We show very initial work on a specific bioelectrochemical system (BES), a bacteriologically driven 'fuel cell' (BFS), that is intended to process waste products, such as CO2 and brine. (1) Processing is the priority, not power generation (2) Really a Microbial Electrolysis Cell (MEC

Coker, Robert

Mansell, James

NASA Technical Reports Server

Constructing COMSOL Models of 
a Bacteriological Fuel Cell
Robert Coker
James Mansell
NASA/MSFC
https://ntrs.nasa.gov/search.jsp?R=20130000642 2019-08-30T23:31:37+00:00Z
Introduction
• NASA is pioneering new approaches for future human 
missions beyond Earth orbit.
• All spacecraft systems must be minimized with respect 
to mass, power, and volume. 
• Space Synthetic Biology (SSB) seeks cutting‐edge 
Synthetic Biology (SB) tools to redefine tradespaces.
• Here, we show very initial work on a specific 
bioelectrochemical system (BES), a bacteriologically
driven 'fuel cell‘ (BFS), that is intended to process 
waste products, such as CO2 and brine.
– Processing is the priority, not power generation
– Really a Microbial Electrolysis Cell (MEC)
• High reaction rates with low‐energy 
substrates
• Increased efficiency
• No costly precious metal catalysts
• Mild operating temperature and pressure
• Flexibility in reactants
• Need to add nutrients
• Need to minimize hydrogen peroxide
• Need to maximize contact of low‐solubility 
gases in liquid compartments without 
gravity
Space Bacteriological Fuel Cell
• Anode:  water oxidation
H2O→ 2H+ + 2e‐ + ½O2
• Cathode:  carbon dioxide reduction to 
methane
CO2 + 8H+ + 8e‐ → CH4 + 2H2O
Notional Reactants
Initial Experimental Setup
• Abiotic
testing first
• Nafion PEM 
separating 
flasks
• Appropriate 
salts
• Graphite 
rod (A) 
carbon 
paper (C)
• pH buffered
• Runs are 4 hours
• Current 
generated by 
hydrogen
• Cathode 
potential sweep 
shows 
production 
behavior over 
large voltage 
ranges
First Results
0
0.01
0.02
0.03
0.04
0.05
0.06
-2.25-2-1.75-1.5-1.25-1-0.75-0.5
C
u
r
r
e
n
t
 
(
A
)
Potential (V)
Equilibrium Current
-1.6
-1.4
-1.2
-1
-0.8
-0.6
-0.4
1E-7 1E-6 1E-5 1E-4 1E-3 1E-2 1E-1 1E+0
P
o
t
e
n
t
i
a
l
 
(
V
)
Current (A)
Potential Sweep
• Physics nodes
– Secondary Current Distribution
• Two electrolyte‐electrode boundary interfaces with 
reactions
– Transport of Diluted Species
• Convection, diffusion, and migration
• Two electrode‐electrolyte interface couplings
• Flux boundary across PEM (set by SIEC)
• Simplified Geometry
• Just Hydrolysis for now
• Problem:  need to track pH
Comsol Model Description
• The devil is in 
the details:
– BCs
– Signs
– Low 
concentrations
– Initial 
conditions
Comsol Model Description
• Just starting to use Comsol for SynBio
problems
• Variety of numerical stability issues
• Need to understand how Comsol does 
currents and reactions
Summary


Constructing COMSOL Models of a Bacteriological Fuel Cell

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