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

Graphical P doped CNTs are prepared as catalysts for VO 2+ /VO 2 + redox reaction for vanadium redox flow batteries (VRFB) by high-temperature pyrolysis at different temperatures. The electrocatalytic properties of CNTs for the VO 2+ /VO 2 + redox reaction are significantly enhanced by P doping. The sample treated at 800 °C exhibits the highest electrocatalytic activity. This sample can act as superior catalyst to improve the energy storage performance of VRFBs. In this paper, phosphorus doped (P doped) multi-walled carbon nanotubes (CNTs) were prepared and investigated as catalyst for VO 2+ /VO 2 + 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 VO 2+ /VO 2 + 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 VO 2+ /VO 2 + 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 VO 2+ /VO 2 + redox reaction in VRFB systems.