New 2D material transforms air into fuel and fertilizer

Among these materials, a family called MXenes stands out. MXenes are low-dimensional compounds capable of converting components from the air into ammonia that can be used in fertilizers and transportation fuels. Their unique chemistry allows scientists to adjust their composition, providing precise control over their properties and performance.

This research was detailed in the Journal of the American Chemical Society by chemical engineering professors Drs. Abdoulaye Djire and Perla Balbuena, along with Ph.D. candidate Ray Yoo.

Rethinking Catalyst Design

Djire and his team are challenging long-held beliefs about how transition metal-based materials function. Traditionally, scientists believed a catalyst's effectiveness was determined solely by the type of metal it contained. Djire's group aims to expand that understanding.

"We aim to expand our understanding of how materials function as catalysts under electrocatalytic conditions," Djire said. "Ultimately, this knowledge may help us identify the key components needed to produce chemicals and fuels from earth-abundant resources."

Tuning Atomic Properties for Better Performance

The structure of MXenes can be adjusted by modifying how nitrogen atoms interact within the lattice. This change, known as lattice nitrogen reactivity, influences the way molecules vibrate, known as their vibrational properties. These properties are critical in determining how effectively a material can catalyze chemical reactions.

Because MXenes can be fine-tuned, they can be optimized for a wide variety of renewable energy applications. Yoo explained that this makes them promising alternatives to costly electrocatalyst materials.

"MXenes are the ideal candidates as transition metal-based alternative materials. They have promising potential due to their many desirable qualities," Yoo said. "Nitride MXenes play an important role in electrocatalysis, as shown through their improvement in performance compared to the widely studied carbide counterparts."

Computational Insights and Molecular Interactions

To deepen their understanding, Ph.D. student Hao-En Lai from Dr. Balbuena's group conducted computational studies to model how MXenes behave at the molecular level. The simulations revealed how energy-relevant solvents interact with MXene surfaces, helping the researchers quantify molecular interactions important to ammonia synthesis.

Djire, Yoo, and their collaborators also analyzed the vibrational behavior of titanium nitride using Raman spectroscopy, a non-destructive method that reveals detailed information about a material's structure and bonding.

"I feel that one of the most important parts of this research is the ability of Raman spectroscopy to reveal the lattice nitrogen reactivity," Yoo said. "This reshapes the understanding of the electrocatalytic system involving MXenes."

According to Yoo, continuing to explore nitride MXenes and their interactions with polar solvents through Raman spectroscopy could yield major advancements in green chemistry.

Toward Atom-by-Atom Control of Energy Conversion

"We demonstrate that electrochemical ammonia synthesis can be achieved through the protonation and replenishment of lattice nitrogen," Djire said. "The ultimate goal of this project is to gain an atomistic-level understanding of the role played by the atoms that constitute a material's structure."

This research received support from the U.S. Army DEVCOM ARL Army Research Office Energy Sciences Competency, Electrochemistry Program (award # W911NF-24-1-0208). The authors noted that the opinions and conclusions presented are their own and do not necessarily reflect the official policies of the U.S. Army or the U.S. Government.