Surface Functionalization Of Graphene And Its Application In Zinc-air Batteries

Graphene is a kind of two-dimensional?2D?material with high mechanical strength,which has many properties in various field,including excellent acoustic,optical and mechanical properties,it has important application prospects in the fields of materials science,nanofabrication,energy field,medicine and drug delivery,graphene is a revolutionary material of the future.There is hexagonal honeycomb shape lattice structure of the carbon atoms in graphene which in the form of sp² hybridization,besides,there is one electron per carbon atom was not involved in the hybridization,leads to superior electron conductivity of graphene.Moreover,the graphene has a large specific surface area,which means it has great development prospect in the field of energy material science.Over the years,the researches based on the graphene has never been stopped in the energy material engineering.Graphene has two surfaces that could be functionalized to produce graphene-based materials with different functions.However,there is inevitable fold and stack occurs between the graphene layer,which would definitely a great loss of electrochemical active sites in the field of energy material.To settle this issue,we could construct the 2D graphene into three dimensional?3D?structure.In this thesis,various of 3D graphene based nanomaterials were synthesized via the template method.The size of metal active sites was controlled by the spatial restriction effect of templates and graphene on metal precursors?metal nanoclusters and metal single atoms?.And their electrocatalytic properties for hydrogen evolution reaction?HER?,oxygen evolution reaction?OER?and oxygen reduction reaction?ORR?were studied,and further evaluated the practicability through the Zn-air battery test.The main results are summarized as follows:1.The Pt nanoclusters functionalized graphene hollow spheres denoted as Pt/GHSs were synthesized by using the K₂Pt Cl₄ and positively charged Si O₂ nanospheres template with graphene oxide step by step self-assembly to obtain the Si O₂@Pt Cl₄^2-@GO intermediates,followed by direct pyrolysis and alkali wash to remove the template.The research shows that the Pt/GHSs almost perfectly inherited the original shape of Si O₂ nanospheres template,the GHSs were 150-200 nm in diameter.Pt were anchored on the GHSs in the metallic nanocluster form,the loading amount of Pt in the Pt/GHSs were calculated at 4.1 wt.%through the ICP-AES test.Electrochemical studies showed that the synthesized Pt/GHSs possessed the comparable HER property to that of commercial Pt/C of 20 wt.%,and the overpotential was 27 and 21 m V,respectively.After 1000 cycles of CV,the overpotential of Pt/GHSs attenuated by only2 m V,which was significantly better than that of Pt/C whose overpotential attenuated by 5 m V under the same conditions.Above results indicated that in the Pt/GHSs,which metal Pt loading is one-fifth of commercial Pt/C has the same catalytic activity for HER as compared to commercial Pt/C,as well as better electrochemical stability.2.The single atom Ni functionalized GHSs noted as Ni-N_x/GHSs were synthesized by using the K₂[Ni?CN?₄]and positively charged Si O₂ nanospheres template with graphene oxide step by step self-assembly to obtain the Si O₂@[Ni?CN?₄]^2-@GO intermediates,followed by direct pyrolysis and alkali wash to remove the template.The study shows that the Ni-N_x/GHSs almost perfectly inherited the original shape of Si O₂nanospheres template,the GHSs were 150-200 nm in diameter,and Ni were atomically anchored in the GHSs.The electrochemical test indicated that the Ni-N_x/GHSs exhibited the comparable OER activity towards the state-of-the-art Ru O₂,and the overpotential was 389 m V and 336 m V,respectively.Besides,the Ni-N_x/GHSs could acquire higher current density than Ru O₂ when under higher potential in the OER catalysis.In the chronoampermetry test,the Ni-N_x/GHSs only exhibited a small current degradation?75.5%remained?,significantly superior than that of Ru O₂?57.3%remained?.Above results demonstrated the single Ni atoms and graphene fabricated Ni-N_x/GHSs possessed exceptional catalytic activity and electrochemical stability towards OER.3.The Janus material Ni-N₄/GHSs/Fe-N₄ were synthesized by using the K₂[Ni?CN?₄],positively charged Si O₂ nanospheres template with graphene oxide and iron???phthalocyanine?Fe Pc?step by step self-assembly to obtain the Si O₂@[Ni?CN?₄]^2-@GO@Fe Pc intermediates,followed by direct pyrolysis and alkali wash to remove the template.The study shows that the GHSs were 150-200 nm in diameter,and Ni/Fe were atomically dispersed on the inner and outer surface of graphene,respectively.Moreover,the X-ray absorption spectra of synchrotron radiation results indicated that the Ni and Fe atoms were coordinated by four N atoms respectively.The electrochemical studies demonstrated the outer Fe-N₄ species exhibited high ORR catalytic activity which half-wave potential(E_1/2)located at 0.83V,and the inner Ni-N₄ species exhibited high OER catalytic activity which overpotential(E_j10)located at 0.39 V,consistent with the theoretical calculation.In terms of practicality,there were no obvious attenuation of the Ni-N₄/GHSs/Fe-N₄based Zn-air battery when after 600 cycles?about 200 h?battery charge-discharge,the charge and discharge efficiency remained at 52.2%.Furthermore,the specific capacity and energy density of Ni-N₄/GHSs/Fe-N₄based Zn-air battery were 777.6 m Ahg _Zn^-1 and970.4 Wh kg _Zn^-1 respectively,which is 94.8%and 89.5%of the theoretical specific capacity(820 m Ahg _Zn^-1)and energy density(1084 Wh kg _Zn^-1),superior than the state-of-the-art Pt/C+Ru O₂ based Zn-air battery(659.6 m Ahg _Zn^-1and 844.3 Wh kg _Zn^-1).Above results proved that the synthesized Ni-N₄/GHSs/Fe-N₄ Janus material is a kind of bifunctional electrocatalyst both for the ORR and OER,and in the practical application,Ni-N₄/GHSs/Fe-N₄ based Zn-air battery exhibited large specific capacity and energy density,high charge-discharge efficiency and cycling stability.