Post on 11-Apr-2018
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IE MAX-PLANCK-INSTITUTFÜR BIOANORGANISCHE CHEMIE
SOLAR PRODUCTION OF HYDROGEN AND OXYGEN INCLUDING STORAGE THEREOF
WITH SILICIDES IN WATER
Prof. Martin Demuth and Dipl. Ing. Peter Ritterskamp
Max-Planck-Institut für Bioanorganische Chemie Stiftstr. 34-36, D-45413 Mülheim an der Ruhr
Phone: +49 208 306-3671/ -3680/ -4 Fax: +49 208 306-3951demuthm@mpi-muelheim.mpg.de http://www.mpibac.mpg.de
PATENT APPLICATION: Generation of Hydrogen and Oxygen from Water and Storage thereof with Silicides 10 2005 040 255.0 (Germany)
and PCT/EP application 2006 / 008333
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IETHE CHALLENGE –
WE ARE APPROACHING A SOLUTION
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IESCHEMATIC REPRESENTATION OF A SEMICONDUCTOR
(SC, plain vs doped material)
• Electrons are moved from the valence band to the energetically higher
conduction band creating a „„charge hole““ in the valence band enablingthe reduction and oxidation of water to yield hydrogen and oxygen, resp.
• An energetically appropriate bandgap is required for this purpose
• Furthermore, the sc should absorb light in the solar range of 300-800 nm
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IECONDUCTION-BAND, VALENCE-BAND AND
BANDGAP ENERGIES OF SOME SEMICONDUCTORS
Potential (NHE), pH=7
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IEBANDGAP RANGE OF TITANIUM SILICIDES
(TiSix)
• An ideal semiconductor should have:bandgap > 1.23 eVconduction band < - 0.41 eVabsorption of visible light < 2.2 eV
-1
0
1
2
3
-0.41
+0.82
-0.41
+0.82
H / H2+
O2 / OH -
~3.4 eV360 nm
~1.5 eV800 nm
pH = 7
pH > 7
EV Potential (NHE)
-0.8 sensitizer (perylenes)
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FACHBEIRAT UND KURATORIUM · MÄRZ 2004
1 M + H2O → MOn + H2
formation of hydrogen energetically driven by metal oxide formation
forms oxide (layer)
thermally
2
M + O2 → MOnoxidation of
catalyst by oxygen3
M + H2O → M + H2 + 1/2 O2 water splitting
thermally
POSSIBLE (SIDE) REACTIONS IN METAL-DRIVENWATER SPLITTING
photochemically
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Ti-
-Ti4+Si4-light H2
2H+
11
H2
H2
44
x
3 3 O2
Current Current investigationsinvestigations concernconcern the the mechanismsmechanisms of and of and 22 3 3
ReactivityReactivity of of TiSiTiSixx
22½ O2 + 2H+18
18H2O
TiSi
+ +
TiO2
SiO2
Si
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IEHYDROGEN AND OXYGEN EVOLUTION KINETICS
(including partial hydrogen storage and very efficient oxygen storage)
0
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30
40
50
0 50 100 150 200 250Time (h)
ml
a (hydrogen, reaction under nitrogen) a (oxygen from storage) c (hydrogen, reaction under air)b (hydrogen, reaction under nitrogen) b (oxygen from storage)
24±1 ml
12±1 ml
A (a)
B (a)
60° C 5-8° C
a (H2)
a (O2 ) c (H2)
Phase A: oxidationby water addition (major) and water splitting (minor)
Phase B: exclusive water splitting
b (O2)
b (H2)
2±1 ml
50° C 5-8 50° C
30° C
30° C
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0
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30
40
50
60
70
80
0 100 200 300 400 500 600hours
mL
PRESSURE DEPENDENCE OF WATER SPLITTING EFFICIENCY
η = 4.5 – 11.5 % (1.2 bar)(hydrogen evolution shown)
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IEHydrogen (sacrificial vs splitting) and oxygen production
UNLOADING OF OXYGEN FROM STORAGE
--10243086
< 614161217
< 3 d,e
5 e12 e15 e43 e
6244042
103
12345
H2 (from water splitting, ml) c
H2 (sacrificial)(ml) b
O2(ml) a
H2 (total in gasphase, ml)
Run
Table. a Gas phase + 3 ml dissolved in water; b H2 (total) - H2 (splitting); c calc: ml O2 x 2; d below detection limit in gas phase; e unloaded by cooling-warming cycle. Exptl. error 5-10%.
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-0.41 eV
(3)
4e−
TiO2+ H2
SiO2+ H22H2O
(2)
H2
H2O
-0.43 eVO2
SiO2
(1)
TiO2
O2
(1)
H2O
(1) formation of passivating/catalytic/storage layer (thermal)(2) water splitting (→ O2 + 4H+) (light)(3) reduction 2H+ → 2H● → H2 (thermal)
O2 + 4H+
H2
(4)
(4) reversible storage of H2 and O2 (thermal)
O2(4) (chargedstacks)
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IEARE SILICIDE SEMICONDUCTORS IDEAL FOR
WATER SPLITTING? - YES -INCLUDING REVERSIBLE STORAGE OF THE GASES
• Full solar light absorption (350 – 800 nm)
• Conduction band (CB) < H2/H2O (< - 0.41 eV)
• Valence band (VB) > O2/H2O (> + 0.82 eV)
• Cheap and abundant
• Reversible storage of hydrogen and oxygen under different reaction conditions (-> easy separation of the gases)
• Exothermic unloading of oxygen
• High efficiency of water splitting (presently ca 12%)
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IERESEARCH TEAM AND COOPERATIONS
Dipl. Ing. Peter RitterskampDr. Andriy Kuklya
Klaus KerpenMarc-André Wüstkamp
Max Planck Institute for Bioinorganic Chemistry
Dr. Claudia Weidenthaler Max Planck Institute for Coal Research
Prof. Dr. Horst KischUniversity of Erlangen
Dr. Jürgen KleinwächterBSR Solar Technologies, Lörrach
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IEPROJECT PARTNERS
Hydrogen HeatingsZürich
2HSystems
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IENEAR FUTURE GOAL: ONE-FAMILY HOUSE
HEATING TECHNOLOGY BY HPS(Hydrogen Power System)
Demand: 12-15 kW h – 12-15 m3 H2/day
Hydrogen Power System (present):24 kg cat. / 60 m2 / 0.6 m3 H2/day (halogen light)
/ 3 – 12 m3 H2/9 h (solar)
Generation and Storage of H2 and O2
Pump
Combustion(HPS)
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IECATALYTIC COMPOSITION – TiSix and/or oxides thereof?
TiSix TiO2: Ti(0) : Six(0) : SiO2
Redox potentials (- 0.41 eV to – 0.43 eV/ + 3.4 – 1.5 eV)active form?
Generation of H2 TiO2 : Ti(0)Generation of O2 Six(0) : SiO2
Light absorber TiSix
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Ti-
-Ti4+Si4-light H2
2H+
11
H2
H2
44
x
3 3 O2
Current Current investigationsinvestigations concernconcern the the mechanismsmechanisms of and of and 22 3 3
ReactivityReactivity of of TiSiTiSixx
22½ O2 + 2H+18
18H2O
TiSi
+ +
TiO2
SiO2
Si
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-0.41 eV
(3)
4e−
TiO2+ H2
SiO2+ H22H2O
(2)
H2
H2O
-0.43 eVO2
SiO2
(1)
TiO2
O2
(1)
H2O
(1) formation of passivating/catalytic/storage layer (thermal)(2) water splitting (→ O2 + 4H+) (light)(3) reduction 2H+ → 2H● → H2 (thermal)
O2 + 4H+
H2
(4)
(4) reversible storage of H2 and O2 (thermal)
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-0.41 eV
(3)
4e-
SiO2+ H2
TiO2+ H22H2O
(2)
H2
(1) formation of passivating/catalytic/storage layer (thermal)(2) water splitting (→ O2 + 4H+) (light)
(4) reversible storage of H2 and O2 (thermal)(3) reduction 2H+ → 2H● → H2 (thermal)
TiSiXH2
(4)
O2 + 4H+
H2O
H2O
TiO2
(1)
-0.43 eV
(1)
SiO2
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• Hydrogen can be gained from reforming processes(e.g. catalytically from methane or propane)
Disadvantages: High pressure and temperature are required, besidesmethane and propane being fossil sources
• Biomimetics: Attempts to mimic biosynthesis in green leafs in whichnature produces primarily oxygen and protons (H+), the latter of whichcould potentially be subjeced to enzymatic transformation with ahydrogenase to form hydrogen.
SOURCES OF HYDROGEN
Biosynthesis -Photosystem II
Mn4 cluster
Hydrogenase
+
[NiFe] cluster
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• A further and in our opinion in the near future technically realizable
variant of „„farfar--fetchedfetched biomimetics““ concerns the use of novelsemiconductors (scs) as catalysts for „water splitting“ together with sunlight
Semiconductor
sc
Mn4 cluster
+
[NiFe] cluster
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IEHYDROGEN AND OXYGEN EVOLUTION KINETICS
0
5
10
15
20
25
30
35
40
45
50
0 50 100 150 200 250
Time (h)
ml
a (hydrogen) a (oxygen evolution from storage) c (hydrogen, reaction under air) b (hydrogen)
24±1 ml
12±1 ml A
B
C
55 Co 5-8 Co
a (H )2
a (O )2
c (H )2
Phase A: InitiationPhase B: Corrosion (major) and splitting (minor)Phase C: Water splitting (exclusive)
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IE OUR OLD AND LITERATURE RESULTS
• Experiments with doped titanium dioxide (e.g. TiO2 doped with ruthenium; 300-380-nm irradiation):
→ insufficient solar light absorption and catalysis→ degradation of „catalyst“→ applicable in water of high purity only
CURRENT RESEARCH ACTIVITIES
• Our hitherto most successful result in this area is based on the use of semiconductor-type nanomaterials which had so far not been used for water reduction and oxidation to produce hydrogen and oxygen, resp.:
→ Silicides: TiSix, V2Si, ZrSix, Pt2Si, MnSi2 and Ni2Si→ 300-800-nm irradiation
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IE HowHow to to improveimprove 2 vs. 3 ?2 vs. 3 ?
-- reducereduce oxygen oxygen solubilitysolubility in in waterwater layerlayer
-- dopingdoping of of TiSiTiSixx with Pt or with Pt or II II / / IVIV--valentvalent MOMOxx
-- controlcontrol of metal of metal impuritiesimpurities
-- avoidavoid Si and Ti Si and Ti contactscontacts with with waterwater andandoxygen by oxygen by coatingcoating ((NafionNafion membranemembrane) )
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IECONCLUSION
Superiority of the silicides:
• Not yet known literature-wise for the title application
• Cheap and abundant
• Thermal and light stability
• Adequate solar light absorption (350-800 nm)
• BONUS: The silicides are able to store reversibly hydrogen at ambient temperature
• Catalysis? 2:1 ratio for H2/O2 generation : yes
• Modifications of the silicide compositions and surface engineering, as well as further technological improvements can likely secure the lead in this field.
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IE SUMMARY OF CURRENT AND PLANNED R&D ACTIVITIES
• Further silicide nanostructures (FeSix, B4Si, CoSi2, MnSi2, IrSi2, Ti3C2Si, ZrSi2, TaSi2 CrSi2 etc.)
• Surface engineering: a) Doping of the silicides, b) coating andc) in situ complexation of e.g. conducting HOR-type materials to the semiconductor surface
• Check light and sc concentration, temperature and pH dependence
• Evaluation of the reaction mechanisms, especially the fate of oxygen
• Immobilization of the silicides
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M. Grätzel, The artificial leaf,Bio-mimetic Photocatalysis
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Schematic of operation of the dye-sensitized electro-chemical photovoltaic cell. The photoanode, made of a mesoporous dye-sensitized semiconductor, receives electrons from the photo-excited dye which is thereby oxidized, and which in turn oxidizes the mediator, a redox species dissolved in the electrolyte. The mediator is regenerated by reduction at the cathode by the electrons circulated through the external circuit. Figure courtesy of P. Bonhôte/EPFL-LPI.
Scanning electron micrograph of the surface of a mesoporous anatase film prepared from a hydrothermallyprocessed TiO2 colloid. The exposed surface planeshave mainly {101} orientation.
„Grätzel„Grätzel--Zelle“Zelle“
M. Grätzel, Nature 414, 338 (2001) ~20 nm particles
Wirkungsgrad ~10%gute Langzeitstabilität preiswertes Material
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Figure 1 Principle of operation of photoelectrochemicalcells based on n-type semiconductors. Cell that generates a chemical fuel, hydrogen, through the photo-cleavage of water.
Figure 6 The Z-scheme of photocatalytic water decomposition by a tandem cell.
Photoelektrochemische WasserspaltungPhotoelektrochemische Wasserspaltung
M. Grätzel, Nature 414, 338 (2001)
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IEPhotokatalyse mit neuen Photokatalyse mit neuen HalbleiternanomaterialienHalbleiternanomaterialien
-- WasserspaltungWasserspaltung
Titan-Silicid-Katalysatoren :
Vorteile: Nutzung des Bereichs des sichtbaren Lichts (350-800 nm)Einsatz von normalem Wasserhohe H2-Erzeugungsratengute Langzeitstabilität reversible O2- und H2-Speicherung bei RT
Zukunft: Fixierung auf /in polymeren (leitenden) Materialiengetrennte oder kombinierte O2/H2 -Entwicklungvariables Ti:Si-Verhältnis
Alte Experimente mit1) TiO2 dotiert2) TiX (X ≠ O) / TM beschichtet
Nachweis der H2/O2-Entwicklung
Demuth, Ritterskamp, Patentanmeldung 2005
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IEREACTION PATHWAYS
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FACHBEIRAT UND KURATORIUM · MÄRZ 2004
# Reaction scheme Description Nature
1 M + H2O → MOn + H2Formation of hydrogen by
metal oxide formationPhotochemical /
Thermal
2 M+O2 → MOnOxidation of catalyst by
oxygen Thermal
3 M + H2O → M+ H2 +1/2 O2 Water splitting Photochemical
3 is not the case: H2 : evolution due to metal oxide formationO2 : no evolution, consumption due oxidationOxygen consumption is not dependent to hydrogen production
1 is not the case:H2 : evolution due to water splittingO2 : evolution due to water splitting (1/2 to H2) and consumption due oxidationAs more hydrogen produced as less measurable consumption.
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FACHBEIRAT UND KURATORIUM · MÄRZ 2004
measured hydrogen production and oxigen consumption
0
10
20
30
40
50
60
70
80
0 50 100 150 200
hours
ml
20C-H2 prod20C-O2 prod50C-H2 prod50C-H2 prod20C-O2 prod50C-O2 prod
hydrogen production and calculated oxygen consumtion at 50 and 20 degry.
0
10
20
30
40
50
60
70
80
0 50 100 150 200
hours
ml
20C-H2 prod20C-O2 cons50C-H2 prod50C-O2 cons
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0 50 100 150 200 2500
20
40
60
80
100
120
140
160
180
200
> 30 ml H2 / day / g cat
ml o
f hyd
roge
n (H
2)
time (h)
6-10 ml H2 / day / g cat
HYDROGEN PRODUCTIONWITH TiSi2-4 FROM WATER USING HALOGEN
LIGHT
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-0.41 eV
(1)
(3)
4e-
TiO2+ H2
SiO2+ H22H2O
(2)
H2(1)
-0.43 eV
(1) formation of passivating/catalytic/storage layer (thermal)(2) water splitting (→ O2 + 4H+) (light)
(4) reversible storage of H2 and O2 (thermal)(3) reduction 2H+ → 2H● → H2 (thermal)
TiSiXH2
(4)
O2 + 4H+
H2O
H2O