A numerical evaluation of felt electrodes in a vanadium redox flow battery

ABSTRACT

The charge and mass transport phenomena of the different types of commercial electrodes such as KFD 2.5, GFD 2.5, GFD 4.6 and GFA 6 in a vanadium redox flow battery with the single-cell are presented in this study, comparatively. In order to perform these comparisons, all properties of the four different types of electrodes are applied to the numerical model which validated experimental data. The results indicated that the biggest electrode potential difference between the positive electrode and negative electrode belongs to GFD 4 .6 electrode with 1.20244 V, the smallest difference in the electrode potential belongs to KFD 2.5 electrode with 1.19832 V. Although KFD 2.5 and GFD 2.5 have the same electrode thickness, GFD 2.5 exhibits a better current density variation throughout both positive and negative electrode sides due to its higher electrical conductivity. While the V²⁺ and V⁵⁺ vanadium concentrations remain constant at 300 mol/m³ for KFD 2.5 and GFD 2.5 electrodes, these concentrations are approximately 310 mol/m³ for GFD 4.6 and GFA 6 after x/L = 0.5.

KEYWORDS:

• Vanadium redox flow battery
• electrode
• 2D modeling
• mass transport
• charge transport

Nomenclature

A	=	:specific surface area of porous electrode, m2/m3
c	=	:concentration, mol/m3
df	=	:carbon electrode fiber diameter, m
D	=	:diffusion coefficient, m2/s
F	=	:Faraday’s constant, C/mol
I	=	:applied current density, A/m2
j	=	:Faradic interfacial current density, A/m2
k	=	:reaction rate constant, m/s
km	=	local mass transfer coefficient, m/s
kCK	=	Kozeny– Carman constant, dimensionless
N	=	flux, mol/m2 s
P	=	:liquid pressure, Pa
R	=	:universal gas constant, J/(mol K)
soc	=	state of charge, dimensionless
S	=	:source term, mol/(m3 s)
T	=	:temperature, K
E	=	:Nernst or equilibrium potential, V
v	=	:velocity of the electrolyte flow, m/s
z	=	:charge of the ionic species, dimensionless
α	=	transfer coefficient, dimensionless
ε	=	porosity of the carbon electrode, dimensionless
η	=	overpotential, V
ΦS	=	electronic potential, V
Φl	=	ionic potential, V
k	=	ionic conductivity, S/m
σs	=	electronic conductivity, S/m
$K_{l\mathrm{\_}m}^{eff}$	=	conductivity of membrane, S/m

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Scientific Research Projects Unit of Erciyes University (Grant number: FDK-2020-10376). Author M.T. has received research support from The Scientific and Technological Research Council of Turkey (TUBITAK) 2211-C Priority Areas PhD Scholarship Program (Grant number: 1649B032000390).