Department of Physics, Gazi University, 06500, Teknikokullar/Ankara, Turkey.
Department of Mechanical Engineering, Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands.
Phys Chem Chem Phys. 2023 Jul 12;25(27):18465-18480. doi: 10.1039/d2cp05491d.
In the present work the adsorption of N and the nitrogen reduction reaction (NRR) intermediates have been investigated on oxygen modified MnNO ( + = 4, ≠ 0)/graphene layers through periodic density functional theory calculations. Various number of oxygen atoms substitute nitrogen atoms within the MnNO, with their effect on the layer stability, chemical bonding and N adsorption being explored. As the oxygen amount increases in the porphyrin unit, Mn-O interactions weaken with reference to that of Mn-N, bonding orbitals become less populated while the antibonding orbitals between Mn-N-O atoms become partially occupied, as evidenced by the Crystal orbital Hamiltonian population (COHP) and integrated crystal orbital bond index (ICOBI) analyses. During N adsorption on the different layers, the substitution of two and three nitrogen atoms by oxygen leads to the longest NN molecular bond length. Two main orientations for the N molecules sorption have been investigated: side-on and end-on which are perpendicular and parallel to the surface normal, respectively. When the interaction of N with MnNO layer is considered, d-band center variation of the Mn with reference to the pre-adsorbed state is more obvious after side-on adsorption configuration. For the selected layers based on initial N adsorption energies, the adsorption energies of nitrogen reduction reaction intermediates follow a trend based on the number of oxygen atoms in the porphyrin units. Charge density difference (CDD) maps and partial density of states (PDOS) analysis reveal that the interaction of N with oxygen modified layers takes place through electron acception-donation mechanism between the partially occupied Mn-d orbitals and the 2p orbitals of the N molecule. DDEC6-derived bond orders and atomic charges support the PDOS and adsorption/formation energy trends, and further clarify the bonding strengths of the atoms in the porphyrin units, as well as the Mn-N interactions in the adsorbed systems.
在本工作中，通过周期性密度泛函理论计算，研究了氧气修饰的 MnNO(+ = 4, ≠ 0)/石墨烯层对 N 的吸附和氮还原反应（NRR）中间体。在 MnNO 中，不同数量的氧原子取代氮原子，研究了它们对层稳定性、化学键和 N 吸附的影响。随着卟啉单元中氧原子数量的增加，Mn-O 相互作用相对于 Mn-N 相互作用减弱，成键轨道的占据减少，而 Mn-N-O 原子之间的反键轨道部分占据，这可以通过晶体轨道哈密顿布居（COHP）和积分晶体轨道键指数（ICOBI）分析来证明。在不同层上吸附 N 时，用氧取代两个和三个氮原子会导致 N-N 分子键长最长。研究了两种主要的 N 分子吸附取向：侧式和端式，分别垂直和平行于表面法线。当考虑 N 与 MnNO 层的相互作用时，与预吸附状态相比，侧式吸附构型后 Mn 的 d 带中心变化更为明显。基于初始 N 吸附能，对于选定的层，氮还原反应中间体的吸附能遵循卟啉单元中氧原子数量的趋势。电荷密度差（CDD）图和部分态密度（PDOS）分析表明，N 与氧修饰层的相互作用是通过部分占据的 Mn-d 轨道和 N 分子的 2p 轨道之间的电子接受-供体机制发生的。基于 DDEC6 的键序和原子电荷支持 PDOS 和吸附/形成能趋势，进一步阐明了卟啉单元中原子的键合强度以及吸附体系中 Mn-N 的相互作用。
