Electric-Field Controllable Metal-free Materials as Efficient Electrocatalysts for Nitrogen Fixation

An electrochemical dinitrogen (N2) reduction reaction (NRR) under mild conditions has been considered as a promising and sustainable alternative to the conventional Haber–Bosch method. However, searching for an efficient, stable, and low-cost electrocatalyst is still challenging and attractive. Here, based on density functional theory, a single B atom adsorbed on a series of carbon phosphide monolayers [B/PCx single-atom catalysts (SACs), x = 2, 3, 5, and 6] was constructed as metal-free catalysts and their NRR catalytic activities were systematically investigated. Consequently, among the investigated systems, the B/PC6 SAC is identified as the most promising candidate, on which the N2 molecule can only be sufficiently activated through the enzymatic pathway with a limiting potential of −0.37 V, and importantly, it remains as a stable structure after ab initio molecular dynamics simulations at 300 K. It can be found from the electronic property calculations that the p-orbitals of the B atom have a good degree matching with the p-orbitals of the adsorbed N2 species, favoring the activation of the N2 molecule. Besides, both the N2 adsorption Gibbs free energy and the NRR-limiting overpotential decrease with the increase of the positive electric-field intensity, suggesting that an electric field can be regarded as an effective external stimulus to further improve the catalytic activity of the B/PC6 SAC. This study not only provides an eligible NRR electrocatalyst but also offers a useful tool, that is, applying an external electric field, for the NRR activity enhancement.