Making Oxygen from Sunlight. T.J. Meyer UNC EFRC. Solar Fuels Notre Dame April 16, 2015

Transcription

1 Making xygen from Sunlight T.J. Meyer UC EFRC. Solar Fuels otre Dame April 16, 2015

2 Energy Issues. Energy Supply World energy demand, % of the increase in global energy demand will come from developing nations Currently: >85% of energy supply is from hydrocarbons. 1 Source: US Energy Information Administration

3 Energy Issues. Hydrocarbons and Climate Change ew York with sea levels 5 feet higher. Shanghai +2 meters May 2013: Atmospheric C 2 levels reached 400 ppm, highest in 3 million years Greenhouse gas effect. By 2100, sea levels could be up to 6-7 feet higher By 2070, 150 million people in port cities could be displaced, losing $35 trillion worth of property (9% global GDP)

4 Energy Future. Strategy For a ew Energy Future Utilize all energy options (All of the Above): Efficiency, conservation Clean coal Shale and tar sands Coupled with C 2 capture and storage (sequestration)? uclear Hydrogen and fuel cells Renewable energy (wind, solar, biomass, geothermal) Energy use and infrastructure: Energy storage and distribution Energy and environmental modeling Water for energy

5 Solar Energy. ~10,000 Times Current Energy Use. But.. Diffuse: ~60,000 sq miles to meet current US power demands (3 TW)* 3 TW 20 TW *at 10% efficiency, REL. $60 Trillion at $400/m 2. Intermittent: 6 hours of useful sunlight per day Requires Energy Storage

6 Energy Conversion and Storage with Solar Fuels. Artificial Photosynthesis -Hydrogen, C, natural gas, liquid hydrocarbons and oxygenates -Use the existing energy infrastructure 2 H hν 2H (ΔG o = 4.92 ev, n = 4) 2 H 2 + C hν CH (ΔG o = 10.3 ev, n = 8)

7 Photosynthesis in Chloroplasts, Thylakoid Membrane. An Inspiration, ot a Model. (~5 μ; /cell) Primary processes are efficient Biomass production is inefficient PSII, unchanged for 2.5 B years

8 Photo-induced Electron Transfer in PSII. 5 electron transfers, ~50 Å. Trans-Membrane H + Transfer glu, Q B H + stroma * Mn ( 4) H + lumen Photon 1: S o S 1 ET: 5 steps, > 50 Å PT: Mn(4)-H 2 lumen(h + ) stroma(h + ) Glu net: Mn II -H 2 + Q B + Glu - Mn III H + Q B. + GluH stroma (H + ) lumen(h + )

9 Artificial Photosynthesis. Honda-Fujishima Photoelectrochemistry, e CB - - hν Direct Band Gap Excitation, Anatase Ti 2 Honda and Fujishima Downside: UV Light 0.2 V bias KEEP IT SIMPLE! VB + Ti 2

10 Artificial Photosynthesis. Excited State Electron Transfer (Bock-1974) Energy conversion by excited state electron transfer- to give transiently stored redox equivalents. (bpy) 2+ 3 (dπ 6 ) h III (bpy -. )(bpy) 2+ 2 * (dπ 5 )(π*) 1 ν (bpy) 3 2+ * + MV 2+ (bpy) MV +. M - Me 2 + (MV 2 + ) (bpy) 3 3+ / 2+ MV 2+/+ E o = 1.26 V E o = -0.4 V 2 H H 2 E o = 1.23 V Bock, Meyer, Whitten, JACS , Weller et al; Adamson et al. CHALLEGES: -Water xidation -Architecture

11 Single Site Catalysis of Water xidation, Mechanism. 2H H + (Blue Dimer 1982) 2 Loss + H + [V- ] 3 + k 6 H 2 [IV- ] 2 + k 4 [III- H ] 2 + k bond formation k 5 [II- H2 ] 2 + H 2 H 2 + H + [III- H ] 2 + [IV= ] 2 + H 2 H + [V= ] 3 + k H + + H + Thummel JACS 2005; Concepcion,Chen- JACS,2008,JACS 2010, 2011,PAS,2011.;PAS k 1 k 2 k 7 PCET (1981) Binstead, et al JACS 1981, 103, H 2 2+ [(tpy)(mebim-py)(h 2 )] 2+ k cat (2) ~ 2.0 s -1 (0.1 M H 3 ) 2 weeks- 43,400 turnovers (ph = 7, 0.1 M H 2 P 4- /HP 4 2- ) 4+ [(bpy) 2 (H 2 ) III III (H 2 )(bpy) 2 ] 4+ Gersten, et al JACS. 1982, 14, 4029.

12 Dye Sensitized Photoelectrosynthesis Cell. DSPEC DSPEC for H 2 Splitting ( ) TC Ti 2 hυ P 3 H 2 H P H P H 2 3 P H KEEP IT SIMPLE! LET THE MLECULES D THE WRK. Moss. Treadway, Inorg Chem Song, et al Pure and Appl. Chem, 2011, 749.

13 Tandem 2 Reduction of Carbon Dioxide. Syngas (2H 2 :C) and Formate (HC 2 - ) Tandem, DSPEC for C 2 reduction. C 2 /H 2 /H + reduction to syngas (2H 2 :C). Syngas CH 3 H hydrocarbons by Fischer-Tropsch synthesis Integrated PEC/formate-oxygen fuel cell.

14 DSPEC. Let the Molecules do the work. Photoanode for Water Splitting TC Ti 2 hν 1/2 H 2 1/4 2 + H + Ti 2 hν 1/2 H 2 1/4 2 + H + 1/2 H 2 H + Particles nm Films 5-10 micron ELECTRDE IT/FT H H P P P 3 H 2 H 2 P 3 H 2 4+ H H H +

15 Systems Analysis DSPEC Photoanode FT Semiconductor: Band energy matching, transport M x y k diff k inj H P P H (H)2P * (H)2P III k BET Surface binding, stability: Stable over wide ph range k intra Light absorption: Capture solar spectrum H 2 4+ Electron Transfer Dynamics; η inj ~ 1: k BET << k cat k intr Molecular Catalysis: 13 million turnovers a year Device Evaluation DSPEC design and scale-up

16 Chromophore-Catalyst Assemblies. Strategies Co-Loaded JACS, 2013, jacs,2014,. Polymer Scaffolds Polym. Chem., 2014, 2363 JPCL, 2012, 2457 Molecular verlayers Inor. Chem., 2012, 8637 Layer-by-Layer ACIE, 2012, Chem. Sci., 2014, 3115 JPCA, 2014, ASAP Surface Assembled Electro-assembly JACS, 2013, JACS, 2014, 6578 Peptide Scaffolds JCPB, 2013, 6352 JACS, 2013, 5250 Inor. Chem., 2012, Inor. Chem., 2014, In Press Pre-formed Molecular Assemblies ACIE, 2009, 9473 Inor. Chem., 2012, 6428 JACS, 2012, JACS, 2013, 2080 JPPC, 2013, ACIE, 2013, JPCL, 2011, 1808

17 Interfacial Dynamics on Ti 2 in Water. Ti 2 -[ a II - b II -H 2 ] 4+ (Brennaman, Papanikolas, Moran) [(4,4 -(P 3 H 2 -CH 2 ) 2 -bpy) 2 a (bpy-h-c-py) b (bpy)(h 2 )] ps (H)2P e hv ps (H)2P (H)2P H e (H)2P Chromophore 1 μs 0.1 M HCl 4 From fsec to msec. e H 2 Catalyst Dennis Ashford

18 I (µa) I (µa) Specific Base Catalysis. Atom-Proton Transfer (APT) and H - Attack 0 (a) M 0.01 M 0.05 M 0.1 M E (V vs. Ag/AgCl) 800 (a) ph = 7.45, pk a = (GC; 0.1 M K 3 ; 100 mv/s) ph = 5, pk a = 4.75 ph = 2.4, pk a = [B - ] Ac - HP 4 2- Ac - H 2 P 4 - Concerted Atom-proton transfer: Rate enhancements of > weeks- 43,400 turnovers (ph = 7, 0.1 M H 2 P 4- /HP 4 2- ) V = 3+ --Ō H 2 { V = 3+ + H 2 M III --H 2 3+ } H H + H---B V = H APT High ph. Direct H - attack Chen,Meyer,Concepcion,Yang, PAS, III -H HB III ---H 2+

19 Water xidation by 1 st Row Catalysts (Zhang,Chen,Coggins) MTZhang JACS I (ma/cm 2 ) Cu(II) in 1 M a 2 C 3 (ph 10.8) 0 mm 1 mm 2 mm 3 mm 4 mm 5 mm I (ma/cm 2 ) Chen, EES, E (V vs. HE) E (V vs. HE) Coggins,JACS,2014. Cu II Coggins and Zhang Cu II (Py 3 P) ACIE 2014.

20 Electrocatalytic Reduction of C 2 /H 2 tosyngas (H 2 /C). MeC/H 2 /H 2 P 4 - (Z. Chen, P.Kang) C + HC 3 S + H 2 /H + + C 2 [(tpy)(bpy) II (C2 2- )] 0 [(tpy)(bpy) II (S)] 2+ 2 Complex 1 H 2 C 2 [(tpy - )(bpy - ) II (S)] 0 S + H 2 /H + H 2 /H + S S [(tpy)(bpy) II (H)] + (b) 100 Coulomb efficiency (Φ) for C and H 2 ; added H 2 P 4 -. RVC electrode, 1.30 V. S φ (%) C H [H 2 P - 4 ] (mm)

21 Syngas (H 2 :C) by Electrocatalysis in C 2 /HC 3 - Single Site C 2 /H 2 Splitting (Z.Chen,P.Kang,EES 2014) Anode: 3H 2 + 6HC 3-3/ H 2 C 3 Cathode: C 2 + 6H 2 C 3 C + H 2 + 2H 2 + 6HC 3 et: 2H 2 + C 2 2H 2 + C + 3/2 2 Varying the syngas ratio. 0.5 M HC 3 - E app -1.2 V C 2 (sat d), 1mM ; M ahc 3 (1-2 ma/cm 2 ; ~50% energy efficiency) [(tpy)(mebim-py)(s)] 2+

22 Surface Water xidation on nanoit. Water xidation Cycle 1 μm Unstable toward hydrolysis in base! + + H + [V- ] 3 + k 6 H 2 [IV- ] 2 + k 4 2 k 5 [III- H ] 2 + [II- H2 ] 2 + P ELECTRDE 2H 2 P 2 + 4H + H H 2 + H + k H + [III- H ] 2 + k 2 k 7 [IV= ] H nanoit on FT (Sn(IV):In 2 3 ) k - H 2 H + [V= ] 3 + k 3 Z.Chen, P. Hoertz Dalton Trans., 2010, 6950

23 Surface Stabilization. Atomic Layer Deposition Expose M-H surfaces to reactive metal oxide precursors, hydrolyze, repeat conformal, multi-layers. AlMe 3 CH 4 Parsons - CSU CH 3 surface: purge Recycle H Surface ALD cycle H 2 CH 4 purge 23

24 Atomic Layer Deposition (ALD) Surface Stabilization. Rate Enhancement of 10 6! (Vannucci,Alibabaei,Hanson) k ~ 10 4 s -1 V = Water xidation: k(ph 11; 1M P 43 ))/k(ph1) = 10 6! Atom-Proton Transfer to P 3-4 ; H - attack H H + H---P 3 3- APT III -H 2+ + HP 3 2-

25 Chromophore-Catalyst Assembly Mechanism of water oxidation (orris) nanoit-[ II a - II b -H 2 ] 4+ - e, H + - nanoit-[ II a - III b H] 4+ nanoit-[ II a - III b -H] 4+ e, H + nanoit-[ II a - IV b =] 4+ - e nanoit-[ II a - IV b =] 4+ nanoit-[ III a - IV b =] 5+ -H + nanoit-[ III a - IV b =] 5+ + H nanoit-[ II a - III b -H] 4+ 2 RDS H + H +, 2 nanoit-[ II a - III b -H] 4+ nanoit-[ II a - III b -H 2 ] H 2 Electron Atom Proton Transfer nano-it nano-it H P H P P 3 H 2 H 2 3 P H i/µa mv/s CV SW E/V vs. HE

26 DSPEC Water Splitting. Timescales Interfacial Dynamics Semiconductor: 5-10 μ; ~1 msec FT k diff H k inj H P P Injection: fsec-psec H 2 3 P P 3 H 2 Light absorption: 1-2 s -1 ( s -1 ; 4 photons) k intra psec-nsec 4 + Molecular Catalysis: > 0.5 s -1 M x y Surface Binding: Indefinite H 2 k BET Back Electron Transfer: μsec-msec

27 Solar Water Splitting. Atomic Layer Deposition Core Shell Advantage (Alibabaei,Brennaman,Farnum) FT nanoit Ti 2 P H P P 3 H 2 H 2 3 P FT nanoit/ti 2 -[ a II - b II -H 2 ] 4+ Pt 1 H /4 + 4h υ PtFT nanoit/ti 2 -[ a II - b II -H 2 ] Pt + 2H 2 Parsons CSU Core Shell Advantage. 1-4 nm of Ti 2 on nano- IT APCE = 4.5% Current ( A) Time (sec)

28 Comparison: Sn 2 /Ti 2 and nanoit core/shells Photoanodes for water splitting 4+ H 2 (H)2P P ALD Ti 2 Sn 2 r nanoit FT P P(H)2 verlayer Ti 2 or Al 2 3 Core Shell 1-4 nm of Ti 2 at ph 4.6 in HAc/Ac - APCE(445nm) core APCE nanoit 4.5% Sn 2 >20% Ti 2 (3.3 nm); Pt counter, 200 mv (vs. Ag/AgCl) in 0.5 M LiCl 4.

29 Surface Stabilization by Electropolymerization DSPEC Electro-assemblies (Ashford, Sherman) Electro-Assembly formation by reduction in MeC. Solar Simulator ph 7 phosphate buffer Sustained photocurrents hv Duan, L. et al. at. Chem. 2012, 4 (5), ; Ashford, D.L. et al. JACS submitted 29

30 UC Energy Frontier Research Center SLAR FUELS DE-BES ($28.3M/ ) DSPEC devices for solar energy conversion

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32 C 2 Reduction to Formate. Ir Pincer Hydrides (Kang,Brookhart, 2012) 32 MeC:5% water: 1 atm C 2 k cat = 20(2) s 1 C 2 (1 atm), 0.1 M n Bu 4 PF 6 in CH 3 C glassy carbon, 100 mv/s. Kang, Brookhart J.ACS 2012, 5500

33 Selective C 2 Reduction to Formate in Water. Water-Soluble, Flow Reactor (Kang,2013) M ahc 3 in H 2, GCE; 100 mv/s, 1atm C 2 X3.5 in water. Highly selective; formate (82%), no C, no H 2. Kang, ChemSci,2013 Flow Reactor

34 P Ir X P Assemblies (Mallouk, et al). DSPEC Water xidation (Michaux, Murray,Alibabaei). [(4,4 -(P 3 H 2 ) 2 bpy) 2 (bpy)] 50 % % Core/shell 10 % anoit/ti 2 P (Ir 2 ) x (2 nm) Ir X 50 % P + Ir X Ti 2 anoit/ti 2 Core/Shell, 50 cycles anoit/ti 2 Core/Shell 100 cycles Ir X P P + Ir X Phorocurrents: (µa/cm 2 ) 10s at 0 mv bias, 455 nm, 50% Light Intensity, ph

35 PMMA coated FTlTi 2 -P. Surface Stabilization (Kyung-Ryang Wee) 2 + θ c =12.5 o R = R R= CH or P(H) 2 PMMA n verlayer Ti 2 or nanoit nanoparticle Dipping in PMMA solution (0.5~3.0wt%) Ti 2 or nanoit nanoparticle Control sample Glass/FT/Ti 2/P PMMA coating Glass/FT/Ti 2/P/PMMA Hydrophilic PMMA-coated nanoparticle film θ c =71.6 o Hydrophobic verlayer thickness control by solution wt% in CH 2 Cl Ti 2 Hydrophobic PMMA verlayer R R Thickness up to ~2.1 nm 2 + FT Ti 2 -P 2+ hv FT Ti 2 -P 2+ * FT Ti 2 -P 2+ * FT Ti 2 ( )-P 3+ FT Ti 2 ( )-P 3+ FT Ti 2 -P 2+ Wee, et al JACS 2014, 136, ormalized Delta Abs (AU) ph dependence ph 1 ph 7.5 ph 12 zero ref line 3wt% PMMA coated FT Ti 2 -P E-8 1E-7 1E-6 1E-5 1E-4 Time (sec)