Synergistic Catalyst–Support Interactions in
a Graphene–Mn<sub>3</sub>O<sub>4</sub> Electrocatalyst for
Vanadium Redox Flow Batteries
- Publication date
- Publisher
Abstract
The development of vanadium redox
flow batteries (VRFBs) is partly
limited by the sluggishness of the electrochemical reactions at conventional
carbon-based electrodes. The VO<sup>2+</sup>/VO<sub>2</sub><sup>+</sup> redox reaction is particularly sluggish, and improvements in battery
performance require the development of new electrocatalysts for this
reaction. In this study, synergistic catalyst–support interactions
in a nitrogen-doped, reduced-graphene oxide/Mn<sub>3</sub>O<sub>4</sub> (N-rGO-Mn<sub>3</sub>O<sub>4</sub>) composite electrocatalyst for
VO<sup>2+</sup>/VO<sub>2</sub><sup>+</sup> electrochemistry are described.
X-ray photoelectron spectroscopy (XPS) confirms incorporation of nitrogen
into the graphene framework during co-reduction of graphene oxide
(GO), KMnO<sub>4</sub>, and NH<sub>3</sub> to form the electrocatalyst,
while transmission electron microscopy (TEM) and X-ray diffraction
(XRD) confirm the presence of ca. 30 nm Mn<sub>3</sub>O<sub>4</sub> nanoparticles on the N-rGO support. XPS analysis shows that the
composite contains 27% pyridinic N, 42% pyrrolic N, 23% graphitic
N, and 8% oxidic N. Electrochemical analysis shows that the electrocatalytic
activity of the composite material is significantly higher than those
of the individual components due to synergism between the Mn<sub>3</sub>O<sub>4</sub> nanoparticles and the carbonaceous support material.
The electrocatalytic activity is highest when the Mn<sub>3</sub>O<sub>4</sub> loading is ∼24% but decreases at lower and higher
loadings. Furthermore, electrocatalysis of the redox reaction is most
effective when nitrogen is present within the support framework, demonstrating
that the metal–nitrogen–carbon coupling is key to the
performance of this electrocatalytic composite for VO<sup>2+</sup>/VO<sub>2</sub><sup>+</sup> electrochemistry