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The goal of this research was to develop a series of mixed-metal supramolecular complexes through systematic component variation to better understand the role of structural modification on basic chemical and photochemical properties including photocatalysis of H₂O to H₂. Varying bidentate polypyridyl terminal ligands (TL), non-chromophoric halides (X), or number of Ru(II) light absorbers (LA) tunes the electrochemical, spectroscopic, photophysical, and photochemical properties within the supramolecular architecture. Ru(II),Rh(III),Ru(II) trimetallics of the design [{(TL)₂Ru(dpp)}₂RhX₂](PF₆)₅ (TL = phen = 1,10-phenanthroline or Ph₂phen = 4,7-diphenyl-1,10-phenanthroline; dpp = 2,3-bis(2-pyridyl)pyrazine; X = Cl⁻ or Br⁻) covalently couple two Ru(II) LAs to a central Rh(III) electron collector (EC) through dpp polyazine bridging ligands (BL). Ru(II),Rh(III) bimetallics of the design [(TL)₂Ru(dpp)RhCl₂(TL′)](PF₆)₃ (TL = Ph₂phen or bpy = 2,2′-bipyridine; TL′ = Ph₂phen or tBu2bpy = 4,4′-Di-tert-butyl-2,2′-bipyridine) couple only one Ru(II) LA to a Rh(III) metal center through the dpp BL. The Ru(II),Rh(III),Ru(II) trimetallic and Ru(II),Rh(III) bimetallic complexes are synthesized using a building block approach, permitting facile modification of the supramolecular architecture throughout molecular assembly. Electrochemical analysis of both architectures displays a Ru-based HOMO tuned by TL identity (RuII/III = +1.62 V and +1.58 V vs. Ag/AgCl for TL = phen and Ph₂phen, respectively) and a Rh-based LUMO tuned by X identity (RhIII/II/I = -0.35 V and -0.32 V vs. Ag/AgCl for X = Cl⁻ and Br⁻, respectively). Modification of TL′ at Rh(III) within the bimetallics provided varying LUMO identity. The trimetallics and bimetallics are efficient light absorbers throughout the UV and visible with π⟶ π* intraligand (IL) transitions in the UV and Ru(dπ)⟶ligand(π*) metal-to-ligand charge transfer (MLCT) transitions in the visible. While X identity does not vary the light absorbing properties within Ru(II),Rh(III),Ru(II) trimetallics, TL identity and the number of Ru(II) LAs strongly impacts spectral coverage and the extinction coefficient. Photoexcitation of the Ru(dπ)⟶dpp(π*) ¹MLCT results in near unity population of the weakly emissive, short-lived Ru(dπ)⟶dpp(π*) ³MLCT excited state, which is efficiently quenched by intramolecular electron transfer to populate a non-emissive Ru(dπ)⟶Rh(dσ*) metal-to-metal charge transfer (³MMCT) excited state. Photolysis of the complexes in the presence of the sacrificial electron donor N,N-dimethylaniline (DMA) results in multi-electron collection at Rh, thereby converting Rh(III) to Rh(II) to Rh(I) accompanied by halide loss at each step. This establishes the Ru(II),Rh(III),Ru(II) and Ru(II),Rh(III) complexes as photochemical molecule devices (PMD) for photoinitiated electron collection (PEC). The ability of these systems to undergo multiple redox cycles, absorb light efficiently, populate photoreactive excited states, and collect electrons at a reactive Rh metal center fulfills the requirements for H₂O reduction photocatalysts. Photolysis of trimetallic or bimetallic complexes at 470 nm in the presence of DMA and H₂O substrate yields photocatalytic H2 production. Within [{(TL)₂Ru(dpp)}₂RhX₂]⁵⁺ trimetallics (TL = phen or Ph₂phen; X = Cl⁻ or Br⁻), varying the TL from phen to Ph₂phen and X from Cl⁻ to Br⁻ yielded the most active and robust photocatalyst with [{(Ph₂phen)₂Ru(dpp)}₂RhBr₂]⁵⁺ producing 44 ± 6 mL H₂, 610 ± 90 mol H₂/mol Rh catalyst, and 7.3% maximum quantum efficiency (max. ΦH₂) in a DMF solvent system after 20 h photolysis. The proposed mechanism of PEC suggests bimetallic systems might be prepared that are active photocatalysts. Ru(II),Rh(III) bimetallics are synthetically more challenging and the energetic proximity of dpp(π*) and Rh(dσ*) orbitals make electronic tuning with steric protection of the photogenerated Rh(I) difficult. Within [(TL)₂Ru(dpp)RhCl₂(TL′)]³⁺ bimetallics (TL = Ph₂phen or bpy; TL′ = Ph₂phen or tBu₂bpy), a careful balance of steric and electronic effects was required to produce active photocatalysts. The bimetallic [(Ph₂phen)₂Ru(dpp)RhCl₂(Ph₂phen)]³⁺ produces 1.1 ± 0.07 mL H₂, 81 ± 5 TON, and 0.88% max. ΦH₂ in a DMF solvent system after 20 h photolysis. This establishes the [(Ph₂phen)₂Ru(dpp)RhCl₂(Ph₂phen)]³⁺ complex as the first Ru(II),Rh(III) bimetallic to function as a homogeneous single-component H₂O reduction photocatalyst. This dissertation reports the detailed analysis of the electrochemical, spectroscopic, photophysical, and photocatalytic properties of [{(TL)₂Ru(dpp)}₂RhX₂]⁵⁺ trimetallic (TL = phen or Ph₂phen; X = Cl or Br) and [(TL)₂Ru(dpp)RhCl₂(TL′)]³⁺ bimetallic (TL = Ph₂phen or bpy; TL′ = Ph₂phen or tBu₂bpy) supramolecular complexes. The design of the molecular architecture and the intrinsic properties of each component contribute to the overall function and efficiency of these systems. The careful design, meticulous synthesis and purification, detailed characterizations, and methodical experimentation have led to an in-depth understanding of the properties and factors needed for more efficient photocatalytic reduction of H₂O to H₂. / Ph. D.

Fuel cell is a device that can directly convert chemical energy into electrical energy. For low-temperature fuel cells, catalysts are required. Fuel cells using Pt-based or other non-biological materials as catalysts are known as conventional fuel cells. Inspired from Nature, enzymes can be used as catalysts in fuel cells known as enzyme-based fuel cells. The conventional and enzymatic fuel cells share the same underlying electrochemical principles, while enzyme-based fuel cells have their intrinsic advantages and disadvantages due to enzyme properties. The objective of this thesis is to investigate the current/voltage/ power/stability capabilities of enzyme-based membrane-less H2 fuel cells in order to design the enzymatic fuel cells with improved performance. This thesis presents a facile, effective method for the construction of 3D porous carbon electrodes. The 3D porous carbon electrodes are constructed by compacting suitable carbon nanomaterials into discs. The 3D porous carbon electrodes, with large roughness, high specific surface area, and optimized pore size distribution, are able to increase the loading density of enzymes, that is, reaction sites per unit geometric electrode area. The high loading density of enzymes can result in the high current/power density of the enzyme-based membrane-less H2 fuel cells. Moreover, the large enzyme loading can bring about the improvement in fuel cell stability because current becomes limited by mass transport of dissolved gases rather than enzyme immobilization so that neither inactivation nor desorption of enzymes would influence the current output. Based on one type of 3D porous carbon electrodes, the maximum power density of enzyme-based membrane-less H2 fuel cells has increased to the mW•cm2 level by at least one order of magnitude and the half-life has also increased from several hours to one week. This thesis presents a method for the increase in power density otherwise limited by low cathodic currents due to meagre O2 in non-explosive H2-rich H2-air mixtures. The power density of enzyme-based membrane-less H2 fuel cells can be increased by re-proportioning cathode/anode geometric area ratio to balance the cathodic and anodic currents under such an unusual H2-air mixture. This thesis also demonstrates that the 3D porous carbon electrode can improve the apparent O2 tolerance of anodic catalysts – hydrogenases, which are very important for the fuel cell performance. The degrees of apparent O2 tolerance for both O2-tolerant and O2-sensitive [NiFe]-hydrogenases are greatly increased based on the 3D porous carbon electrodes, so that even an O2-sensitive [NiFe]-hydrogenase can be used as an anodic catalyst in the enzyme-based membrane-less H2 fuel cell under a non-explosive H2-rich H2-air mixture. This thesis presents a design of a test bed in which series and parallel connections of sandwich-like electrode stacks can be varied. The fuel cell test bed has demonstrated low-loss interconnects and efficient stack configuration. Operated under a non-explosive H2-air mixture containing only 4.6% O2 at 20 °C, the maximum volume power density of the fuel cell test bed exceeds 2 mW•cm3, capable of powering electronic gadgets, which is a good demonstration of electricity that originates from the buried active sites of enzymes and is transmitted by long-range electron hopping in accordance with Marcus theory.

<p>Since the discovery in 1977 that conjugated polymers can be doped to achieve almost metallic electronic conduction, the research field of conducting polymers has escalated, with applications such as light emitting diodes, solar cells, thin film transistors, electrochemical transistors, logic circuits and sensors. The materials can be chemically modified during their synthesis in order to tailor the desired mechanical, electronic and optical properties of the final product. Polymers are also generally possible to process from solution, and regular roll-to-roll printing techniques can therefore be used for manufacturing of electronic components on flexible substrates like plastic or paper. On top of that, the nature of conjugated polymers enables the creation of devices with novel properties, which are not possible to achieve by using inorganic materials such as silicon.</p><p>The work presented in this thesis mainly focuses on devices that utilize two rather unique properties of conducting polymers. Conducting polymers are generally electrochromic, i.e. they change color upon electrochemical oxidation or reduction, and can therefore be used as both conductor and pixel element in simple organic displays. As a result of the electrochemical reaction, some polymers also alter their surface properties and have proven to be suitable materials for organic electronic wettability switches. Control of surface wettability has applications in such diverse areas as printing techniques, micro-fluidics and biomaterials.</p><p>The aim of the thesis is to briefly describe the physical and chemical background of the materials used in organic electronic devices. Topics include molecular properties and doping of conjugated polymers, electrochromism, surface tension etc. This slightly theoretical part is followed by a more detailed explanation of device design, functionality and characterization. Finally, a glance into future projects will also be presented.</p> / ISRN/Report code: LiU-TEK-LIC-2005:50

published_or_final_version / Education / Master / Master of Education

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<p>Proton exchange membrane fuel cells (PEMFCs) are considered as one of the most promising alternative clean and sustainable energy sources to fossil fuels. In general, PEMFC is consisted of anodic and cathodic electrode assembly, electrolyte, and proton-exchange membrane. While renewable fuels, such as hydrogen gas and formic acid, get oxidized at the anode to produce protons, oxygen molecules are reduced to form water at the cathode. Platinum has been widely used for both anodic and cathodic reactions due to its excellent catalytic reactivity.</p> <p><br></p> <p>Significant effort has been devoted to improving the reactivity and selectivity of Pt-based catalysts by alloying with a second metal. AuPt alloy nanoparticles have been studied extensively for electrochemical formic acid oxidation reaction, and isolated Pt species are recognized as the most active sites. While the majority body of literature focuses on structure-reactivity relationships</p> <p>based on as-synthesized materials, less attention is paid to the structural evolution during electrochemical catalysis. In this work, we develop a colloidal synthetic method to deposit Pt shell onto Au nanoparticles with variable thickness to study the microstructural evolution under electrocatalytic formic oxidation. We find that Pt atoms are submerged from the surface to form isolated Pt species in the first 100 cycles, which show enhanced FAO activity by shifting the reaction pathway. Additional CV scanning causes further depletion of Pt from the surface, resulting in the deactivation of the catalyst.</p> <p><br></p> <p>Despite the high activity of Pt-based catalysts, the use of these materials is limited by its high cost. Recently, transition metal sulfides such as cobalt sulfides have been found to show comparable activity to Pt-based catalysts in pH 7 ORR. However, it is challenging to isolate the role of coordination environment amidst multiple geometries and oxidation states that exist within any given phase. In this effort, we synthesize isolated Co atoms supported on colloidal WS₂nanosheets. By doing post synthetic treatment on these nanosheets, we are able to achieve a range of Co-S coordination number. Correlating Co-S CN to their ORR activities, we find the optimal active sites for ORR in neutral media possess a Co-S coordination number of 3-4.</p>