In the pursuit of a carbon-neutral electricity generation, hydrogen fuel cells offer a promising solution. Among these, Proton Exchange Membrane Fuel Cells (PEMFCs) stand out for their ability to convert hydrogen into clean energy, with water as the only by-product. However, widespread adoption of PEMFCs is limited by the supply of platinum (Pt) catalysts, which are essential for the oxygen reduction reaction (ORR) at the heart of these fuel cells.

Our recent study, published in Nature Communications, addresses a key challenge in PEMFC performance: how does the structure of the carbon support affect the efficiency of Pt catalysts. We report a sustainable synthesis for carbon catalyst supports using xylose to produce highly ordered mesoporous carbon (HOMC). By investigating the interactions between Pt catalysts and ionomers, such as Nafion™, we demonstrated biomass-derived HOMC significantly enhances fuel cell efficiency compared to traditional petroleum-based carbon supports via the optimal mesoporosity.

Why Carbon Structure Matters

The performance of PEMFCs depends not just on the amount of Pt used, but also on how effectively the Pt is distributed on the carbon support. Traditional carbon supports, such as Vulcan or Ketjenblack, have their own limitations: Pt particles can either be too exposed, leading to ionomer poisoning, or too buried in the carbon’s pores, limiting the oxygen accessibility.

Fig 1. Ionomer-support-nanoparticle interactions in Pt/C catalysts.

In this study, we introduced a new carbon support synthesized from xylose, a carbohydrate derived from plants. This material—highly ordered mesoporous carbon—features uniform, cylindrical pores that allow optimal placement of Pt nanoparticles. These mesopores provide the perfect balance: they prevent the ionomer from poisoning the Pt surface while still allowing oxygen to reach the active sites, making the fuel cell more efficient.

Key Insights from Operando X-ray Absorption Spectroscopy

A highlight of our work was the use of operando X-ray Absorption Spectroscopy at both Diamond Light Source Ltd., UK and the European Synchrotron Radiation Facility. Following the acceptance of our proposal (SP29913-1 and 28-01-1311), we were given two days’ access to beamline B18 at Diamond and three days’ access to XMaS beamline at ESRF.  The expertise of their dedicated teams, including Dr. Celorrio, Dr. Ramanan, Dr. Thompson, and Dr. Bouchenoire, was invaluable to our measurements and analyses.

Fig 2. Operando electrochemical cell in action at Diamond Light Source B18 (left) and ESRF XMaS (right), capturing real-time interactions between platinum nanoparticles and ionomer.

During our experiment we scanned the potential whilst firing five hundred billion X-rays at our sample every second, changing the energy of these rays to excite platinum electrons and watching how they interacted with nearby atomic neighbours. Synchrotron X-ray radiation allowed us to follow the local structure and coordination of platinum in near real-time, enabling us to observe how the ionomer interacted with the platinum nanoparticles. We discovered that the mesoporous structure of our biomass-derived carbon support reduces the ionomer’s tendency to block oxygen access to the catalyst; the opposite of what we observed with traditional carbon supports. By precisely controlling the location of platinum nanoparticles, we were then able to enhance the oxygen reduction activity, leading to better performance under real-world fuel cell conditions.

Sustainability at the Core

Our approach not only enhances fuel cell performance but also supports the shift toward sustainability. By using biomass-derived carbon instead of petroleum-based materials, we reduce dependence on fossil fuels while creating high-performance materials for energy applications.

By fine-tuning the structure of carbon supports, our work contributes to making hydrogen fuel cells more efficient, affordable, and sustainable. We believe that sustainable materials like biomass-derived carbon will be key to advancing future fuel cell technologies.