Plasmonic Photocatalysis for Efficient Hydrogen Generation

Researchers at Rice University have developed a catalyst that uses light instead of heat to drive the reaction in Steam Methane Reforming (SMR), a key process in global hydrogen production. This innovation could make SMR entirely emissions-free, addressing the significant greenhouse gas emissions associated with the chemical process. The research may help extend catalyst lifespans, improve efficiency, and reduce costs in various industrial processes affected by coking—a form of carbon buildup that deactivates catalysts. 

Hydrogen is a powerful, versatile, and clean-burning energy resource that could play a crucial role in the transition to a sustainable energy system. However, the chemical process responsible for producing more than half of the world's hydrogen today remains a significant source of greenhouse gas emissions.

The newly developed copper-rhodium photocatalyst features an antenna-reactor configuration that, when exposed to a specific wavelength of light, converts methane and water vapor into hydrogen and carbon monoxide—a key feedstock for the chemical industry. This process occurs without the need for additional heating, making it a more environmentally friendly alternative.

This is one of our most impactful findings so far because it offers an improved alternative to what is arguably the most important chemical reaction for modern society. We developed a completely new, much more sustainable way of doing SMR.

Peter Nordlander, Wiess Chair and Professor, Rice University

The corresponding authors of the study are Nordlander and Naomi Halas, a Professor at Rice University, and Stanley C. Moore, a Professor of Electrical and Computer Engineering.

The new SMR reaction pathway builds upon a 2011 discovery by the Halas and Nordlander labs at Rice. They found that plasmons—collective oscillations of electrons in metal nanoparticles exposed to light—can emit "hot carriers," or high-energy electrons and holes. These hot carriers can be harnessed to drive chemical reactions, providing the foundation for the innovative approach to SMR.

We do plasmonic photochemistry—the plasmon is really our key here—because plasmons are really efficient light absorbers, and they can generate very energetic carriers that can do the chemistry we need them to much more efficiently than conventional thermocatalysis.

Yigao Yuan, Doctoral Student and Study First Author, Rice University

Copper nanoparticles act as the energy-harvesting antennas in the novel catalytic system, while rhodium atoms and clusters are strategically added as reactor sites, since the plasmonic surface of the copper nanoparticles does not bond well with methane.

The rhodium sites bind methane and water molecules to the plasmonic surface and use the energy from the heated carriers to power the SMR process.

“We tested many catalyst systems, but this one turned out to work best,” Yuan said.

The study also demonstrates how the antenna-reactor technique can efficiently regenerate the catalyst with light by using heat carriers to eliminate carbon deposits and oxygen species, overcoming catalytic deactivation caused by oxidation and coking. According to Nordlander, the "ingenious placement of the rhodium," dispersed irregularly and sparingly throughout the surface of the nanoparticles, was key to this "remarkable effect."

Currently, most hydrogen production occurs in large, centralized facilities, requiring transportation of the gas to its final destination. In contrast, light-driven SMR enables on-demand hydrogen generation, offering advantages for applications in mobility, such as hydrogen fueling stations and even automobiles.

This research showcases the potential for innovative photochemistry to reshape critical industrial processes, moving us closer to an environmentally sustainable energy future.

Naomi Halas, Professor, Rice University

The Robert A. Welch Foundation and the Air Force Office of Scientific Research funded the study. Rice's Shared Equipment Authority offered insightful information and assistance with data analysis.

Journal Reference:

Yuan, Y., et al. (2024) Steam methane reforming using a regenerable antenna–reactor plasmonic photocatalyst. Nature Catalysis. doi.org/10.1038/s41929-024-01248-8.