Phthalocyanines Based Two-Phase Catalysts for Lithium Oxygen Batteries

Abstract

Li-air batteries, which are considered to offer much higher energy density than the current Li-ion batteries suffer from poor cycle life due to electrolyte decomposition and clogging of the air cathode by insoluble discharge products. Efficient bifunctional catalysts could improve the stability of Li-air batteries by lowering the overpotential and prolonging the battery cycle life. This study focuses on Iron phthalocyanines (FePc) as possible bifunctional electrocatalysts. Metal phthalocyanines were utilized mainly because of their structural analogy which could be fine- tuned by the metal being used, accessibility, and low cost. In this work, firstly, FePc supported on graphite nanofibres (GNF) was investigated as solid electrocatalyst in non-aqueous LiTFSI (TEGDME) electrolyte. Secondly, FePc was dissolved in the non-aqueous electrolyte and studied as liquid catalyst with GNF cathode. FePc/GNF (solid catalyst) delivered superior electrocatalytic performance for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) comparable to that of commercial Pt/C. FePc_electrolyte (liquid catalyst) exhibited a steady profile for chronoamperometry, and good diffusivity of lithium ions as measured from electrochemical impedance spectroscopy. The bifunctional catalysts when applied as electrocatalysts in non-aqueous lithium air batteries delivered better electrochemical performance mainly by reducing the large overpotential associated with ORR and OER. Both the cells with solid and soluble FePc exhibited better reversibility and cyclability. The performance of FePc catalyst as solid and liquid has been comparative analyzed in detail.