, ORR activity values are also lower than expected. These effects are attributed to the different chemical properties of Pt clusters size (atomic scale) compared with Pt nanoparticles (with sizes from approximately 2 nm) or the bulk metal. Here, we propose a new definition of the real electrochemical active area, ECAA (i.e., ECSA/SSA × 100), which is an important factor in evaluating d and ORR activity.
Another important factor affecting ORR activity is the so-called particle size effect, which has been investigated in studies of Pt catalysts. Some researchers have reported an increase in activity as the particle size is reduced. This occurs because the area occupied by highly active sites on which the ORR occurs is determined by particle size [5,6,7,8,9,10]. Even so, it has also been proposed that activity should be constant regardless of particle size [11,12,13,14] or even decrease with decreasing particle size [15,16,17]. At present, there is no clear consensus on this matter. One reason is that most discussion focus only on the relationship between the ORR mass activity (MA) and/or specific activity (SA) and d. For example, as reported by Shao et al. [16], ORR activity has been associated with specific crystal planes on the particle surface that vary with particle size. There are also reports that changes in interparticle distance with particle size is an important factor in improving ORR activity, as suggested by Inaba et al. [17]. However, the MA is the product of the SA and ECSA (MA (A g−1) = SA (A m−2) × ECSA (m2 g−1)), and the value of ECSA (i.e., ECAA) has no small effect on MA. Therefore, we believe that the most important factor for ORR activity is the ECAA value, which has not received much attention.
Thus, it was suggested that the synergistic effect of ECAA and SA could be used to determine the particle size for maximization of catalytic capacity in a very narrow particle size range. One obstacle to evaluating this hypothesis is a current lack of methods for the synthesis of highly uniform platinum particles having sizes of less than 2 nm.
The present work developed a method for preparing Pt/C catalysts with precisely controlled particle sizes (denote as Ptdnm/C). This process involves dissolving a predetermined amount of platinum chloride in alcohol together with carbon acting as a support. In this study, several Ptdnm/C catalysts having particle sizes of less than 2 nm were prepared, and the relationship between d, ECAA and ORR activity (MA and SA) was investigated in detail to identify the optimum d.

2. Materials and Methods

2.1. Preparation of Ptdnm/C Catalysts

Typical conditions and properties of prepared catalysts (Ptdnm/C) are summarized in Table 1. Hydrogen hexachloroplatinate (IV) hexahydrate (H2PtCl6·6H2O) was dissolved in ethanol. To control the d, the H2PtCl6·6H2O concentration was varied from 4.6 to 47.9 mmol L−1 with the amount of solvent (EtOH). To avoid the possibility of Pt particles entering the pores and affecting the ECSA in high-surface-area microporous carbon, such as Ketjen Black (800 m2 g−1) [18], graphitized carbon black (C, 150 m2 g−1, Tanaka Kikinzoku Kogyo, Tokyo, Japan) was added as a support material and mixed into the mortar. The mixture was stirred while the materials were warmed using a heat gun until the ethanol was almost evaporated. The powders obtained were then completely dried under vacuum at 60 °C for 30 min. Finally, they were heat-treated in an Ar atmosphere at 200 °C for 2 h in a furnace. The heat treatment temperatures were determined experimentally. Figure S1 in the Supporting Information (SI) shows TEM images of Ptdnm/C heat-treated at different temperatures. The aggregation of Pt occurs at temperatures above 300 °C. Therefore, the optimal heat treatment temperature in this study was set at 200 °C. The loading amount of the Pt on the C was quantified from the weight loss by combustion of C at 800 °C in air. The Ptdnm/C powders before and after electrochemical assessments were observed using transmission electron microscopy (TEM, Hitachi H-9500, Hitachi High-Tech Japan, acceleration voltage = 200 kV) and scanning transmission electron microscopy (STEM, Hitachi HD-2700, Hitachi High-Tech Japan acceleration voltage = 200 kV) to determine the d value, the distribution of d values and the fine structure of the Pt particles.

2.2. Electrochemical Analyses

Electrochemical evaluations were performed on five of the prepared catalysts. Catalyst inks were prepared by mixing 2 mg of catalyst powder with 2 mL of ethanol, followed by ultrasonication for 10 s. A ca.20 μL quantity of this ink was then pipetted onto a carbon disk electrode having a diameter of 5 mm to form a thin catalyst layer. Following this, 2 μL of 0.2 wt% Nafion solution was dropped onto the catalyst layer, after which the sample was dried in air at 60 °C for 30 min. The amounts of Pt attached on the carbon disk of each electrode are summarized in Table 2. All of the electrochemical trials were performed with a rotating disk electrode system (RRDE-3A, ALS Co., Ltd., Tokyo, Japan) together with a gas-tight water-jacketed Pyrex glass cell. A Pt wire and a reversible hydrogen electrode (RHE) were used as the counter and reference electrodes, respectively. Cyclic voltammetry (CV) data were acquired from 0.05 to 1.2 V at a scan rate of 50 mV s−1 in a 0.1 M HClO4 solution deaerated with Ar at 30 °C. The ECSA of each specimen was estimated from the electrical charge associated with the hydrogen desorption wave, ΔQH, in the CV data, with a value of ΔQH = 210 μC cm−2 expected for smooth polycrystalline Pt [19,20]. Hydrodynamic linear sweep voltammetry (LSV) data for the ORR were recorded from 0.3 to 1.0 V at a scan rate of 10 mV s−1 employing the same electrolyte solution as used in the CV experiments but saturated with O2.

3. Results and Discussion

3.1. Characterization of Catalysts

Figure 1 presents TEM images and particle size distribution histograms for the five different Ptdnm/C powders prepared with 4.6, 11.8, 23.4, 24.0, and 47.9 mmol L−1 H2PtCl6·6H2O concentrations. The d values and standard deviations of these Ptdnm/C were 1.1 ± 0.2, 1.2 ± 0.2, 1.3 ± 0.2, 1.4 ± 0.2, and 1.8 ± 0.2 nm, respectively. For comparison, the TEM image and the particle size distribution histogram for a commercial Pt/C (TEC10EA20E, 20 wt% Pt dispersed on the same graphitized carbon black support as that of our Ptdnm/C) in Figure S2 in the SI. It was found that the Pt particles in our Ptdnm/C are very uniformly dispersed on the C support, and their size distribution is fairly narrow. The d values increased approximately in proportion to the increases in H2PtCl6·6H2O concentration, as demonstrated in Figure 2. A conceptual diagram of the platinum particle formation process is shown in Figure S3 in the SI. The homogeneous mixing of platinum salts and carbon in the ethanol solvent results in the uniform formation of platinum nuclei on defects in the carbon. These nuclei grow to any size depending on the concentration of platinum salts, as shown in Figure 1 and Figure 2. As an example, the results of the microstructural analysis of the Pt1.4nm/C are provided in Figure 3. Figure 3B shows the electron diffraction (ED) pattern of the region selected in Figure 3A. This pattern could be assigned to the (111), (220) and (420) planes of a face-centered cubic structure. The high-resolution STEM (HR-STEM) image presented in Figure 3C also demonstrates that the inter-lattice distance in the front-facing plane was 2.21 Å, corresponding to the (111) plane distance. The orientation of the (111) plane and the angle of the particle contour indicate that these particles had a cuboctahedron geometry, as shown in the diagram in Figure 3D. As a result, this work assessed the Pt particles based on a cuboctahedral model.

3.2. CV Measurements

Figure 4 shows the CV data in the region corresponding to the hydrogen desorption wave together with the full range data (inset). Prior studies with well-defined Pt(hkl) single-crystal electrodes have provided an improved understanding of the properties of each lattice plane [7,21,22,23,24]. On the basis of these previous results, it is possible to discuss the significance of the change in the shape of the hydrogen desorption wave in Figure 4. Here, the peaks in the lower potential region (around 0.1 V) correspond to hydrogen adsorption and desorption at the structure with the lower Miller index (110) (i.e., the step-like site) [23,24]. The peaks at 0.2 V include a contribution from the strong adsorption of hydrogen on the steps of the (100) structure [24]. On the other hand, it is difficult to identify the hydrogen waves associated with the (111) structure on Pt nanoparticles because the potential region exhibiting hydrogen waves in the (111) structure overlaps with the potential region of the polycrystalline structure [24,25]. With decreases in particle size, the shoulder peak at low potential increased in intensity, whereas the (110)/(100) peak intensity ratio reached a maximum in the case of the Pt1.1nm/C catalyst.
Assuming a cuboctahedral shape for the Pt1.1nm particles, the number of atoms, Natom = 55, contained in a Pt1.1nm particle with L = 3 layers can be calculated using the following equations [26,27]:
Natom = (d/aPt)3 × (2π/3)
and
(10/3) × L3 − 5 × L2 + (11/3) × L − 1 = Natom
where aPt is the lattice constant of the Pt (aPt = 0.392 nm). The present cuboctahedral model for platinum, which can comprise any number of layers, is provided in Figure 5. It is evident that, as L decreases (i.e., as d decreases), the proportion of the surface occupied by the (100) and (111) planes decreases. At L = 3, the majority of the Pt1.1nm/C surface is expected to consist of (110) planes.
The SSA values were calculated as follows:
SSA = ((4/3) × πr3)/(ρ4πr2) = 6/(ρ × d)
where ρ and r are the density of Pt (ρ = 21.5 g cm−3) and the radius of the particle, respectively. These values, along with the ECSA data, are summarized in Table 2. The ECSA values for the Pt1.8nm/C and Pt1.4nm/C were 176 and 195 m2 g−1, respectively, which were close to the SSA values calculated by assuming a spherical shape for the Pt particles. These results indicate that the ECAA was nearly 100%, as shown in Table 2. However, the ECAA values decreased in the case of particles having sizes of less than d = 1.3 nm due to a decrease in the ECSA values. This electrochemical inactivation, which occurred with decreasing particle size, has also been observed in theoretical studies [29,30]. The hydrogen adsorption energy of Pt particles consisting of 147 atoms (corresponding to a diameter of 1.6 nm) was found to be almost the same as that of the bulk metal but increased for 55 atoms (corresponding to a diameter of 1.1 nm) [30]. Thus, the adsorption energy of hydrogen atoms gradually increased with decreases in particle size [29,30]. Thus, Pt1.1nm/C likely did not adsorb the expected amount of hydrogen on its surface.

3.3. ORR Activities

The LSV data and Koutecky–Levich plots (I−1 vs. ω−1/2) generated at 0.85 V and 0.90 V using electrodes made with four different Ptdnm/C specimens coated in Nafion are shown in Figure 6. In each case, a linear relationship with a constant slope was obtained for the plots. The kinetically controlled currents (I) were calculated by extrapolating these relationships to ω = 0. The kinetically controlled SA and the MA for each catalyst were calculated based on the ECSA determined from the CV results and the mass of Pt initially loaded (mPt), respectively, as follows:
SA = I/(ECSA × mPt)
MA = I/mPt
Figure 7 and Figure 8 show the changes in SA and MA associated with the ORR at 0.85 V and 0.90 V, respectively, as a function of d. As shown in Figure 7, the SA value of the Pt1.8nm/C catalyst was 1.2 mA cm−2, which was similar to that of a standard commercial Pt/CB catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, d = 2.5 nm). It can be assumed that there would be no change in SA at particle sizes greater than 1.8 nm. In fact, the particle size range obtained in the present work was consistent with the ranges in prior studies that found no particle size effect. As an example, Yano et al. demonstrated no change in SA in the size range above 2 nm [14]. In contrast, the SA values increased rapidly when the particle size dropped below 1.8 nm, reaching a maximum at 1.3 nm (SA = 4.8 mA cm−2, approximately four times the value for a standard Pt/CB material) and then decreasing rapidly. The MA values exhibited trends much the same as those shown by the SA values (Figure 7B). As can be seen from Figure 8, the variations in SA and MA at 0.90 V also showed very similar trends. However, the SA values were lower than those of the standard Pt/CB. One possible cause is the effect of surface oxidation of Pt. The formation of oxide species on a Pt surface at 0.90 V during ORR has been demonstrated via X-ray photoelectron spectroscopy combined with an electrochemical cell (EC-XPS) research [31]. Another possible cause is that the local coordination number and/or distance of Pt is different between our catalyst and the standard catalyst, which affects the oxidation state and electronic state of the Pt surface [32]. The details are currently under investigation using the in situ X-ray absorption fine structure (XAFS) technique and will be reported separately as part of the clarification of the activity mechanism.
Here, we discuss why the ORR activity shows a maximum around d = 1.3 nm. Prior research concerning well-defined single-crystal Pt electrodes has confirmed that ORR activity increases with changes in the crystal plane in the order of (111) << (100) < (110) [7,33]. In addition, the proportion of (110) planes (edges + corners) on the surface of the particles increased as the d decreased (Figure 5). Therefore, the present results showing increased ORR activity on going from a d of 1.8 to 1.3 nm are consistent with the crystallographic data. Even so, this effect related to the proportion of (110) planes on the surface cannot be applied to the Pt1.1nm specimen. This is due to the increased proportion of corners with relatively low ORR activity between the two types of platinum (i.e., edges and corners) in the (110) surface [34].
This work attempted to explain why the SA values decreased at d smaller than 1.3 nm. An important point to consider here is the relationship between ECAA and SA. The data indicate that the d value associated with the maximum SA coincided with the value at which ECAA began to decrease (Table 1 and Figure 4). As noted, the value of ECAA was affected by the hydrogen adsorption energy. The adsorption energy of oxygen on particle surfaces smaller than 1.3 nm may also have been different from that on larger particles, leading to a decrease in activity. Because MA is defined as SA × ECSA, both these variables will have a synergistic effect on MA. In the present study, maxima of both ORR activity and ECAA and minima of d values were found in a very narrow particle size range (approximately 1–2 nm).

4. Conclusions

Ultrafine Pt nanoparticles were prepared on a carbon support with well-controlled particle sizes of less than 2 nm. The effect of the Pt particle size (d) on ORR activity was investigated. Both the ORR specific activity, SA, and the Pt particle surface utilization efficiency, ECAA, showed maximum values in a very narrow size range from 1 to 2 nm. The present results demonstrate that the maximum ORR activity can be determined by plotting ECAA values as a function of d. With respect to ORR activity, we have been able to identify the minimum size of Pt particles to maximize their catalytic potential. In the future, we believe that how to maintain this catalytic potential, i.e., compatibility with durability, will be an important key to the widespread use of PEFCs.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/surfaces7030030/s1, Figure S1: TEM images for prepared Pt/C powders with heat-treatment at various temperature.; Figure S2: TEM images and particle size distribution histogram for commercial Pt/C powders (TEC10EA20E, Tanaka Kikinzoku Kogyo).; Figure S3: Illustration of the formation process of Pt particles.

Author Contributions

H.Y. designed and performed the experiments and conducted the experimental data analysis. K.I. managed the planning and execution of research activities. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Conflicts of Interest

Hiroshi Yano and Kouta Iwasaki are employed by the Toyota Boshoku Corporation. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. St. John, C.S.; Dutta, I.; Angelopoulos, A.P. Synthesis and Characterization of Electrocatalytically Active Platinum Atom Clusters and Monodisperse Single Crystals. J. Phys. Chem. C 2010, 114, 1315–1325. [Google Scholar] [CrossRef]
  2. Siburian, R.; Kondo, T.; Nakamura, J. Size Control to a Sub-Nanometer Scale in Platinum Catalysts on Graphene. J. Phys. Chem. C 2013, 117, 3635–3645. [Google Scholar] [CrossRef]
  3. Shen, Y.; Zhang, Z.; Xiao, K.; Xi, J. Electrocatalytic Activity of Pt Subnano/Nanoclusters Stabilized by Pristine Graphene Nanosheets. Phys. Chem. Chem. Phys. 2014, 16, 21609–21614. [Google Scholar] [CrossRef]
  4. Gao, J.J.; Du, P.; Zhang, Q.H.; Shen, X.; Chiang, F.-K.; Wen, Y.R.; Lin, X.; Liu, X.J.; Qiu, H.J. Platinum Single Atoms/Clusters Stabilized in Transition Metal Oxides for Enhanced Electrocatalysis. Electrochim. Acta 2019, 297, 155–162. [Google Scholar] [CrossRef]
  5. Peuckert, M.; Yoneda, T.; Betta, R.A.D.; Boudart, M. Oxygen Reduction on Small Supported Platinum Particles. J. Electrochem. Soc. 1986, 133, 944–946. [Google Scholar] [CrossRef]
  6. Kinoshita, K. Particle Size Effects for Oxygen Reduction on Highly Dispersed Platinum in Acid Electrolytes. J. Electrochem. Soc. 1990, 137, 845–848. [Google Scholar] [CrossRef]
  7. Markovic, N.; Gasteiger, H.; Ross, P. Kinetics of Oxygen Reduction on Pt (hkl) Electrodes: Implications for the Crystallite Size Effect with Supported Pt Electrocatalysts. J. Electrochem. Soc. 1997, 144, 1591–1597. [Google Scholar] [CrossRef]
  8. 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. Appl. Catal. B Environ. 2005, 56, 9–35. [Google Scholar] [CrossRef]
  9. Shinozaki, K.; Morimoto, Y.; Pivovara, B.S.; Kocha, S.S. Re-examination of the Pt Particles Size Effect on the Oxygen Reduction Reaction for Ultrathin Uniform Pt/C Catalyst Layers without Influence from Nafion. Electrochim. Acta 2016, 213, 783–790. [Google Scholar] [CrossRef]
  10. Garlyyev, B.; Kratzl, K.; Rück, M.; Michalička, J.; Fichtner, J.; Macak, J.M.; Kratky, T.; Günther, S.; Cokoja, M.; Bandarenka, A.S.; et al. Optimizing the Size of Platinum Nanoparticles for Enhanced Mass Activity in the Electrochemical Oxygen Reduction Reaction. Angew. Chem. Int. Ed. 2019, 58, 9596–9600. [Google Scholar] [CrossRef]
  11. Zeliger, H.I. Fuel Cell Performance as a Function of Catalyst Surface Area. J. Electrochem. Soc. 1967, 114, 144. [Google Scholar] [CrossRef]
  12. Vogel, W.M.; Lundquist, J.T. Reduction of Oxygen on Teflon-Bonded Platinum Electrodes. J. Electrochem. Soc. 1970, 117, 1512–1516. [Google Scholar] [CrossRef]
  13. Blurton, K.F.; Greenberg, P.; Oswin, H.G.; Rutt, D.R. The Electrochemical Activity of Dispersed Platinum. J. Electrochem. Soc. 1972, 119, 559–563. [Google Scholar] [CrossRef]
  14. Yano, H.; Watanabe, M.; Iiyama, A.; Uchida, H. Particle-Size Effect of Pty Cathode Catalysts on Durability in Fuel Cells. Nano Energy 2016, 29, 323–333. [Google Scholar] [CrossRef]
  15. Mayrhofer, K.J.J.; Strmcnik, D.; Blizanac, B.B.; Stamenkovic, V.; Arenz, M.; Markovic, N.M. Measurement of Oxygen Reduction Activities via the Rotating Disk Electrode Method: From Pt Model Surfaces to Carbon-Supported High Surface Area Catalysts. Electrhochim. Acta 2008, 53, 3181–3188. [Google Scholar] [CrossRef]
  16. Shao, M.; Peles, A.; Shoemaker, K. Electrocatalysis on Platinum Nanoparticles: Particle Size Effect on Oxygen Reduction Reaction Activity. Nano Lett. 2011, 11, 3714–3719. [Google Scholar] [CrossRef] [PubMed]
  17. Inaba, M.; Zana, A.S.; Quinson, J.; Bizzotto, F.; Dosche, C.; Dworzak, A.; Oezaslan, M.; Simonsen, S.B.; Kuhn, L.T.; Arenz, M. The Oxygen Reduction Reaction on Pt: Why Particle size and Interparticle Distance Matter. ACS Catal. 2021, 11, 7144–7153. [Google Scholar] [CrossRef]
  18. Park, Y.-C.; Tokiwa, H.; Kakinuma, K.; Watanabe, M.; Uchida, M. Effects of carbon supports on Pt distribution, ionomer coverage and cathode performance for polymer electrolyte fuel cells. J. Power Sources 2016, 315, 179–191. [Google Scholar] [CrossRef]
  19. Watanabe, M.; Motoo, S. Electrocatalysis by Ad-atoms: Part III. Enhancement of the Oxidation of Carbon Monoxide on Platinum by Ruthenium Ad-atoms. J. Electroanal. Chem. 1975, 60, 275–283. [Google Scholar] [CrossRef]
  20. Uchida, H.; Ikeda, N.; Watanabe, M. Electrochemical Quartz Crystal Microbalance Study of Copper Adatoms on Gold Electrodes Part II. Further Discussion on the Specific Adsorption of Anions from Solutions of Perchloric and Sulfuric Acid. J. Electroanal. Chem. 1997, 424, 5–12. [Google Scholar] [CrossRef]
  21. López, M.R.; Gullón, J.S.; Herrero, E.; Tuñón, P.; Feliu, J.M.; Aldaz, A.; Carrasquillo, A., Jr. Electrochemical Reactivity of Aromatic Molecules at Nanometer-Sized Surface Domains: From Pt(hkl) Single Crystal Electrodes to Preferentially Oriented Platinum Nanoparticles. J. Am. Chem. Soc. 2010, 132, 2233–2242. [Google Scholar] [CrossRef]
  22. Jerkiewicz, G. Electrochemical Hydrogen Adsorption and Absorption. Part 1: Under-potential Deposition of Hydrogen. Electrocatalysis 2010, 1, 179–199. [Google Scholar] [CrossRef]
  23. Solla-Gullón, J.; Rodriguez, P.; Aldaz, E.; Feliu, J.M. Surface Characterization of Platinum Electrodes. Phys. Chem. Chem. Phys. 2008, 10, 1359–1373. [Google Scholar] [CrossRef]
  24. Santos, V.P.; Camara, G.A. Platinum Single Crystal Electrodes: Prediction of the Surface Structures of Low and High Miller Indexes Faces. Results Surf. Interfaces 2021, 3, 100006. [Google Scholar] [CrossRef]
  25. Mensharapov, R.M.; Spasov, D.D.; Ivanova, N.A.; Zasypkina, A.A.; Smirnov, S.A.; Grigoriev, S.A. Screening of Carbon-Supported Platinum Electrocatalysts Using Frumkin Adsorption Isotherms. Inorganics 2023, 11, 103–116. [Google Scholar] [CrossRef]
  26. van der Klink, J.J.; Brom, H.B. NMR in Metals, Metal Particles and Metal Cluster Compounds. Prog. Nucl. Magn. Reason. Spectrosc. 2000, 36, 89–201. [Google Scholar] [CrossRef]
  27. Yano, H.; Inukai, J.; Uchida, H.; Watanabe, M.; Babu, P.K.; Kobayashi, T.; Chung, J.H.; Oldfield, E.; Wieckowski, A. Particle-Size Effect of Nanoscale Platinum Catalysts in Oxygen Reduction Reaction an Electrochemical and 195Pt EC-NMR Study. Phys. Chem. Chem. Phys. 2006, 8, 4932–4939. [Google Scholar] [CrossRef]
  28. Tristsaris, G.A.; Greeley, J.; Rossmeisl, J.; Nørskov, J.K. Atomic-Scale Modeling of Particle Size Effects for the Oxygen Reduction Reaction on Pt. Catal. Lett. 2011, 141, 909–913. [Google Scholar] [CrossRef]
  29. Okamoto, Y. Comparison of Hydrogen Atom Adsorption on Pt Clusters with that on Pt Surfaces: A Study from Density-Functional Calculations. Chem. Phys. Lett. 2006, 429, 209–213. [Google Scholar] [CrossRef]
  30. Gudmundsdóttir, S.; Skúlason, E.; Weststrate, K.-J.; Juurlink, L.; Jónsson, H. Hydrogen adsorption and desorption at the Pt(110)-(1×2) surface: Experimental and theoretical study. Phys. Chem. Chem. Phys. 2013, 15, 6323–6332. [Google Scholar] [CrossRef]
  31. Watanabe, M.; Tryk, D.A.; Wakisaka, M.; Yano, H.; Uchida, H. Overview of recent developments in oxygen reduction electrocatalysis. Electrochim. Acta 2012, 84, 187–201. [Google Scholar] [CrossRef]
  32. Song, Z.; Zhu, Y.-N.; Liu, H.; Banis, M.N.; Zhang, L.; Li, J.; Doyle-Davis, K.; Li, R.; Sham, T.-K.; Yang, L.; et al. Engineering the Low Coordinated Pt Single Atom to Achieve the Superior Electrocatalytic Performance toward Oxygen Reduction. Small 2020, 16, 2003096. [Google Scholar] [CrossRef] [PubMed]
  33. Wakisaka, M.; Udagawa, Y.; Suzuki, H.; Uchida, H.; Watanabe, M. Structural Effects on the Surface Oxidation Processes at Pt Single-Crystal Electrodes Studied by X-ray Photoelectron Spectroscopy. Energy Environ. Sci. 2011, 4, 1662–1666. [Google Scholar] [CrossRef]
  34. Wang, S.; Omidvar, N.; Marx, E.; Xin, H. Overcoming Site Heterogeneity In Search of Metal Nanocatalysts. ACS Comb. Sci. 2018, 20, 567–572. [Google Scholar] [CrossRef]
Surfaces 07 00030 g001
Figure 1. TEM images (low and high magnification) and particle size distribution histograms for pristine Ptdnm/C powders having d values of (A) 1.8, (B) 1.4, (C) 1.3, (D) 1.2, and (E) 1.1 nm. The particle size distribution histograms were measured visually with a ruler and determined for 300 particles in randomly selected multiple images.
Figure 1. TEM images (low and high magnification) and particle size distribution histograms for pristine Ptdnm/C powders having d values of (A) 1.8, (B) 1.4, (C) 1.3, (D) 1.2, and (E) 1.1 nm. The particle size distribution histograms were measured visually with a ruler and determined for 300 particles in randomly selected multiple images.
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Figure 2. The relationship between the concentration of the Pt precursor compound ([H2PtCl6·6H2O]) and d.
Figure 2. The relationship between the concentration of the Pt precursor compound ([H2PtCl6·6H2O]) and d.
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Figure 3. (A) TEM image, (B) ED pattern, (C) HR-STEM image and (D) diagram of the cuboctahedral model for the Pt1.4nm/C powder.
Figure 3. (A) TEM image, (B) ED pattern, (C) HR-STEM image and (D) diagram of the cuboctahedral model for the Pt1.4nm/C powder.
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Figure 4. Cyclic voltammograms obtained from Nafion-coated Ptdnm/C electrodes in Ar-purged 0.1 M HClO4 solutions at 30 °C with a potential scan rate of 50 mV s−1.
Figure 4. Cyclic voltammograms obtained from Nafion-coated Ptdnm/C electrodes in Ar-purged 0.1 M HClO4 solutions at 30 °C with a potential scan rate of 50 mV s−1.
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Figure 5. A diagram of the cuboctahedral models used for the Pt particles with various L values. * Fraction of (110) plane and (111) + (100) planes plane on the surface of Pt particles [28].
Figure 5. A diagram of the cuboctahedral models used for the Pt particles with various L values. * Fraction of (110) plane and (111) + (100) planes plane on the surface of Pt particles [28].
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Figure 6. Hydrodynamic linear sweep voltammetries and Koutecky–Levich plots (I−1 vs. ω−1/2) at 0.85 V (●) and 0.90 V (Δ) in an O2-saturated electrolyte solution using Nafion-coated (A) Pt1.8nm/C, (B) Pt1.4nm/C, (C) Pt1.3nm/C, (D) Pt1.2nm/C, and (E) Pt1.1nm/C electrodes with a scan rate of 10 mV s−1.
Figure 6. Hydrodynamic linear sweep voltammetries and Koutecky–Levich plots (I−1 vs. ω−1/2) at 0.85 V (●) and 0.90 V (Δ) in an O2-saturated electrolyte solution using Nafion-coated (A) Pt1.8nm/C, (B) Pt1.4nm/C, (C) Pt1.3nm/C, (D) Pt1.2nm/C, and (E) Pt1.1nm/C electrodes with a scan rate of 10 mV s−1.
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Figure 7. Particle size-dependence of kinetically controlled (A) specific activity (SA) and (B) mass activity (MA) during the ORR on Nafion-coated Ptdnm/C (d = 1.1, 1.2, 1.3, 1.4, and 1.8 nm) electrodes in 0.1 M HClO4 solutions at 30 °C. The square symbols indicate value for a standard commercial Pt/C catalyst (d = 2.5 ± 0.4 nm). All data were acquired with a working electrode potential of 0.85 V.
Figure 7. Particle size-dependence of kinetically controlled (A) specific activity (SA) and (B) mass activity (MA) during the ORR on Nafion-coated Ptdnm/C (d = 1.1, 1.2, 1.3, 1.4, and 1.8 nm) electrodes in 0.1 M HClO4 solutions at 30 °C. The square symbols indicate value for a standard commercial Pt/C catalyst (d = 2.5 ± 0.4 nm). All data were acquired with a working electrode potential of 0.85 V.
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Figure 8. Particle size-dependence of kinetically controlled (A) specific activity (SA) and (B) mass activity (MA) during the ORR on Nafion-coated Ptdnm/C (d = 1.1, 1.2, 1.3, 1.4, and 1.8 nm) electrodes in 0.1 M HClO4 solutions at 30 °C. The square symbols indicate value for a standard commercial Pt/C catalyst (d = 2.5 ± 0.4 nm). All data were acquired with a working electrode potential of 0.90 V.
Figure 8. Particle size-dependence of kinetically controlled (A) specific activity (SA) and (B) mass activity (MA) during the ORR on Nafion-coated Ptdnm/C (d = 1.1, 1.2, 1.3, 1.4, and 1.8 nm) electrodes in 0.1 M HClO4 solutions at 30 °C. The square symbols indicate value for a standard commercial Pt/C catalyst (d = 2.5 ± 0.4 nm). All data were acquired with a working electrode potential of 0.90 V.
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Table 1. Preparation conditions of Ptdnm/C catalysts.
Table 1. Preparation conditions of Ptdnm/C catalysts.
CatalystsH2PtCl6·6H2O
(mmol L−1)		EtOH 1
(mL)		Pt Loaded 2
(wt%)		Average Particle Size, d 3
(nm)
Pt1.1nm/C4.625.020.01.1 ± 0.2
Pt1.2nm/C11.85.011.81.2 ± 0.2
Pt1.3nm/C23.45.019.81.3 ± 0.2
Pt1.4nm/C24.05.012.61.4 ± 0.2
Pt1.8nm/C47.92.517.51.8 ± 0.2
1 Solvent to dissolve H2PtCl6·6H2O. 2 Pt weight percent in Pt/C catalysts estimated by weight loss using thermogravimetry (TG). 3 Average particle size based on the TEM observation.
Table 2. Properties of Nafion-coated Ptdnm/C electrodes.
Table 2. Properties of Nafion-coated Ptdnm/C electrodes.
Electrodes 1mPt2
(μg cm−2)		SSA3
(m2 g−1)		ECSA4
(m2 g−1)		ECAA5
(%)
Pt1.1nm/C2825314256
Pt1.2nm/C3023212152
Pt1.3nm/C3221416678
Pt1.4nm/C2019919598
Pt1.8nm/C30155176113
1 Nafion-coated Ptdnm/C. 2 Amount of Pt attached on the carbon disk substrate. 3 Specific surface area calculated by Equation (3). 4 Electrochemical surface area. 5 Electrochemical active area [=(ECSA/SSA) × 100].
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Yano, H.; Iwasaki, K. Size-Dependence of the Electrochemical Activity of Platinum Particles in the 1 to 2 Nanometer Range. Surfaces 2024, 7, 472-481. https://doi.org/10.3390/surfaces7030030

AMA Style

Yano H, Iwasaki K. Size-Dependence of the Electrochemical Activity of Platinum Particles in the 1 to 2 Nanometer Range. Surfaces. 2024; 7(3):472-481. https://doi.org/10.3390/surfaces7030030

Chicago/Turabian Style

Yano, Hiroshi, and Kouta Iwasaki. 2024. "Size-Dependence of the Electrochemical Activity of Platinum Particles in the 1 to 2 Nanometer Range" Surfaces 7, no. 3: 472-481. https://doi.org/10.3390/surfaces7030030

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