Morphology Engineering Of Ferrocenylpyrrolidine C₆₀ And The Applications In Electrochemical Energy Storage And Conversion

In recent years,π-conjugated carbon materials have been utilized to carry the active sites for electrochemical energy storage and energy conversion.Compared with graphene and carbon nanotubes,fullerenes,possessing well-defined molecular structures,can be rationally designed and decorated with metal/non-metal atoms at the molecular level.The in situ doping of heteroatoms can be expected to introduce extra active sites for electrochemistry.On the other hand,the van der Waals force can enable the self-assembly of fullerene molecules into one-dimensional linear,two-dimensional layered and three-dimensional hierarchical microstructures,which helps to study the phase structure and increase the active area.To this end,the following studies were carried out on a Fe and N decorated fullerene derivative of ferrocenylpyrrolidine C60(Fc-C₆₀).The main contents and achievements are as follows.（1）The liquid-liquid interface precipitation（LLIP）method was applied to modulate the morphology of Fc-C₆₀ microstructures by simply mixing the good solvents(soluble of Fc-C₆₀)and poor solvents(insoluble of Fc-C₆₀).Firstly,conventional benzene and alcohol solvents were used in the LLIP process to assemble Fc-C₆₀ molecules into twodimensional layered and three-dimensional hierarchical structures.The patterns of the morphology and typical fullerene crystallization phenomenon are systematically studied.The use of conventional LLIP method could not fabricate the one-dimensional microstructures due to the rapid inter-solvent diffusion.Therefore,the one-dimensional needle-like Fc-C₆₀ microstructures were successfully prepared by introducing water into the LLIP process.This strategy was also proved versatile in other solvent combinations.Benefitting from the high crystallinity and the embedding of solvent molecules,The onedimensional microstructures exibit enhanced photoresponse and photoluminescence properties.This strategy of introducing water provides a new strategy of surmounting the low symmetry of fullerene derivatives and assembling them into well-defined 1D crystals for developing far-reaching applications.（2）Fc-C₆₀ molecules were assembled into a unique cross-like hierarchical structure.By high-temperature treatment under inert atmosphere,Fe3O4 and N co-doped carbon materials were obtained and applied to supercapacitor electrode.Benefiting from the interlaminar diffusion channels of the hierarchical microstructure,the pseudocapacitive properties of the metallic phase,and the highly graphitized carbon matrix,the sample activated at 700 °C exhibited a specific capacitance as high as 505.4 F g-1,along with excellent rate performance and cycling stability.This performance broke through the limit of low double-layer capacitance of metal-free fullerene-derived carbon.The current work provides a new synthetic method to prepare doped carbon materials for energy storage applications,and boost the supercapacitor performance using fullerene derivative-based materials.（3）During the pyrolysis period of Fc-C₆₀ hierarchical microstructures,ammonia was introduced to replace the inert atomosphere.The subsequent composites were characterized with porous carbon frameworks and high specific surface area and were successfully applied into electrocatalytic oxygen reduction reaction.The sample treated at 700 °C under ammonia possesses short-range ordered nanographene with large lattice spacing of 4.1⁴.8 ?,uniform Fe3O4 active sites,improved nitrogen doping and high specific surface area,and exhibit superior electrochemical oxygen reduction and zincair battery performance to C60-based carbon materials.This study provides a new perspective for the preparation of electrocatalysts with a wide range of applications from fullerene molecules.（4）The in situ growth of Fc-C₆₀ molecules to multi-walled carbon nanotubes was firstly achieved by reducing the ramp rate in the high-temperature treatment under ammonia,and carbon nanotubes with different morphologies can be obtained by rising the temperature and lowering the ramp rate.The low ramp rate（5-10 °C/3 min）is favorable for the formation of Fe3 C phase that catalyzes the formation of carbon nanotubes.The obtained entangled carbon nanotubes were successfully applied to solid-state zinc-air batteries and alkaline electrochemical hydrogen evolution,and exhibited high activity and stability.The employment of Fe-decorated fullerene derivative opens a remarkable synthetic avenue for in situ growth of carbon nanotubes from fullerene molecules and provides a new path for preparing high-performance electrocatalysts.