A recent study by researchers at Cornell University has provided new insights into the role of electrocatalytic intermediates in hydrogen production. Published on October 27 in Nature Catalysis, this research could lead to advancements in both hydrogen generation and the detoxification of pollutants in water.
The study highlights the significance of surface metal-hydrogen intermediates, which serve as essential components in electrocatalytic transformations. These intermediates, however, are challenging to examine due to their transient nature and low concentrations, particularly at the nanoscale. The research team employed single-molecule super-resolution reaction imaging to observe these intermediates more clearly.
Under the guidance of Peng Chen, the Peter J.W. Debye Professor of Chemistry, former postdoctoral researcher Wenjie Li and the team focused on a palladium-hydrogen model system. They utilized a probing molecule that interacted with palladium nanocubes, which allowed them to visualize the resulting fluorescent molecules at the level of individual reactions.
This innovative imaging technique enabled the researchers to track individual palladium particles, revealing that they exhibit varied hydrogenation behaviors and properties. Notably, the study found that hydrogen intermediates can form at multiple sites on the same particle, leading to different characteristics and behaviors across those sites.
“Once this hydrogen intermediate is formed on the palladium catalyst, it turns out the hydrogen atom on the palladium surface is not a static object,” Chen explained. “The hydrogen can move around, not only on palladium particles but also off to the surrounding electro surface.” This movement, known as hydrogen spillover, was previously understood but had not been visualized to the extent achieved in this study.
By utilizing their probing molecule, the researchers measured the distance of hydrogen spillover, discovering that it could extend several hundred nanometers away from the palladium surface. Traditionally, studies of metal-hydrogen intermediates have relied on ensemble-averaged methods, which assess intermediate formation in bulk and often overestimate their stability while obscuring variations between different particles and sites.
“In our measurements, we can differentiate particles and estimate the differences between sites on the same particle,” Chen added. “With this capability, we can more accurately determine the reduction potential necessary for the formation of the palladium-hydrogen intermediate.”
The versatility of the research approach may enable the investigation of a broader spectrum of electrochemical intermediates, which could be particularly beneficial for enhancing electrocatalysis in hydrogen production and for purifying contaminated aqueous environments containing pollutants like chlorinated compounds.
Additional co-authors of the study include former postdoctoral researchers Muwen Yang, Ming Zhao, Rong Ye, Bing Fu, and Zhiheng Zhao, a Ph.D. candidate. The project received support from the National Science Foundation, the Army Research Office, and the U.S. Department of Energy. The team also utilized facilities at the Cornell Center for Materials Research, which is backed by the NSF MRSEC program.
