Calculation Design Of Low-Dimensional Electrocatalyst For Ammonia Production

Ammonia is a key ingredient in fertilizer and has many other uses,but its production through traditional methods is energy-intensive and releases a large number of greenhouse gases.To address climate change concerns,scientists are seeking new ways to produce ammonia that are more sustainable.One promising approach is electrocatalytic N2 reduction,which involves using renewable electricity from solar or wind sources to power small-scale electrolysis cells that convert nitrogen into ammonia at lower temperatures and with lower emissions.This could enable more efficient and environmentally-friendly ammonia production.Currently,there is limited exploration of new electrocatalysts for the electrochemical conversion of N2 to NH3 at room temperature and atmospheric pressure.The main hurdle in this field is to achieve both high catalytic activity and selectivity simultaneously.Developing low-cost and highly efficient electrocatalysts of NRR is closely related to establishing the composition-structure-activity relationships and fundamental understanding of catalytic mechanisms.Density functional theory(DFT)is emerging as an important computational tool that can provide insights into the relationship between the electrochemical performances and physical/chemical properties of catalysts.This thesis focuses on the design and discovery of efficient electrocatalytic nitrogen reduction catalysts through the investigation of electrochemical nitrogen reduction processes.The main findings are summarized below:(1)Ligands dependent electrocatalytic nitrogen reduction performance in d-πconjugated molecules.The coordination environment of metal atoms in single-atom catalysts(SACs)has a greater impact on the catalytic performance of electrocatalysts.However,the influence mechanism of interacting ligands on the electrocatalytic nitrogen reduction reaction(NRR)process is still insufficient.Herein,by means of large-scale density functional theory(DFT)computations,the effect of organic ligands on the NRR process is investigated in-depth using half organometallic sandwich molecular SACs,i.e.TMBzs and TMCps(Bz=benzene,Cp=cyclopentadienyl,and TM=transition metal).The results revealed that the NRR performance of all the systems is highly dependent on the choice of d-π interaction within the TM-Ligand complexes.Compared with TMBzs,the TMCps exhibit outstanding NRR activity and significantly suppress HER.Among 16 candidates,CrCp and MnBz are the most promising candidates with an ultra-low limiting potential of-0.29 V and-0.37 V via consecutive mechanism,respectively.Moreover,the systems with higher spin polarizations have better NRR activity.The work provides new insight into the NRR to molecular SACs with different organic ligands.(2)Theoretical Exploration on the Role of Magnetic States to the N2 Fixation behaviors of 2D Transition Metal Tri-borides(TMB3s).Fixing nitrogen(N2)by electrosynthesis method has become a promising way to ammonia(NH3)production,nevertheless,developing electrocatalysts combining longterm stable and low-cost feathers is still a great challenge to date.Using comprehensive first-principles calculations,we herein investigate the potential of a new class of two-dimensional(2D)transition metal tri-borides(TMB3s)as nitrogen reduction reaction(NRR)electrocatalysts,and explore the effect of magnetic orders on the NRR.Our results show that the TMB3s can sufficiently activate N2 and convert it to NH3.Particularly,TiB3 is identified as a high-efficiency catalyst for NRR because of its low limiting(-0.24 V)potential suppression of the competitive hydrogen evolution reaction(HER).For the first time,we present that these TMB3s with various magnetic states exhibit different performances in the adsorption of N2 and NRR intermediates,and a minor effect on activation of N2.Besides,VB3,CrB3,MnB3,and FeB3 monolayers possess the superior capacity to suppress surface oxidation via the self-activating process,which reduces*O/*OH into*H2O under NRR electrochemical conditions,thus favoring the N2 electroreduction.This work paves the way for finding high-performance NRR catalysts for transition metal borides and pioneering the research of magnetic states effects in NRR.