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