Effects of nitrogen doping on the electrochemical performance of graphite felts for vanadium redox flow batteries

Abstract

Vanadium redox flow batteries (VRFB), originally proposed by Skyllas-Kazacos et al., have been considered as one of the most promising energy storage systems for intermittently renewable energy. However, the poor electrochemical activity and hydrophobicity of graphite felt electrode greatly limit energy storage efficiency of VRFB system. In this paper, two nitrogen-doped (N-doped) graphite felts, obtained by heat-treating in an NH 3 atmosphere at 600°C and 900°C, have been investigated as electrodes with high electrochemical performance for vanadium redox flow batteries. In particular, the one obtained at 900°C exhibits an excellent electrochemical activity for both V 2+ /V 3+ and VO 2+ /VO 2 + redox couples. The cells with different graphite felt electrodes were assembled, and the charge-discharge performance was evaluated. The cell with the N-doped graphite felts has larger discharge capacity, discharge capacity retention, and energy efficiency, especially with the sample treated at 900°C. The average energy efficiency of the cell with the 900°C treated N-doped graphite felts is 86.47%, 5.44% higher than that of the cell with the pristine graphite felt electrodes. These enhanced electrochemical properties of the N-doped graphite felt electrodes are attributed to the increased electrical conductivity, more active sites, and better wettability provided by the introduction of the nitrogenous groups on the surface of graphite felts. It indicates that N-doped graphite felts have promising application prospect in VRFB.

Graphite felt electrode modified by square wave potential pulse for vanadium redox flow battery

“…Large-scale energy storage system (ESS) are required to utilize the new energy reasonably because of its intermittent, varied nature [1][2][3]. Large-scale energy storage system (ESS) are required to utilize the new energy reasonably because of its intermittent, varied nature [1][2][3].…”

Electrocatalytic activity of Nb-doped hexagonal WO3 nanowire-modified graphite felt as a positive electrode for vanadium redox flow batteries

“…6 More notably, during charging and discharging, a VRFB employs the same metal (vanadium) of the active species in both positive V(IV)/V(V) and negative V(II)/V(III) electrolytes; this strategy precludes crossover contamination caused by the transfer of metal ions across the ion exchange membrane. 4,[7][8][9][10] However, despite these merits, the VRFB has limited practicability because of its low energy efficiency; the efficiency of VRFB is significantly influenced by the electrochemical activity of the electrode because the redox reaction of vanadium ions occurs at the electrode surface. 11 Therefore, selecting suitable electrode materials is crucial in VRFB design.…”

An optimal electrolyte addition strategy for improving performance of a vanadium redox flow battery

“…To advance overall performance of the all vanadium redox flow battery, much effort has been made to enhance the electrode properties of the VRFB by utilizing sulfonation treatment, functional groups that include chlorine atoms and nitrogen atoms, as well as TiO 2 nanoparticles . Besides, properties of the electrolyte and the membrane are also improved by the researchers .…”