Iron phthalocyanine supported on 3D nitrogen-doped graphene aerogel as an electrocatalyst for non-aqueous Li−O2 batteries

Abstract

Solid electrocatalysts of iron phthalocyanine (FePc) embedded in 3D porous N-doped graphene aerogel (NGA) are designed and applied as cathode catalysts for non-aqueous lithium-oxygen (Li−O2) batteries. Two composites with different axial bonding types between FePc and NGA, including a coordinate covalent bond (FePc/NGA-c) and non-covalent π−π stacking interaction (FePc/NGA-π), are fabricated by reflux and physical mixing methods, respectively. Systematical characterizations confirmed the FePc/NGA-c composite using axial coordination between FePc and NGA substrate via the FeNC bond exhibited more thermal stability and less stack and aggregation of FePc molecules in the composite. Combining the bifunctional catalytic activity of the FePc molecule with oxygen reduction reaction/oxygen evolution reaction (ORR/OER) processes and a flexible porous 3D structure and N-doping in NGA, the electrochemical test demonstrated both FePc anchored on NGA composites display higher activity as bifunctional catalysts for O2 electrodes in Li−O2 batteries. However, the FePc/NGA-c electrode displays better electrochemical performance than the FePc/NGA-π composite due to the axial covalent connection of the FePc catalyst with NGA substrate, leading to higher electrocatalytic activity and exceptional structural durability during cycling for FePc/NGA-c. This work provides new insight into the steric effect of the coordination bond between FePc and NGA on the electrocatalytic activity of O2 electrodes. These results indicate our unique structural design of FePc/NGA-c using solid FePc axially anchored on NGA via covalent bonding is a promising cathode material for high performance of rechargeable LiO2 batteries.