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Electrochemical Reduction of CO2 to Fuels 

Nicole Bernstein, Dr. Michael Janik

Department of Chemical Engineering, The Pennsylvania State University, University Park, PA

Goals and Motivation

Comparison of Copper and Iron Catalysts

Potential Impediments to CO2 Reduction on Iron (1 0 0)

References  Acknowledgements 

Research Objectives and Methods

Future Plans Summary and Conclusions

Carbon Reduction to Fuels:

• Electrocatalytic reduction of CO2 can convert

electricity to hydrocarbon fuels

• Copper metal has already been proven to produce

methane in CO2 reduction (1) 

• Computational methods using Density Functional

Theory model reactions on the catalyst s urface

Iron Catalysts:

• Thermal reduction of CO2 with H2 on Fe produces methane,

 but electrochemical reduction produces only H2 (5) 

• Our goal: explain why hydrocarbons are not produced on

Fe, towards defining catalyst design principles for optimal

CO2 reduction to fuels

Objectives:

• Understand what factors impede CO2 reduction to

hydrocarbons on Fe.

• Computationally determine the relative energies of the

reaction path for CO2 to hydrocarbons on an Fe (1 0 0)

surface.

Copper Catalysts for Co2 Reduction:

• Both computationally and experimentally, Cu(111) reduces CO2 to CH4 

rather than CH3OH at significant overpotentials (-1.15 VRHE) (1) 

• The rate limiting step appears to be CO reduction to COH or COH

reduction to C+H2O (1) 

Path of Co2 Reduction:

• This study examines two possible paths of reduction, resulting in

the production of methane or methanol

• Branching point occurs in the reduction of CO to either CHO or

COH

Iron Catalysts for Co2 Reduction:

• Experimentally, Fe fails to reduce CO2 to hydrocarbons

• DFT results for Fe(1 0 0) indicate favorable CO2 reduction to CO and CO reduction

to CH3OH and CH4 at lower overpotential than Cu, contrary to experimental results

Oxygen Buildup:

•

On Fe (1 0 0), conversion of water to surface bound oxygen may be favorable

• Oxygen could bind to active sites on the surface, preventing further

CO2 reduction.

Carbon Buildup:

•

xC*

 Cx* + (x-1)*• Carbon buildup appears to be unfavorable on Fe after several

 preliminary calculations

Hydrogen Evolution Reaction:

•

Hydrogen Evolution is a competitive reaction on Iron, and experimentallyhydrogen gas is the major product observed when CO2 reduction is attempted.

• H may simply outcompete CO2 derived species for active sites, limiting the rate of

CO2 reduction to an undetectably small amount

Transition State Study:

• A clear understanding of carbon dioxide reduction is

not complete without study of transition state energies

• Future plans involve using the climbing image nudged

elastic band method to computationally determine

transition states of key reactions

Methods:

• Use of Density Functional Theory to computationally

determine ground state energies of molecules in CO2 

reduction pathway through the Vienna ab-initio

Simulation Package(2,3,4)

 

• Calculations of relative energies of intermediates

(1) X. Nie, M. R. Esopi, M. J. Janik, A. Asthagiri. “Selectivity of CO2 reduction on copper electrodes: The role of the kinetics of elementary steps”  Angew,

Chem. Int. Ed. 52 (2013) 2459-2462.

(2) G. Kresse, J. Hafner, Phys. Rev. B 47 (1993) 558-561

(3) G. Kresse, J. Furthmaller, Comput. Mater. Sci. 6 (1996) 15-50.

(4) G. Kresse, J. Furthmaller, Phys. Rev. B 54 (1996) 11169-11186

(5) Hori, Y. Electrochemical CO2 Reduction on Metal Electrodes. In Modern Aspects of Electrochemistry; Springer: New York, 2008; pp 89−189. 

CO2

COOH

COCHO

CH2O

CH3O

CH3OH

COOH

CO

CHO

CH2O

CH3O

CH3OH

-6

-5

-4

-3

-2

-1

0

   R  e   l  a   t   i  v  e   E  n  e  r  g  y   (  e   V   )

A*

A*

0 V-RHE

-0.5 V-RHE

CO2

COOH

CO

COH

C CH

CH2

CH3

CH4

COOH

CO

COH

C

CHCH2 

CH3 

CH4 -8

-7

-6

-5

-4

-3

-2

-1

0

   R  e   l  a   t   i  v  e   E  n  e  r  g  y   (  e   V   )

A*

A*

0 V-RHE

-0.5 V-RHE

CO2* + nH+ + ne- CHn-4+2xOx* + (2-x)H2O(g) 

Relative Energy A* (URHE) = EA*− ECO2,g + (2−x)EH2O−

2GH2 + eURHE

where URHE is the electrode potential on a relative hydrogen electrode scale

Continued Study of Carbon Build-up:

• Analyze more conformations of multiple carbon atoms

on Fe (1 0 0) surface

NASA Pennsylvania Space Grant Consortium

Women in Science and Engineering Program

Iron has Potential as a

Catalyst for CO2 Reduction:

• Computati

onally, the

reaction pathway of CO2 

reduction appears favorable

• Unknown factors are at play

to prevent experimental

success of the reaction

• A better understanding of

CO2 reduction on Fe (1 0 0)

could guide design ofeffective catalysts

2H+ + 2e-  H2 

H+ + e- 

+

Cu

Cu

Cu

CuCu Fe

H H HH H H H H H H H

CO2 

X

hydrocarbons