Poly(vinylidene fluoride-co-hexafluoropropylene) phase inversion
coating as a diffusion layer to enhance the cathode performance in
microbial fuel cells
Wulin Yang
a
, Fang Zhang
a
, Weihua He
b
, Jia Liu
a
, Michael A. Hickner
c
, Bruce E. Logan
a, *
a
Department of Civil and Environmental Engineering, The Pennsylvania State University, University Park, PA 16802, United States
b
State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, No. 73 Huanghe Road, Nangang District,
Harbin 150090, China
c
Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA 16802, United States
highlights
A PVDF-HFP phase inversion coating produced good resistance to water leakage.
The PVDF-HFP phase inversion coating enabled higher power production.
Power production correlated with a more porous diffusion layer.
article info
Article history:
Received 21 May 2014
Accepted 22 June 2014
Available online 7 July 2014
Keywords:
MFC
Cathode
Water resistant diffusion layer
PVDF-HFP phase inversion coating
Power production
abstract
A low cost poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) phase inversion coating was
developed as a cathode diffusion layer to enhance the performance of microbial fuel cells (MFCs). A
maximum power density of 1430 ± 90 mW m
2
was achieved at a PVDF-HFP loading of 4.4 mg cm
2
(4:1
polymer:carbon black), with activated carbon as the oxygen reduction cathode catalyst. This power
density was 31% higher than that obtained with a more conventional platinum (Pt) catalyst on carbon
cloth (Pt/C) cathode with a poly(tetrafluoroethylene) (PTFE) diffusion layer (1090 ± 30 mW m
2
). The
improved performance was due in part to a larger oxygen mass transfer coefficient of 3 10
3
cm s
1
for
the PVDF-HFP coated cathode, compared to 1.7 10
3
cm s
1
for the carbon cloth/PTFE-based cathode.
The diffusion layer was resistant to electrolyte leakage up to water column heights of 41 ± 0.5 cm
(4.4 mg cm
2
loading of 4:1 polymer:carbon black) to 70 ± 5 cm (8.8 mg cm
2
loading of 4:1 poly-
mer:carbon black). This new type of PVDF-HFP/carbon black diffusion layer could reduce the cost of
manufacturing cathodes for MFCs.
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
Microbial fuel cell (MFC) technologies can be used to convert
organic and inorganic substrates to electrical power [1e5]. Exoe-
lectrogenic bacteria on the anode oxidize substrates to generate
electrons, which flow through an external circuit to the cathode
where typically oxygen reduction occurs. Platinum is often used as
the oxygen reduction catalyst in these cathodes [6,7], although
different catalysts have also been investigated such as carbon
nanotubes, cobalt oxides, and an iron-nitrogen-carbon catalyst
[8e10]. Activated carbon (AC) has emerged as the most attractive
alternative catalyst to platinum due to its low cost ($2.6 kg
1
), and
it can have comparable or superior performance to Pt-based cata-
lysts over time in MFCs [11e 13].
A typical AC cathode consists of an AC catalyst layer on the
electrolyte side that is directly attached to a current collector, and a
diffusion layer on the air side. The diffusion layer has two important
roles in cathode performance: it serves as a barrier to separate the
solution phase from air phase, and therefore to avoid water leakage
through the cathode; and it can be used to limit oxygen transfer
into the anode solution, but it must allow oxygen to reach the
cathode catalyst sites. Hydrophobic polymers, such as polytetra-
fluoroethylene (PTFE) and poly(dimethylsiloxane) (PDMS), are
often used to make diffusion layers [11,14]. Carbon black (CB) is
added into these polymers to enhance porosity and thereby
improve oxygen mass transfer to the catalyst. A PTFE/CB diffusion
* Corresponding author. Tel.: þ1 814 863 7908; fax: þ1 814 863 7304.
E-mail address: blogan@psu.edu (B.E. Logan).
Contents lists available at ScienceDirect
Journal of Power Sources
journal homepage: www.elsevier.com/locate/jpowsour
http://dx.doi.org/10.1016/j.jpowsour.2014.06.119
0378-7753/© 2014 Elsevier B.V. All rights reserved.
Journal of Power Sources 269 (2014) 379e384