In SOFCs, we observe that the porous electrodes tend to agglomerate and thus decrease the cell performance over time. The agglomeration (or sintering) of a porous oxide can be understood as the diffusion of the oxide atoms along the surface of a material to minimize the surface energy of the structure. Therefore, even an ultrathin overcoat is expected to deter the sintering process and thus maintain the porous geometry for longer period of time. In this thesis, the actual role of YSZ overcoat in the ORR process is presented through a series of electrochemical analyses. Without an overcoat, a nanoporous Pt is significantly agglomerated during a high-temperature operation, and ORR kinetics becomes limited by the availability of TPB. An ultrathin YSZ overcoat significantly suppressed the sintering kinetics and preserved the morphology of its underlying Pt layer. More importantly, the overcoat acts as an excellent facilitator of the atomic oxygen species-mediated chemical process(es), which used to be rate-limiting in the ORR of a non-coated Pt/YSZ system.

In the next step, to understand the impact of spincoated layer on the interface of cathode/electrolyte, EIS data obtained at different temperatures and oxygen partial pressures. Beside SEM imaging and XRD, to support the hypothesis of ORR kinetics, infiltration and ALD coating also performed on different samples. We found out that spin-coated layer has smaller nanoparticle sizes and 3~4 times smaller nanocrystalinity that increase the active cites for dissosiative adsorption on the cathode side, comparing to the available cites on bare LNF. EIS data along with ALD coating also strongly support the hypothesis that ion conducting pass through the LNFGDC FL playes an important role in decreasing the polarization resistance comparing the bare LNF cathode as well. It helps the available cites not limited to the vicinity of GDC interlayer but be available in entire FL and the ion transport to the GDC interlayer through GDC nanoparticles paths.

To sum up, a combination of nanoscale treatments including cathode infiltration, metal oxide ALD coating, and cathode-electrolyte interface spin-coating pursued to achieve a significantly enhanced performance and durability by addressing the issues. In addition, I also performed a systematic studies on the change in electrochemical kinetics and a possible shift of bottleneck process by the treatments to better understand the effect of each of this nano-functionalization on oxygen reduction catalysis process in SOFCs.

This study focuses on the development of (La(0.6)Sr(0.4))(0.95)Co(0.2)Fe(0.8)O(3-d) LSCF-based cathodes for solid oxide fuel cells, with the purpose of lowering operating temperature and improving cell performance for commercialization. The first part of the study investigated the effects of using Co3O4 as a sintering aid, which was shown to enhance grain growth and interconnectivity and to dramatically lower cell impedance for both LSCF and LSCF- Gd(0.1)Ce(0.9)O(2-d) (gadolinia-doped ceria; GDC) composite cathodes. Co3O4 concentration was optimized for both the functional layer and the current collecting layer of the cathode. The second portion of the study explores the relationship between electrode layer thickness and cell impedance. It was shown that increasing functional layer thickness beyond a limiting value increases cell impedance, and that both ohmic resistance and polarization resistance asymptotically decrease with increasing thickness of the current collecting layer. Optimal thicknesses were found for each of the electrode layers. Finally, ultra-thin layers of yttria-doped ceria were deposited via atomic layer deposition (ALD) onto the functional layer of bilayer LSCF-GDC/LSCF cathodes as well as pure LSCF cathodes. It was shown that for both sets of cells, ohmic resistance initially increased with YDC deposition, but that subsequent increases in YDC thickness had an inverse relationship with ohmic resistance. This behavior has been observed in previous studies, and prolonged heat treatment will be needed to fully realize the benefits of the functionalization. Polarization resistance was negatively affected by YDC functionalization for both sets of cells due to a blocking of oxygen reaction sites on the surface of the LSCF electrode. In summary, Co3O4 concentration and electrode layer thickness were optimized to maximize performance for LSCF-based cathodes, and ALD functionalization was investigated as a method for further improving cathode performance.

The development of high efficiency and cost-effective bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is critical to a wide commercialization of metal-air batteries and unified regenerative fuel cells. Pt and IrO2 and their alloys have been applied as favorable catalysts due to their prominent performance. However, their high cost, low stability and susceptibility to poisoning greatly limit their widespread commercial adoption. Transition metal has been regarded as a good alternative to noble metal-based catalysts because of their tunable valence state, cost-effectiveness and variety of chemical composition, structure, and morphology. However, the catalytic activity of the transition metal electrocatalysts is largely hindered by their inherent corrosion and oxidation susceptibility. Therefore, my research mainly focusses on the development and modification of transition metal-based catalysts with enhanced catalytic activity towards ORR and OER.

In the first project (Chapter 4), I propose to investigate the beneficial effect of atomic layer deposition (ALD)-derived incorporation of transition metal-based materials for electrocatalytic oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Gas-evolving electrochemical reactions primarily occurs at the triple phase boundary regions where electrons, ions and reactant molecules meet altogether. Therefore, ALD-based dispersion of atomic-scale transition metal species can be an ideal approach for maximizing catalytically active sites. Our proposed research is to investigate the effect of ALD treatment of functionalized carbon-based materials with different transition metals on electrocatalytic ORR and OER reactions via both experimental and theoretical studies. In the first work, a mixed metal/metal oxide-integrated N-doped carbon is prepared by performing atomic layer deposition (ALD) of CeO2 nanodots on a three-dimensional Co and N co-doped carbon polyhedron nanostructure derived from zeolitic imidazolate framework (ZIF; a type of metal-organic framework). An optimally prepared hybrid catalyst achieved excellent bifunctional oxygen electrocatalytic performance comparable to or even better than noble metal-based benchmark catalysts (Pt/C for ORR and IrO2 for OER) thanks to the synergistic effect between Co and Ce, high-surface-area backbone structure, rich Co-Nx moieties and oxygen vacancies. This work proves the effectiveness of ALD in uniformly incorporating the second metal/metal oxide onto a monometallic system for enhanced electrocatalytic performance.

In the second project (Chapter 5), I demonstrate a unique 3D core-shell nanostructure for efficient OER electrocatalysis. Two-dimensional (2D) layered double hydroxides (LDHs) are promising as an effective electrocatalyst towards OER, but their poor conductivity and tendency to stack together limits their activity and durability as an electrocatalyst. Herein, 3D core-shell structures are synthesized through a facile one-step reaction strategy, in which the terephthalic acid and urea is employed as the organic ligand for the metal organic framework (MOF) precursor and surface coordination buffer between LDH and MOF. Benefiting from the hierarchical 3D microstructure with uniform nanosheets grown on the surface, the as-prepared electrocatalyst exhibits rich carbon edge sites and high electrochemical surface area. The representative sample (CoNi-BDC@LDH) achieves an OER activity with the overpotential of 280 mV at 100 mA cm−2 and robust cyclic and chronoamperometric stability. A series of quasi-operando studies by X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, Raman and Fourier-transform infrared spectroscopy further elucidate that Co-Ni acts as the main active site while the high valence state of Ni facilitates O2 desorption from O-O bond linking metal sites. The high OER performance is additionally attributed to a high valence state of metal ions in γ-NiOOH/CoOOH, lattice edge sites of carbon, and a synergistic effect between neighboring metal atoms.

In the third study (Chapter 6), a Co-Ni based LDH structure with thin layer coating of ceria and/or titania by ALD is synthesized. Benefiting from the result of the first two projects, ALD was applied to the LDH structure directly. The effects of tri-metal incorporation on the electrocatalytic properties of the resulting hybrid systems toward OER is further investigated. The primary electrochemical studies and XPS characterization results suggests the improved OER performance is mainly attributed to the synergistic effect between metal cations.

In this dissertation, there are three topics including nanoscale engineering effects on cathodes for intermediate-temperature solid oxide fuel cells, effects of mechanical and electrical application on atomic force microscopy, and ionic diffusivity and mobility study of oxygen reduction/evolution reaction by nanoscale in situ characterization via atomic force microscopy. Their abstracts are listed below.

Topic I: The impact of various infiltrates on the kinetics and rate-limiting step of oxygen reduction reaction (ORR) is examined with LaNi0.6Fe0.4O3-δ (LNF) as the cathode backbone of solid oxide fuel cells (SOFC). Multiple materials were infiltrated on the backbone. The dependencies of electrode polarization resistance on the precursor concentration, temperature, and oxygen partial pressure are presented, and related discussions are made to interpret the differences in ORR kinetics and the rate-determining step for ORR.

Topic II: Conductive atomic force microscopy (CAFM) has been widely employed to study the localized electrical properties of a wide range of substrates in non-vacuum conditions by the use of noble metal-coated tips. In this topic, the impact of mechanical and electrical stimuli on the apex geometry of gold-coated tips and electrical conduction properties at the tip-substrate contact is discussed by choosing gold and highly-ordered pyrolytic graphite as the representative tip and substrate materials, respectively.

Topic III: The ionic transport in solid oxides after becoming thermally activated is understood as hopping to point defects (i.e. oxygen vacancies), and the kinetics behind it are highly dependent upon the bonding state of the ionic species with their surrounding lattice environment. In this study we report the findings of our recent efforts to directly observe ionic transport in SrTiO3 (STO) and Y2O3-stabilized ZrO2 (YSZ)–the most widely used cathode material in intermediate temperature SOFC–by use of Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM).

Porous materials are ubiquitous in nature as well as in engineering applications. The pores provide exceptional properties of large surface area, efficient transport of mass and energy between the solid matrix, and fluid flowing through the pores and capillarity which facilitates liquid transport without external pumping. Designing and processing porous materials to meet engineering challenges are important for the advancement of society. Currently, porous materials are frequently used as electrode materials for energy storage, construction materials, and importantly, in the thermal management of electronic devices.

Thermal management of electronic materials plays a crucial role in the effective implementation of highly efficient devices. Recent advancements in efficient materials and device designs have paved the way for exceptional computing and electrical power transfer performances. A key bottleneck for the ubiquitous deployment of these devices are large heat fluxes generated by the devices. The inability to dissipate these fluxes limits device performance and often leads to device failure. Novel materials synthesis and engineering of materials for thermal management are key to scientific advancement and society at large.

Among the various techniques available, capillary-driven liquid-vapor phase change, facilitated by porous materials, has exhibited exceptional capabilities in efficiently dissipating large heat fluxes exceeding 1 kW/cm2. This supersedes the cooling performances of single-phase liquid or air-cooling strategies. To illustrate the challenge at hand for two-phase cooling, modern electronic devices can exceed junction heat fluxes of 5 kW/cm2. This is anticipated to increase as more sophisticated devices are developed to serve the needs of society, for example, large data centers, high-power lasers, nuclear fusion and fission reactors, electric vehicles, electric vertical takeoff and landing vehicles, and integrated three-dimensional chips, to name a few. There is a pressing demand for breakthrough research and development aimed at achieving highly efficient thermal management via two-phase heat transfer.

In this dissertation, we delve into approaches to leverage thin, free-standing porous materials to achieve liquid delivery through capillary action. We developed methods to characterize fluid flow properties in the free-standing meshes for two-phase flow conditions. We developed methods to enhance the wettability of mesh structures growing microstructures on the surfaces. The capillary-driven flow in these porous structures is enhanced by careful design of their surfaces to increase their wettability, with the aim of maintaining a thin, evaporating liquid film while retaining high fluid permeability. Our investigation extends to strategies for elevating the system's efficiency by controlling the distribution of liquid and vapor phases. We design and process a three-dimensional manifold that increases the efficiency of uniform fluid delivery and vapor escape during the two-phase heat transfer process. This delivery is targeted at laser-processed porous heat spreaders crafted from Aluminum Nitride (AlN). We identified AlN as an effective substrate material that can be used for liquid-vapor phase change cooling applications directly.

We assess the long-term reliability of AlN under the rigors of prolonged operational conditions for liquid-vapor phase change electronics cooling. We investigate the corrosion of AlN in contact with boiling water. We measure the corrosion rate and its dependency on different heat fluxes during boiling. Furthermore, we delve into corrosion mitigation strategies of AlN in pool boiling conditions. Particularly, we develop surface protections of AlN that effectively mitigate the corrosion behavior of AlN in pool boiling conditions. We find that a thin layer of alumina grown thermally by a one-step process of oxidation of AlN at elevated temperatures is effective in the corrosion protection of AlN.

The findings from this research including the experimental methods and mathematical models developed are expected to propel further research on materials engineering for two-phase electronics cooling of high heat flux dissipating devices and realizations of working commercial devices.

The studies presented in this thesis focus on developing non-precious metal electrodes for oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and hydrogen evolution reaction (HER), the core catalysis of fuel cells and electrolyzers. Metal oxides on carbon support are mainly considered as the catalytically active materials in this study. Two approaches of fabrication are presented: one based upon atomic layer deposition (ALD) and one by a wet synthesis process known as the solvothermal method. The resulting catalysts are characterized to reveal the process-performance relationship for ORR, OER, and HER. In the first study (Chapter 4), we demonstrate a bimetallic Co/Cu-embedded N-doped carbon structure for trifunctional catalysis of ORR, OER, and HER in alkaline media. A hybrid catalyst synthesized through a metal-organic framework-based process (M-NC-CoCu) enables active trifunctional catalysis due to its multi-faceted favorable characteristics. It is believed that a range of catalytically active sites are formed through the approach including well-dispersed tiny CuCo2O4 phases, a high concentration of pyridinic and graphitic N, and Cu-Ox, Cu-Nx, and Co-Nx moieties. In addition, a high-surface-area morphology with a high concentration of sp2 bonding, which is beneficial for facilitated electron conduction, further contributes to the performance as an electrocatalyst. The second study (Chapter 5) investigates the catalytic activities of titanium dioxide (TiO2) incorporated onto graphene oxygen (GO) by atomic layer deposition (ALD). The catalytic activity was systematically measured by cyclic voltammetry (CV). Evidence shows that TiO2 bonded on the surface of GO is catalytic active. An ALD treatment of TiO2 shows improvement in the catalytic activity compared to non-treated graphene. The ALD temperature also affects the catalytic performance. A higher temperature results in a higher catalytic activity, which is ascribed to the simultaneous reduction of GO and the addition of catalytically active TiO2/GO interfaces by ALD. In addition, there is also an optimal number of ALD cycles for enhanced catalytic activity. In the third study (Chapter 6), a zinc-based zeolitic imidazole framework (ZIF-8) is carbonized to form organized N-doped carbon nanostructures. The carbonized ZIF-8 (C-ZIF-8) was then used as a substrate (support) for ALD. Titanium (Ti) and/or cerium (Ce) precursors were introduced to the ALD chamber to form bimetallic (Ti and Ce) or monometallic (Ti or Ce) hybrids with C-ZIF-8. I investigated the effects of bimetal incorporation in the electrocatalytic properties of the resulting hybrid systems toward OER and HER. The optimization of ALD parameters, such as the number of cycles, temperature, and pressure for catalytic performance are also discussed.

This study focuses on developing non-precious metal electrodes for oxygen reduction reactions (ORR) and oxygen evolution reactions (OER), the core catalysis of fuel cells and electrolyzers, respectively. Specifically, metal oxides on carbon support are considered as the catalytically active electrode materials in this study. Two approaches of fabrication are presented: one based upon atomic layer deposition (ALD) and one by a wet synthesis process known as the solvothermal method. The resulting catalysts are characterized to reveal the process-performance relationship for ORR and OER.

The first study investigates the catalytic activities of titanium dioxide (TiO2) incorporated onto graphene oxygen (GO) by atomic layer deposition (ALD). The catalytic activity was systematically measured by cyclic voltammetry (CV). Evidence shows that TiO2 bonded on the surface of GO is catalytic active. Comparing the CV before and after ALD of TiO2 shows improvement on the catalytic activity after deposition of TiO2. Temperature effects, during deposition, were also measured by CV. The trends show that at higher temperature there is an increase in catalytic activity, which is due to the simultaneous reduction and addition of TiO2 during ALD. In addition, there is also an optimal amount of TiO2 that can be deposited for enhanced catalytic activity, which is 25 cycles.

In the second study, a bimetallic metal organic framework (MOF) was synthesized using cobalt and copper chloride, complexed with 2-aminoterephthalic acid and incorporated with graphene oxide (GO), which resulted in flower-like nanostructures. Effects of post-annealing on catalytic activity for this material were measured using CV and linear sweep voltammetry (LSV). This bimetallic MOF material showed both ORR and OER activity in an alkaline environment. In addition, as the annealing temperature was increased to 700°C, the ORR and OER catalytic capabilities improved for this material resulting in an ORR half-way potential at around 0.72 V and OER on-set potential of 1.57 V (at 10 mA/cm2). With the overall oxygen electrode performance gauged by the difference of ORR and OER metrics (E = EOER,j=10 – EORR,1/2 = 0.85 V), the bimetallic MOF material has a potential of serving as an excellent bifunctional electrocatalyst for regenerative fuel cells.

Well known for its centralized local economic system under the national equity principle, Japan has experimented with transforming this regional redistribution system into a new local economic system of governance for more autonomous local economic growth over the past decade. This new local economic governance has been characterized by the increasing involvement of social actors, such as large private corporations and local communities, in policy processes.

This dissertation reveals that new local economic growth strategies for the new local economic governance have operated under very different models in different regions of Japan, although all new local programs have been introduced under the banner of public-private partnership. New partnership programs in the local economic policy arena in the 2000s have moved toward the market model, in which local authorities pursue growth by attracting international business resources, in the major metropolitan areas around Tokyo, Osaka, and Nagoya, whereas they have moved toward the community model, in which local authorities purge growth by mobilizing local organizational resources, in the rest of Japan. The market model is embedded in market reform for deregulation that makes large private corporations' freer activities easy, whereas the community model is an attempt to strengthen the structure of endogenous networks among local authorities and local economic and social elites.

This dissertation highlights two variables to explain regional variations of local economic growth strategies: dual local economic structures and diverging politico-economic coalitions. First, under the rule of Koizumi Junichiro, a coalition of promoting market reform among neoliberal politicians and large private corporations has won politically over a coalition for maintaining national equity among politicians embedded in traditional conservative center-local linkages, local business groups, and local leadership of underdeveloped areas, in national politics. The regional redistribution mechanism stopped functioning in this political choice. Instead, market reform and local community participation have been introduced as alternatives to regional redistribution mechanisms. Second, the major metropolitan areas and other underdeveloped areas, which came to stand on equal conditions for autonomous local economic growth strategies under decentralization reforms, are characterized by different situations in attracting private investment. The competitive regions of the major metropolitan areas have taken the market model as their main local economic growth strategy because they are competitive to attract private investment. In contrast, the protected regions outside the major metropolitan areas have taken the community model as their key local economic growth strategy because they have less competitive local economic structure of fading industries and scare population for attracting private investment.

Over the past decade, reforms for public-private partnership in the local economic policy arena resulted in the disturbance of the Japanese way of balancing market powers and local interests in the postwar period. In the postwar period, the centralized regional redistribution mechanism, led by national politicians and central bureaucracies, functioned as a tool for social integration with consideration for national equity. However, experiments with the new form of local economic governance were not successful in balancing market reform with local community mobilization. The mobilization of local community resources could not match the political role of the regional redistribution mechanism outside the major metropolitan areas. In addition, market reform, which has been more effective in the advanced major metropolitan areas, has produced increasing regional economic disparity. Japan has faced a complicated stand-off between large private corporations detached from specific localities and local communities locked in place, which were connected by national political coordination mechanisms in the postwar period. Although each of two diverging local economic growth strategies has been effective in different regions, there was no national political mechanism for mediating local variations of these localized programs in the 2000s.