Departments

ARIS NOO Fundamental project

The reduction of nitrogen (N₂) to ammonia (NH₃) is a key reaction for sustaining life on this planet (NH₃ is the second most-produced chemical globally). Industrially, NH₃ is synthesized via the hydrogenation of N₂ through the Haber-Bosch process (HB), arguably the most important invention of the 20th century. The HB process enabled large-scale fertilizer production, triggering a massive increase in the global population. Unfortunately, the process is highly energy-intensive and operates on such a large scale that it accounts for approximately 2% of global energy demand. Moreover, HB indirectly contributes around 3% of global CO₂ emissions, producing over 450 million tons of CO₂ annually.

In contrast, biological systems (e.g., nitrogenase enzymes) produce NH₃ at room temperature and pressure with much higher efficiency than HB (~75% Faradaic efficiency). However, from a practical standpoint, enzymatic platforms are unlikely to be suitable due to their (probable) inability to achieve high NH₃ production rates. Therefore, we believe that an enzymatic-inspired process can be replicated in an electrochemical cell with lower energy consumption than the current HB process. Electrochemical nitrogen reduction (NRR) is particularly attractive for agriculture, as NH₃ could be produced in remote areas using sunlight and N₂, eliminating transportation constraints. This would be especially significant in underdeveloped regions where poor infrastructure limits nitrate fertilizer use.

However, the main scientific challenge in NRR remains fundamental: it is arguably the least developed and least understood reaction in electrochemistry. This implies that NRR has the greatest potential for breakthroughs, as there is a lack of efficient electrochemical systems. Critical advancements are needed in the core component—the NRR electrode—whose fundamental understanding is almost entirely unexplored.

Currently, the only credible NRR platform involves lithium metal (LM-NRR) mediation. This reaction occurs in a non-aqueous electrolyte with a proton donor. Unfortunately, LM-NRR was overlooked for three decades due to the widespread "Edisonian approach," which led to misinterpretations. Lithium is unique in that it spontaneously breaks the nitrogen triple bond under ambient conditions. Only recently has LM-NRR been confirmed as the most viable method for electrochemical NH₃ synthesis. The primary reason previous NRR research was misguided was the use of inadequate experimental protocols, which are crucial for unequivocally determining the electrochemical origin of NH₃.

The main objective of the current project, NITRO FLOAT, is to establish principles for electrochemical NH₃ synthesis via LM-NRR. To achieve this, the project will develop a novel methodological platform that first enables observation, then understanding, and finally the manipulation/design of electrodes for NH₃ production. LM-NRR will be studied under conditions of enhanced N₂ mass transport, offering an entirely new perspective on the reaction. Our primary focus will be on interpreting current-voltage characteristics through a dedicated electrode (i.e., a floating electrode) as an incremental representation of real reactor electrodes. Since no existing electrochemical platform can capture LM-NRR under a precisely defined kinetic regime, we anticipate that NITRO FLOAT will significantly deepen our fundamental understanding of the LM-NRR process.

The Project Comprises Two Main Activities:

1. Holistic Analytical Approach: LM-NRR will be studied under enhanced mass transport conditions using a floating electrode. This diagnostic approach will be coupled with:

(i) Electrochemical mass spectrometry (EC-MS)

(ii) Electrochemical Fourier-transform infrared spectroscopy (EC-FTIR). This combination will enable real-time investigation of LM-NRR under increased mass transport conditions. Notably, EC-MS can detect electrochemical products down to ~10 ppm in a single electrode monolayer within 1 second. The high sensitivity of the EC-MS chip is due to the fact that every volatile molecule produced at the electrode (e.g., NH₃ and H₂) travels through the chip into the mass spectrometer. Thus, the MS signal will be correlated not only with analyte concentration but also with the absolute number of analyte molecules. This will enable temporally resolved, fully quantitative measurements of transient LM-NRR phenomena, providing fundamental insights into reaction mechanisms.In the case of EC-FTIR diagnostics, we will introduce a completely new approach by conducting in situ FTIR measurements at the solid-gas interface during floating electrode operation. This configuration will allow high gas accessibility to the electrode surface, overcoming mass transport limitations of previous setups. Unlike standard in situ FTIR, the EC-FTIR configuration will avoid the use of a prism. The electrolyte will be placed on the backside of the floating electrode, forming a thin layer (<1 μm thick). The electrode (e.g., an Au TEM grid) will be illuminated through the gas phase, acting as the interface between the electrolyte and IR beam. This setup will allow the detection of both adsorbed and dissolved species while reducing IR signal absorption by the electrolyte, significantly improving the signal-to-noise ratio.

2. Porous electrodes: LM-NRR will be investigated using "model" electrodes (porous grids). These will be fabricated through electrochemical deposition using hydrogen bubble templating. Due to the inability of lithium to form alloys, copper will be selected as the electrode material. Hydrogen bubble electrodeposition will allow systematic control over the morphology of the deposited porous copper grids, which will likely influence N₂ mass transport and the formation of the solid-electrolyte interphase (SEI). The porous copper grids will be deposited onto gas-permeable floating electrodes (TEM grids). Various structures and porosities will be achieved by adjusting copper ion concentrations and electrodeposition current. To avoid the pitfalls of the "Edisonian approach," we emphasize that only copper-based electrode studies are planned. The structure of the electrode—rather than the "electrocatalyst"—is the only credible approach for NH₃ production, as LM-NRR is a mediated process rather than an electrocatalytic one.

PI: Dr. Primož Jovanović

• 1. October 2023 – 30. June 2026
• Budget: 267 480 €

The project is funded by the Public Research Agency of the Republic of Slovenia (ARIS) within the framework of the Recovery and Resilience Plan, the 3rd development area "Smart, sustainable and inclusive growth" and the RDI component - "Research, development and innovation" and Investment C: "(Co)financing of projects and programs to strengthen the mobility of Slovenian researchers and research organizations and to promote the international mobility of Slovenian applicants."

"Funded by the European Union - NextGenerationEU"