Fabrication Of Heteroatoms Doped Graphene-Like Materials And Their Application In Electrocatalysis

Oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)are critical reactions for renewable energy conversion and storage devices,but the slow kinetics,high cost,low abundance,and poor stability restrict their large-scale usage.In this work,to address these problems,we designed and prepared a series of graphene-liked materials,explored the electrocatalytic properties of different heteroatoms doping and the principles of different active sites,and revealed mechanism of electrocatalytsis.The main works were as follows:1.CoFe2O4/oxygen-doped graphitic carbon nitrogen(O-C3N4)was prepared by thermal annealing method.O-C3N4 as a support can effectively reduce the particle size of CoFe2O4 nanoparticles and prevent their aggregation.The OER performance was remarkably improved including conductivity,long-term stability,and the overpotential of CoFe2O4/O-C3N4 hybrid for 10 mA/cm2 current densities with a decrease of 131 mV and 61 mV compared with CoFe2O4 and CoFe2O4/graphitic carbon nitrogen(g-C3N4)hybrid,respectively.These indicated that oxygenated functional groups on O-C3N4 can lead to homogeneous distribution of CoFe2O4 NPs and more active sites exposed.Meanwhile,the introduction of O atoms enhanced the interaction between CoFe2O4 and g-C3N4 to accelerate the electron transfer rate.2.CoOx/N-doped graphene/graphitic carbon nitrogen(CoOx/NG/g-C3N4)was prepared by thermal annealing method.The introduction of NG greatly prevented the aggregation of CoOx nanoparticles.Further doping g-C3N4 into CoOx/NG,CoOx/NG/g-C3N4 showed wrinkle and cross-linked structure.And the introduction of g-C3N4 can effectively increase the contents of pyridinic N and numbers of O defects to result in the improved ORR and OER performance.Detailed experiments suggested that the onset and half-wave potentials(Eonset and E1/2)of CoOx/NG were with positive shifts of 110 mV and 100 mV,respectively as compared with CoOx nanoparticles.The introduction of g-C3N4 can further improve the ORR activity.Eonset and E1/2 of CoOx/NG/g-C3N4 were futher with positive shifts of 40 mV and 110 mV,respectively,which showed not only similar ORR activity to commercial Pt/C,but also more superior stability and excellent methanol tolerance than commercial Pt/C.Additionally,the resultant CoOx/NG/g-C3N4 also showed superior OER activity.The overpotential of CoOxc/NG/g-C3N4 for 10 mA/cm2 current densities with a decrease of 160 mV and 180 mV compared with CoOx/NG and CoOx,respectively.3.A series of three-dimensional porous B and N co-doped graphene aerogels(BN-GAs)using NH4B5O8 as precursor for B and N source by hydrothermal method and freeze-drying process.In this facile strategy,we can tune doping contents of B and N configurations in BN-GAs by simply changing the synthesis time and ratio of precursors.Detailed experiments suggested that the increasing content of pyridinic N and BC3 phases in BN-GAs can boost ORR activity.Eonset and E1/2 of BN-GAs-2 were at-0.05 V and-0.20 V,respectively,which showed not only similar ORR activity to commercial Pt/C,but also more superior stability and excellent methanol tolerance than commercial Pt/C.Remarkably,BN-GAs-2 also showed superior OER activity.The overpotential of BN-GAs-2 for 10 mA/cm2 current densities with a decrease of 70 mV and 200 mV as compared with singly doped GAs(N or B),respectively.Moreover,a homemade zinc-air battery comprising such bifunctional catalysts shows superior performance.The maximum power density of BN-GAs-2 catalyst is equal to 88.9%of that achieved by commercial Pt/C.The improved electrocatalytic performance may be because BN-GAs-2 with three-dimensional porous structure can accelerate electron transfer and the synergetic effect between pyridinic N and BC3 phase.