The Controllable Preparation Of High-performance Porous Carbon-based Nonprecious Metal Catalysts And Their Electrocatalytic Properties

Energy crisis and climate pollution are major problems for the sustainable development of human society.The development of green and environmentally friendly energy storage and conversion systems are one of the effective approach to address this dilemma.Metal-air batteries and fuel cell have attracted great research interest because of the high energy conversion efficiency and pollution-free characteristics,however,which largely impeded by the sluggish oxygen reduction reaction（ORR）kinetics.Therefore,the rational design of high perform electrocatalysts with improving ORR kinetics is the key to the rapid development these sustainable energy technologies.It is well known that Pt is the excellent ORR electrocatalyst,while the scarcity,high costs and poor long-term stability hinder the large-scale applications.Therefore,the rational design of non-metal and nonprecious-metal ORR electrocatalysts with high performance is one of the most promising strategies for the global-scale application of these energy storage and conversion devices.Herein,this thesis focus on the non-metal and non-noble metal carbon-based electrocatalysts.Increasing the active site density and improving the porous structure of the electrocatalyst are the starting points,and by using the combination of experiment and theory,the relationship between geometry and ORR activity was explored in detail.We have successfully developed the electrocatalyst with high ORR performance and the main contents are as follows:1:Preparation of nitrogen-doped porous carbon high-efficiency bifunctional electrocatalyst and its application in zinc-air battery.First,we used activated carbon spheres as a template and dopamine as a nitrogen source to prepare a heteroatom nitrogen-doped porous carbon bifunctional electrocatalyst by a simple high-temperature pyrolysis method,named N-CNSP.The porous carbon-based template obtained in the first activation treatment has a super large specific surface area and abundant defects.The template rich in porous and defect structure helps to capture and enrich the precursor of dopamine nitrogen source.The specific surface area of the nitrogen-doped porous carbon high-efficiency bifunctional electrocatalyst is as high as 1200.3 m2g^-1.The high specific surface area facilitates the exposure of active sites and the full contact of active sites with the reaction medium.After optimization,the nitrogen-doped porous carbon high-efficiency bifunctional electrocatalyst exhibits excellent oxygen reduction reaction and oxygen evolution reaction properties.In N-CNSP,the onset potential and half-wave potential are as high as 0.96 V and 0.85 V,respectively,which are comparable to commercial Pt catalysts.For OER,the potential is 1.62 V at the current density of 10 m A cm^-2.The properties of OER are comparable to those of precious metal catalysts.The zinc-air battery assembled with the catalyst as the air cathode has a high power density(160 m W cm^-2)and excellent charge-discharge cycle stability(after 20 cycles,the rechargeable zinc-air battery lasts for more than 160 h,The small potential gap is only 0.90 V.This work provides important guiding ideas for the effective design and controllable synthesis of high-performance,multi-functional,non-precious metal catalysts.2:Co nano-island activation enhanced Co and N co-doped porous carbon high-efficiency dual-functional electrocatalyst.Porous activated carbon spheres with high specific surface area were used as template.Cobalt acetate and dopamine were used the source of Co and nitrogen.The pores and defects in the porous template are used to limit the Co and N precursors and achieve the role of anchoring metal ions and heteroatom nitrogen.The three-dimensional porous bifunctional electrocatalyst Co/Co-Nx-PCNSs co-doped with Co and nitrogen modified by Co nano-islands were obtained by high-temperature carbonization treatment.Studies have shown that Co nano-islands can reduce the work function of ORR,activate the surrounding carbon,and increase the types and density of active sites.In alkaline medium,the onset potential and half-wave potential of Co/Co-Nx-PCNSs electrocatalysts in ORR are better than that of precious metal Pt/C electrocatalysts.Co/Co-Nx-PCNSs electrocatalysts also show excellent OER properties and the Faraday efficiency close to 100%.At the same time,Co/Co-Nx-PCNSs showed good catalytic stability and methanol tolerance.Under the same conditions,it surpasses most of the reported non-noble metal electrocatalysts.Through effective regulation of composition and structure,the enhancement of catalytic performance is realized.The zinc-air battery assembled based on the Co/Co-Nx-PCNSs electrocatalyst exhibits a power density of140 m W cm^-2 and a charge-discharge cycle stability of up to 120 h.The experimental results demonstrated that the excellent bifunctional catalytic properties Co/Co-NX-PCNSs electrocatalyst originated from the synergistic action of porous structure and the abundant active sites.