Researchers have explored the electrochemical reduction of nitrogen gas (N2) to ammonia (NH3) using a nickel-thiolate cluster as a homogeneous catalyst. The cluster demonstrated high selectivity for NRR over the hydrogen evolution reaction (HER), and it achieved a Faradaic efficiency of approximately 25% for NH3 synthesis. The structural characteristics and electrochemical behavior of the cluster were thoroughly investigated, providing insights into the mechanistic aspects of the nitrogen reduction process.
Summary
- 🔬 The nitrogen cycle involves the conversion of atmospheric nitrogen (N2) into ammonia (NH3) through various processes, including biological nitrogen fixation and industrial methods.
- ⚛️ Noble and non-noble metal-based electrocatalysts are effective in dissociating the strong triple bond in N2 and promoting the nitrogen reduction reaction (NRR).
- 🧪 Thiol-protected metal nanoclusters have garnered attention for their unique structures and catalytic properties.
- 💎 The nickel-thiolate cluster [Ni6(PET)12] demonstrated electrocatalytic activity for N2 reduction, selectively producing NH3 without other nitrogenous products.
- ⚡️ Cyclic voltammetry experiments revealed the redox behavior of the cluster and the occurrence of NRR and HER processes.
- 🌡️ The addition of an external proton source, such as phenol, promoted both NRR and HER, leading to increased cathodic current.
- 🎯 The study contributes to the development of efficient electrocatalysts for nitrogen reduction and sheds light on the design principles for future catalysts.
The nitrogen cycle is a crucial process for the utilization of atmospheric nitrogen in various biological and industrial applications. Nitrogen gas (N2) is inert and cannot be directly utilized by humans, necessitating its conversion into more reactive forms such as ammonia (NH3). The electrocatalytic reduction of N2 to NH3 offers a sustainable alternative to traditional industrial methods, such as the Haber-Bosch process.
In this study, researchers focused on a nickel-thiolate cluster, [Ni6(PET)12], as a potential electrocatalyst for N2 reduction. The cluster’s unique structure, consisting of six nickel ions coordinated with 12 2-phenylethanethiol (PET) ligands, provided a suitable environment for N2 activation. The cluster was synthesized and characterized through various techniques, including ESI-MS, single crystal X-ray diffraction, and UV/Vis spectroscopy.
Cyclic voltammetry experiments were conducted to investigate the electrochemical behavior of the cluster. The voltammograms exhibited redox peaks corresponding to Ni2+/Ni+ processes at different crystallographic sites within the cluster. The addition of an external proton source, such as phenol, led to enhanced cathodic current, indicating the promotion of both NRR and HER processes.
To distinguish NRR from HER, experiments were performed under nitrogen (N2) and argon (Ar) atmospheres. In the presence of N2, the cathodic current at a specific potential was attributed to NRR due to the absence of N2 in the system. Conversely, in the presence of Ar, the current observed at the same potential was attributed to HER, as N2 was not present.
[Ni6(PET)12] cluster was highly selective for producing NH3 with a Faradaic efficiency of around 25% over HER.The findings contribute to the understanding of the mechanistic aspects of electrocatalytic N2 reduction and provide insights into the design principles for future catalysts.
Nitrogen is important for life processes, but it is difficult to make it usable for humans.The electrocatalytic nitrogen reduction reaction (NRR) offers a sustainable alternative to the industrial Haber-Bosch process for ammonia synthesis. The authors investigate the use of a nickel-thiolate cluster as a homogeneous catalyst for NRR.
Transition metals, including nickel, are known for their ability to induce back-bonding with the N2 molecule, which activates the N≡N triple bond and facilitates NRR. The orientation of the metal ion in the molecular complex influences the effectiveness of back-bonding. Various strategies have been explored to enhance the NRR activity of heterogeneous electrocatalysts, such as tailoring the nanostructure morphology, creating vacancies, and alloying. Metal complexes with thiolate auxiliary ligands have shown promise in N2 activation due to increased electron density on the metal and the ability of thiolate to assist in protonation and H+ transfer.
Thiol-protected metal nanoclusters (NCs) have garnered attention in catalysis and possess unique properties due to their small size, atomic-level purity, and specific structures. The catalytic activity of metal NCs depends on the number of metal atoms, and even a single atom can significantly influence catalysis. The uniformity and solubility of NCs in electrolyte solutions allow for increased activity and selectivity in catalytic reactions.
The article describes the synthesis and structural characterization of a nickel-thiolate cluster used as an electrocatalyst for NRR. The cluster exhibits a tiara-like architecture with a cavity suitable for interacting with the N2 molecule. The authors investigate the electrochemical activity of the cluster through cyclic voltammetry (CV) and observe redox processes corresponding to Ni2+/Ni+ transitions. The addition of an external proton source promotes NRR and HER, leading to increased reduction currents. The experimental results, coupled with theoretical calculations, provide insights into the mechanistic aspects of NRR by the nickel-thiolate cluster.
- Dr. Manju P. Maman, Dr. Tamilselvi Gurusamy, Dr. Arun K. Pal, Dr. Rajkumar Jana, Dr. Kothandaraman Ramanujam, Dr. Ayan Datta, Dr. Sukhendu Mandal
- Indian Institute of Science Education and Research Thiruvananthapuram, India
- The nitrogen cycle is a crucial biogeochemical process for the utilization of atmospheric nitrogen.
- Thiol-protected metal nanoclusters have gained interest as catalysts due to their unique structure, atomic-level precision, and catalytic properties.
