(560bx) Defect-Engineered Interface for Efficient Electrocatalyst

The expansion of economical, effective, and durable electrocatalyst for the oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER) have significant importance for numerous electrochemical devices, such as fuel cells, water electrolyzer, and rechargeable metal-air batteries. Heteroatom-doped catalyst has arisen as one of the best emergent material to replace the precious metal catalyst for electrochemical reactions, but to control their delicate structure and the lack of atomic-level mechanistic understanding are still a challenging issue. Herein, we advocate the assembly of separate single atoms of Ni and Fe (SSAs-NiFe) dual sites, anchored in defects engineered graphene (DG) substrate prepared by a nitrogen (N) elimination from N-doped precursor by an adsorption-calcination strategy. The concept of defect mechanism showed that the topological defect (e.g. multiple pentagon—octagon—pentagon or pentagon—heptagon—pentagon rings) appeared correspondingly in the combination of carbon atoms that avoided random dislocations and disclinations. We believe that these specific combinations of carbon atom rings in DG substrate with the decoration of Ni and Fe SSAs can provide more active sites, better electrical conductivity, and low energy barrier during catalytic reaction. We used the combination of high-resolution transmission electron microscopy/high-angle annular dark field (HAADF) images in scanning transmission electron microscopy (STEM) for studying the desired atomic structure. At a very low resolution (1nm) the individual metal atoms in the field of view are detected through STEM and resolved in graphene lattices. The electron energy loss spectroscopy (EELS) atomic spectra are used to identify the difference between Ni and Fe SSAs on graphene substrate. The chemical structure insights of the material are examined by pre-edge peaks in X-rays absorption near edge structure (XANES) spectra. Furthermore, we demonstrated the electrocatalytic performance of our hybrid material in acidic/alkaline mediums and found it active and stable trifunctional electrocatalyst for ORR, OER and HER. This work offers new prospects and underscores the importance of identifying the active species for multiple reaction catalysts.