Vanadium redox flow battery (VRFB) is a very promising electrical energy storage device (EES), particularly for use with intermittent-type renewable energies. In operation, the commonly used graphite felt (GF)-based electrode has to be modified and activated to generate a proper electrode reaction condition before use. This study proposes a novel modification and activation approach, mainly by impregnation treatment using a Nafion^® ionomer solution, which effectively renders the electrode surface a needed hydrophilic environment. Various instrumental characterizations are carried out. The cyclic voltammogram (CV) of the ionomer-treated GF electrode, designated as N90, obtained in a 2M H₂SO₄ solution containing 0.8M V(III) and 0.8M V(IV) ions, respectively, demonstrates a wider electrochemical window and more pronounced redox signals than those of electrochemically oxidized counterpart. It shows that the ionomer is partially but uniformly coated on the graphite felt fibers after it is put into operation. In addition, the N90 electrode is found to be more resistant to corrosion and crystalline salt formation. Moreover, the prepared single-cell VRFB exhibits a good performance without the need of using any catalyst and the electrolyte unbalance phenomenon of the cell is substantially alleviated. The redox reaction mechanisms on both electrodes are proposed.