FUELS (~90%)

CHEMICALS (~10%)

Syngas Methanol Ethylene Propylene Butadiene Benzene, Aromatics

FUELS (90% ?)

CHEMICALS (10% ?)

Ethanol Glycerol Carbohydrates Seed Oils Lignin

Fossil Resources (1800’s – present)

Renewable Resources (Energy and Feedstocks of Future?)

silk, cotton, wool Cellulose acetate Rayon Polylactide (PLA) Polyhydroxy- alkanoates (PHA)

Polyethylene Polypropylene Polybutadiene PET PVC

Energy Chemical Industry Catalysis

“The Electron Economy”: Energy Conversion/Storage Waymouth, Chidsey, GCEP

Liquid Fuels + O2

CO2, H2O

H2 + O2

HEAT

WORK

Low Free Energy Electrons

High Free Energy Electrons

Chemical Energy Conversion

“The Electron Economy”: Energy Conversion/Storage Waymouth, Chidsey, GCEP

fuel oxygenH+

motore- e-motor

reductioncatalyst

oxidationcatalyst

graphiticcarbonelectrode

graphiticcarbonelectrode

polymerelectrolytemembrane(PEM)

H2

2 H+ + 2 e-

O2

2 H2O

4H+ + 4 e-

Polymer-Electrolyte-Membrane Fuel Cell (PEM)

Electrocatalysis at Stanford Waymouth, Chidsey, Stack Kanan (Chemistry) Jaramillo, Norskov (Chem. Eng.)

CH3OH+ H2O

CO2+ 6 e- + 6 H+

Electrocatalytic Efficiency: Potential

0.0 0.2 0.4 0.6 0.8 1.0 1.2

bestexistingoxygen

O2

bestexistingoxygen

O2workheat heat

Oxidant

oxygenO2

Fuel

reversiblepotentials

E0H+/H2

E0CO2+H2O/CH2

E0O2/H2O

hydrocarbon(CH2)n

bestexisting

methanolCH3OH

bestexisting

hydrogenH2

How much work can be obtainedand heat avoided

with discrete electrocatalysts?

free energy converted

to work

free energy wasted as heat of fuel oxidation

free energy wasted as heat of O2 reduction

heat

heatwork

Electrochemical Potential (V vs. H+/H2)

H2

2 H+ + 2 e-

CH3OH+ H2O

CO2+ 6 e- + 6 H+

O2 4 e- + 4 H+

2 H2O

Pt electrode

O C

CO2

H Hn H+

CH3 OH

Oe

O CO

-2.2 V

H H H H

H2O

C

OH2O

CO2

Energy Storage: Opportunities and Challenges

Reversible Generation of Fuels:

2 e- + 2 H+ H2

CO2 + 6 e- + 6 H+ CH3OH + H2O

high overpotential for CO2 reduction

Pt electrode

HHHH

HH2 H+

overpotential for CH3OH oxidation

Energy Storage: Opportunities and Challenges

HCO2HCO2 + 2 e- + 2 H+

H2C=O + H2OCO2 + 4 e- + 4 H+

CO2 + 6 e- + 6 H+ CH3OH + H2O

CO2 + 3H2

HCO2H 2H2

CH3OH H2O

H2C=O H2 + H2O8.9 kcal/mol6.6 kcal/mol

-4.3 kcal/mol

0 kcal/mol

Δ G°

(6 e- + 6 H+)

E° (V vs NHE)

-0.194

-0.071

0.031

As this reaction is thermoneutral (when R = R’),

it occurs at the reversible electrochemical potential

Transfer Hydrogenation: Insights for Reversible Electroatalysts

K ~ 1

Transfer Hydrogenation: Alcohol is oxidized by a ketone

Proposed Mechanism Proposed Electrocatalytic

Mechanism

OH

HR'R'

O

R R+

OH

HRR

O

R'R'+

Haack, K. J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R., ACIEE 1997, 36 (3), 285-288.

RuX N

R R

H

RuX N

R R

H

HHO

R R

OH

HRR

OH

HR'R'

O

R'R'

RuX N

R R

H

RuX N

R R

H

HH

OH

H

O

- 2 H+

- 2 e -

RuX N

R R

H

OH

HR'R'

Transfer Hydrogenation: Strategies for CO2 Activation and Reduction

•  Metal Hydrides will activate and Reduce CO2

•  Hypothesis: Outer-sphere Bifunctional Activation of CO2 preferred

Ru

NTs N

R R

H

HH RuN P

Ph2N

Ph2P

H

Ru

O N

R R

H

HH

N Co NCCH3

2+

NNOC Mo HOC

ORRR

R

CO

H

HH

Transfer Hydrogenation: Insights for Reversible Electroatalysts

Transfer Hydrogenation: Reversible Transfer of H2 between ketone and alcohol

Ph

O

H

OH

Ph H

O O+ +

H

TOF 20 h-1 113 h-1 6 s-1 0.03 h-1

Kristin Brownell

Kate Waldie

Tomo Seki

Sungkwan Kim

Noyori, Ikariya Baratta

0.7 h-1

Megan Buonauito, Anthony DeCrisci Tom Jaramillo

Ru(OH)x /Oxidized Ti electrode

Electrocatalytic Oxidation of MeOH

RuHN O

on graphite electrode

CH3

OHH O

O

H

or CO

+ 4 e- + 4 H+

0

10

20

30

40

50

0 0.2 0.4 0.6 0.8 1 1.2

400 rpm 800 rpm 1600 rpm 3000 rpm

E / V vs. NHE

curr

ent /µA

Edge plane graphite electrode, 1M NaClO4, 0.01 M phosphate buffer, pH = 11.5

overpotenial: ~1.2 V (pH 11.5)

Brownell, Chidsey, Waymouth, Zare, J. Am. Chem. Soc., 2013, 135,14299.

Wills, M., et.al JOC 1997, 62 (15), 5226-5228.

4 electron oxidation with a rate of 1 MeOH s-1

•  Ru(OH)x/Titanium electrodes: Catalytic transfer hydrogenation •  Electrochemical oxidation of 2-propanol to acetone: bulk electrolysis

•  mild conditions (25oC, neutral pH), low Ru loadings •  Faradaic efficiencies above 95% with TOF ~ 0.6 hr-1 •  Recyclability of electrode with only 20% reduction in activity and efficiency •  Onset potential approximately 1000 mV vs RHE, overpotential ~ 870 mV

Heterogeneous Transfer Hydrogenation Catalysts: Ru(OH)x on anatase TiO2

Buonaiuto, M.; DeCrisci, A.; Jaramillo, Waymouth, manuscript in preparation

CH

O

HH

H

CR

O

R'

80oC1 atm N2/Ar C

H

O

R'R

H

CH

O

H

Ru(OH)x/TiO2

O

TiO

Ti

ORu

OTi

ORu

OH

O

TiO

Ti

ORu

OTi

ORu

OH H

H

CH

O

HH

H

CH

O

H

2H+, 2e-

CR

O

R'

CH

O

R'R

H

OR

Mizuno N. Chem. Eur. J. 2008,14, 11480.

Deposit Ruthenium onto Titanium Electrodes

Titanium

<10nm TiO2 amorphous

Submonolayer Ru(OH)x/Titanium foil

Reactivity ü  2-propanol electrooxdation to acetone under N2 ü Chemical Transferhydrogenation of acetophenone

under Mizuno conditions

Electrooxidation

CTH

20 nm TiO2

Ru Ru O  

O  

O  

O  

O  

O  

O  

O  

O  

O  

Ru(OH)x/TiO2 2.1%Ru

Our Approach: Ru(OH)x Electrocatalysis on Oxidized Titanium foils

Entry R1 R2 ΔG°298K (kcal/mol)

Exp. Calc.

1 CH3 CH3 -3.1 -2.4

2 CH3 n-C5H11 -2.7 -2.1

3 CH3 C6H5 -4.0 -5.7

4 CO2 - -10.5

Thermodynamics of Ketone/CO2 Insertion: Experiment and Calculations

Kate Waldie

Srinivasan Ramakrishnan. TeraChemTM (Todd Martinez)

Level of Theory: ωB97xD/6311g*(C,H,N,O,P)/LANL2DZ(Ru)/SMD(THF)

•  Fast, reversible insertion of Ketones

•  Fast insertion of CO2, irreversible

Theory Experiment

R1 R2

ORuN

NO

PPΔG298K

Ph2

Ph2

R1HR2 H

H

RuN

NH

PP

Ph2

Ph2

HH

d8-THF

1-H

R R

RuN

NO

PPΔG298K

Ph2

Ph2

H

HH

RuN

NH

PP

Ph2

Ph2

HH

d8-THFC OO

O

R R

0.0

+5.0

-8.7 -10.5

+6.5 11

1-H + CO2

12

13 1-OCHO

TS11-12 +11.0 TS12-13

+10.8

Insertion Pathway: CO2

RuN

NH

PPh2

Ph2P

H HCO

O

Cooperative Addition of Ru-H and N-H to CO2

+6.8

+14.9 +17.2

+10.2 +13.7

+7.5

0.0 -2.4 1-OiPr

10

TS7-8 8

9 1-NH + iPrOH

7

1-H + CH3(CO)CH3

+15.8 TS8-9

0.0

+5.0

-8.7 -10.5

+6.5 11

1-H + CO2

12

13 1-OCHO

TS11-12 +11.0 TS12-13

+10.8

(a)

(b)

Insertion Pathways: Acetone and CO2

4-OiPr (-6.5)

2-OiPr (+0.4)

1-OiPr (-2.4)

3-OiPr (-9.1) 2-OCHO (-7.4)

4-OCHO (-14.5)

3-OCHO (-15.3)

1-OCHO (-10.5)

0.0

1-H 2-H 3-H 4-H

acetone or CO2

+

RuN

NX

PN

Ph2

H2

HH

X = H (2-H) OiPr (2-OiPr) OCHO (2-OCHO)

RuN

NX

PP

Ph2

Ph2

HH

X = H (1-H) OiPr (1-OiPr) OCHO (1-OCHO)

RuN

NX

NN

H2

H2

HH

X = H (4-H) OiPr (4-OiPr) OCHO (4-OCHO)

X = H (3-H) OiPr (3-OiPr) OCHO (3-OCHO)

RuN

NX

NP

H2

Ph2

HH

Theory: Predictions for More Effective Catalysts Crucial Role of the cis and trans ligands

Electrochemical Generation of Metal Hydrides:

(MeO)3P

CoI

P(OMe)3

CoIII

(MeO)3PP(OMe)3

H

H

(MeO)3P

CoIII

P(OMe)3

2 +

e e

Hydrogen Evolution Rxn, Electrogeneration of M-H: CpCo complexes

Koelle, Inorg. Chem.1986, 2689

2 H+ H2-1.15 V, pH 5

water

(MeO)3P

Co

P(OMe)3

Proposed Reactivity:

Synthetic Target: Redox-active ligand to facilitate generation of Metal Hydride

Challenge: Neg potentials to reduce Co(III)

N Co NCCH3

2+

NN

N CoIII NCCH3

2+

NN

N CoII

NN

N CoIII H

+

NN

H+

2 e -

-­‐3.0 -­‐2.5 -­‐2.0 -­‐1.5 -­‐1.0 -­‐0.5 0.0 0.5

-­‐60

-­‐40

-­‐20

0

20

40

60

80

Currnet  (µA

)

E /V  vs  F c /F c +

 [C pC o(A zpy)(C H3C N )][C lO

4]2

 [C pC o(bpy)(C H3C N )][C lO

4]2

E1/2

1= -­‐0 .158V

Ec

1= -­‐0.186V

E1

a= -­‐0.130V

E1/2

1= -­‐1 .822V

Ec

2= -­‐1.860V

Ea

2= -­‐1.784V

E Ea1 Ec

1 E1/21 Ea

2 Ec2 E1/2

2 Ec3

Azpy V -0.130 -0.186 -0.158 -1.784 -1.860 -1.822 N.A. Bpy V -0.377 -0.442 -0.407 -0.976 -1.052 -1.014 -2.617

CVs of [CpCo(Azpy)(MeCN)][ClO4]2

N CoIIINCMe

2ClO4

N

N CoIIINCMe

2ClO4

NN

azpy

bpy

•  2 electron reduction of Co(III) at – 0.15 V

-­‐2.5 -­‐2.0 -­‐1.5 -­‐1.0 -­‐0.5 0.0 0.5

-­‐100

-­‐80

-­‐60

-­‐40

-­‐20

0

20

40

60

80Current  (µA

)

E /V  vs  F c /F c +

 1mM  C o,  0mM  ac id  1mM  C o,  1mM  ac id  1mM  C o,  3mM  ac id  1mM  C o,  5mM  ac id  1mM  C o,  7mM  ac id  1mM  C o,  9mM  ac id  1mM  C o,  11mM  ac id

Electrocatalytic Reduction of H+ with [CpCo(azpy)(CH3CN)][ClO4]2

Conditions: 1mM Co,0.1 M NBu4ClO4 in acetonitrile N, DMF/DMFH+, Scan rate 100 mV/s (In N2 glovebox )

Kim, Waldie, Ingram, Waymouth, Inorg. Chem., 2014, submitted for publication

2 H+ + 2 e- H2

N Co NCCH3

2+

NN

ElectroReduction of [CpCo(azpy)(CH3CN)][ClO4]2

CoIN

N N

CoIIN

N N

CoIII

NCMeN

N N

2+2 e-

diamagnetic

CoIII

NCMeN

NNH

+

+ H+

not CoIII

HN

NN

+

CoIII

NCMeN

N N

2+2 e-

diamagnetic

Molecular Designs for Electrocatalysts

•  Transfer Hydrogenation Catalysts Alcohol Electrooxidation Catalysts

•  Theory and Experiment Critical for Molecular Design

•  Rapid and Reversible Ketone Reduction

•  Rapid and Reversible CO2 Activation and Reduction

•  Facile Electrogeneration of Metal Hydrides at low overpotential

•  Need Better Molecular Understanding:

•  Electronic Communication: Ligand e- reservoirs (redox-active ligands) and Metals •  Coupled Proton / Electron Transfers

Kate Waldie, Kevin Chung, Tim Blake, Andrew Ingram, Tyler Stukenbroeker, James Flanagan, Wilson Ho, Megan Buonaiuto, Young Chang, Colin McKinlay, Xiangyi Zhang, Wei-Wei Wu, Dr. Tomo Seki, Dr. Andrey Rudenko Prof. Eun Joo Kang Srini Ramakrishnan Dr. Jelena Samonina-Kosicka

Collaborators Prof. Chris Chidsey (Stanford) Prof. Tom Jaramillo (Stanford) Prof. Todd Martinez (Stanford) Prof. Dick Zare (Stanford) Dr. James Hedrick (IBM) Julia Rice, Hans Horn (IBM) Prof. Paul Wender (Stanford)

DOE, National Science Foundation ONR, GCEP (Stanford Global Climate and Energy Program) Center For Molecular Analysis and Design (Stanford Chemistry)