Phosphorus Doped Multi‐Walled Carbon Nanotubes: An Excellent Electrocatalyst for the VO2+/VO2+ Redox Reaction

Abstract

AbstractIn this paper, phosphorus doped (P doped) multi‐walled carbon nanotubes (CNTs) were prepared and investigated as catalyst for VO2+/VO2+ redox reaction for vanadium redox flow batteries (VRFB). X‐ray photoelectron spectroscopy (XPS) confirms the equable incorporation of P atoms into carbon layers of the CNTs, and that P doping has no obvious effect on the morphologies of the CNTs. The results of cyclic voltammetry and electrochemical impedance spectroscopy indicate that the electrocatalytic properties of the CNTs are significantly enhanced for the VO2+/VO2+ redox couple by P doping. The sample treated at 800 °C (CNTs‐P8) exhibits the highest electrocatalytic activity, with two times higher peak currents for the redox reaction catalyzed by CNTs‐P8 deposited on glassy carbon than for pristine CNTs. A dynamic cell using the CNTs‐P8 catalyst for VO2+/VO2+ redox couple was assembled and the cell performance was evaluated. This cell exhibits better electrochemical properties including higher discharge capacity and energy efficiency, especially at high current density. The average energy efficiency of the cell for 50 cycles increases by 4.2 % at 50 mA cm−2 by using CNTs‐P8. This study demonstrates that the P doped CNTs are an efficient and promising catalyst material for VO2+/VO2+ redox reaction in VRFB systems.