Modeling of Electrochemical Reduction of CO2 to Methanol in a Micro Flow Cell
Yosra Kotb1, Seif-Eddeen K. Fateen1, Jonathan Albo2, Ibrahim Ismail1
1 Renewable Energy Engineering Program, Zewail City of Science and Technology, Egypt
2 Department of Chemical Engineering, University of the Basque Country, Spain
Introduction
• Fossil fuels depleted at a rate of 4
billion tons a year
• CO2 levels spiked up from 280
ppm to 400 ppm nowadays
• To reduce climate change effect:
decrease the CO2 emissions by
50% by 2050!
Global Energy Consumption (BP, 2015)2
Introduction
• Methanol Based Economy
The methanol-based economy cycle model (J.Albo, M. Alvarez-Guerra, P. Castaño and A. Irabien, 2015)3
Scope of Work
1- An electrochemical micro flow cell of CO2 reduction
to methanol modeled using COMSOL Multiphysics
2- Model validated against experimental data
3- Model used to determine different operating
conditions effects and optimize the cell performance
4
Schematic of Cell and Reactions
Cell configuration and geometry
Cathode
CO2 + 6H+ + 6e− ⇄ CH3OH + H2O
CO2+ 2H++ 2e- ⇄ CO + H2O
2H+ + 2e− ⇄ H2
Anode 5H2O ⇄ 2.5 O2+10H++10e−
5
Methodology
Physical interactions inside the cell
Mass Transport
Electrolytic species concentration
Charge Transport
Electric and ionic potential
Electrode Reactions Kinetics
6
MethodologyGoverning Equations
Ri,src= 𝜈𝑖 𝑖𝑙𝑜𝑐
𝑛𝑖𝐹
Catholyte AnolyteMembrane
n. i l, e = n. i l, m
n. NH+,e= n. il,m𝐹
Φl,m= Φl,e + 𝑅𝑇
𝐹ln
𝑎𝐻+,𝑚
𝑎𝐻+,𝑒
For: H+, CO2, OH-, K+,
HCO3-, CO3
2-, H2, CH3OH,
CO
For: H+, CO2, OH-,K+,
HCO3-, CO3
2-, O2
-∇ (il,m)=0
H+
n. i l, e = n. i l, m
n. NH+,e= n. il,m𝐹
Φl,m= Φl,e -𝑅𝑇
𝐹ln
𝑎𝐻+,𝑚
𝑎𝐻+,𝑒
7
∇ Ni=Ri,src
∇ il=F ∑ziRi,src
∑zici=0
∇ Ni=Ri,src
∇ il=F ∑ziRi,src
∑zici=0
Ri,src= 𝜈𝑖 𝑖𝑙𝑜𝑐
𝑛𝑖𝐹
MethodologyElectrochemical Reaction Kinetics
8
AnodeCathode
OER
iloc= i0(α𝑎+α𝑐 𝐹
𝑅𝑇)η
Methanol and Carbon monoxide
reactions
iloc=i0[CRexp(𝛼𝑎𝐹 𝜂
𝑅𝑇)-COexp(
−𝛼𝑐𝐹 𝜂
𝑅𝑇)]
HER
iloc= i0(α𝑎+α𝑐 𝐹
𝑅𝑇)η
9
• Module
Electrochemistry
• Interfaces
Tertiary current distribution for electrolytes channels
Secondary current distribution for membrane
• Mesh
User controlled mesh (Mapped Distribution)
COMSOL Implementation
Results and Discussion• Base Case
10
Results and Discussion
• Base Case
11
Results and Discussion
12
• Base Case
16.903
24.7
0
5
10
15
20
25
30
Local current density of CH3OH reacx Local current density of HER
Cu
rre
nt
de
nsi
ty (
A/m
^2)
Results and Discussion
• Methanol Flow Behavior
13
Methanol convective flux is
100 times its diffusive flux
Reconsidering membrane function in the cell
Model Validation
14
Flowrate Effect
0
0.02
0.04
0.06
0.08
0.1
0.12
10 15 20 25 30 35 40
Met
han
ol o
utl
et c
on
cen
trat
ion
(m
ol/
m^3
)
Q (ml/min)
Experiment Model
0
40
80
120
10 15 20 25 30 35 40
Cu
rre
nt
de
nsi
ty (
A/m
^2
)
Q (ml/min)
Experiment Model
15
Model Validation
Applied Cathode Potential Effect
0
50
100
150
200
250
300
-1.7-1.6-1.5-1.4-1.3
Cu
rre
nt
de
nsi
ty (
A/m
^2
)
Cathode potential (V)
Experiment Model
0.086
0.088
0.09
0.092
-1.5-1.45-1.4-1.35-1.3
Met
han
ol o
utl
et c
on
cen
trat
ion
(m
ol/
m^3
)
Cathode potential (V)
Experiment Model
Conclusions and Next Steps
• Model showed good agreement with the experimental results
• Other by products reactions to be added at the cathode decrease the
discrepancy in the current density values
• As the model predicted, preliminary experimental results without the membrane
proved that the methanol outlet concentration is not greatly reduced a more
effective cell design will be adopted
• Further modeling and experimental studies enhance process feasibility and decide
on the optimum operating conditions
• Thorough thermodynamic analysis investigate the whole process’s energy efficiency
and reduce the energy waste16
Thank you for you attention!
Questions?
17
Top Related