I. Introduction

Against the backdrop of the global energy structure transitioning towards cleaner, low-carbon solutions, hydrogen fuel cell technology, particularly Proton Exchange Membrane Fuel Cells (PEMFCs), is regarded as a revolutionary solution in areas such as transportation and energy storage due to its significant advantages, including high energy conversion efficiency, zero carbon emissions, and rapid start-up capability. However, a key challenge remains for the large-scale commercial adoption of this technology: the sluggish kinetics of the Oxygen Reduction Reaction (ORR), which severely limits the overall output power and efficiency of the cells. To accelerate this core reaction, highly active electrocatalysts must be used in the electrodes. Currently, platinum-based catalysts, especially platinum-on-carbon catalysts where platinum nanoparticles are supported on carbon materials, remain an irreplaceable choice that balances high activity with relative stability.

Platinum-based catalysts are those that use metallic platinum as the primary active component. In Proton Exchange Membrane Fuel Cells, platinum-based catalysts are among the most commonly used because they possess extremely high electrocatalytic activity, effectively promoting the oxidation and reduction reactions of hydrogen and oxygen at the electrodes to generate electricity. Platinum-based catalysts typically consist of platinum nanoparticles and a support, with commonly used support materials including carbon black, alumina, and carbon nanotubes. In practical applications, fuel cells often use carbon-supported platinum (Pt/C) as the catalyst for both the anode and cathode reactions. The platinum loading is typically as high as 20% or more, making their preparation significantly more difficult compared to conventional supported catalysts used in the chemical industry.

II. Application of XRD and SEM Techniques in the Analysis of Platinum-Carbon Catalysts

The activity of platinum-carbon (Pt/C) catalysts is influenced by a combination of multiple factors, including the size and dispersion state of platinum nanoparticles, the interaction between platinum and the carbon support, the pore structure and surface characteristics of the support, and the crystal structure of the catalyst. These factors are intertwined and collectively determine the catalytic performance of the catalyst. XRD technology can non-destructively and efficiently provide "fingerprint" information of these microstructures. By analyzing the diffraction patterns, one can determine the types of compounds present, the occurrence state of elements, and further calculate crystallite size information. SEM technology can intuitively reveal the distribution uniformity of platinum nanoparticles on the carbon support surface, their agglomeration state, and the pore structure of the support itself. This report utilizes both of these analytical techniques to characterize Pt/C catalysts, aiming to provide technical support for optimizing preparation processes and analyzing failure mechanisms.

III. Application Case

3.1 Instrument

Figure 1.  FRINGE EVS Benchtop X-Ray diffractometer, SuperSEM N10XL Desktop Scanning Electron Microscope (Click to learn more)

3.2 Sample Preparation

Figure 2. Pt-C catalyst sample

Place an appropriate amount of the sample into the groove of a glass sample holder, gently press it flat, and place it into the XRD instrument for testing.

Adhere conductive tape onto a pin-type sample stub, apply a small amount of powder onto the conductive tape, use an ear wash bulb to blow away excess large particles, and place the stub into the SEM instrument for testing.

IV. Analysis Results and Discussion

4.1 Phase Analysis Results

Figure 3 shows the diffraction pattern and phase analysis results of the platinum-carbon catalyst sample. The diffraction peaks in the pattern exhibit broadening and diffuse characteristics, indicating that each phase in the sample has a low degree of crystallinity and is primarily distributed at the nanoscale. Phase identification against the ICDD database confirmed the primary presence of metallic platinum (Pt) with a face-centered cubic (fcc) structure. No significant phases corresponding to platinum oxides or carbides were detected, indicating that the Pt in the sample exists as nano-metallic elemental substance.

Figure 3. XRD pattern and phase analysis results of the platinum-carbon catalyst.

4.2 Crystallite Size Calculation

The LaB6 standard reference material was used to correct for instrumental broadening. Based on the Scherrer equation, the average crystallite size of the platinum nanoparticles was calculated to be approximately 2.3 nm. This small crystallite size is favorable for achieving a high specific surface area, thereby enhancing catalytic activity and platinum atom utilization efficiency, while also helping to reduce the amount of precious Pt required. However, Pt nanoparticles with a size in the range of 2–5 nm possess extremely high surface energy. As the Pt content increases, these nanoparticles tend to agglomerate, making their preparation process considerably challenging. This represents a major difficulty in the development of high-performance platinum-carbon catalysts.

Table. Peak List

Figure 4. Crystallite Size Calculation

4.3 Evaluation of Nanoparticle Distribution

Due to the difference in atomic number between carbon and platinum, the particle contrast between the two differs in backscattered electron mode: carbon particles appear as dark regions, while platinum particles appear as bright regions. Figure 5 shows the micro-morphology of the platinum-carbon catalyst obtained by SEM observation, at a magnification of 5000×. The platinum nanoparticles appear as bright dots, relatively uniformly dispersed on the carbon support. This observation corroborates the nanoscale characteristics determined by XRD analysis, indicating good catalyst activity.

Figure 5. SEM morphology observation at 5000X

4.4 Conclusion

This combined analytical experiment confirmed that platinum in the platinum-carbon catalyst exists as a face-centered cubic metallic element, with an average crystallite size of 2.3 nm. Additionally, the SEM images revealed the dispersion state of the particles. This methodological system can provide comprehensive microstructural information and technical support for the research and development, process optimization, and quality evaluation of platinum-carbon catalysts.

V. Concluding Remarks

In fields such as fuel cells, petrochemical industry, and fine chemical synthesis, the improvement of catalyst performance often relies on the precise control of the active site structure. The synergistic application of XRD and SEM allows researchers to bridge the gap between the atomic scale and the micrometer scale, correlating structural characteristics with catalytic performance, thus providing solid characterization support for the design and development of high-performance catalysts. In the future, with the advancement of in-situ characterization techniques, the combined use of XRD and SEM under dynamic reaction conditions will further reveal the structural evolution of catalysts during operation, opening new possibilities for a deeper understanding of catalytic mechanisms and accurate prediction of catalyst lifespan.