Preparation And Oxygen Reduction Performance Study Of Graphdiyne-Based Non-Precious Metal Single-Atom Catalysts

Since the successful synthesis of graphdiyne(GDY)in 2010,it has garnered widespread attention and research within the scientific community.Distinguished from traditional carbon materials,the unique sp-C in the two-dimensional carbon framework of GDY endows it with non-uniform charge distribution and electronic structure,making it one of the star materials in the field of electrocatalysis.By altering the local structure of graphdiyne molecules,their pore structures and chemical compositions can be modulated for direct application in catalysis.Simultaneously,the metal anchoring effect of its unique structure allows it to serve as an exceptional support for single-atom catalysts.In this paper,a series of non-precious metal single-atom catalysts are designed and synthesized based on the structural advantages of graphdiyne.By analyzing the atomic-level mechanism of the catalysts,a structure-activity relationship is established to guide the rational design and precise control of catalytic sites,which holds significant implications for the development of efficient electrocatalytic materials.The following original research findings have been obtained:(1)Exploiting the unique characteristics of the graphdiyne framework,an Fe-N-GDY single-atom catalyst is constructed,which investigates novel graphdiyne-based active sites and their efficient oxygen reduction electrocatalytic performance.Synchrotron radiation results indicate that Fe atoms are anchored onto the GDY framework via bonding with sp-hybridized carbon and nitrogen atoms.The coordination of hydroxyl groups further modulates the electronic structure of the Fe center,reducing the energy barrier for the detachment of*OH,which is supported by theoretical calculations.The half-wave potential of Fe-N-GDY is 0.89 V,which is much higher than the ORR activity of Pt/C.Fe-N-GDY demonstrates an impressive power density of 249 mW cm-2,along with excellent cycling stability when employed as an air electrode in zinc-air batteries.(2)Capitalizing on the tunable structure of graphdiyne,hydrogenated graphdiyne(HsGDY)is synthesized as a carbon substrate for the preparation of single-atom catalysts.Owing to the unique molecular structure of HsGDY,the synthesized Mn-N-HsGDY catalyst features Mn atoms coordinated with pyridinic nitrogen(py-N)and sp-hybridized nitrogen(sp-N),forming asymmetric sites.Additionally,the abundant pore structure within HsGDY accommodates large diameter heteroatoms like hydroxyl groups.Computational and experimental findings reveal that sp-N exhibits a higher negative charge density compared to other nitrogen types,resulting in asymmetric sites when py-N and sp-N coordinate simultaneously with Mn atoms,breaking the conventional M-N4 symmetric site.Theoretical calculations further confirm that the synergistic coordination of sp-N and hydroxyl groups enhances the ORR performance of the Mn active center.Mn-N-HsGDY demonstrates ORR activity far superior to commercial Pt/C and exhibits tremendous application potential in zinc-air batteries.(3)Research on the interactions between metal atom clusters and single atoms has made progress in the field of catalysis.Based on literature studies,different forms of Co catalysts are synthesized by controlling the amount of Co precursor added.Upon testing the ORR performance of these Co catalysts,Co-N-HsGDY-ACSA(ACSA:atomic cluster single atom)exhibits the best performance.This is attributed to the charge difference between Co atom clusters and Co single-atom sites,which induces electron redistribution and enhances the ORR activity through a synergistic effect.However,an excessive number of large-sized nanoparticles hinders mass transfer during the reaction and reduces atomic utilization,resulting in the poorest ORR performance for Co-N-HsGDY-NPSA(NP:nanoparticle).Meanwhile,Co-N-HsGDYACSA demonstrates a range of exceptional electrochemical properties as the cathode in zincair batteries.(4)A nitrogen-independent Co single-atom catalyst(Co-HsGDY)is synthesized.Owing to the non-uniform charge distribution of HsGDY,Co atoms are successfully anchored onto HsGDY by sp-hybridized carbon and sp2-hybridized carbon.Synchrotron radiation results reveal a local atomic configuration of CoC3(OH)1 at the Co center,and theoretical calculations confirm that the coordination of hydroxyl groups induces a negative shift in the d-band center of Co,promoting ORR activity.The prepared Co-HsGDY exhibits satisfactory performance in both oxygen reduction reactions and zinc-air batteries.This discovery not only unveils new ORR active sites but also provides insightful guidance for the design of carbon-based substrates.