Preparation Of Chitosan-derived Carbon-based Iron And Cobalt Chainmail Catalysts Towards The Application In Zinc-Air Battery

Confronted with environmental pollution and energy shortage,the development of non-polluting and environmental-friendly new energy devices has become an effective route to solve these problems.Fuel cells and zinc-air batteries have become the focus of current research due to their offering of high energy density,low cost of raw materials and high safety.However,the cathodic reaction with low reaction kinetics severely limits their large-scale commercial applications.Therefore,the development of efficient and durable cathodic catalysts is currently the main task.It is known that merited by the unique structure of chainmail catalysts,the chainmail layers can protect the inner metal cores from being damaged in those harsh working conditions;as a consequence,the architected chainmail catalysts afford excellent catalytic activity and stability.They are the most promising alternatives to the noble metal catalysts.In recent years,biomass-based materials have been widely used in the electrocatalysis because of their abundant sources,wide variety,low price and excellent physical and chemical properties.As a result,they are qualified as the promising precursor materials for the preparation of carbon-based chainmail catalysts.In this thesis,chitosan with low cost and rich nitrogen content was selected as the precursor for the synthesis of chainmail catalysts.Our efficient chainmail catalysts with excellent catalytic activity and stability were constructed by using different preparation strategies.The specific work content is as follows:1.Based on the rich functional groups such as amino and carboxyl groups in chitosan,the armored catalyst Co-NC-AD with graphitic carbon layers encapsulating cobalt nanoparticles was prepared via the competitive complexation strategy and high-temperature pyrolysis.As a result,they showed excellent electrochemical performance in ORR reaction and zinc-air battery.The"gasification pore formation"of metallic zinc species in the precursor enables for the targeted catalysts to obtain hierarchical porous structures,which is beneficial to expose more active sites and accelerate the catalytic mass transfer progress.Electron microscopy identified the formation of the chainmail structures.Spectrum characterization combined with DFT calculation jointly confirmed that the electron transfer process between the outer graphitic carbon layers and the inner cobalt nanoparticles enables effectively activating the outer graphitic carbon layers,thus accelerating their adsorption process with oxygen molecules.Therefore,our prepared Co-NC-AD catalyst exhibited superior catalytic activity and stability over the commercial Pt/C in the alkaline condition,with the onset potential and half-wave potential of 0.95 V and 0.86 V,respectively.The Co-NC-AD catalyst afforded high energy density(194 m W cm^-2)and specific capacity(808 m Ah g_Zn^-1)in zinc-air batteries,which were superior to those of commercial Pt/C-based zinc-air batteries.2.The chainmail catalyst G-Fe-NC with iron nanoparticles wrapped by graphitic carbon layers was prepared by using high-temperature pyrolysis using a combination of mechanical ball milling and gas-phase diffusion.Firstly,chitosan,urea and zinc salt were uniformly mixed by mechanical ball milling,and the resulting mixture was pyrolyzed at high temperature to obtain nitrogen-doped carbon support with abundant defects.Then,ferrocene was reduced to iron-containing gaseous species by gas diffusion strategy and captured by the carrier to obtain armor catalysts with excellent ORR activity and stability.Electrochemical tests showed that the half-wave potential of G-Fe-NC catalyst is as high as 0.87 V under the alkaline condition,which is superiro to that of commercial Pt/C.In addition,G-Fe-NC catalyst also showed improved cycle stability and methanol toxicity resistance than the commercial Pt/C,due to the protective effect of the chainmail structure.The architected zinc-air battery tests indicated that the G-Fe-NC catalyst possessed a promising application prospect than the commercial Pt/C catalyst.