Preparation And Electrocatalytic Properties Of Transition Metal Doped Carbon Nanomaterials

Platinum-based catalysts are currently the most effective oxygen reduction catalysts.Due to their low reserves,high price,and susceptibility to poisoning,the large-scale commercial application of these two devices has been seriously exacerbated.It is urgent to develop a catalyst with low price,high activity and stability.Because of the many advantages of carbon-based catalysts,researchers have attracted widespread attention.In this dissertation,Fe–Ni dual-functional catalysts and Zn single-atom oxygen reduction catalysts were prepared,and the catalysts were systematically studied by density functional theory.The main contents and results are as follows:1.Nitrogen coordinated bimetal atomic catalysts sparkle in the nonprecious metal electrocatalysts with compelling catalytic activity and selectivity for oxygen reduction（ORR）and oxygen evolution（OER）reactions.Nevertheless,further improvement on the catalytic performance for such systems remains challenging,and the design of bimetal atomic pairs demand theoretical instructions.We found through first-principles calculations,the cooperative interplay between charge itineration and spin polarization of electrons of center metals is of great significance to the catalytic activity.Following this concept,a Fe–Ni atomic pair is developed as a superior bifunctional catalyst for both ORR and OER.Density functional theory（DFT）study reveals that by coupling with Ni,the spin polarization on Fe is alleviated,and the delocalization of Fe 3d（the reaction center）is efficiently enhanced,which thus facilitate the optimal ad（de）sorption of intermediates and facile electrons delivery between catalyst and intermediates.Consequently,the as-constructed catalyst exhibits impressive ORR and OER performance.The ORR half-wave potential(E_1/2)of 0.861V and the OER overpotential(E_J=10)was 0.322 V vs RHE.Meanwhile,the potential difference（ΔE）from ORR to OER,i.e.,0.691 V,is much smaller than those of commercial Pt/C（1.025 V）and IrO₂（1.051 V）benchmarks,an indicator of bifunctional promise.2.M–N–C（M=transition metals）based single-atom catalysts are revolutionary to replace noble-metal catalysts,among which Zn–N–C is distinguished for the superior stability yet great development space is reserved to improve its activity.Herein,a competitive complexation strategy is proposed to introduce extra B heteroatom to enhance the charge disproportion by taking the advantage of large electronegativity difference.It is revealed that the unique B–Zn–N path is crucial in which the Zn 4s orbital acts as an“electron bank”whose electrons are“deposited”since B is more willing to offer its electrons.Meanwhile,these electrons are facile to be“withdrew”by O₂ in the ORR process in view of the large screening effect from the fulfilled inner 3d¹00 texture.Consequently,the ORR activity is greatly improved in both acidic and alkaline media,wherein the half-wave potentials are 0.886 V and 0.714 V,respectively.While improving the catalytic activity of the ORR,the special electronic structure of the Zn atom ensures the stability of the Zn/BNC catalyst.In the long-cycle stability test,at a high potential of 0.85 V and a speed of 1600rpm,after a test of 40,000 s,the current retention rate was 92%,which showed excellent stability.