Design And Properties Of Noble Metal-based Catalysts For Photo-and Electrocatalysis Hydrogen Evolution

In recent decades,global energy demand has continued to grow sharply,meanwhile,due to the decreasing supply of non-renewable resources such as oil and natural gas,research and exploration of sustainable,efficient,cheap and clean energy become an urgent task.As a clean new energy,hydrogen energy is one of the most ideal substitute for traditional energy.With the rational development of wind,hydro,solar energy and other resources,and the increasingly mature technology of power generation using natural resources,the cost of solar energy equipment and electric energy has gradually decreased,making it possible for photo-and electrocatalysis hydrogen evolution as a sustainable and environmentally friendly hydrogen preparation method,which has further attracted more and more researchers to invest a lot of energy to research and develop highly efficient catalysts.For hydrogen production by electrolysis of water,the current catalysts are mainly platinum group noble metals.Pt element is low in content in the crust and the price is expensive,which is not suitable for large-scale industrial production.Therefore,it is necessary to develop electrocatalytic materials with moderate cost and high performance,that is,on the premise of guaranteeing catalytic activity,improving the use efficiency of noble metals,reducing the use of noble metals,or finding substitutes for noble metal-based catalysts.For the photolysis of water to produce hydrogen,the photon absorption capacity of the catalyst and the electron-hole recombination rate determine the level of photocatalytic efficiency.On the one hand,the current catalyst's efficiency in converting solar energy into hydrogen energy is very low,which is far below the expected period of 10%for industrial applications.On the other hand,the light absorption range of commercial catalysts based on titanium oxide is mainly in the ultraviolet region,and ultraviolet light only accounts for 4%of the sunlight reaching the earth's surface,which greatly limits the use of sunlight.The development of high-efficiency photocatalysts to achieve high conversion efficiency from solar energy to hydrogen energy is of great significance to the industrialization of hydrogen production by photolysis of water.At this stage,one of the more mature approach is to support noble metals as a cocatalyst to improve the overall catalytic efficiency.In recent years,researchers have been looking for alternatives to Pt-based catalysts with low price and good catalytic effect.Compared with noble metals,most of these catalysts have poor performance,but they also bring us more ideas and guidances.In recent years,researchers have continued to explore and develop alternatives to low-cost and highly active Pt-based catalysts.However,the activity of many catalysts is still far behind that of noble metals.The principle of our catalyst design is to minimize the use of noble metals and reduce the cost of the catalyst under the premise of ensuring the catalytic activity.The main research results of this paper are as follows:(1)In Chapter 3:The classic ZIF-8 is used as the precursor for the synthesis of NC,and the ZIF-8 is coated with Si O₂ as a protective calcination strategy.After the high temperature pyrolysis,the Si O₂ shell is removed by chemical etching.The prepared PNC carrier has high dispersibility,large specific surface area,and rich pore structure.It is an ideal carrier for supporting small particle size noble metals,and avoids the phenomenon of activity reduction caused by small particle size precious metals due to agglomeration during the catalytic process.The Ru/PNC catalyst prepared by the ethylene glycol reduction method at only 1/3 of the cost of Pt shows excellent catalytic activity and good cycle stability.It provides reference for the method of adjusting the catalytic performance of noble metal by improving the carrier.(2)In Chapter 4:The noble metal-doped iron-based metal organic framework compound is synthesized as the precursor by immersion-adsorption,and the precursor is pyrolyzed in an inert atmosphere to prepare Fe M(M=Pt,Pd,Ru,Rh)with a nitrogen-doped graphene shell.Due to the synergistic effect of the alloy and carbon layer structure,the optimized Fe Pt@CN overpotential is 28 m V@10 m A cm^-2 in acid,and an overpotential of 18 m V@10 m A cm^-2 in alkaline solution for optimized Fe Ru@CN.The results showed that the catalysts adapted to different electrolytes could be found in the same alloy system.(3)In Chapter 5:Single crystal Pd nanoparticles with different crystal planes and sizes were prepared by shape and size control technology.With the help of chromatography and in-situ nuclear magnetic resonance,the reducing and oxidizing ends of the photolysis of water to hydrogen were studied in detail.The results show that the crystal face has a greater influence on the selectivity of catalyst oxidation production,and the particle size has a greater influence on the reaction activity.This method of observing both the reducing and oxidizing ends can be extended to other similar reactions.(4)In Chapter 6:The Pt/Ti O₂ catalyst was prepared by photochemical deposition method,and a series of Pt NPs with different chemical states and particle sizes were obtained by changing the synthesis conditions such as light source wavelength,light intensity,and light time.The prepared Pt-Ti O₂ catalyst has good potential in both photocatalytic hydrogen evolution and electrocatalytic hydrogen evolution.Furthermore,it is found that metallic Pt contributes to photocatalytic reaction and ionic Pt has electrocatalytic advantage.This work provides a green and effective method for the regulation of the chemical states of precious metals,and proves that the regulation of chemical states is an effective strategy for the development of novel photo/electrocatalysts.