Research in the UNC EFRC for Solar Fuels The Dye Sensitized Photoelectrosynthesis Cell (DSPEC)

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1 Research in the EFRC for Solar Fuels The Dye Sensitized Photoelectrosynthesis Cell (DSPEC) T.J. Meyer EFRC: SOLAR FUELS DOE Yellow Team Presentation May 14, 2015

2 Solar Energy ~10,000 Times Current Energy Use. But.. 3 TW 20 TW *at 10% efficiency, NREL. $60 Trillion at $400/m 2. Diffuse: ~60,000 sq. miles to meet current US power demands (3 TW)* 1,000 homes = 32 acres Intermittent: 6 hours of useful sunlight per day Requires Energy Storage

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

4 Dye Sensitized Photoelectrosynthesis Cell DSPEC DSPEC for H 2 O Splitting ( ) hυ E bias = 0.2 V Ru(bpy) 3 2+ (d 6 ) + hυ Ru III (bpy -. )(bpy)2 2+ * Ru(bpy) 3 2+ * + MV 2+ Ru(bpy) MV +. KEEP IT SIMPLE! LET THE MOLECULES DO THE WORK. Moss, Treadway, Inorg. Chem., 1999 Song et al. Pure and Appl. Chem, 2011, 749 Bock, Meyer, Whitten, JACS, 1974, 96, 4710

5 Tandem DSPEC: CO 2 Reduction to Formate; Syn-Gas (H 2 :CO) Bias-Free Water Splitting Tandem DSPECs for CO 2 reduction and bias-free water splitting Integrated PEC/formate-oxygen fuel cell for off-grid energy conversion and storage CO 2 /H 2 O/H + reduction to syngas (2H 2 :CO) Syngas CH 3 OH hydrocarbons by Fischer-Tropsch synthesis

6 Chromophore-Catalyst Assemblies Strategies (Kirk Schanze) Co-Loaded JACS, 2013, JACS, 2014, 9773 Molecular Overlayers Inorg. Chem., 2012, 8637 Polymer Scaffolds Polym. Chem., 2014, 2363 JPCL, 2012, 2457 Layer-by-Layer ACIE, 2012, Chem. Sci., 2014, 3115 JPCA, 2014, Electro-assembly JACS, 2013, JACS, 2014, 6578 Surface Assembled Peptide Scaffolds JCPB, 2013, 6352 JACS, 2013, 5250 Inorg. Chem., 2012, Inorg. Chem., 2014, 8120 Pre-formed Molecular Assemblies ACIE, 2009, 9473 Inorg. Chem., 2012, 6428 JACS, 2012, JACS, 2013, 2080 JPPC, 2013, ACIE, 2013, JPCL, 2011, 1808

7 Interfacial Dynamics on TiO 2 in Water. TiO 2 -[Ru a II -Ru b II -OH 2 ] 4+ (John Papanikolas) [(4,4 -(PO 3 H 2 -CH 2 ) 2 -bpy) 2 Ru a (bpy-nh-co-py)ru b (bpy)(oh 2 )] ps e hυ ps e 1 μs 0.1 M HClO 4 From fsec to msec Chromophore e Dennis Ashford Catalyst

8 Single Site Catalysis of Water Oxidation, 2008 Mechanism. 2H 2 O O 2 + 4e - + 4H + (Blue Dimer 1982) O 2 Loss O---O bond formation PCET (1981) Binstead et al., JACS, 1981,103, 2897 [Ru(tpy)(Mebim-py)(OH 2 )] 2+ k cat (2) ~ 2.0 s -1 (0.1 M HNO 3 ) 2 weeks - 43,400 turnovers (ph = 7, 0.1 M H 2 PO 4- /HPO 4 2- ) 4+ Thummel, JACS, 2005 Concepcion, Chen, JACS, 2008, 2010; PNAS, 2010, 2012; Inorg. Chem., 2010 [(bpy) 2 (H 2 O)Ru III ORu III (H 2 O)(bpy) 2 ] 4+ Gersten, et al., JACS, 1982, 14, 4029

9 Specific Base Catalysis Atom-Proton Transfer (APT) and OH - Attack I ( A) (a) M 0.01 M 0.05 M 0.1 M OAc - (GC; 0.1 M KNO 3 ; 100 mv/s) Concerted Atom-proton transfer: Rate enhancements of > weeks - 43,400 turnovers (ph = 7, 0.1 M H 2 PO 4- /HPO 4 2- ) E (V vs. Ag/AgCl) 800 (a) ph = 7.45, pk a = ph = 5, pk a = 4.75 ph = 2.4, pk a = 2.15 HPO 4 2- {Ru V =O 3+ + H 2 O M III -O-OH 2 3+ } I ( A) 400 OAc [B - ] H 2 PO 4 - High ph. Direct OH - attack Chen, Meyer, Concepcion, Yang, PNAS, 2010; Tamaki et al., JACS, 2014

10 Surface Water Oxidation on nanoito Water Oxidation Cycle + 1 μm Unstable toward hydrolysis in base! nanoito on FTO (Sn(IV):In 2 O 3 ) Z. Chen, P. Hoertz, Dalton Trans., 2010, 6950

11 Atomic Layer Deposition (ALD) Surface Stabilization Rate Enhancement of 10 6! (Vannucci, Alibabaei, Hanson) k ~ 10 4 s -1 -RuP 2+ (Al 2 O 3 ) Alex Lapides, Chris Dares Water Oxidation: k(ph 11; 1M PO 43 ))/k(ph1) = 10 6! Atom-Proton Transfer to PO 4 3- ; OH - attack

12 Chromophore-Catalyst Assembly Mechanism of water oxidation (Norris, Concepcion) Electron Atom Proton Transfer i/ A mv/s CV SW E/V vs. NHE

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

14 Solar Water Splitting. Atomic Layer Deposition Core/Shell Advantage (Alibabaei, Brennaman, Farnum) e - e - nanoito TiO 2 e nm TiO nm Core/Shell Advantage 3.6 nm shell nanoito/tio 2 FTO FTO nanoito/tio 2 -[Ru a II -Ru b II -OH 2 ] 4+ Pt e - 4h Parsons NCSU PtFTO nanoito/tio 2 -[Ru a II -Ru b II -OH 2 ] 4+ + O 2 Pt + 2H APCE = 4.5% 455 nm E bias = -0.2V Current ( A) Time (sec)

15 Comparison: SnO 2 /TiO 2 and nanoito core/shells Photoanodes for water splitting (Alibabaei) Overlayer TiO 2 or Al 2 O 3 at ph 4.6 in HAc/Ac - ALD TiO 2 SnO 2 Or nanoito FTO 3.6 nm TiO nm Core/Shell 3-4 nm of TiO 2 TiO 2 (3.3 nm); Pt counter, 200 mv (vs Ag/AgCl) in 0.5 M LiClO 4 (455nm LED at 46.2 mw/cm 2, E bias = -0.6 V) APCE (445nm) core APCE nanoito 4.5% SnO 2 >20%

16 Water Splitting DSPEC: Maximize Efficiency, Stability Challenges, New Assembly Strategies Surface assembly, new strategies Surface stabilization Avoid losses from oxidized chromophores Control rates and interfacial dynamics Extend light absorption further into the visible Implement tandem configurations Donor-Acceptor dye Phosphonated Porphyrins (Nayak) Water Oxidation Catalyst Organic Dyes (Wee)

17 Chromophore-Catalyst Assemblies New Assembly Strategies (Ashford, Chem. Rev., 2015) TiO 2 RuP 2+ (10AO)-RuCat-OH nm Al 2 O 3 TiO 2 Derivatized Polymers (U Florida, Georgia Tech) Al 2 O 3 ALD Mummy Assemblies (Lapides) Intra-Cavity Electro-Assemblies (Fang)

18 Electro-Assembly DSPEC TiO 2 -RuP- Ru(bda) Ashford, Sherman et al. ACIE, 2015 RuPdvb Chromophore Catalyst 0.1 M H 2 PO 4- /HPO 4 2- ph 7; 0.4 M NaClO 4 ; AM1 White light 100 mw cm -2 ; E bias = -0.4V vs. SCE RuP-Ru(bda) RuP Light on Light off RuP-Ru(bda) RuP SnO 2 -RuP O 2 TiO 2 Collector (ITO) electrode V vs. SCE SnO 2 /TiO 2 Core/Shell

19 CO 2 reduction, j CO, are relatively s of the electrolysis experiments g dissociative character. A mass ay exist resulting in a constant Electrocatalyzed CO 2 Reduction Selectivity, Aqueous, Rapid, Robust (Alex Miller) Controlling Electrocatalytic CO 2 Reduction Selectivity In Water Ru catalysts reduce CO 2 to syn gas with tunable H 2 :CO ratio Ir catalysts reduce CO 2 to formate with no H 2 or CO byproduct Nanoparticle film catalysts produce CO, formate, CH 4 N N N N OH 2 Ru N N r syngas Proc. Natl. generation Acad. Sci., catalyzed 2012, 109, by Energy Environ. Sci., 2014, 7, 4007 Chem. Commun., 2014, 50, (Chen, Kang) O O H Ir PtBu 2 NCMe H PtBu 2 J. Am. Chem. Soc., 2012, 134, 5500 Chem. Sci. 2013, 4, 3497 J. Am. Chem. Soc. 2014, 136, 1734 (Zhang) Continuous, large-scale formate production Angew. Chem. Int. Ed. 2014, 53, 8709 sities j (blue rhombus) and partial

20 Photocathodes for CO 2 Reduction NiO and beyond NiO (Jim Cahoon) Redesigned 2D NiO Zinc-cobalt oxide Spinel Zn 2+ Co 2+ Co 3+ New cathode oxides Ni(OH) 2 P-type DSSC Improved Charge Transport and Device Performance Substitution of Zn 2+ into tetrahedrally coordinated Co 2+ results in p-type behavior. Co-O Zn-O FTO Mercado and Nozik

21 Energy Frontier Research Center Solar Fuels SCIENTIFIC ACHIEVEMENTS DSPEC: Modular approach, assembly design Application of core/shell structures to water splitting Water oxidation catalysis Assembly based interfacial dynamics Selective reduction of CO 2 to formate or syngas 206 peer-reviewed publications (h-index 35) 65% co-authored by >1 senior investigator 24 patent applications World-class user facilities in catalysis, spectroscopy, photolysis, device fabrication, synthesis - staffed by Ph.D. research scientists TRAINING THE ENERGY WORKFORCE OF THE FUTURE Trained or in training: 60 postdoctoral fellows 80 graduate students 30 undergraduates 50 graduate degrees awarded > 120 careers in industry, academia, government, policy, public sector

22 EFRC MODULAR INTEGRATED TEAM-BASED RESEARCH Tom Meyer Director, John Papanikolas Deputy Director, Jerry Meyer Deputy Director, Maurice Brookhart Jim Cahoon Jillian Dempsey Gary Glish Yosuke Kanai Rene Lopez Andy Moran Alex Miller Jim Muckerman* BNL Royce Murray Art Nozik* UC Boulder/NREL John Reynolds* Georgia Tech Kirk Schanze* U Florida Cindy Schauer Joe Templeton Marcey Waters

23 Annual EFRC Research Review with External Advisory Board May 2014