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