Solutions for Today | Options for Tomorrow

Catalytic Conversion of CO2 into Value Added Products

08/17/2018Douglas R. Kauffman

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Excess Renewables

CO2

Catalyst

H2O

AlcoholsHydrocarbonsCarbon Monoxide

(syngas)

NETL Materials Research: Creating Value from Waste CO2

Polymers & Plastics

H2

Waste heat

Fuels

Sunlight

3

General Approach: Electrochemical CO2 Conversion

e−

e−

Electrochemistry moves electrons

(−) (+)

4

General Approach: Electrochemical CO2 Conversion

Use carbon-free electrons to convert CO2 !

e−

CO2 Products

e−

H2O O2

AnodeCathode

Environmentally Benign Aqueous Solution

(−) (+)

5

Designing CO2 Electrocatalysts

• Large energy input or poor efficiency ... Wasted energy = $$$$!

• Large Product Distribution... Separation = $$$$!

Ener

gy

CO2

Intermediate(s)

Reaction Coordinate

Product(s)

No Catalyst

Catalyst

Ideal

Energy Input

$

$

$

$

$

$ $

6

“Coinage” Metal Catalysts

Synthesis gas (CO + H2)

H2 + COformic acidmethaneC2+ hydrocarbonsalcohols

Purified product

Industrial Chemicals

Fuels Polymers and PlasticsGold

Copper

$ $ $

CO2

Water

7J. Am. Chem. Soc. 2012; J. Phys. Chem. Lett. 2013; Chemical Science 2014; ACS Applied Materials and Interfaces 2015; J. Chem. Phys. 2016; ACS Catalysis 2016; MRS Commun. 2017, J. Phys. Chem. C. 2018, US Patent 9,139,920.

Previous Success with Ligand-Capped Nanocatalysts

Extremely active for CO2 CO

Gold-Copper Nanocatalysts

Retained performance with ~50% reduction in gold

Au25(SR)18 Nanocluster JPCC cover in December 2018

** Just accepted and chosen for JPCC Cover! **

1.5 nm

DOI: 10.1021/acs.jpcc.8b06234

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Nanostructured copper oxides as a starting point• Previously shown that surface oxides promote CO2 CO

Kauffman et. al. JPCL 2011. Li and Kannan JACS 2012

Can We Eliminate Precious Metals?

We want• High surface area & large density of reactive sites• High concentration of oxide groups• High porosity for good mass transport

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Nanostructured CuO Inverse Opals

3D opal template (200 nm PMMA colloids on substrate)

Precursor@opalheterostructure Inverse opal

Phan & Kauffman, et al.; manuscript in preparation

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Selective and Stable CO Formation

-1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.20

20

40

60

80

100

CO

sel

ectiv

ity /

%

Potential / V vs. RHE

CuO-HIOCuO npsBulk CuO

• ~8x more selective than commercially available CuO powder• ~10-60x more selective than commercially available CuO nanoparticles

Almost no H2 below -1V , minor CH4 and HCOOH, trace C2

Phan & Kauffman, et al.; manuscript in preparation

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Selective and Stable CO Formation

Excellent stability during 12-24 hour tests

Phan & Kauffman, et al.; manuscript in preparation

-1.2 -1.1 -1.0 -0.9 -0.8 -0.7 -0.6 -0.5 -0.4 -0.3 -0.20

20

40

60

80

100

CO

sel

ectiv

ity /

%

Potential / V vs. RHE

CuO-HIOCuO npsBulk CuO

• ~8x more selective than commercially available CuO powder• ~10-60x more selective than commercially available CuO nanoparticles

Almost no H2 below -1V , minor CH4 and HCOOH, trace C2

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Quasi In-Situ XRD (ANL / APS Synchrotron)

copper oxide peaksreduced copper metal peaks

Catalyst retains significant fraction (~20-30%) of oxides during 6 hour CO2 reduction

• Ongoing DFT calculations for CO2 reduction on Cu-oxide vs Cu

• Provide atomic level details on product selectivity

Phan & Kauffman, et al.; manuscript in preparation

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Transitioning from H-Cell into Gas Diffusion Electrolyzers

Cathode Anode

• CO2 dissolved in 0.1M KHCO3

• Mass transfer & current density limitations• Not very scalable

CathodeAnode

Humidified CO2 gas

• Gaseous CO2 reacted at cathode• Much higher mass transfer & current density• Scalable (e.g. electrolyzer stacks)

Very different reaction conditions; process parameters need optimized

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“Bridging the pressure gap”

Combining Electrochemistry and Surface Science

• Well-defined catalysts via precisely controlled growth: composition, size (lateral and vertical), shape

• Characterizations at atomic scale possible

• High electrical conductivity

Surface Science

Electrochemistry

+

Tip atoms

Sa

++

Tip atoms

Sa

STM

XPS

LEED

• Extremely sensitive to surface composition and structure

Combination provides exquisite structure-property details

Evaporation

Surf. Sci. 2008, 602, 932.; J. Phys. Chem. C 2009, 113, 11104.; Surf. Sci. 2010, 604, 627; J. Phy. Chem. C 2011, 115, 4163; J. Chem. Phys. 2011, 134, 104707; J. Am. Chem. Soc. 2011, 133, 10066; J. Phys. Chem. Lett. 2011, 2, 3114; J. Phys. Chem. Lett 2012, 4, 53; J. Phys. Chem. C 2016, 120, 8157; J. Phys. Chem. Lett. 2016, 7, 1335; Surf. Sci. 2017, 658, 9; Phys. Chem. Chem. Phys., 2017, 19, 5296; Top. Catal. 2018, 61, 499.

NETL Surf. Sci. Pubs:

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Combining Electrochemistry and Surface Science

1.2 1.3 1.4 1.5 1.6 1.7 1.80

50,000

100,000

150,000

200,000

250,000

Mas

s A

ctiv

ity (m

A m

g-1 met

al)

E-iR (V vs. RHE)

Fe2O3 (2.0x10-10 mol cm-2) IrO2 (2.0x10-10 mol cm-2)

Kauffman , Deng, Sorescu; Manuscript in preparation

Tafel slope = 75 ± 9 mV dec-1Iron is 1000s times cheaper than Iridium

(precious metal … ~ $40k per kg)

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Combining Electrochemistry and Surface Science

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0

5.0x104

1.0x105

1.5x105

2.0x105

2.5x105

Mas

s A

ctiv

ity @

1.8

V (m

A m

g-1 Fe)

NP Perimeter to Area Ratio (nm-1)

0

5

10

15

20

25

30

35

TOF

@ 1

.8V

(s-1)

High Loading Low Loading

Kauffman , Deng, Sorescu; Manuscript in preparation

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OH to Olattice ratio scales w/ perimeter site density

540 535 530 525

1.0E-9 mol

4.0E-10 molCou

nts

(a. u

.)

Binding Energy (eV)

529.3Lattice O

530.9OH

532.0carbonate

1.1E-10 mol

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.5

1.0

1.5

2.0

2.5

OH

to O

latti

ce R

atio

NP Perimeter to area Ratio (nm-1)

High Loading Low Loading

Spectroscopic Signature of OER Active Sites: Perimeter Fe sites

High Loading

Low Loading

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0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.20.0

5.0x104

1.0x105

1.5x105

2.0x105

2.5x105

Mas

s A

ctiv

ity @

1.8

V (m

A m

g-1 Fe)

NP Perimeter to Area Ratio (nm-1)

0

5

10

15

20

25

30

35

TOF

@ 1

.8V

(s-1)

Combining Electrochemistry and Surface Science

High Loading Low Loading

Perimeter Fe Sites are O2 Evolution Reaction Centers

4L2L(2L,edge) Bulk

DFT Analysis

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Conclusions and future efforts

1. Developing a variety of approaches for catalyst design• Precise identification of structure-property relationships • Couple with DFT modeling

2. In situ X-ray characterization (XANES, EXAFS, XRD, XPS)• Provide information on structure and chemical properties during reaction• Refine DFT models

3. Incorporate into realistic reactor architectures

4. New concepts (next year’s presentation) … microwave-assisted thermal catalysis

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Acknowledgements

Dominic Alfonso Dan SorescuDe Nyago Tafen

Yunyun Zhou, Thuy Duong Nguyen Phan; Jonathan LekseCongjun Wang, Yang YuAmitava Roy (LSU / CAMD), Junsik Lee (SSRL)Houlin L. Xin (BNL / CFN)

DFT

XAS, XRD & TEM

Acknowledgement: This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Governmentnor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights.

Thuy Duong Nguyen PhanDouglas KauffmanEchem

Xingyi Deng Junseok LeeSTM

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