Copper-based catalyst paves the way for sustainable ammonia production

Ammonia plays a vital role in food production and industrial development, with a global market of approximately 175 million tonnes and a market value of $67 billion. In addition, it is a highly energy-dense carrier, making it a key player in the emerging hydrogen economy.

The disadvantage of current ammonia production is that synthesis relies heavily on the Harber-Bosch process, which is energy-intensive and produces high CO emissions.₂ emissions.

However, a research group led by Hao Li of Tohoku University’s Advanced Institute for Materials Research (WPI-AIMR) focused on the electrochemical conversion of nitrate (NO₃^–) in ammonia (NH₃), revealing a process that could potentially revolutionize industrial practices while offering new perspectives in the development of efficient and sustainable catalytic processes.

Details of the results were published in the journal Advanced sciences August 9, 2024.

Unlike the nitrogen reduction reaction (NRR), which requires the breaking of the strong N=N triple bond of nitrogen (N₂), reduction of nitrates (NO₃“RR) offers a more efficient path,” Li emphasizes.

“Nitrate has a much lower dissociation energy and higher solubility in water, making it easier to use as a nitrogen source for ammonia production. This not only improves the efficiency of the process, but also addresses the environmental challenge of nitrate accumulation in water systems.”

Li and his team synthesized a spherical copper(II) oxide (CuO) catalyst, characterized by the stacking of small particles with oxygen-rich vacancies. This catalyst demonstrated a significant improvement in ammonia yield, reaching 15.53 mg h^-1 mgcat^-1with a Faraday efficiency of 90.69% in a neutral electrolyte at a voltage of -0.80 V (compared to a reversible hydrogen electrode).

The team also revealed that the high catalytic activity of CuO electrodes comes from both the structural and phase changes that occur during the electrochemical reduction process.

“Our research indicates that the transformation of CuO to Cu/Cu(OH)₂ “The structure during the reaction process is critical to the performance of the catalyst,” said Qiuling Jiang, a co-doctoral student at WPI-AIMR and co-author of the paper.

“This phase change not only increases the number of active sites, but also enhances the transfer of electrons to the electrode surface, thereby increasing the efficiency of the nitrate reduction reaction.”

In addition, the study used density functional theory (DFT) calculations to better understand the catalytic mechanism. These calculations showed that the formation of Cu(OH)₂ reduces the energy barrier for nitrate adsorption, making the process energetically favorable.

In addition, Cu(OH)₂ The phase was found to inhibit the competitive hydrogen evolution reaction, while the presence of Cu(111) crystal surfaces facilitated the hydrogenation process.

“This research provides a new perspective on the design of copper-based catalysts for electrocatalytic ammonia production,” Li adds. “By controlling the reaction conditions and understanding the phase transitions, we can optimize the catalyst performance, which could lead to more efficient and scalable ammonia synthesis processes.”

In the future, the team plans to explore the factors that influence catalyst phase transitions during the reduction process. By further refining the design of these catalysts, they aim to improve their stability, activity and selectivity, bringing the goal of sustainable ammonia production closer to reality.