Electrocatalytic Nitrogen Fixation Of Graphdiyne Composite Material:a First-principles Study

Ammonia is an important chemical raw material and a clean energy carrier.At present,the global annual production of ammonia is about 200 million tons,mainly from industrial synthesis of ammonia by the Haber-Bosch process.However,Haber-Bosch process requires harsh reaction conditions of high temperature and high pressure.In addition,Haber-Bosch process has high energy consumption,low ammonia yield and large amount of greenhouse gases.Therefore,it is of great significance for the sustainable development of energy to find a new method of ammonia synthesis with low energy consumption and environmental protection.Electrocatalytic nitrogen reduction reaction（NRR）has attracted more and more attention due to its ability to synthesize NH₃ at normal temperature and pressure.Therefore,it is an urgent problem to develop NRR catalysts with high efficiency and high selectivity.Based on the idea of“chainmail”-protected catalysts proposed by recent studies,we designed a sandwich structure with BN-doped graphdiyne（GDY）covering atoms and supported by GDY as a catalyst for NRR.The specific research content is as follows:1.Starting from the single atom catalyst,we systematically studied the sandwich structures doped with nine transition metal（TM）single atoms（Sc,Ti,V,Cr,Mn,Fe,Co,Ni,and Cu）,which are labeled as BN-TM-G（BN=BN-doped GDY;G=GDY）.The catalytic properties of the structures were studied in detail by calculating charge density difference,atomic charge,free energy and state density.The results show that the sandwich structure enables the TM atom to transfer electrons to the adjacent B atom as the active site,thus driving the reduction of N₂.The NRR catalytic activity of BN-TM-G system is closely related to the degree of positive charge polarization of TM atoms.The BN-Sc-G,BN-Ti-G,BN-V-G and BN-Cr-G systems showed high NRR selectivity while inhibiting HER.In particular,BN-Cr-G is a potential NRR catalyst with the lowest limiting voltage of-0.63 V.2.We further studied the sandwich structures doped with nine identical TM double atoms（Sc,Ti,V,Cr,Mn,Fe,Co,Ni and Cu）,labeled as BN-TM₂-G.By calculating and screening the sites of adding TM double atoms,it is easier for B atom to adsorb and activate N₂.Then the catalytic properties of different kinds of TM double atoms for nitrogen reduction in this configuration were investigated.The results show that BN-Cu₂-G has excellent NRR catalytic performance at both the distal and alternating paths,with the lowest limiting voltage of-0.56 V,and BN-Mn₂-G has excellent NRR catalytic performance at the alternating path,with the limiting voltage of-0.87 V.3.We studied the sandwich structures doped with six main group metal（M）single atoms（Li,Na,K,Mg,Ca and Al）,labeled as BN-M-G.The configurations for N₂ adsorption and activation were selected by calculation.Then,we further investigated their NRR catalytic performance.The results show that the optimal mechanism of NRR catalyzed by BN-Mg-G is alternating mechanism,and the corresponding limiting voltage is-0.47 V.The optimal mechanism of BN-Al-G catalysis for NRR is alternating mechanism,corresponding to the limiting voltage of-0.67 V.Both of them exhibit a high selectivity for NRR compared with hydrogen evolution reaction（HER）.