Supplementary Fig.1 The energy diagram of a solar-battery composed of a single

Transcription

1 Supplementary Fig.1 The energy diagram of a solar-battery composed of a single semiconductor-liquid junction photoelectrochemical cell (SC stands for the semiconductor) Supplementary Fig.2 The cyclic voltammetry of the I 3 - /I - redox shuttle in DMSO solvent with argon and oxygen atmosphere

2 Supplementary Fig.3 Detailed electrochemical, Raman, FTIR, XRD and SEM analyses of the Li-O 2 battery performance with I - 3 /I - redox shuttle: (a). The deep discharge-charge curve of the Li-O 2 battery at different current density; (b). The Raman spectra of the Li-O 2 battery s oxygen electrode after different cycles of discharging and charging process; (c). The ART-FTIR spectra of of the Li-O 2 battery s oxygen electrode after different cycles of discharging and charging process; (d). The X-ray diffraction (XRD) patterns of the Li-O 2 battery s oxygen electrode after discharging and charging process; (e) and (f). Representative SEM images of the discharging product on the oxygen electrode.

3 Supplementary Fig.4 The X-ray photoelectron spectroscopy (XPS) analyses of the oxygen electrode after the battery discharging process: (a) standard Li 2 O 2 pellet and (b) Discharging product on the oxygen electrode. All the spectra were calibrated by C 1s (C-C/C-H peak) at ev (same below).

4 Supplementary Fig.5 The XRD pattern of the TiO 2 nanorods decorated on Ti gauze as the photoelectrode Supplementary Fig.6 The light-response of the charging voltage of a solar-battery when illumination was switched from on to off

5 Supplementary Fig.7 The determination of Li 2 O 2 amount on the oxygen electrode before and after a solar-battery charging process Supplementary Fig.8 The Raman spectra of the solar battery oxygen electrode after discharging and charging process

6 Supplementary Fig.9 The XPS analyses of the Li anode in the solar-battery: (a) fresh-cut Li metal; (b) Li anode before battery cycling (pretreated in 0.1 M LiClO 4 / PC solution and then immersed in 0.1 M LiI / 1.0 M LiClO 4 / DMSO electrolyte) and (c) Li anode after battery cycling.

7 Supplementary Fig.10 The XPS analyses of the oxygen electrode in the solar-battery: (a) Pristine P50 carbon paper; (b) the carbon paper oxygen electrode that has been immersed in the electrolyte overnight before cycling (washed by dimethoxyethane(dme) before XPS analysis) and (c) the carbon paper electrode after cycling.

8 Supplementary Fig.11 The XPS analyses of the photoelectrode in the solar-battery: (a) TiO 2 nanorods on Ti gauze before dye sensitization; (b) the Dye sensitized TiO 2 photoelectrode and (c) the photoelectrode after solar-battery cycling.

9 Supplementary Fig.12 The solar-battery based on hematite photoelectrode: (a). representative SEM image of the hematite nanorods grown on the Ti gauze; (b). the light response of the hematite based solar-battery; (c) the long-term cyclability of the hematite photoelectrode based solar-battery

10 Supplementary Discussion Cyclic voltammetry(cv) study for the I - 3 /I - redox couple The redox potential of I - 3 /I - couple is at about 3.55V (vs Li + /Li, same reference below). 1-2 The oxidation peak occurred ~ 4.15 V and the drastic increasing of current when scanned beyond 4.2 V are attributed to the decomposition of DMSO solvent. 3-6 Detailed analyses and discussion of the Li-O 2 battery performance with I - 3 /I - redox shuttle The batteries with LiI can be charged with a voltage around 3.6 V even at a current flow as high as 0.47 macm -2. As the current density increased, the capacity decreased. This is attributed to the limited charge transportation and the resistance associated with solid-state Li + diffusion in the bulk insulating Li 2 O 2 particles. 7 During cycling, lithium carbonate (Li 2 CO 3 ) was detected by FT-IR as the main discharging byproduct according to the infrared spectroscopy. Its formation is attributed to the side-reactions that occurred on the carbon paper oxygen electrode/ DMSO solvent interface. 6,8-10 By optimizing the oxygen electrode and anode materials as discussed in previous literature 4,8,10-13, these side-reactions can be eliminated and the battery performance can be further improved. Both the Raman and XRD results showed that the Li 2 O 2 phase is formed after the discharging process and disappears after the charging process. The SEM images show that after the discharging process, particles with a toroid morphology and a size of nm, have been deposited on the oxygen electrode. Such morphology is in consistent with the Li 2 O 2 that reported in

11 literature. 14 The XPS analysis of the carbon oxygen electrode after battery discharging process C 1s XPS: The surface of standard Li 2 O 2 contained a small amount of carboxylate group since Li 2 O 2 is reactive even with adventitious carbon. After discharging, the main carbon peak was from adventitious carbon and there was very little amount of carboxylate group on the surface, probably due to contaminations that introduced during the sample transferring process. O 1s XPS: The O 1s peak of Li 2 O 2 pellet was at ~531.0eV, in consistent with previous literature 15. After the discharging process, the main product was Li 2 O 2 with a very small amount of Li 2 CO 3 as byproduct. Li 1s XPS: The Li 1s peak at ~54.5 ev indicated the discharge product as Li 2 O There was a little I on the surface of the oxygen electrode after discharging due to the residual LiI from the electrolyte. 16 Molar ratio of lithium to oxygen: The ratio of lithium to oxygen (O 1s peak at ~531.0 ev for Li 2 O 2 ) can be calculated by the area and the relative sensitivity factor (RSF) of each element: Lithium Oxygen Area Relative Sensitivity factor The ratio of Li : O = (Area of Li 1s / RSF Li 1s ): (Area of O 1s / RSF O 1s ) = :1, matching well with the 1:1 ratio in Li 2 O 2.

12 The XPS analysis of the Li anode of the solar-battery C 1s XPS: For the fresh-cut Li metal, the C 1s XPS spectrum showed that most of the carbon was from C-C bond, caused by the adventitious carbon. Besides trace amount of carbon from ethers /alkoxides (286.6 ev) and esters /carboxylates (288.9 ev), a small amount of C-OH and carbonate was also observed, due to the fast surface passivation of Li by residual CO 2 and H 2 O in the glovebox. For the anode before battery cycling, the pretreatment introduced Li 2 CO 3 on the metal surface, as a passivation layer which stabilized the Li foil. 4 After the battery cycling, the amount of Li 2 CO 3 increased. O 1s XPS: For the fresh-cut Li metal, the O 1s signal was still detectable since it is hard to totally avoid the surface oxidation through the sample transferring process. It matched well with the reported result for commercial Li metal without surface etching. 17 For both the Li anode before and after battery cycling, the O 1s spectra confirmed the existence of Li 2 CO 3 on the Li metal surface. Li 1s XPS: For fresh-cut Li metal, the surface oxidation caused the Li-O peak at 54.5 ev. 15,18 For the Li anode before battery cycling, the I 4d peak was also observed, due to the residual LiI (from the electrolyte) that left on the Li anode. 16 After battery cycling, the formation of Li 2 CO 3 was observed here, agreeing with the C 1s and O 1s spectra. I 3d XPS: For the Li anode before battery cycling, the I 3d signal was caused by the LiI residue from the electrolyte. 19 After battery cycling, there was no detectible I 3d

13 signal on the Li anode. S 2p XPS: The S 2p spectra changed after the battery cycling, indicating the Li had reacted with DMSO to certain extent during the cycling To summarize, the 0.1M LiClO 4 / PC pre-treatment for Li foil has introduced a passivation layer which mainly consists of Li 2 CO 3. It helps to stabilize the anode from reacting with DMSO. However, the anode is not 100% stable in DMSO electrolyte. Reactions between the Li anode and DMSO still occur after long-time cycling. The XPS analysis of the oxygen electrode of the solar-battery C 1s XPS: The carbon paper oxygen electrode before cycling showed very similar spectrum as the pristine P50 carbon paper. After battery cycling, several different carbon peaks appeared. They can be assigned to the C-S bond 22, ethers/alkoxides 20 and carbonates 19, respectively. O 1s XPS: The O 1s peak for pristine P50 was very weak since it didn t contain oxygen. There were some signals C-O or O-C-O for the carbon paper oxygen electrode before cycling. After battery cycling, the peaks of C-O bond and Li 2 CO 3 were observed. Li 1s and I 4d XPS: The Li 1s spectra confirmed the formation of Li 2 CO 3 on the carbon oxygen electrode after cycling. The I 4d peak was also observed, due to the residual LiI on the oxygen electrode. 16 I 3d XPS: The I 3d spectra confirmed the residual I - (from LiI) on the oxygen electrode after battery cycling.

14 S 2p XPS: The result showed that certain reactions have happened between the carbon oxygen electrode and the DMSO solvent during the battery cycling, causing the formation of SO 2-4. The observation of S 2p peak of C-SO 2 -C also agreed well with the C-S bond from C 1s XPS spectra. To summarize, the P50 carbon paper oxygen electrode is chemically stable in the DMSO electrolyte. However, the battery cycling would introduce reactions between the oxygen electrode and electrolyte, forming Li 2 CO 3 as the main by-product as well 2- as some SO 4 species. The XPS analysis of the photoelectrode of the solar-battery O 1s XPS: The shift of O 1s after battery cycling was attributed to the OH group that formed on the TiO 2 surface 23, which is probably related to the decomposition product of N719 dye molecules. Ti 2p XPS: After cycling, the Ti 2p peak shifted to a lower energy, which might be caused by the change in the surface dipole or the shift of Fermi level of electrons in TiO C 1s and Ru 3d XPS: After sensitized by N719, the C 1s peak shifted to higher energy (from ev to ev) due to the overlap with Ru 3d 3/2 peak The peak from Ru 3d was observed after the dye sensitization. However, after battery cycling, no Ru peak was observed, indicating that dye molecules were decomposed and detached to the TiO 2 surface. To summarize, the XPS spectra of the photoelectrode have revealed that the

15 decomposition of the N719 sensitizer happens during the battery cycling and is the main cause for the fade of our device. The solar-battery based on hematite photoelectrode Compared to the dye-sensitized TiO 2, the hematite has a better stability as an inorganic compound. The conduction band edge of hematite is about +3.4 V (vs Li + /Li). The material has an optical band gas as about 2.1 ev. 27 Therefore, it is suitable to be used as a light-absorber to construct a single semiconductor-liquid junction photovoltaic cell. When it is applied in our solar-battery as a photoelectrode, we expect a charging voltage reduction of about 100 mv. The hematite nanorods were hydrothermally grown on a 80-mesh Ti gauze. 28 The solar-battery was assembled with the hematite decorated Ti gauze as photoelectrode and all other parameters kept unchanged. The charging voltage fluctuation was observed when illumination removed. This clearly proves that hematite also acts as a photoelectrode in the solar-battery. The comparison of charging voltage with and without illumination clearly shows that the hematite photoelectrode was generating a photovoltage about 50 mv. This result agreed with the conduction band edge value of hematite (i.e. ~3.4 V vs Li + /Li). Since the inorganic hematite does not have the decomposition issue, the solar-battery can be cycled for a long time and presented a much better stability compared to the ones with dye-sensitized TiO 2 photoelectrode.

16 Supplementary References: 1 Gibson, E. A. et al. Role of the Triiodide/Iodide Redox Couple in Dye Regeneration in p-type Dye-Sensitized Solar Cells. Langmuir 28, (2012). 2 Boschloo, G. & Hagfeldt, A. Characteristics of the Iodide/Triiodide Redox Mediator in Dye-Sensitized Solar Cells. Accounts of Chemical Research 42, (2009). 3 Jung, H.-G., Hassoun, J., Park, J.-B., Sun, Y.-K. & Scrosati, B. An improved high-performance lithium air battery. Nature Chemistry 4, (2012). 4 Peng, Z., Freunberger, S. A., Chen, Y. & Bruce, P. G. A reversible and higher-rate Li-O 2 battery. Science 337, (2012). 5 Chen, T. et al. An Integrated Energy Wire for both Photoelectric Conversion and Energy Storage. Angewandte Chemie International Edition 51, (2012). 6 Bryantsev, V. S. et al. The Identification of Stable Solvents for Nonaqueous Rechargeable Li-Air Batteries. J Electrochem Soc 160, A160-A171 (2013). 7 Lu, Y.-C. et al. The discharge rate capability of rechargeable Li-O 2 batteries. Energy & Environmental Science 4, (2011). 8 Ottakam Thotiyl, M. M., Freunberger, S. A., Peng, Z. & Bruce, P. G. The Carbon Electrode in Nonaqueous Li O 2 Cells. Journal of the American Chemical Society 135, (2012). 9 Trahan, M. J., Mukerjee, S., Plichta, E. J., Hendrickson, M. A. & Abraham, K. M. Studies of Li-Air Cells Utilizing Dimethyl Sulfoxide-Based Electrolyte. J Electrochem Soc 160, A259-A267 (2013). 10 McCloskey, B. D. et al. Twin Problems of Interfacial Carbonate Formation in Nonaqueous Li O 2 Batteries. The Journal of Physical Chemistry Letters 3, (2012). 11 Chen, Y., Freunberger, S. A., Peng, Z., Fontaine, O. & Bruce, P. G. Charging a Li O 2 battery using a redox mediator. Nature Chemistry 5, (2013). 12 Thotiyl, M. M. O. et al. A stable cathode for the aprotic Li O 2 battery. Nature Materials (2013). 13 Chen, Y., Freunberger, S. A., Peng, Z., Bardé, F. & Bruce, P. G. Li O 2 Battery with a Dimethylformamide Electrolyte. Journal of the American Chemical Society 134, (2012). 14 Lu, J. et al. Aprotic and Aqueous Li O 2 Batteries. Chemical Reviews 114, (2014). 15 Yao, K. P. C. et al. Thermal Stability of Li 2 O 2 and Li 2 O for Li-Air Batteries: In Situ XRD and XPS Studies. J Electrochem Soc 160, A824-A831 (2013). 16 Brown, M. A., Ashby, P. D., Ogletree, D. F., Salmeron, M. & Hemminger, J. C. Reactivity of ozone with solid potassium iodide investigated by atomic force microscopy. The Journal of Physical Chemistry C 112, (2008). 17 Shiraishi, S., Kanamura, K. & Takehara, Z. I. Influence of initial surface condition of lithium metal anodes on surface modification with HF. J Appl

17 Electrochem 29, (1999). 18 Younesi, R., Norby, P. & Vegge, T. A New Look at the Stability of Dimethyl Sulfoxide and Acetonitrile in Li-O 2 Batteries. Ecs Electrochem Lett 3, A15-A18 (2014). 19 Morgan, W. E., Van Wazer, J. R. & Stec, W. J. Inner-orbital photoelectron spectroscopy of the alkali metal halides, perchlorates, phosphates, and pyrophosphates. Journal of the American Chemical Society 95, (1973). 20 Lee, H. et al. Chemical aspect of oxygen dissolved in a dimethyl sulfoxide-based electrolyte on lithium metal. Electrochim Acta 123, (2014). 21 Roberts, M. et al. Increased Cycling Efficiency of Lithium Anodes in Dimethyl Sulfoxide Electrolytes For Use in Li-O 2 Batteries. ECS Electrochem Lett 3, A62-A65 (2014). 22 Stankovich, S. et al. Stable aqueous dispersions of graphitic nanoplatelets via the reduction of exfoliated graphite oxide in the presence of poly(sodium 4-styrenesulfonate). J Mater Chem 16, (2006). 23 Sham, T. K. & Lazarus, M. S. X-Ray Photoelectron-Spectroscopy (XPS) Studies of Clean and Hydrated TiO 2 (Rutile) Surfaces. Chem Phys Lett 68, (1979). 24 Lee, K. E., Gomez, M. A., Regier, T., Hu, Y. F. & Demopoulos, G. P. Further Understanding of the Electronic Interactions between N719 Sensitizer and Anatase TiO 2 Films: A Combined X-ray Absorption and X-ray Photoelectron Spectroscopic Study. J Phys Chem C 115, (2011). 25 Lyon, J. E., Rayan, M. K., Beerbom, M. M. & Schlaf, R. Electronic structure of the indium tin oxide/nanocrystalline anatase (TiO 2 )/ruthenium-dye interfaces in dye-sensitized solar cells. J Appl Phys 104 (2008). 26 Singh, J. et al. XPS, UV-Vis, FTIR, and EXAFS Studies to Investigate the Binding Mechanism of N719 Dye onto Oxalic Acid Treated TiO 2 and Its Implication on Photovoltaic Properties. J Phys Chem C 117, (2013). 27 Sivula, K., Le Formal, F. & Grätzel, M. Solar Water Splitting: Progress Using Hematite (α-fe 2 O 3 ) Photoelectrodes. ChemSusChem 4, (2011). 28 Mulmudi, H. K. et al. Controlled growth of hematite (α-fe 2 O 3 ) nanorod array on fluorine doped tin oxide: Synthesis and photoelectrochemical properties. Electrochemistry Communications 13, (2011).