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Towards Efficient Solar Energy Conversion and Storage Devices—the p-type Dye-sensitized Solar Cell and Sodium-Oxygen Battery

He, Mingfu
http://rave.ohiolink.edu/etdc/view?acc_num=osu1480521221820685

Abstract Details

2016, Doctor of Philosophy, Ohio State University, Chemistry.
To meet the growing worldwide demand of energy, efficient solar energy conversion and energy storage systems are highly desired. The dye-sensitized solar cell (DSC) and Na-O2 battery represents promising solutions to achieve the solar energy-to-electricity conversion and the electricity storage, respectively. This dissertation details the work on 1) improving the performance of the p-type DSC via sensitizer design and mechanistic investigation and 2) developing a concentrated electrolyte to achieve superior cycle life in the Na-O2 battery. The sensitizer plays a critical role in harvesting light energy in the p-type DSC. A panchromatic cyclometalated Ru (II) complex, denoted as O18, is reported. This dye shows intense metal-to-ligand charge transfer transitions in the visible to near-IR region with the absorption tail extending to 800 nm. The panchromatic spectra response and enhanced molar extinction coefficient (ε = 1.9×104 M-1 cm-1 at 593 nm in solution) of O18 are attributed to the stabilization of the lowest unoccupied molecular orbital and the increased absorption cross section via rationally extending the π-conjugated system of 2,2'-bipyridyl (bpy) ligands. As a result, NiO solar cells sensitized with O18 show short-circuit currents up to 3.43 mA cm-2 and efficiencies up to 0.104 %, which are the best among all cyclometalated-Ru (II)-sensitized p-type NiO DSCs. Femtosecond transient absorption spectroscopy reveals decreased geminate recombination across the O18-NiO interface by 1 order of magnitude compared to our previous report. Searching alternative electrode material to NiO is also critical to improve the efficiency of the p-type DSC. Dye-sensitized tin-doped indium oxide (ITO) is discovered to work as a high-current photocathode and the working mechanism of this novel photocathode is investigated by combined spectroelectrochemical and transient absorption spectroscopic techniques. The hole injection from the photoexcited dye into ITO is proved as the first step of the electron transfer events, which explains the unexpected cathodic photocurrent from the dye-sensitized ITO photocathode. Alkali metal-oxygen batteries are of great interests for energy storage because of their unparalleled theoretical energy densities. Particularly attractive is the emerging Na-O2 battery because of the formation of superoxide as the discharge product. Dimethyl sulfoxide (DMSO) is a promising solvent for this battery but its instability towards Na makes it impractical in the Na-O2 battery. The enhanced stability of Na in DMSO solutions containing concentrated sodium trifluoromethanesulfonimide (NaTFSI) salts (> 3 mol/kg) is reported. Raman spectra of NaTFSI/DMSO electrolytes and ab initio molecular dynamics simulation reveal the Na+ solvation number in DMSO and the formation of Na(DMSO)3(TFSI)-like solvation structure. The majority of DMSO molecules solvating Na+ in concentrated solutions reduces the available free DMSO molecules that can react with Na and renders the TFSI anion decomposition, which protects Na from reacting with the electrolyte. Using these concentrated electrolytes, Na-O2 batteries can be cycled forming sodium superoxide (NaO2) as the sole discharge product with improved long cycle life, highlighting the beneficial role of concentrated electrolytes for Na-based batteries.
Yiying Wu, Prof (Advisor)
Claudia Turro, Prof (Committee Member)
Anne Co, Prof (Committee Member)
139 p.
Chemistry; Energy; Inorganic Chemistry; Molecules; Physical Chemistry
solar energy to electricity conversion

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Citations

  • He, M. (2016). Towards Efficient Solar Energy Conversion and Storage Devices—the p-type Dye-sensitized Solar Cell and Sodium-Oxygen Battery [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480521221820685

    APA Style (7th edition)

  • He, Mingfu. Towards Efficient Solar Energy Conversion and Storage Devices—the p-type Dye-sensitized Solar Cell and Sodium-Oxygen Battery . 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1480521221820685.

    MLA Style (8th edition)

  • He, Mingfu. "Towards Efficient Solar Energy Conversion and Storage Devices—the p-type Dye-sensitized Solar Cell and Sodium-Oxygen Battery ." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1480521221820685

    Chicago Manual of Style (17th edition)

osu1480521221820685
429
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This open access ETD is published by The Ohio State University and OhioLINK.