Abstract
This paper treats the polyacrylonitrile (PAN)-based graphite felt (GF) with hydrothermal NH4H2PO4 solution and adopts the treated GF as the positive electrode of all-vanadium redox flow battery (VRFB). Specifically, the GF was treated in a teflon-lined stainless-steel autoclave with 1.6M NH4H2PO4 solution for 4h at 60°C. Then, structure, composition and electrochemical properties of the GF were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The test results indicate that the NH4H2PO4 was successfully absorbed on the surface of GF after the treatment; the treated GF had better electrochemical activity in V(IV)/V(V) redox reaction (at 10mVs-1) than the untreated GF; the oxidation and reduction peak current densities of the treated GF increased by 19.5% and 57.1%, respectively. According to the CV measurement at various scan rates, the treated GF enjoyed better mass transfer properties of V(V) ions than the untreated GF. These results demonstrate that NH4H2PO4 absorbed on the carbon surface can enhance the electrochemical activity of the GF in the VRFB system.
