Design,Synthesis And Studies Of Transition Metal Phosphides For Artificial Photosynthesis

By simulating the principle of natural photosynthesis,artificial photosynthesis is an important way to convert solar energy into chemical energy.Semiconductor photocatalytic water splitting is an important means for artificial photosynthesis.In order to promote the photocatalytic hydrogen evolution activity of semiconductors,scientists have focused much attention on the integration of cocatalysts with semiconductors.In recent years,transition metal materials have developed rapidly in the photocatalytic water splitting,and a series of transition metal hydroxides,sulfides and complexes have been developed as efficient hydrogen evolution cocatalysts.But the study of phosphides is still absent.Therefore,this dissertation focuses on designing and synthesizing various transition metal phosphide materials,and using these materials for artificial photosynthesis.In the first section,we introduce the background and challenges of artificial photosynthesis,and summarize the recent research progress of the noble metals and transition metal materials modified semiconductors for artificial photosynthesis.In the second section,we synthesized Fe2P as a cocatalyst for photocatalytic hydrogen evolution.After calcining Fe2P/CdS mixture to increase their interface contact,the photocatalytic hydrogen production rate could be further increased by more than 30 times,and the quantum efficiency at 450 nm was 15%.Results have shown that there is a rapid electron transfer between CdS and Fe2P,which is the key to promoting photocatalytic hydrogen evolution.In the third section,we combined the p-type semiconductor CU3P with the n-type semiconductor CdS to form a p-n heterojunction structure,and investigated its photocatalytic hydrogen evolution activities.Results have shown that this p-n heterojunction structure possesses a fast electron transfer process,and the hydrogen production rate under visible light irradiation can reach 200?mol h-1 mg-1,with the quantum efficiency at 450 nm can be increased to 25%.In the fourth section,we used CdS as a substrate to in situ grow amorphous cobalt phosphides(CoPx)on CdS,and formed a CoPx/CdS core-shell structure.Results have shown that the amorphous phase of cobalt phosphide can also quickly transfer photoelectrons from CdS and perform proton reduction.This CoPx/CdS core-shell structure hydrogen production rate up to 500 ?mol h-1 mg-1 under visible light irradiation,quantum efficiency further increased to 35%at 450 nm.Moreover,the turnover number relative to cobalt can reach 630,000 with a turnover frequency of 9000 h-1.This amorphous cobalt phosphide cocatalyst exhibits the superior photocatalytic hydrogen production performance among cobalt-based materials.In the fifth section,we in situ grew Ni2P nanoparticles on CdS surface.Ni2P is anchored on the surface of CdS nanorods with a flat structure.The photocatalysis results show that Ni2P is a good cocatalyst for photocatalytic hydrogen evolution,and the rate can reach 1200 ?mol h-1 mg-1 based on photocatalysts,with a quantum efficiency as high as 41%at 450 nm.The turnover number is as high as 3,270,000,the turnover frequency is 36,400 h-1 for Ni2P.And the hydrogen production rate remains unchanged during the hydrogen production up to 90 hours.As a cocatalyst,it exhibits very excellent photocatalytic hydrogen evolution activity and stability.In the sixth section,we used a convenient electrodeposition method to rapidly synthesize iron-phosphorus-drived(Fe-P)nanoplates structures on nickel foam,and performed an electrocatalytic water oxidation study on oxygen production.Compared to conventional long time and high temperature phosphorization method,this method can be completed in a short time at room temperature.Moreover,the as-prepared Fe-P nanoplates exhibited superior properties compared to the conventional phosphorization method.In the 1 M KOH solution,only a 205 mV overpotential is needed to reach a current density of 10 mA cm-2,showing excellent electrocatalytic properties of water oxidation reaction.In the seventh section,we synthesized Co2P nanorods as an efficient catalyst for photocatalytic CO2 reduction using[Ru(bpy)3]Cl2 as the photosensitizer.Co2P nanorods exhibit high activity and stability for photocatalytic CO2 reduction.It can effectively convert CO2 into CO with selectivity as high as 80%.Through spectral analysis and theoretical calculations,we found that Co2P can efficiently capture electrons from the[Ru(bpy)3]Cl2 and act as an active center for CO2 reduction.Finally,the research situation with the artificial photosynthesis property of the transition metal phosphide is discussed briefly,and providing a direction for the future research.