Nitrogen fixation is the process through which molecular dinitrogen (N2) present in the atmosphere is converted into ammonia (NH3) or other related nitrogenous compounds. This process can be achieved naturally or through artificial nitrogen fixation. The latter, which is applicable in industries, involves application of the Haber–Bosch process; a process that consumes large amounts of energy and requires strict reaction conditions, such as: high temperature and pressure. In recent times, the electrocatalytic reduction of dinitrogen to ammonia, has emerged as a promising alternative, and has thus attracted much attention. This process employs transition metals as catalysts, such as; iron, ruthenium and molybdenum. Alternatively, due to complications resulting from using these metals, boron(B) -an electron-deficient element that exhibits Lewis acid characteristics- has emerged as a potential for the N2 reduction reactions (NRR).
Few studies have already confirmed its hypothesis, further suggesting the application of B doped graphene. Even better, hexagonal boron nitride (BN), which exhibits high activity and exposes plenty of B atoms that provide sufficient active sites for NRR, has been reported. Unfortunately, limited information on the applicability of metal-free catalysts for N2 conversion are available.
Recently, Queensland University of Technology researchers: Dr. Xin Mao, Dr. Si Zhou, Dr. Cheng Yan, Professor Zhonghua Zhu and Professor Aijun Du presented a novel N2 fixation approach that employed BN edge. Specifically, the researchers focused on employing the density functional theory to predict, for the first time that a single B-atom decorated BN edge ([email protected]) could act as a metal-free catalyst for the conversion of an N2 molecule to NH3 under ambient conditions. Their work is currently published in the scientific journal, Physical Chemistry Chemical Physics.
To begin with, the density functional theory as implemented in the Vienna Ab Initio Simulation Package (VASP) code was employed to optimize geometry structures. Next, exchange–correlation interactions were described by the generalized gradient approximation in the form of the Perdew–Burke–Ernzerhof functional. A cut-off energy of 500 eV for plain-wave basis sets was adopted. Lastly, the reaction Gibbs free energy changes for each elementary step were employed.
Based on the DFT calculations, the authors established that the distal mechanism was the most effective reduction pathway, with an overpotential of only 0.13 V. More importantly, fast removal of produced ammonia molecules was also observed with an uphill Gibbs free energy change of only 0.35 V, lower than those for other ever-reported electrocatalysts.
In summary, a novel metal-free catalyst has been designed and presented by Queensland University scientists, i.e., the [email protected] edge, which portrayed excellent catalytic performance for the NRR process. The finding presented highlight a novel single atom metal-free catalyst for N2 fixation, providing a cost-efficient process for sustainable ammonia production. Altogether, the study, as presented, offers a new way to convert dinitrogen to ammonia using a metal-free catalyst with high catalytic performance.
Xin Mao,a Si Zhou, Cheng Yan, Zhonghua Zhu, Aijun Du. A single boron atom doped boron nitride edge as a metal-free catalyst for N2 fixation. Physical Chemistry Chemical Physics, 2019, volume 21, page 1110.Go To Physical Chemistry Chemical Physics