**2. Results and discussion**

#### **2.1 Physical characterization of the prepared electrocatalysts**

X-ray diffraction (XRD) and the high-resolution transmission electron microscope (HRTEM) were used to learn more about the catalyst structure. The XRD patterns were performed with the Bruker AXS D8 advance equipment with Cu-K radiation and a wavelength of 1.5406 nm. With a scanning step of 0.035°, the Bragg angle range was 2θ = 10–90°. The instrumental contribution to peak profile characteristics was determined using a standard α-Al2O3 sample. A JEOL 2010 TEM system operating at 200 kV was used to obtain the HRTEM micrographs. The HRTEM samples were made by dispersing the carbon-supported electrocatalysts in ethanol and then casting a drop of the suspension onto a Cu-grid covered in carbon film for analysis. For each electrocatalyst, the particle size determined by HRTEM was obtained using Image J software over multiple areas.

#### **2.2 XRD analysis**

XRD measurements were performed to obtain the crystallographic information of the prepared catalysts. The XRD results presented in **Figure 1** indicate that all prepared metal catalysts presented a typical face-centered cubic crystallographic structure of PtRu crystals. The Bragg angles indicate that varying bimetallic interactions or alloying occurred in the PtRu crystals due to different catalyst preparation methods. The diffraction peak for carbon is at about 2θ = 25°. Other peaks are at 2θ values of 39.9°, 46.21°, 67.8°, and 81.2°, which are indexed to (111), (200), (220), and (311) planes of PtRu/MWCNT crystal structure, respectively. The strongest and sharpest diffraction peak for all four samples is at around 2θ = 39.9° indexed as (111) reflection of PtRu/MWCNT crystal planes prepared through the modified polyol and polyol methods, while the other characteristic PtRu/MWCNT diffraction peaks at 2θ of about 46.21°, 67.8°, and 81.2° corresponded to (200), (220), and

#### **Figure 1.**

*XRD spectra of PtRu electrocatalysts supported on multi-walled carbon nanotubes (MWCNTs) prepared through the impregnation, polyol, modified polyol, and microwave-assisted modified polyol methods.*

*Investigation of Synthesis Methods for Improved Platinum-Ruthenium Nanoparticles… DOI: http://dx.doi.org/10.5772/intechopen.104541*

(311), respectively. Similar results were also reported by Kim et al. [20] and Wu et al. [21].

The crystalline size of the metal particles is calculated using Debye-Scherrer's equation, Kα/βCosθ, where K, Scherrer constant = 0.9, α, X-ray wavelength = 0.154 nm, and β(2θ), the width of the diffraction peak (rad). From **Table 1** the average particle size can be seen, with PtRu/MWCNT nanoparticles prepared through microwave-assisted modified polyol having the smallest crystalline size of 1.95 nm, followed by PtRu/MWCNT nanoparticles prepared through the modified polyol method with a crystalline size of 4.33 nm.

Catalyst nanoparticles are the dark dots as shown in the HRTEM micrographs in **Figure 2**. PtRu/MWCNT nanoparticles are well distributed with little agglomeration. PtRu/MWCNT electrocatalysts prepared through the microwave-assisted modified polyol method has the least agglomeration, followed by PtRu/MWCNT modified polyol when compared with other electrocatalysts evident from their higher electroactive catalyst surface areas of 4.15 102 m2 /g and 3.2 102 m2 /g, respectively an advantage for enhanced electrocatalytic activities. Both of these catalysts gave the smallest particle sizes of 1.87 and 4.14 nm, respectively. The other electrocatalysts PtRu on MWCNT support particle sizes were between 5.77 and 6.90 nm. The particle sizes of the electrocatalysts obtained were comparable with the average particle sizes following the order PtRu/MWCNT impregnation > PtRu/MWCNT polyol > PtRu/ MWCNT modified polyol > PtRu/MWCNT microwave-assisted modified polyol.

In **Figure 2** the histograms reveal the mean particle sizes and their nanoparticle size distributions for all PtRu/MWCNT electrocatalysts prepared through all four synthesis methods; however, the two electrocatalysts prepared through the impregnation method and polyol method exhibited better distribution of nanoparticles as compared to other electrocatalysts. The particle size was determined using Image J software estimated from 50 particles selected randomly from HRTEM micrographs of the PtRu/MWCNT nanoparticles. The mean particle sizes of PtRu/MWCNT impregnation, PtRu/MWCNT polyol, PtRu/MWCNT modified polyol, and PtRu/MWCNT microwave-assisted modified polyol were 6.90, 6.51, 4.14, and 1.87 nm, respectively.

#### **2.3 Electrochemical characterization of the electrocatalysts**

Electrochemical measurements were carried out at ambient temperatures using a three-electrode configuration, which includes a working electrode, a counter electrode, and a reference electrode. An Ag/AgCl electrode as a reference electrode and a Pt foil of a large area as a counter electrode were used. The working electrode was a glassy carbon disc (5 mm in diameter with a geometric area of 0.196 cm2 ) covered with a thin layer of catalyst of fine film. Before the experiment, the electrode substrate was pre-treated by polishing it with a 0.05 μm Al2O3 particle suspension on a moistened microcloth. All the electrochemical experiments were carried out, namely electrochemical impedance spectroscopy (EIS),


**Table 1.** *Properties of the PtRu electrocatalysts.*
