Tuning Nitrate Electroreduction Activity via an Equilibrium Adsorption Strategy: A Computational Study

Theoretical insight into the essential role of charged surface for ammonia synthesis: Si-decorated carbon nitride electrode

We report a new Si-decorated carbon nitride (C5N2H2) electrode for the sustainable generation of a hydrogen storage medium, ammonia (NH3), which not only possesses sound electrical conductivity, dynamic stability, and electrochemical activity for the nitric oxide/nitrogen reduction reaction (NORR/NRR), but also provides an option for designing metal-free electrodes. Most importantly, it is found that the charged surface is of great significance to the improved catalytic performance compared to the neutral condition, but this has always been overlooked. Herein, by means of DFT computations, the stubborn chemical bonds of NO and N2 can be entirely activated under an electron density of -2.15 × 10-2 e Å-2 on the Si-C5N2H2 material with an inconsiderable kinetic energy barrier (0.28 eV) along the protonation path. In brief, this finding paves a way for understanding false results by theoretical calculations compared to experiments.

Computational screening of high activity and selectivity of CO2 reduction via transition metal single-atom catalysts on triazine-based graphite carbon nitride

Single-atom catalysts (SACs) are emerging as promising catalysts in the field of the electrocatalytic CO2 reduction reaction (CO2RR). Herein, a series of 3d to 5d transition metal atoms supported on triazine-based graphite carbon nitride (TM@TGCN) as a CO2 reduction catalyst are studied via density functional theory computations. Eventually, four TM@TGCN catalysts (TM = Ni, Rh, Os, and Ir) are selected using a five-step screening method, in which Rh@TGCN and Ni@TGCN show a low limiting potential of -0.48 and -0.58 V, respectively, for reducing CO2 to CH4. The activity mechanism shows that the catalysts with a negative d-band center and optimal positive charge can improve the CO2RR performance. Our study provides theoretical guidance for the rational design of highly active and selective catalysts.

Novel honeycomb-like metal organic frameworks as multifunction electrodes for nitrate degradation: A computational study

Electrocatalytic reduction of ubiquitous waste nitrate to ammonia (NH₃) is a promising converting route toward recovering the disrupted nitrogen cycle. However, this carbon neutral synthesis process suffers from sluggish kinetics and flat Faradaic efficiency owing to the lack of efficient catalysts. Herein, we reported a novel two-dimension metal organic framework (MOF) as multifunction electrode via combining metal Zr atoms and benzenehexaselenolate skeletons (denoted as Zr-BHS) for nitrate remediation, featured with an impressive limiting potential of - 0.47 V, satisfactory selectivity, and favorable stability. A reasonable electronic indicator φ proposed here successfully explains why early transition metal elements in recently reports exhibit excellent electrochemical nitrate reduction activity. More importantly, as a derivative, Co-BHT has surprisingly superior hydrogen evolution performance comparable to the Pt-based material since the striking H-s and Co-d orbital hybridization overlap tailors the H attachment. Our studies not only offer a brand new multifunction MOF material for hydrogen energy carrier (NH₃ and H₂) electroreduction, but also put forward an ingenious self-assembly tactic, paving road for guiding the top-down synthesis.

ZrN6 -Doped Graphene for Ammonia Synthesis: A Density Functional Theory Study

Considering the pivotal role of ammonia in the modern chemical industry, designing effective catalysts for the N₂ -to-NH₃ conversion stimulates great research enthusiasms. In this work, by means of density functional theory calculations, we systematically investigated the electrocatalysis of six-coordinated transition metal atom anchored graphene for nitrogen fixation. The free energy analysis shows that the ZrN₆ configuration has a good activity toward ammonia synthesis under overpotential of 0.51 V. According to the electron transfer analysis, ZrN₆ site plays a bridging role in charge transfer between the functional graphene and the reactant. Furthermore, the presence of N₆ coordination increases the electron accumulation on the NNH_x intermediates, which weakens the intermolecular N-N bond, reducing the thermodynamic barrier of protonation process. This work provides a basic understanding of the interaction between transition metal and the adjacent coordination in tuning the reactivity.

Theoretical insights into the electroreduction of nitrate to ammonia on graphene-based single-atom catalysts

Electrocatalytic reduction of harmful nitrate (NO₃^-) to valuable ammonia (eNO₃RR) is critical and attractive for both environmental remediation and energy transformation. A single atom catalyst (SAC) based on graphene represents one of the most promising eNO₃RR catalysts. However, the underlying catalytic mechanism and the intrinsic factors dictating the catalytic activity trend remain unclear. Herein, using first-principles calculations, eNO₃RR on TMN₃ and TMN₄ (TM = Ti-Ni) doped graphene was thoroughly investigated. Our results reveal that FeN₄ doped graphene exhibits excellent eNO₃RR performance with a low limiting potential of -0.38 V, agreeing with the experimental finding, which can be ascribed to the effective adsorption and activation of NO₃^-via the charge "acceptance-donation" mechanism and its moderate binding due to the occupation of the d-p antibonding orbital. In particular, we found that eNO₃RR activities are well correlated with the intrinsic properties of TM centers and their local environments. With the established activity descriptor, several other graphene-based SACs were efficiently screened out with excellent eNO₃RR performance. Our studies could not only provide an atomic insight into the catalytic mechanism and activity origin of eNO₃RR on graphene-based SACs, but also open an avenue for the rational design of SACs for eNO₃RR towards ammonia by regulating the metal center and its local coordination environment.