Pyrolysis-free Path Toward Synthesis And Performance Research Of Non-noble Metal Oxygen Reduction Electrocatalysts

New generation clean energy storage and conversion devices such as fuel cells and metal-air batteries have attracted much attention due to their higher conversion efficiency and environmental friendliness.Nowadays,platinum-based catalysts are still considered as the most effective materials to facilitate the sluggish kinetics of oxygen reduction reaction（ORR）in cathode.In view of the expensive cost and rarity of Pt-based catalysts,the development of non-precious metal-based materials will help reduce the expenditure of battery systems.Although the electrocatalytic performance of some pyrolytic non-precious metal materials are comparable to Pt-based catalysts,there are numerous uncertainties in high temperature calcination process,which brings many challenges to clarify the reaction mechanism and achieve high-throughput synthesis.It is an important part for the commercialization of fuel cells to explore pyrolysis-free path to obtain electrocatalysts with clear structure and efficient performance.Herein,this paper focuses on the pyrolysis-free approach toward synthesis of non-noble metal oxygen reduction electrocatalysts.Atomically dispersed iron electrocatalysts for acidic ORR and bifunctional electrocatalysts toward ORR and OER were successfully prepared,respectively.The main research contents are as follows:（1）A novel fluorinated polyphthalocyanine material was prepared by the binary ligand strategy,which showed excellent oxygen reduction performance in acidic electrolyte after integrating with graphene.The atomically dispersed iron catalyst（termed as F₃PFePc/G-2）was obtained by adjusting the ratio and loading of the two ligands during the synthetic process.The atomic iron loading content of F₃PFePc/G-2 was up to 2.5wt%,and the half-wave potential was 0.73V（vs.RHE）in 0.5M H₂SO₄ solutions.（2）To explore the origin of the improvement of F₃PFePc/G-2 in oxygen reduction activity,density functional theory（DFT）calculations were carried out.The introduction of the secondary ligand changed the environment around the active site Fe-N₄.The doping of F atom with electron-withdrawing reduces the adsorption between active centers with O₂ intermediates,which leads to the easier disintegration of O₂ intermediate on the catalyst surface,thus accelerating the oxygen reduction process.This strategy by adjusting electron effects provides a direction for design of other highly efficient oxygen reduction catalytic materials.（3）A multielement mixed strategy for the synthesis of bifunctional electrocatalyst toward ORR and OER was developed.We exerted polyphthalocyanine material with outstanding oxygen reduction activity and hydrotalcite material with remarkable oxygen evolution character on conductive carbon nanotubes.The bifunctional electrocatalysts with outstanding performance were obtained.When the mass ratio of CNTs and pFePc and NiFe-LDH was 1:1:2,the optimal catalyst（named as CPL-112）has exhibited excellent bifunctional catalytic activity（ΔE=0.68V vs.RHE）in 0.1M KOH solutions.The assembled zinc-air flow batteries with CPL-112 as cathode catalyst delivered the higher peak power density of 104mWcm^-2 and could stably work for more than 120 h under the current density of 10mAcm^-2.Therefore,the CPL-112-based Zn-air battery exhibits a superior performance,indicating a promising industrialization prospect in metal-air batteries applications.