Study On The Improvement Of Photocatalytic Hydrogen Production Over Zn_0.5Cd_0.5S By Nitride Cocatalysts

Since the first industrial revolution in the 1860 s,energy has become an indispensable part of almost every industry.Energy consumption is getting faster and faster.So the development of efficient and clean energy has attracted more and more attention.Hydrogen is considered to be a sustainable energy source in the future,and the high thermal energy generated during combustion is an important factor as a fuel.Photocatalytic hydrogen production is considered to be a feasible approach in the future.CdS is a visible light-responsive photocatalyst and one of the most prominent semiconductor photocatalysts in the field of photocatalytic hydrogen production.Zn_0.5Cd_0.5S?ZCS?solid solution not only has the same excellent photocatalytic performance as CdS,but also can alleviate the shortcomings of CdS such as susceptible photocorrosion.Carbon nitride materials have received more and more attention in recent years due to their unique properties such as excellent semiconductors,good chemical stability,and controllable band gap.Transition metal nitrides have excellent characteristics such as high melting point,high hardness,high thermal conductivity,and good chemical stability.They are widely used in cutting tools,wear-resistant parts,coating materials and many other fields.Due to their unique metal-physical physical and chemical properties and electronic structure,they are usually considered as the electrocatalyst of hydrogen evolution reaction?HER?and oxygen evolution reaction?OER?.The purpose of this article is to investigate whether nitrides with excellent electrocatalytic HER performance will still have good photocatalytic activity in ZCS photocatalytic systems.The main works of the paper are as follows:1.In order to study the photocatalytic effect of Co₃N in the ZCS-based photocatalytic system,we introduced Co₃N into the ZCS photocatalytic system.Since Co₃N is an intermetallic compound,it has excellent conductivity.After loading Co₃N,it provides an active center for photocatalytic hydrogen evolution,improves the separation of photogenerated electrons and holes,suppresses photocorrosion of photocatalyst,and improves H₂ production rate of ZCS.With 2 wt% Co₃N loaded on ZCS,its photocatalytic hydrogen production rate reached 160.7 mmol h^-1g^-1,which is almost 25 times than that of ZCS.This shows that Co₃N also has a good co-catalytic activity in the ZCS photocatalytic system.2.We successfully synthesized a sample of Ni_xN co-catalyst containing both Ni₃N and Ni₄N by changing the experimental temperature.Nickel nitride shows the advantages of metal properties,good electrical conductivity,and toxicity resistance.In addition,Ni₃N can provide many active centers,which make it have faster carrier transport speed and good catalytic performance.We successfully synthesized NixN / ZCS composites through a simple physical mixing method and tested the photoelectrochemical properties of composites.2 wt% Ni_xN/ZCS composite showed very excellent photocatalytic hydrogen evolution performance,and its photocatalytic hydrogen evolution rate reached 241.3 mmol h^-1g^-1,which was even 12 times higher than the photocatalytic hydrogen evolution rate of 2% Pt/ZCS.3.In order to further explore the activity of transition metal nitrides in ZCS photocatalytic systems,we successfully synthesized some nanoparticles such as Ni₃N,Fe₃N and W₂N and composited them with ZCS to prepare ccomposite materials.The photocatalytic hydrogen production rate of these three ccomposite materials were 70.3,138.4 and 80.4 mmol h^-1g^-1,respectively.4.In order to further explore the activity of nitrides in ZCS-based photocatalytic hydrogen production systems,we successfully synthesized g-C₃N₅ micron flakes by using potassium bromide as a structure directing agent and prepared CN/ZCS composites.At the same time,in 0.35 M Na₂S and 0.25 M Na₂SO₃ solution,the photocatalytic hydrogen production rate of the composite is about 142.8 mmol h^-1g^-1.We analyzed the photocatalytic principle using data such as fluorescence spectrum,and concluded that it may form a direct Z-scheme heterojunction,which effectively promoted the separation of photo-generated electrons and holes and improved the efficiency of photocatalytic hydrogen evolution.