photocatalytic water splitting – towards robust water oxidation catalysts józsef s. pap has...

Photocatalytic Water Splitting – Towards Robust Water Oxidation

Catalysts

József S. Pap

HAS Centre for Energy Research

3rd European Energy Conference

Budapest, October 27-30

2013

I. The Energy Carrier Problem

H

CH H

H + O O C OO + OHH2 2

DHr° = -890 kJ/mol

HH + O OO

HH22

DHr° = -286 kJ/mol

How to make it renewable?

PHOTOCATALYTIC WATER SPLITTING

(18×109 tons of water,carried by Danube in 3 months)

Energy from Covalent Bonds

Sunlight: 105 x our consumptionProblem: intermittant and diffuse

II. Energy Storage in Plants

Energy Storage in Covalent Bonds: Photosynthesis

energy gradientslow

fast

(P+QA-) charge separation: 25 Å, in a few ps

O2

NADP-H (H-H)

Reaction center (RC) RC lmax (nm) Efficiency

quantum (hn->P+QA-) energy (QB)

B. viridis 960 0.96 34%

Rhs. sphaeroides 870 0.96 37%

PS II 680 0.92 46%

DSSC 550 0.90 11.2%

I. McConnell, G. Li, G. W. Brudvig, Chem. Biol. 2010, 17, 434

+O22 4H+ + 4e-H2O + 4h

Sn = Mn4Ca clusterMnV

OO

H

H

(100-400 s-1)

Water oxidation by the Oxygen Evolving Complex (OEC)

S0

S1S4

S2S3

2H2O

O2 P680+

P680

P680+

P680

P680+P680

P680

P680+

III. Artificial systems – General Considerations

Why Molecular Catalysts?

„Whether water splitting is achieved by electrolysis using electricity generated by photovoltaic devices or dye-sensitized solar cells, or by artificial photosynthesis remains at this point unclear. ... The durability, scalability, cost and efficiency will in the long run decide which approach to water splitting and hydrogen generation will win this competition.”

P. Du, R. Eisenberg, Energy Environ. Sci. 2012, 5, 6012

M

L

L L

L

LL

transitionmetal (M)ligand (L)complexes

h

Chromophore

(Photo)anode

2H+

H2

Cathode

e-acceptor:1. Chemical oxidant: CAN, S2O8

2-, IO4-, SO5

-

2. Electrode: GCE, ITO, TiO2, FTO3. Photosensitizer + electrode, or chemical

oxidant, [Ru(bpy)3]2+

Buffer, or base

WOC2H2O

O2 + 4H+

eeee

Investigation of Water Oxidation Catalysts (WOCs)

IV. General considerations, advances ...and plans

Sc Ti V Cr Mn Fe Co Ni Cu Zn

Y Zr Nb Mo Tc Ru Rh Pd Ag Cd

La Hf Ta W Re Os Ir Pt Au Hg

oxo-wall

How to form an O=O bond?

[Mn+2]

O

OH

H++O2 [Mn-2]

OH2

H2O(1) M=O

[Mn+2]

O+

[Mn+2]

O2 [Mn] + O2

M MO

O

(2)

M MO

OM M

O

OM M

O

O

Which transition metal?

WOC e-acceptor TON pH Ref.

[{Ru(bpy)2(OH2)2}2O]4+ CAN 13 1 J. Am. Chem. Soc. 1982, 104, 4029

[Ru2II(OH)2(3,6-t-

Bu2quinone)2(btpyan)]2+ ITO electrode 33500 4 Angew. Chem. Int. Ed. 2000, 39, 1479

[{Ru3O3(H2O)Cl2}(SiW9O34)]7- S2O8

2- 23 5.8 Green. Chem. 2012, 14, 1680

[Ru(bda)(isoq)2] CAN 8400 1 Nat. Chem. 2012, 4, 418

N N

NNN NRu Ru

O

O

O

O tBu

tButBu

tBu

OH HO

Catalysts – strategies Ru

N N

OO

OORu

N

N

N N

OO

OORu

N

NN

N

N

N

Ru O Ru

N

N

OH2

H2O

NN

- heterocyclic ligands

- bridging ligands

- carbon-free ligands

- axial co-ligands

N

NQ

Q = NH, N-R, O, S(O)

N

N

VS

Non-symmetric Bidentate Ligands – an Outlook

J. S. Pap, J. Kaizer, W. R. Browne, et al., Chem. Commun., submitted

N

N

NN

Fe Fe

N

N

O ON

N

S S+H2O2

N

N

NN

Ru Ru

N

N

O

O

N

N

S S

key intermediate

N

N

O

O

OO

N

N

O

O

OO

N N

N N

OO

Ru Ru

CuWOC e-acceptor pH Ref.[Cu(bpy)(OH)2] ITO electrode >12 Nat. Chem. 2012, 4, 498Cu-peptide GC electrode 11 J. Am. Chem. Soc., 2013, 135, 2051

Catalysts – strategies

N

N

Cu

OH

OH

pH >12

N

N

Cu

NH2

N

pH >11

O

OO

O

O

OH2

- cheap

- modular design

- easy to characterise

- minimal light absorption

in the visible region

CuCatalysts – strategies

L. Szywriel, J. S. Pap, et al., unpublished results

NHNH

HN

O

O

O

H2N

NH2

NH2

O

3G

NHNH

HN

O

O

O

H2N

NH2

NH2

O

2HG

N

HN

N

HN

1. Stability (106<TON)

2. Sensitivity (anions, impurities)

3. High overpotential of electrocatalytic water oxidation (>0.2 V Ru, >0.5 V Cu)

4. Rate (small TOFs, typical for heterogeneous systems)

Further Obstacles

Thank you for attention!

Köszönöm a figyelmet!

Acknowledgements

János Bolyai Research Scholarship (HAS)

University of PannoniaJózsef KaizerGábor Speier

University of GroningenWesley R. Browne

Apparao Draksharapu

University of WroclawLukasz Szywriel

Aix-Marseille UniversitéMichel Giorgi

J. Gascon, M. D. Hernández-Alonso, A. R. Almeida, G. P. M. Van Klink, F. Kapteijn, G. Mul, ChemSusChem 2008, 1, 981Metal-Organic Frameworks, Ed. L. R. MacGillivray, John Wiley & Sons, Hoboken, New Jersey, 2010

N NQ

N NQM

Linker

N

N

Linker

N

N

Linker:

N N

N

N

HN

N

HN ...

3. Metal-Organic Frameworks (MOF) as photocatalysts?

CoWOC e-acceptor TON pH Ref.Co-WOC (PO4

3-) ITO elektród - 7 Science 2008, 321, 1072

[Co(Py5)(OH2)]2+ ITO elektród 33500 4 Angew. Chem. Int. Ed. 2000, 39, 1479

[Co4(H2O)2(a-PW9O34)2]10-

HETEROGENEOUS!

[Ru(bpy)3]3+

S2O82- + Ru

ITO elektród/ MCNGCE elektród

>1000200

-

887

8

Science 2010, 328, 342J. Am. Chem. Soc. 2011, 133, 2068ChemSusChem 2012, 5, 1207

J. Am. Chem. Soc. 2011, 133, 14872

Co O

CoCoO

OCo

O

OCo

O

O

Co

O

O O

OO O

OO

O

O

O

O O

NN

N

OO

N NCo

OH2

Catalysts – strategies

2. Ligandumok tervezése és komplexeik vizsgálata

ML complexprecursor MOx

L-dependent WOC

V. Artero, M. Fontecave, Chem. Soc. Rev. 2013, 42, 2338D. Hong, J. Jung, J. Park, Y. Yamada, T. Suenobu, Y.-M. Lee, W. Nam, S. Fukuzumi, Energy Environ. Sci. 2012, 5, 7606

Homogeneous or heterogeneous?- surface analytical methods (XPS, TEM, DLS)- kinetics (induction period, reproducibility)- poisoning of catalyst (Hg, PPh3, thiophene, ...)- comparison with metal oxides

N NX

N NX

N NX

N NX

N

NX

X = NH, N-R, O, S(O)

Mn, Co Cu

Ar

NLi

Ar

X

X

2 +-LiX

N

N

Ar

Ar

Ar

Ar

Ar =N

N

HN

C.-F. Leung, S.-M. Nq, C.-C. Ko, W.-L. Man, J. Wu, L. Chen, T.-C. Lau, Energy Environ. Science 2012, 5, 7903

1. Ligands and Complexes

WOC e-acceptor TON pH Ref.[{(tpy)(H2O)Mn}2(O)2]3+

on clay

HSO5-

CeIV

CeIV

5018

211

J. Am. Chem. Soc. 2001, 123, 423Inorg. Chim. Acta 2007, 360, 2983J. Am. Chem. Soc. 2006, 126, 8084

[Mn2(mcbpen)2(H2O)2]2+ TBHP 10-20 <7 Angew. Chem. Int. Ed. 2005, 44, 6916[Mn2(bcbimp)(O)(Oac)] S2O8

2- + Ru* 17 - Angew. Chem. Int. Ed. 2011, 50, 11715

[(dpp)6Mn4O4]Nafion/GC elektród + hn 1000 7 Angew. Chem. Int. Ed. 2008, 47, 1

N

N

N

N

N

N

Mn

Mn

O

O

OH2

OH2

NH

NN

NH

O

O

O

O

O

Mn Mn

O OO

Mn

OMn

Mn

O OMn

O O

PPh2

O

Catalysts – strategies Mn

WOC e-akceptor TON TOF (s-1) pH Ref.[Fe-TAMCL] CeIV 16 1,3 0,7 Inorg. Chem. 2008, 47, 3669[Fe(N2py2)] CeIV, NaIO4 >1000 - 1 Nat. Chem. 2011, 3, 807

Cl Cl

N N

N N

FFOO

OO

Fe

H2ON OTf

N OTfFe

N

N

Katalizátorok – stratégiák Fe