Vanadium‐Ion Redox Reactions in a Three‐Dimensional Network of Reduced Graphite Oxide

Abstract

A three‐dimensional (3D) fine network structure of thin carbon microflakes inside a loosely entangled carbon‐fiber matrix was formed by applying an ice‐template method to a graphite oxide (GO) dispersion in the matrix and thermal reduction of the GO. Vanadium‐ion redox reactions were investigated in the network of reduced GO (RGO) for potential application as electrodes in vanadium redox flow batteries (VRFB). The development of the fineness, the degree of graphitization, the structural disorder, and the surface composition were characterized. The interaction between the carbon surface species and the vanadium ions was implied by the X‐ray absorption fine structure (XAFS). The structure of the 3D RGO network was clearly correlated to the activity for the VRFB positive electrode reactions, and the development of the fine network structure effectively enhanced the reactions due to increased exposure of the edge planes and sufficient dispersion of the active sites.

Composition of the Electrode Determines Which Half-Cell’s Rate Constant is Higher in a Vanadium Flow Battery

“…The mechanism schematically shown in Fig. 9a combines our findings with X-Ray Absorption Fine Structure (XAFS) results by Maruyama et al 36 : XAFS measurements indicate the presence of adsorbed vanadium oxides on a carbon electrode after immersion in an electrolyte containing 50 mM VO 2+ and 50 mM VO 2 + 36 . As the interaction of the solvated ions and the carbon surface is expected to be weak, the vanadium ions are assumed to be chemisorbed on oxygen-functional groups on the carbon surface 37 .…”

Electrocatalysis at Electrodes for Vanadium Redox Flow Batteries

“…Higher treatment temperature resulted in a decrease even of this effect and this was attributed to decreasing wettability. Maruyama et al prepared a network of reduced graphite oxide using carbon paper as a scaffold followed by heat-treatment resulting in partial reduction of the oxide [172]. Further studies of the positive electrode V 4+/5+ reaction showed significant decreases of electrode overpotential, smaller peak separation and increased peak current most pronounced for samples treated at 1000 • C. This material had shown the finest structure suggesting a large surface area (no BET or EASA data were provided) and smooth ion transport.…”

Anion effects on the redox kinetics of positive electrolyte of the all-vanadium redox flow battery

“…The sequence of these steps is not fixed but their contribution depends on the applied over-potential and other parameters. To complicate things further, a deposition of vanadium oxides on carbon electrodes from the electrolyte has been observed [4,6,7]. To increase the power density of the VRFB catalysis of the vanadium reactions is desirable.…”