Three carbon nanowalls (CNWs) thin films, synthesized by Radiofrequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) using different processing parameters, are studied as electrode materials in the positive half-cell of a Vanadium Redox Flow Battery (VRFB). These 2D-networks of interconnected graphenes exhibit an excellent electrochemical performance towards the V(IV)/V(V) redox couple in terms of a low overpotential and fast electron transfer kinetics. This can be attributed to certain specific features of CNWs such as the arrangement of the graphene planes perpendicular to the substrate, thus facilitating the electron transfer from the substrate and resulting in a large amount of exposed reactive graphitic edge planes. Repetitive cyclic voltammetry measurements, at various scan rates, together with SEM images evidence the long term stability of these materials. The obtained results represent a significant step forward in the development of highly effective VRFB electrode materials.