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Improving Catalyst Efficiency in Hydrogen Fuel Cells with X-ray Absorption Spectroscopy

A recent article in Nature Communications examined interactions between ionomers and catalysts in proton exchange membrane fuel cells (PEMFCs), focusing on how carbon support morphology and porosity affect platinum (Pt) catalyst performance during oxygen reduction reactions (ORR).

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The researchers used X-ray absorption spectroscopy (XAS) to assess ionomer coverage on Pt catalysts, analyzing these interactions to understand their impact on fuel cell electrode efficiency.

The study aimed to optimize catalyst designs to improve fuel cell performance and address challenges in ionomer-catalyst interactions, particularly to reduce dependence on precious metals like platinum.

Advancements in Fuel Cell Technology

The transition to sustainable energy sources, especially hydrogen, has increased interest in fuel cell technology due to its potential for low carbon emissions. PEMFCs play an important role in the hydrogen economy by converting hydrogen fuel into energy, with water as the only by-product.

However, their widespread adoption is hindered by the high cost and limited supply of Pt-based catalysts, which are essential for the ORR at the cathode. Despite advancements in non-precious metal catalysts, Pt remains vital in fuel cell technology due to its superior activity and stability in acidic environments.

To address these challenges, the U.S. Energy Department has set strict goals for reducing platinum group metal (PGM) content in fuel cells, prompting new approaches in catalyst and support material design. Research has shown that interactions among ionomers, catalysts, and carbon supports are important for PEMFC efficiency and durability, highlighting the need to understand these interactions to improve performance.

About the Research

In this paper, the authors synthesized highly ordered mesoporous carbon (HOMC) from biomass, specifically xylose, using hydrothermal carbonization. The synthesis process involved dissolving xylose and Pluronic F-127 in sulfuric acid, followed by hydrothermal treatment at 150 °C. The resulting material was characterized by transmission electron microscopy (TEM) and nitrogen sorption analysis, which confirmed its mesoporous structure and uniform pore size distribution.

Three Pt/C catalysts were prepared: Pt/HOMC, Pt/Ketjenblack, and Pt/Vulcan XC-72. Platinum nanoparticles were deposited onto the carbon supports using a polyol method, with careful pH control, to maintain consistent particle sizes. The catalysts were then evaluated using electrochemical measurements under gas diffusion electrode configurations, allowing for a realistic assessment of their ORR performance.

The researchers used operando XAS to monitor ionomer coverage on the Pt surface during the ORR process, providing insights into the dynamic interactions between the ionomer and catalyst. The electrochemical surface area (ECSA) was measured using carbon monoxide (CO) stripping voltammetry. Performance was also assessed at varying current densities to examine mass transport limitations. Additionally, gas sorption analysis characterized the porosity of the supports before and after ionomer incorporation.

Key Findings and Insights

The authors showed that the Pt/HOMC catalyst exhibited superior ORR performance compared to Pt/Ketjenblack and Pt/Vulcan. This improvement resulted from the optimal positioning of Pt nanoparticles at the entrances of the mesopores. This arrangement enhanced reactant accessibility while reducing ionomer-induced transport resistance.

Operando XAS results showed that Pt nanoparticles in the Pt/Vulcan catalyst experienced considerable sulfonate adsorption from the ionomer, which negatively impacted catalytic activity. In contrast, Pt/Ketjenblack displayed limited ionomer interaction, but severe transport limitations were noted due to the deep positioning of Pt nanoparticles within the support pores.

The study found that ionomer coverage primarily affected the microporosity of the supports, with significant pore blocking observed in both Pt/HOMC and Pt/Vulcan catalysts. The findings suggest that optimizing catalyst performance involves preserving mesopore accessibility while carefully managing ionomer distribution. The researchers also noted that non-precious metal catalysts would require a 200 % performance improvement to meet the efficiency targets established for Pt-based PEMFCs, emphasizing the challenges remaining in the field.

Applications

This research has significant potential for advancing fuel cell technology. By understanding ionomer-catalyst interactions, scientists and engineers can design more efficient PEMFCs that utilize less precious metal, thereby reducing costs and environmental impact.

The findings suggest that future catalyst designs should prioritize placing Pt nanoparticles near mesopore openings to balance accessibility and reactivity. Furthermore, operando XAS can be extended to study other catalytic systems beyond PEMFCs. This approach also supports the development of new catalyst formulations that can improve the performance of hydrogen fuel cells to achieve net zero goals.

Conclusion and Future Directions

The development of HOMC from biomass not only provides a sustainable alternative for catalyst support but also enhances the catalytic activity of Pt nanoparticles. The findings highlight the importance of a balanced design that considers the structural features of both the catalyst and support to boost fuel cell efficiency.

Future work should focus on scaling HOMC synthesis and exploring alternative carbon sources to reduce petroleum dependency. Molecular-level studies of ionomer-catalyst interactions could also deepen insights for fuel cell optimization. Overall, this research paves the way for innovative catalyst designs that support sustainable energy technology.

Discover More: Nanotechnology in Fuel Cells

Journal Reference

Wang, M., et al. Resolving optimal ionomer interaction in fuel cell electrodes via operando X-ray absorption spectroscopy. Nat Commun 15, 9390 (2024). DOI: 10.1038/s41467-024-53823-z, https://www.nature.com/articles/s41467-024-53823-z

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Muhammad Osama

Written by

Muhammad Osama

Muhammad Osama is a full-time data analytics consultant and freelance technical writer based in Delhi, India. He specializes in transforming complex technical concepts into accessible content. He has a Bachelor of Technology in Mechanical Engineering with specialization in AI & Robotics from Galgotias University, India, and he has extensive experience in technical content writing, data science and analytics, and artificial intelligence.

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