Study On The Performance Of Black Phosphorus-Based Catalyst In Photo/Electrocatalytic Nitrogen Fixation

Ammonia（NH₃）is one of the most important chemical products in modern society,and it is essential to the normal operation of industry and agriculture.At present,the most widely used method to produce ammonia is the Haber-Bosch method in industry.However,this production process is accompanied by the consumption of a large amount of fossil fuel and emission of pollutant.It is urgent to develop green production methods.Photocatalysis and electrocatalysis technology has received great attention.It can directly synthesize ammonia from water and nitrogen,without pollutant emissions,which has been considered to be an ideal production method for pollution-free of energy and raw materials.Phosphorus is one of the most abundant elements on the earth,black phosphorus（BP）is one of the existing forms.Black phosphorus has the characteristics of ultra-high carrier mobility,superior light absorption performance and excellent band gap adjustability,which has very broad application prospects.There are many methods for preparing black phosphorus nanosheets,but they are all limited by the low exfoliating rate and are difficult to promote.As an emerging two-dimensional material exfoliating technology,the electrochemical expansion method has the advantages of high preparation rate and easy adjustment of the number of material layers to be regarded as an ideal technology.This article will prepare the black phosphorus nanosheets by electrochemical expansion method,and explore the application of black phosphorus materials in photocatalysis and electrocatalytic nitrogen reduction.As a typical two-dimensional material,black phosphorus nanosheets（BPNSs）have an ultra-high surface area.the BPNSs/Cd S heterojunction catalyst is prepared by directly synthesizing cadmium sulfide（Cd S）nanoparticles on BPNSs.After the photocatalytic nitrogen reduction test,the catalytic performance showed a trend of first increasing and then decreasing with the increase amount of black phosphorus.When the amount of black phosphorus raised to 1.5%,the highest photocatalytic activity was achieved,57.64μmol·L^-1·h^-1.In addition,it also shows good cycle stability.Combining theoretical calculations and electrochemical tests,the catalytic mechanism of BPNSs/Cd S materials is studied.Cd S acts as the catalyst to generate photo-generated carriers,and the electrons migrate to the conduction band of black phosphorus.Due to the close contact between the two materials and the barrier between the interface below the Fermi level,the electron migration rate can be significantly increased.Black phosphorus is used as a co-catalyst,and the P atom at its edge is the active site for catalysis.The N₂ molecule is reduced to ammonia through the associative distal method.In order to further explore the effect of the combination of two materials between the heterojunction on the catalytic performance,the combination of nickel ions and P atoms was controlled at the atomic level to form Ni-P chemical bonds.Theoretical calculations proved that the existence of chemical bonds significantly reduces the energy barrier for electron migration between black phosphorus and nickel phosphide（Ni₂P）,which improves the electron migration efficiency.The electrocatalytic nitrogen reduction test shows that the material has a higher ammonia synthesis rate,25.67μg·h^-1·mg^-1 _cat（-0.35V vs RHE）,which is much higher then Ni₂P+BP samples without chemical bonds.In addition,the Ni₂P-BP sample also exhibits higher electrocatalytic stability than the pure black phosphorus sample.Theoretical calculations show that Ni atoms are the active sites for catalytic reactions,and N₂molecules are reduced to ammonia through the associative distal method.