A Study Of The Theoretical Catalytic Design For The Nitrogen Reduction Reaction (NRR) Of Graphodiynyl Groups

Ammonia(NH₃)is an important industrial raw material for the production of fertilizers,dyes and other products,and a substance which is crucial to human survival and development.At present,the production of NH₃ is mainly through the Haber-Bosch synthesis process.This process consumes a large amount of energy and produces a large amount of CO₂ and by-products,which will further aggravate the global greenhouse effect.Therefore,as an alternative method of Harbor-Bosch technology,the electrocatalytic nitrogen reduction reaction(NRR)under ambient conditions has attracted more and more attention.Current researches are focused on the searching of a proper NRR catalyst.In this thesis,the NRR activity of non-metallic(B,N)and transition metal(TM)doped graphdiyne(GDY)has been studied by first-principles calculation.It is helpful for the design and further research of GDY based NRR catalyst.The main content of this thesis can be divided into the following three parts:In the first part,the NRR activity of N-doped GDY was investigated.Four different models of nitrogen-doped GDY were considered,namely the Graph-n,sp-N-1,sp-N-2 and pyridine-N GDY.Electronic structure analysis reveals that N-doing increases the positive charges on adjacent carbon atoms,which greatly promotes the adsorption and activation of N₂.The sp-N-2 GDY is the most active one among the substitutionally doped models with a limiting potential of-0.99 V.For pyridinic-N GDY,NRR follows a Mars van Krevelen(Mv K)pathway with a limiting-potential of-1.22 V.More importantly,Graph-C vacancy created in the Mv K path can efficiently reduce N₂ with a low limiting-potential of-0.41 V via a hybrid pathway.In the second part,the performance of GDY supported boron(B)as a metal-free single-atom electrocatalyst for N₂ fixation was studied systematically.The doping of isolated B atoms provides a more uniform and well-defined active site.The two-way charge transfer between N₂and B-GDY and the significant positive charge on the B atom indicate that N₂ molecules can be fully activated on the B-doped GDY catalyst in a"donation-back donation"manner.The GDY doped with B atom at the 18C hexagon hollow sites exhibits quite high-electrocatalytic activity with a low limiting potential of about-0.79 V in hybrid mechanism.In the third part,the NRR activity of single transition metal(TM)doped GDY was studied.Using first-principles calculations,we obtain the potential energy surfaces of five GDY supported single transition metal(TM,including Mo,Ni,Nb,Pt and W)atom catalysts.Based on the linear scaling relationship of formation energies of the intermediates,the formation energy of NH₂ can be used as a descriptor to evaluate the NRR catalytic performance of TM-GDY.The activity volcano of GDY supported single-atom catalyst was obtained.Through the calculation of the formation energy of NH₂ on other single-atom catalysts supported by GDY,we screened out the V-GDY single-atom catalyst with the best NRR catalytic performance.Its complete potential energy surface indicates that the limiting potential of NRR is only-0.33 V when it follows the enzymatic path.