2010 The 7th Korea-USA Nano Forum New Nano-structured Semiconductor New Nano structured Semiconductor Photocatalysts for Photocatalytic Solar Hydrogen Production JIN-OOK BAEG Jin-Ook Baeg Korea Research Institute of Korea Research Institute of Chemical Technology Chemical Technology
Photocatalyst Application h Solar Energy Environmental Conversion Remediation - Pollutant Treatment - Water Splitting - Deodorization D d i ti - H 2 S Splitting H S S litti - Sterilization Photo-induced reaction Light energy conversion reaction Pollutant Water splitting degradation (organic comp.) +O 2 Energy Energy H 2 + O 2 CO 2 + H 2 O △ G>0 (up hill) + etc. △ G<0 (down hill) △ G<0 (down hill) E E H 2 O A back reaction The reaction irreversibly easily proceeds. proceeds.
Solar Energy Conversion for Hydrogen Production Photocatalytic Water Splitting for H 2 Production Solar light H 2 O Photocatalyst PV / hybrid H 2
Solar Energy h h Gl b l Global need d Solar Energy 15.7 TW in 2006 1.74 x 10 5 TW 1.74 x 10 TW 10,000 times of Current world demands (~ 0.1% of the Earth’s surface ( : 10% conversion efficiency )
Photocatalytic Water Splitting for Hydrogen Production H + / H 2 + H 2 O CB e - 0 V - Conduction Band tial H 2 2 Potent h Band gap h H O H 2 O + Valence Band h + VB O 2 O 2 / H 2 O + + +1 23 V +1.23 V h 2H 2 + O 2 2H 2 O
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 at a cathode H t ti l t th d 0.1 0 1 O 2 overpotential at an anode 0.5 Band bending for efficient charge 0.2 separation at an anode ti t d Total 1.2
Solar Spectrum 물 광분해 반응의 열역학적 고찰 2400 2400 2000 m) Air Mass 0 AM1.5 ~ 100mW/cm 2 2 / Air Mass 1 5 Air Mass 1.5 ce (W/m 1600 1200 Irradienc 800 Spectral 400 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Wavelength ( m) 46% 0% 0.5% 3.5% Wavelength (nm) UV VIS IR 510 nm 1008 nm 3.10eV 1.55eV (400nm) (800nm) 1.23eV 2.43eV
Band Gap Energy and Band Edge Position of Photocatalysts
Photocatalysts for Water Splitting (UV Light) TiO 2 Photocatalyst H 2 O TiO 2 - H 2 h Pt + H 2 O RuO 2 O O 2 TiO 2 : E g = 3.2 eV, g = 388 nm Catalyst H 2 (μmol/h) Pt/TiO 2 2 Pt/TiO 2 /RuO 2 77 - J. C. Escudero et al ., J. Catal. , 1990, 123 , 319.
Perovskite Photocatalyst (UV Light) Water splitting mechanism of K 4 Nb 6 O 17 h h + e - e - H 2 O Ni Ni Ⅰ Ⅰ e - e - h + H 2 e - h + Ⅱ O 2 H 2 O h + h + Ni Ni e - e h Ni Ⅰ h + h + A [M n-1 Nb n O 3n+1 ] Ⅱ H 2 O O 2 NbO NbO 6 e - e h + h + H 2 O Ni Ni e - A (Alkali Metals) Ⅰ H 2 h + e - = K, Rb, Cs, etc. M (Alkali Earth Metals) M (Alkali Earth Metals) = Ca, St, etc .
Perovskite Photocatalyst (UV Light) Rate of Gas evolution (μmol/h) X Catalyst H 2 O 2 0 Ni-K 4 Nb 6 O 17 403 197 2 Ni-K 4 Ta 2 Nb 6 O 17 409 198 4 2 6 17 3 Ni-K 4 Ta 3 Nb 6 O 17 233 111 4 Ni-K 4 Ta 4 Nb 6 O 17 31 12 0 0 Ni Rb 4 Nb 6 O 17 Ni-Rb 4 Nb 6 O 17 936 936 451 451 2 Ni-Rb 4 Ta 2 Nb 4 O 17 362 179 3 Ni-Rb 4 Ta 3 Nb 4 O 17 126 62 A [M n-1 Nb n O 3n+1 ] 4 Ni-Rb 4 Ta 4 Nb 4 O 17 101 48 6 6 Ni Rb 4 Ta 6 Nb 4 O 17 Ni-Rb Ta Nb O 92 92 46 46 6 Ni-Rb 4 Ta 6 Nb 4 O 17 11 1 0.1 wt% nickel was loaded. Catalyst, 1 g; distilled water, 350 mL; 0 1 t% i k l l d d C t l t 1 ; di till d t 350 L; high pressure Hg lamp (400 W); inner irradiation cell (quartz). - K. Domen et al ., Catal. Today , 1996, 28 , 175.
Summary of Quantum Efficiency of Overall Water Splitting Under UV Light NiO-SrTiO 3 � 1% (300nm) � 1% (300 ) Ni-Rb 4 Nb 6 O 17 NiO-NaTaO 3 :La 56% (270nm) 10% (300nm) NiO-Ni- Rb 2 La 2 Ti 3 O 10 2 2 3 10 30% (300nm)
Photocatalyst for Water Splitting (Visible Light) - CdS has ideal band gap & band edge position for CdS : Eg = 2.4eV, g = 517nm water splitting for H 2 production under visible light irradiation. H 2 But it undergoes photocorrosion! CdS TiO 2 - H + - ----- h ----- H H yield μ 2 yield, μ mol mol Pt Calcination Temp.( C) Catalyst ----- + 1h ----- Pt/TiO 2 /SiO 400 2.0 2 CdS/SiO CdS/SiO 110 110 2 2 Pt/TiO 2 /SiO 400 3.4 H 2 2 CdS/SiO 300 2 Pt/TiO 2 /SiO 400 3.8 H + 2 - CdS/SiO 400 2 h h ----- Pt/TiO 2 /SiO 110 1.3 2 CdS/SiO 400 Pt ----- 2 + Pt/TiO 2 /SiO 300 2.2 2 CdS/SiO 400 Support 2 a Reaction conditions: 10 mg of TiO 2 /SiO 2 ; 0.4 wt% Pt Interparticle electron transfer: (in situ photoplatinization); 10 mL of 1:1 H 2 O-MeOH 0.01 M KOH; light source: 450W Xe lamp, 420 nm (A) Mediated by the conduction band of TiO 2 ; cut-off filter (B) Direct electron transfer to separately supported platinum. - J. M. White et al ., J. Phys. Chem ., 1987, 91 , 3316.
ZnCuS Photocatalyst ZnS Zn 0.957 Cu 0.043 S E g = 3.7eV E g = 2.5eV g = 335nm g = 496nm = 335nm = 496nm b.units CuS * Quantum yield: 3.7% ( > 420 nm) 3 7% ( > 420 nm) nce / ar (Photocorrosion) Zn 0.957 Cu 0.043 S * Rate of H 2 revolution: 430 mol/g.cat.hr 430 mol/g cat hr Absorban (0.5M Na 2 SO 3 ) ZnS 250 300 350 400 450 500 550 600 Wavelength/nm - A. Kudo et al. Catal Letter , 1999, 58, 241.
Rh 2 O 3 : Cr 2 O 3 /(Ga 1-x Zn x )(N 1-x O x ) Photocatalyst for Water Splitting ( ( = 420~440 nm; pH=4.5) 420 440 H 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).
CdIn 2 S 4 Nanotube and Marigold Nanostructure Photocatalyst Cubic spinel nanostructured CdIn 2 S 4 Marigold(aq ) : 3 5㎛ Marigold(aq.) : 3~5㎛ CdIn 2 S 4 - Nanotubs Density of states (DOS) for CdIn S Density of states (DOS) for CdIn 2 S 4 (Calc. Eg = 1.90 eV) (Calc Eg = 1 90 eV) Nanotube(MeOH) : 25nm X 780nm VB (S 3p) ; CB (In 5s, 5p major & Cd 5s, 5p) Advanced Functional Materials , 2006, 16 , 1349.
CdIn 2 S 4 Nanotube and Marigold Nanostructure Photocatalyst CdIn 2 S 4 Photocatalyst for Hydrogen production 1.8 1.6 • High quantum yield! (b) 1.4 - Nanotube(MeOH) : 17.1% (@ = 500 nm) (c) 1.2 (d) - Marigold(aq.) : 16.8% (@ = 500 nm) (a) 1.0 Eg = 2.19 eV bs 0.8 Quantum yield (%) = Quantum yield (%) = ( (570 nm) 0 ) A 0.6 [Number of H 2 molecules evolved x 2] X 100 0.4 [Number of incident photons] 0 2 0.2 •Rate of H 2 revolution: 0.0 200 300 400 500 600 700 800 - Nanotube : 3480 mol/hr wavelength(nm) wavelength(nm) - Marigold : 3476 mol/hr / Diffuse Reflection Spectra ’ s (a) aqueous (b) methanol (c) ethylene glycol (d) polyethylene glycol (5%) mediated CdIn 2 S 4 . 2 4 Advanced Functional Materials , 2006, 16 , 1349.
Nano Nano- -CdS Q.D. Photocatalyst in Glass Matrix 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%) b b a a Ball-milled mixing for 6h Reaction at 1500~1600 o C for 3h Annealing at 500-600 o C Typical photographs of glass matrix, (Tg = 570 580) for 72h (Tg = 570-580) for 72h a) host glass b) after crystal growth of Q-CdS Grinding Powder of Q-CdS in glass matrix Journal of Material Chemistry Journal of Material Chemistry , 2007, 17 , 4297. 2007 17 4297
Nano- Nano -CdS Q.D. Photocatalyst in Glass Matrix CdS Q.D. Photocatalyst in Glass Matrix Photocatalytic Activity for H 2 Production (Visible ) Q-CdS (1% amount ) 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] X 100 [Number of incident photons] [Number of incident photons] Journal of Material Chemistry , 2007, 17 , 4297.
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 Ti O K 2 Ti 4 O 9 , Na 2 Ti 3 O 7 N Ti O V Cr Ti 4+ Mo Mo Zr 4+ Zr Nb 5+ Nb ZrO 2 2 Hf W Ta 5+ Ta 2 O 5 , ATaO 3 (A = Na, K) A 4 Nb 6 O 17 (A=K, Rb) MTa O (M = Ca Sr Ba) MTa 2 O 6 (M = Ca, Sr, Ba) S Nb O Sr 2 Nb 2 O 7 Sr 2 Nb 2 O 7
Density of States of TiO 2 by First Principle Calculation TiO 2 Conduction O Band - h Ti Ti + Valence Band Density of states of TiO 2 TiO 2
Density of States of ZnBiGaO 2 by First Principle Calculation Zn 2 GaO 4 Eg = 3.82 eV -2 0 2 4 ZnBiGaO 4 Eg = 1.92 eV
Photocatalytic Activities of New Photocatalysts (Visible) 물 광분해 반응의 열역학적 고찰 Photocatalytic H 2 Production System(Visible ) Photocatalytic H 2 Production System(Visible ) Band gap H 2 evolution Catalyst y energy rate a ( mol/hr) (eV) ZnBiGaO 4 ZnBiGaO 4 2.80(440nm) 2.80(440nm) 3,030 3,030 CdBiGaO 4 2.43(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).
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