Study On The Composite Inorganic Nanoelectrocatalysts For Oxygen Reduction And Hydrogen Evolution Reaction

The rapid development of the global economy depends on the strong support of energy,major traditional energy sources such as coal,oil,and natural gas have limited storage capacity,and their massive use will cause environmental pollution.Hydrogen energy,as an ideal clean energy,is considered the best substitute for traditional energy.The green generation of hydrogen energy is inseparable from the water electrolysis reaction,while the utilization of hydrogen energy by fuel cell technology produces only water,which realizes the sustainable recycling of resources.Specifically,the research and development of high-efficiency catalyst plays the key role in the sustainable recycling of hydrogen energy.However,current electrocatalysts mainly rely on precious metal catalysts?such as Pt,Ru,Ir,etc.?with low crust content and high economic cost.In order to reduce dependence on precious metal catalysts,there is an urgent need to seek efficient and stable non-precious metal catalysts to accelerate electrocatalytic reactions.In this dissertation,in order to address the key problems such as the slow kinetics and poor stability in the electrocatalytic oxygen reduction reaction?ORR?and hydrogen evolution reaction?HER?for non-noble metal electrocatalysts,the following two parts of the work were carried out:?1?Compositing and double-doping strategies were employed to improve the activity of carbon-based ORR catalyst for non-Platinum carbon-based ORR electrocatalysts.1)Silver nanowire and nitrogen-doped graphene composite catalyst.To solve the problems of intertangling and restacking of nitrogen-doped graphene-based materials and poor conductivity,silver nanowires-nitrogen-doped graphene?AgNWs@NG?composites have been desigened.High activity nitrogen-doped graphene was coated on AgNWs with high aspect ratios via a self-assembly method.The core AgNWs not only can be used as the supporting framework of NG,but also it can be used as a highly conductive pathway in the ORR catalytic process.The ORR electrocatalytic test showed that,in 0.1 mol L^-1 KOH,the mass activities value of AgNWs@NG is 6.4 A g^-1,higher than that of NG(5.2 A g^-1)and AgNWs(1.9 A g^-1)respectively at-0.1 V?vs.Ag/AgCl?.This study shows that the synergistic effect between AgNWs and NG in the composites leads to the superior catalytic properties.2)Double doped porous carbon materials as ORR catalyst.Based on the structural collapse,sintering and pyrolysis loss of carbon materials in the traditional high-temperature carbonization process,three kinds of diatomic doped porous carbon materials,NS-PC,NP-PC and NB-PC,were prepared with potassium chloride as the salt template.Electrochemical assessments showed that,the three samples exhibited high ORR activity,among which,the best NS-PC presented an onset potential of 0.8 V vs.RHE,and half-wave potential of 0.67 V vs.RHE in 0.1 mol L^-1 HClO₄.The enhancement of ORR activity was attributed to the effective doping of dihybrid atoms and the role of potassium chloride templates in the protection and pore formation during porous carbon synthesis.?2?The influence of the synthesis strategies on the morphology and HER activity of main hydrogen evolution materials?including nickel metal,nickel phosphite,transition metal nitride and sulfide?was studied.1)Ni/V₂O₃ composite catalyst for hydrogen evolution.Based on the high overpotential and large Tafel slope of Ni,high-dispersed ultrafine Ni/V₂O₃ composite catalyst was synthesized by selectively segregating Ni element in the Ni_xV_1-xO₂precursor to the surface of the inert V₂O₃.The HER activity of Ni is greatly enhanced due to its particle size control for Ni,good electron transport,3D network structure and metal/oxide interaction.Electrochemical assessments showed that,Ni/V₂O₃ exhibited a low overpotential of 140 mV at 10 mA cm^-2,a small Tafel slope?112 mV/dec?,and improved stability over 18 h during operation in basic operation.This strategy can be applied to synthesize a series of metal/oxide nanostructures with high performance in a variety of catalytic process.2)Ni-P/Ni composite catalyst for hydrogen evolution.Ni-P based HER catalysts are usually prepared by electrodeposition.Previous research didn't study in detail the effect of external plating solution conditions on the physical and electrocatalytic properties of Ni-P catalysts.Based on above questions,three Ni-P/Ni catalysts were synthesized in acidic,neutral and alkaline electrolytes by electrodeposition,and the relationship between the physical and electrochemical properties of the three catalysts and the pH of the electrolyte was systematically studied.The experimental results showed that the electrodeposited Ni-P/Ni electrode in acid electrolyte had the highest electrocatalytic activity??=110 mV?and the exchange current density is 0.216 mA cm^-2,which could be attributed to its minimal charge transfer resistance and maximum double layer capacitance.Meanwhile,this study proved the important effect of P content in Ni-P electrocatalyst on HER activity.3)MoN/CNT composite catalyst for hydrogen evolution.To solve the problem of slow charge transfer and poor stability of sheet molybdenum nitride materials in HER,a composite catalyst of molybdenum nitride nanoparticles/highly conductive carbon nanotubes?MoN/CNT?was designed.Electrochemical measurements showed that,MoN/CNT was highly active for HER and exihibited a low overpotential of 165 mV at10 mA cm^-2,a small Tafel slope?45 mV/dec?,and after a long continuous HER,the catalytic performance of the sample did not decrease significantly,which proved that MoN/CNT composite catalytic materials had the potential to replace noble metal HER materials.4)CoS₂ nanoparticles catalyst for hydrogen evolution.Based on the fact that the morphology control of cobalt disulfide nanomaterials is very important for HER activity on such catalytic materials,the uniform cobalt sulfide nanoparticles were synthesized by a hydrothermal method,and the catalytic performance of CoS₂ NPs in electrochemical hydrogen evolution was studied.Electrochemical measurements showed that,the uniform CoS₂ NPs exihibted a low overpotential of 176 mV at 10 mA cm^-2 and a Tafel slope of 71.6 mV/dec with a high catalytic activity and stability,which proved the importance of controlling morphology in regulating the catalytic properties of cobalt disulfide HER catalysts.