New Nano-structured Semiconductor Photocatalysts for Photocatalytic Solar Hydrogen Production

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1 2010 The 7th Korea-USA Nano Forum New Nano-structured Semiconductor Photocatalysts for Photocatalytic Solar Hydrogen Production JIN-OOK BAEG Jin-Ook Baeg Korea Research Institute of of Chemical Technology

Photocatalyst Application Environmental Remediation - Pollutant Treatment - Deodorization - Sterilization h Solar Energy Conversion - Water Splitting - H 2 S Splitting Energy Photo-induced reaction

2 Photocatalyst Application Environmental Remediation - Pollutant Treatment - Deodorization - Sterilization h Solar Energy Conversion - Water Splitting - H 2 S Splitting Energy Photo-induced reaction Pollutant (organic comp.) +O 2 G<0 (down hill) E G<0 The reaction irreversibly proceeds. degradation CO 2 + H 2 O + etc. Energy Light energy conversion reaction H 2 O Water splitting H 2 + O 2 G>0 (up hill) A back reaction easily proceeds.

3 Solar Energy Conversion for Hydrogen Production Photocatalytic Water Splitting for H 2 Production Solar light H 2 O Photocatalyst PV / hybrid H 2

7 TW in 2006 10,000 times of Current world

4 Solar Energy h Solar Energy 1.74 x 10 5 TW Global l need 15.7 TW in ,000 times of Current world demands (~ 0.1% of the Earth s surface : 10% conversion efficiency )

5 Photocatalytic Water Splitting for Hydrogen Production h Conduction Band H 2 O O Valence Band h 2H 2 O 2H 2 + O 2 H 2 O H 2 Potent tial + h CB Band gap VB e - h + + H + / H2 0V O2/ H2O V

6 Energy Requirement for Overall Water Splitting 2 H 2 O 2H 2 + O 2 G = 237kJ/mol(E = - G /nf = -1.23V) Overpotentials for photo-splitting of water Reaction type Energy required ev Electron transfer at a cathode 0.2 Hole transfer at an anode 0.2 H 2 overpotential ti at a cathode 0.1 O 2 overpotential at an anode 0.5 Band bending for efficient charge separation at an anode 0.2 Total 1.2

2400 Solar Spectrum 물광분해반응의열역학적고찰 Spectral Irradienc ce (W/m 2 / m) 2000 1600 1200 800 400 0 Air Mass 0 Air Mass 1.5 AM1.5 ~ 100mW/cm 2 0.0 0.2 0.4 0.

7 2400 Solar Spectrum 물광분해반응의열역학적고찰 Spectral Irradienc ce (W/m 2 / m) Air Mass 0 Air Mass 1.5 AM1.5 ~ 100mW/cm Wavelength ( m) 0% 0.5% 3.5% 46% Wavelength (nm) UV VIS IR 510 nm 1008 nm 3.10eV (400nm) 2.43eV 1.55eV (800nm) 1.23eV

8 Band Gap Energy and Band Edge Position of Photocatalysts

9 Photocatalysts for Water Splitting (UV Light) TiO 2 Photocatalyst TiO 2 - h Pt H 2 O H 2 H 2 O + O 2 RuO 2 TiO 2 : E g = 3.2 ev, g = 388 nm Catalyst H 2 (μmol/h) Pt/TiO 2 2 Pt/TiO 2 /RuO J. C. Escudero et al., J. Catal., 1990, 123, 319.

10 Perovskite Photocatalyst (UV Light) Water splitting mechanism of K 4 Nb 6 O 17 h A [M n-1 Nb n O 3n+1 ] Ⅰ Ⅱ Ⅰ Ⅱ O 2 h + e - H 2 O Ni Ni e - h e + - e - h + H 2 H 2 O h + h + Ni e - Ni h + h + H 2 O O 2 NbO 6 h + e - h H + 2 O A (Alkali Metals) Ⅰ Ni Ni H e- = K, Rb, Cs, etc. 2 e - h + M (Alkali Earth Metals) = Ca, St, etc. e - h

11 Perovskite Photocatalyst (UV Light) X Catalyst Rate of Gas evolution (μmol/h) H 2 O Ni-K 4 Nb 6 O Ni-K 4Ta 2Nb 6O Ni-K 4 Ta 3 Nb 6 O Ni-K 4 Ta 4 Nb 6 O A [M n-1 Nb n O 3n+1 ] 0 Ni-Rb 4 Nb 6 O Ni-Rb 4 Ta 2 Nb 4 O 17 Ni-Rb 4 Ta 3 Nb 4 O 17 Ni-Rb 4 Ta 4 Nb 4 O 17 Ni-Rb 4 Ta 6 Nb 4 O Ni-Rb 4 Ta 6 Nb 4 O wt% nickel was loaded. d Catalyst, t 1 g; distilled d water, 350 ml; high pressure Hg lamp (400 W); inner irradiation cell (quartz). - K. Domen et al., Catal. Today, 1996, 28, 175.

12 Summary of Quantum Efficiency of Overall Water Splitting Under UV Light NiO-SrTiO 3 1% (300nm) Ni-Rb 4 Nb 6 O 17 10% (300nm) NiO-NaTaO3 :La 56% (270nm) NiO-Ni- Rb 2 La 2 Ti 3 O 10 30% (300nm)

13 Photocatalyst for Water Splitting (Visible Light) CdS : Eg = 2.4eV, g = 517nm - CdS has ideal band gap & band edge position for water splitting for H 2 production under visible light irradiation. h h CdS - TiO 2 - Support H 2 But it undergoes photocorrosion! H + H 2 yield, μmol Pt Catalyst Calcination Temp.( C) h Pt/TiO 2 /SiO CdS/SiO Pt/TiO H 2 /SiO CdS/SiO H + Pt/TiO 2 /SiO CdS/SiO Pt/TiO 2 /SiO Pt CdS/SiO Pt/TiO 2 /SiO CdS/SiO Interparticle electron transfer: (A) Mediated by the conduction band of TiO 2 ; (B) Direct electron transfer to separately supported platinum. - J. M. White et al., J. Phys. Chem., 1987, 91, a Reaction conditions: 10 mg of TiO 2 /SiO 2 ; 0.4 wt% Pt (in situ photoplatinization); 10 ml of 1:1 H 2 O-MeOH 0.01 M KOH; light source: 450W Xe lamp, 420 nm cut-off filter

14 ZnCuS Photocatalyst ZnS Zn Cu S E g = 3.7eV E g = 2.5eV g = 335nm g = 496nm b.units Absorban nce / ar ZnS Zn Cu S CuS * Quantum yield: 37%( 3.7% > 420 nm) (Photocorrosion) * Rate of H 2 revolution: 430 mol/g.cat.hr (0.5M Na 2 SO 3 ) Wavelength/nm - A. Kudo et al. Catal Letter, 1999, 58, 241.

15 Rh 2 O 3 : Cr 2 O 3 /(Ga 1-x Zn x )(N 1-x O x ) Photocatalyst for Water Splitting ( = 420~ nm; ph=4.5) QY: 2.5% Catalyst: 0.3 g, Rh 2 O 3 : Cr 2 O 3 5 wt.%, Domen, et. al., Nature, 440, 295 (2006).

16 CdIn 2 S 4 Nanotube and Marigold Nanostructure Photocatalyst Cubic spinel nanostructured CdIn 2 S 4 Marigold(aq.) : 3~5 μm CdIn 2 S 4 - Nanotubs Nanotube(MeOH) : 25nm X 780nm Density of states (DOS) for CdIn 2 S 4 (Calc. Eg = 1.90 ev) VB (S 3p) ; CB (In 5s, 5p major & Cd 5s, 5p) Advanced Functional Materials, 2006,16, 1349.

17 CdIn 2 S 4 Nanotube and Marigold Nanostructure Photocatalyst CdIn 2 S 4 Photocatalyst for Hydrogen production 1.8 A bs (b) (c) (d) (a) Eg = 2.19 ev (570 nm) High quantum yield! - Nanotube(MeOH) : 17.1% (@ = 500 nm) - Marigold(aq.) : 16.8% (@ = 500 nm) Quantum yield (%) = [Number of H 2 molecules evolved x 2] [Number of incident photons] X Rate of H 2 revolution: wavelength(nm) - Nanotube : 3480 mol/hr - Marigold : 3476 mol/hr Diffuse Reflection Spectra s (a) aqueous (b) methanol (c) ethylene glycol (d) polyethylene glycol (5%) mediated CdIn 2S 4. Advanced Functional Materials, 2006,16, 1349.

18 Nano-CdS Q.D. Photocatalyst in Glass Matrix Procedure of Preparation for Powder of Q-CdS in glass matrix SiO2 + Na2O + K2O + ZnO, B2O3 + TiO2 + BaO & CdS(0.5 wt%) Ball-milled mixing for 6h a b Reaction at 1500~1600 o C for 3h Annealing at o C (Tg = ) 580) for 72h Grinding Typical photographs of glass matrix, a) host glass b) after crystal growth of Q-CdS Powder of Q-CdS in glass matrix Journal of Material Chemistry, 2007, 17, 4297.

19 Nano-CdS Q.D. Photocatalyst in Glass Matrix Photocatalytic Activity for H 2 Production (Visible ) Q-CdS (1% amount ) has 300% higher photocatalytic activity than bulk CdS!! High quantum yield (@ = 470 nm)!! - Q-CdS-glass: 17.5% (1g of powder contains 0.005g of Q-CdS) - CdS: 5.5% (0.5 g of CdS) Quantum yield (%) = [Number of H 2 molecules evolved x 2] [Number of incident photons] X 100 Journal of Material Chemistry, 2007, 17, 4297.

20 Octahedrally Coordinated d 0 Transition Metal Oxide Photocatalysts Octahedrally Coordinated d 0 Transition Metal Oxide Photocatalysts TiO 2, SrTiO 3, A 2 Ti 6 O 13 (A = Na, K, Rb) BaTi 4 O 9, A 2 La 2 Ti 3 O 10 (A = K, Rb, Cs) K 2 Ti 4 O 9, Na 2 Ti 3 O 7 Ti 4+ V Cr ZrO 2 Zr 4+ Nb 5+ Mo Hf Ta 5+ W Ta 2 O 5, ATaO 3 (A = Na, K) A 4 Nb 6 O 17 (A=K, Rb) MTa 2 O 6 (M = Ca, Sr, Ba) Sr 2 Nb 2 O 7 Sr 2 Nb 2 O 7

21 Density of States of TiO 2 by First Principle Calculation O - TiO 2 Conduction Band h Ti + Valence Band Density of states of TiO 2 TiO 2

22 Density of States of ZnBiGaO 2 by First Principle Calculation Zn 2 GaO 4 Eg = 3.82 ev ZnBiGaO 4 Eg = 1.92 ev

23 Photocatalytic 물Activities 광분해반응의 of New 열역학적 Photocatalysts 고찰 (Visible) Photocatalytic H 2 Production System(Visible ) Catalyst Band gap energy (ev) H 2 evolution rate a ( mol/hr) ZnBiGaO (440nm) 3,030 CdBiGaO (510nm) 2,454 a Catalyst 0.5g, 250mL(H 2 O) + KOH(0.5M), H 2 S(2.5mL/min), Xe lamp(450w), light filter(>420nm).

24 Development of Synthetic Method for New Metal Oxide Photocatalyst Low temperature economical photocatalyst preparation method! Procedure of Preparation for ZnBiVO 4 by Solid State Method Procedure of Preparation for ZnBiVO 4 by Hydrothermal Method Zn(II)-oxide Bi(III)-oxide V(III)-oxide Zn(NO 3 ) 2 5H 2 O + Bi(NO3) 3 6H 2 O Mixing & Tableting NH 4 VO (b) (b) hydrothermal Urea & water Reaction at 670 o C for 15h Grinding Abs (a) (a) solid state Reaction at 130 o C for 60-72h Reaction at 725 o C for 12h Grinding ZnBiVO (Eg = 2.30eV: 539nm) wavelength(nm) Specific surface Area BET (m 2 /g) : 0.27 Wash & Dry at 250 o Cfor5h Specific surface ZnBiVO Area BET (m 2 4 /g) : 2.50

25 Preparation of Visible Light Photocatalyst by N-doping Procedure of Preparation for Nb 2 Zr 6 O 17-x N x ZrO 2 Nb 2 O 5 Mixing & Tableting Reaction at 1300 o C for 24h Grinding Nb 2 Zr 6 O 17 NH 3 /20mL/min Reaction at 800 o C for 2h Grinding Nb 2 Zr 6 O 17-x N x

26 New Visible Light Photocatalyst Synthesis by Molten Salt Method Procedure of Preparation for Ga 2 Pb 2 Nb 2 O 7 Pb(II)-oxide Ga(III)-oxide Nb(V)-oxide Mixing & Tableting NaCl (10eq.) Reaction at 1093 o K for 4h Grinding & Washing Reaction at 1473 o C for 12h Grinding Ga 2 Pb 2 Nb 2 O 7

2%(410nm: H 2 O) Quantum efficiency (Visible) : ~ 20%(500nm: H 2 S) Future target Quantum

27 Present Statust Conclusions Quantum efficiency (UV) : ~ 56%(270nm: H 2 O) Quantum efficiency (Visible) : ~ 5.2%(410nm: H 2 O) Quantum efficiency (Visible) : ~ 20%(500nm: H 2 S) Future target Quantum efficiency (Visible) : 30% ( 600nm) Hydrogen production rate (1 km 2 ) : 16,500Nm 3 /h Photoreactor t H 2 Solar Hydrogen Production System Purification Storage

28 Thank you!

Laurea in Scienza dei Materiali Materiali Inorganici Funzionali. Hydrogen production by photocatalytic water splitting

Laurea in Scienza dei Materiali Materiali Inorganici Funzionali Hydrogen production by photocatalytic water splitting Prof. Dr. Antonella Glisenti -- Dip. Scienze Chimiche -- Università degli Studi di