The Controlled Synthesis Of Single Atom Electrocatalyst For Oxygen Reduction Reaction Via The Coordination Environment Modulation

In response to the growing energy and environmental problems,the exploration and development of nanocatalysts with excellent performance and stability as well as high-capacity energy storage devices such as proton exchange membrane fuel cells and metal-air cells are key to achieving carbon peaking and carbon neutrality,and have created a boom in the field of electrochemical energy conversion and storage.Among them,oxygen reduction reactions occurring at the cathode of metal-air cells suffer from sluggish reaction kinetics and low efficiency,while expensive and scarce noble metal-based electrocatalysts are now commonly used to accelerate the reaction kinetics.Therefore,it is imperative to develop some non-precious metal-based electrocatalysts with high efficiency and suitable for mass production,among which transition metal-based single-atom electrocatalysts are of great interest.Transition metal-based single-atom electrocatalysts are of great interest due to their abundant reserves,high catalytic activity and stability.Carbon materials have become a promising carbon matrix due to their high electrical conductivity,porosity,and other characteristics.In this paper,single-atom electrocatalysts（SACs）with excellent performance were synthesized by modulating the coordination environment of the central metal atoms using porous carbon as the carrier.The main studies are as follows:（1）:Single-atom electrocatalysts（Fe-N₄/NP-PHC）modified with heteroatoms N and P were synthesized by supramolecular self-assembly and pyrolysis strategies.First,H-bonded supramolecular nanosheets containing Fe ions were self-assembled by a solvothermal strategy,and then the supramolecules decomposed during high-temperature carbonization to release gas to generate a large number of pore structures.This honeycomb pore structure can expose more accessible active sites.The synthesized single-atom electrocatalysts have excellent ORR activity and stability with onset and half-wave potentials of 1.0 V and 0.89 V,respectively.Density flooding theory（DFT）suggests that the introduction of heteroatoms N and P in the porous carbon matrix can reduce the binding strength between the active site and the ORR intermediates（O*,OH*,OOH*）,thus enhancing the ORR kinetics of Fe-N₄/NP-PHC.（2）:Ru single-atom electrocatalysts Ru-SAs-N/S-PCNSs modified with heteroatoms N and S were synthesized under high temperature pyrolysis conditions using carbon defective sites in porous carbon sphere carriers to anchor metal atoms as well as heteroatoms.The prepared Ru single-atom electrocatalysts exhibited half-wave potentials of 0.87 V and 0.63 V in 0.1 M KOH and 0.5 M H₂SO₄ solutions,respectively,while the Ru-SAs-N/S-PCNSs also exhibited excellent catalytic stability and methanol tolerance.In addition,the zinc-air battery assembled with Ru-SAs-N/S-PCNSs as cathode exhibited high energy density and charge/discharge cycling stability.