A new take on the abilities of hydrogen binding energy for use in single atom catalysts

Hydrogen-based technologies are becoming more of a topic as renewable and clean energy sources are desired. A controversial take in this world is that hydrogen binding energy might not be the first way to go anymore.

Conventional thinking holds that the metal site in single atom catalysts (SACs) has been a limiting factor to the continued improvement of the design and, therefore, the continued improvement of the capability of these SACs. More specifically, the lack of outside-the-box thinking when it comes to the crucial hydrogen evolution reaction (HER), a half-reaction resulting in the splitting of water, has contributed to a lack of advancement in this field. New research emphasizes the importance of pushing the limits of the metal site design in SACs to optimize the HER and addressing the poisoning effects of HO* and O* that might affect the reaction. All of these improvements could lead to an improved performance of the reaction, which can make sustainable energy storage or hydrogen production more available.

The results were published in Angewandte Chemie International Edition in March 2025.

Single atom catalysts (SACs) are catalytically active metal sites that are atomically distributed to support enhanced catalytic activity, which improves the rate a reaction can occur without permanently altering the actual components that need to do the reacting. Hydroxyl radical (HO*) and oxygen radical (O*) poisoning can alter molecules and degrade the performance of the reaction. On the other hand, sites where hydrogen molecules don't readily accumulate can lead to an enhancing effect of the catalyst.

"Our findings reveal that HO* poisoning, realistic H* adsorption strengths at active metal sites, and the potential HER activity at the coordinating N-sites are crucial factors that should be considered for accurate descriptor development," said Hao Li, author and researcher of the study.

By effectively modifying these factors, more efficient catalysts can be developed to improve HER activity while also not relying on the conventional design of metal binding sites as metal-nitrogen-carbon, which can easily lead to the aforementioned poisoning effects.

Researchers found that the hydrogen binding energy (HBE) calculation under a realistic representation of accumulated molecules (adsorption) can serve as a good predictor of HER activity. In both theoretical and actual experiments where a metal site has been poisoned, a neighboring nitrogen atom can perform the duty of an active site and host catalytic activity. This negates the poisoning effect by providing an "alternate" where the catalyst can act and continue the reaction.

The work done by this team of researchers puts to rest the long-lasting debate on HER descriptors, or parameters that would theoretically help predict the catalytic capabilities of the desired materials for the reaction. Additionally, the combination of using HBE and Gibbs free energy (the prediction of whether a reaction will occur spontaneously) as descriptors for SACs provides new guidelines for those working with this catalyst design, while also helping to propel new methods forward to break out of the conventional limitations put on by using just hydrogen binding energy as a solo descriptor.

"Through the design of this advanced model, we aim to further address the limitations of HO poisoning and develop novel single- and dual-atom catalysts for different pH conditions, especially in alkaline environments," said Hitoshi Shiku, contributing author and researcher to this study.

The Hao Li Lab developed the largest experimental catalyst database to date through the Digital Catalysis Platform, where key data and computational structures of this study are available to view.

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