A NEW CARBON-BASED PAINT
FOR LOW-COST CATHODES AND ANODES IN
MICROBIAL FUEL CELLS
Dr. Stefano Trasatti
OUTLINE
Introduction
o  Single Chamber Microbial Fuelcells
o  Principles
o  Carbon Cloth-based SCMFCs: Power evolution
Problem definition:
•  Aim of the present study
•  Electrode configuration
and evolution
The cathodic “teflon problem”
•  Different binder concentrations
•  Cells differentiation
•  Biocathode demonstration
•  Biological electrocatalysis
•  Evidences for binder exchange
The anode cost and scale-up
•  AISI 304 stainless steel
•  Two configurations-two answers
•  MIC 304SS corrosion
•  Conductive paint corrosion
prevention
Introduction
Anode
CH3COONa+2H2O
2CO2+7H++2Na++8e-
Anode: Carbon Cloth.
Solution: Nosedo (MI) wastewater inlet
Food: sodium acetate
acetate
Cathode
2O2+4H++8e4OH-
Cathode standard
production (Fuelcells)
Solution (wastewater)
MPL (C+nafion)
Carbon cloth (C+teflon)
GDL (C+teflon)
AIR
Problem definition
Aims:
•  Evaluate Teflon binder influence on cathodes response
•  Substitution of mechanically-unstable Carbon cloth (CC) with AISI
304 stainless steel.
•  Apply a low-cost conductive graphitic paint as teflon substitute.
SCMFC:
•  CC electrodes
•  Different binder
concentrations
SCMFC:
•  CC cathode
•  AISI 304 anode,
vertical strip
SCMFC:
•  CC cahtode
•  AISI 304 anode,
bottom position
The cathodic “teflon problem”: different binder concentrations
Teflon content
GDL Composition:
HIGH
140%w/w teflon/carbon + teflon layer
MEDIUM
140%w/w teflon/carbon
LOW
80%w/w teflon/carbon
Teflon effect
•  Slow activation
•  Unstable response
•  Higher internal
resistance
•  Lower power integral
•  Lower Coulombic
Efficiency
The cathodic “teflon problem”: different cathodes change the anode
HIGH
Phenomenology
•  activation with time
•  Anode diffusion-limited
LOW
Phenomenology
•  An/Ca intersection at the
highest current
achievable.
•  Redox mediators peak
evolution.
Biocathodes and real electrocatalysis
Tafel slopes: the Derivative method
deductions
•  A change in b, implies a
change in the
mechanism or/and in the
rds.
•  Lowering of b implies
electrocatalytic effects.
•  Change with time:
bioelectrocatalysts.
•  Teflon impedes the bioelectrocatalytic activation
There is space to improve:
•  Best chemical electrocatalysts show a b as low as 30 mV.
No teflon. Is it possible?
Solution (wastewater)
MPL
(C+conductive paint)
The cathodic MPL teflon-free
•  Paint solvent: water
•  No heat treatments
•  Polymer eco-friendly
Carbon cloth (C+teflon)
AIR
Power production
•  Normal activation
•  Sudden deactivation
and low Coulombic
Efficiency.
•  Constant Power after
acetate addition.
Carbon cloth replacement as anode
Metallic anode: AISI 304 stainless steel
C
Si
Mn
P
S
Cr
Ni
N
a
AISI304 0.07 0.75 2.00 0.045 0.030 18.0 8.0 0.10
Power production comparison
•  Same materials, different power
•  304 strip develops later and
unefficiently
•  304 in the anaerobic bottom of
the cell behaves like CC.
AISI 304 SS: Microbial Influenced Corrosion
Scanning Electron Microscope
304 SS vertical strip
304 SS anode
•  Pitting corrosion in the upper zone
•  No corrosion at the bottom
•  Hypotesis: Residual oxygen
Round 304 SS at the bottom
•  No corrosion after ~3 months
•  Anaerobic conditions prevent
corrosion
Residual oxygen: conductive carbon paint for the anode
MFC type
naked
Linear Polarization Resistance
painted
•  Protection from
corrosion
•  Increased bacterial
affinity
•  Multilayer more
effective
•  LPR is decreased
Anode Composition:
AISI 304SS anode
single
AISI 304SS+single paint layer
double
AISI 304SS+double paint layer
SEM : carbon paint colonization (2 months)
Carbon paint after cleaning
Biofilm
•  Complete and homogeneous
coverage
•  Hexopolymers protecting
bacteria
• 
• 
• 
• 
Low porosity
Presence of graphitic sheets
No metal exposed
Anaerobic conditions prevent
corrosion
No evidence of paint degradation
CONCLUSION
Carbon cloth- based SCMFCs
•  High reproducibility and standardization
Cathode Teflon influence
•  Standard Fuelcell synthesis methods appear inappropriate for SCMFCs
•  decreased teflon content give more effective biogenic electrocatalysis
•  Bio-electrocatalysis points to a change in the rds, towards more active
electrodes
•  Substitution of teflon binder with a more hydrophylic paint is demonstrated
Anode carbon cloth
•  As a first attempt, AISI 304 stainless steel was employed
•  Effective power production is connected with strictly anaerobic conditions
•  Presence of oxygen gradients can cause pitting corrosion
•  The residual, unpredictable presence of oxygen can be deleterious
•  Use of Conductive carbon paints can increase AISI 304SS corrosion resistance
Carbon paint show:
•  increased bacterial affinity
•  Effective ligand properties
•  Decreased superficial polarization resistance
•  Effective applicability in SCMFC scale-up