Breaking Local Charge Symmetry of Iron Single Atoms for Efficient Electrocatalytic Nitrate Reduction to Ammonia

Abstract

The electrochemical conversion of nitrate pollutants into value‐added ammonia is a feasible way to achieve artificial nitrogen cycle. However, the development of electrocatalytic nitrate‐to‐ammonia reduction reaction (NO3‐RR) has been hampered by high overpotential and low Faradaic efficiency. Here we develop an iron single‐atom catalyst coordinated with nitrogen and phosphorus on hollow carbon polyhedron (denoted as Fe‐N/P‐C) as a NO3‐RR catalyst electrode. Owing to the tuning effect of phosphorus atoms on breaking local charge symmetry of the single‐Fe‐atom catalyst, it facilitates the adsorption of nitrate ions and enrichment of some key reaction intermediates during the NO3‐RR process. The Fe‐N/P‐C catalyst exhibits 90.3% ammonia Faradaic efficiency with a yield rate of 17980 μg h‐1 mgcat‐1, greatly outperforming the reported Fe‐based catalysts. Furthermore, operando SR‐FTIR spectroscopy measurements reveal the reaction pathway based on key intermediates observed under different applied potentials and reaction durations. Density functional theory calculations demonstrate that the optimized free energy of NO3‐RR intermediates is ascribed to the asymmetric atomic interface configuration, which achieves the optimal electron density distribution. This work demonstrates the enhanced function of heteroatom doping on single atoms for NO3‐RR, and provides an effective strategy for improving the catalytic performance of single atom catalysts in different electrochemical reactions.

Electrocatalytic Urea Synthesis via C–N Coupling from CO2 and Nitrogenous Species

“…Electrocatalytic urea synthesis involves the activation of C-containing and N-containing substances, so it is necessary to match the activation and reaction rates of the above substances to promote C–N coupling; otherwise, the parallel side reaction will be enhanced. Single-atom materials generally exhibit superior activity in electrocatalytic reactions; − for example, single-atom nickel (Ni–N–C) can catalyze CO 2 reduction to produce CO, and single-atom iron (Fe–N–C) can catalyze the nitrate reduction to NH 3 with high efficiency. However, the above single-atom catalysts have the limitation of high activity only for a single C or N species, and it is not applicable to electrocatalytic C–N coupling system involving multiple reactants. , …”

Electrochemical Probing the Site Reactivity in Iron Single-Atom Catalysts for Electrocatalytic Nitrate Reduction to Ammonia

“…Iron single atoms dispersed on nitrogen-doped carbon (Fe-NC) have been prominently featured in electrocatalytic nitrate reduction (NitRR) studies due to their distinct characteristics. − However, its excellent NitRR performance is a result of the combined contribution of both the Fe sites and the carbon substrate (NC). In addition, the NitRR activity for most single-atom NitRR catalysts (SACs) has often been evaluated based on apparent yield rate normalized by the total site number, potentially leading to a significant underestimation of their inherent performance. − It is therefore crucial to develop a versatile and more reliable technique to measure the intrinsic activity of SACs.…”

Enhanced ammonia selectivity on electrochemical nitrate reduction: Cu–Ni metal–organic frameworks with tandem active sites for cascade catalysis

“…Now, the catalytic mechanism is still complicated and unclear in the cascade reaction, which greatly limits the development and application of electrochemical NRA. 29,30 Designing an ideal catalytic model with a controllable chemical structure is the key to constructing the mechanism research platform and untangle the NRA cascade process.…”

“…MOF is a new type of material with a controllable chemical structure and ordered metal active center, which is an optimal catalyst to establish a mechanism platform for the cascade reaction. 29,31,32 Meanwhile, the single-atom active centers, along with their ordered in-plane porous structure, contribute to the maximized metal utilization and efficient mass transfer for Ni x Cu (3− x ) (HITP) 2 catalyst. 33,34 Combined with experimental and theoretical results, the Ni x Cu (3− x ) (HITP) 2 catalyst reveals the cascade mechanism in NRA.…”