???????????? ?????? ???????????? ????????? ?????? ??? ?????? ?????????????????? ??????

Department of ChemistryThe environmental issues caused by the hydrocarbon energy sources have emerged as one of the most urgent challenges in 21st century. The development of clean and renewable energy technologies is critical to meet both the environment regulations and to circumvent dependence upon the fossil fuels. This situation has brought a new idea about the future society solely driven by hydrogen-based energy infrastructures, so-called hydrogen economy. The production and utilization of hydrogen via water electrolysis and fuel cells, respectively, are key ingredients to realize the hydrogen economy. However, the high cost of those devices hinders their wide adoption, which can be attributed primarily to the use of precious metal electrocatalysts such as Pt and Ir that are required for efficient operation. In this context, the development of active non-precious metal catalysts (NPMCs) is of great significance. In this dissertation, new NPMCs based on carbon nanotube (CNT) have been designed and prepared for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution reaction (HER), where the ORR is an important half-reaction that critically affects the fuel cell performance, while the OER & HER are involved in water electrolysis. CNT was selected as the carbon support owing to its high conductivity, chemical stability, and surface tunability, advantageous for electrocatalysis. In Chapter 2, we developed a facile and scalable synthetic method for carbon nanostructures comprising active heteroatom-doped carbon (HDC) layers coated on CNT (CNT/HDC), which was exploited as a metal-free ORR electrocatalyst. The preparation involves the adsorption of heteroatom-containing ionic liquid (IL) on the CNT walls via van der Waals and cationic-?? interactions and subsequent carbonization, yielding CNT/HDC core???sheath nanostructures. The design enables both the efficient utilization of surface active sites of HDC layers and high electric conductivity of the CNT core. The CNT/HDC catalyst exhibited high ORR activity and reaction kinetics comparable to a commercial Pt/C catalyst in alkaline media, and an excellent anion exchange membrane fuel cell (AEMFC) performance. The IL-derived CNT/HDC catalysts could be prepared using various types of IL precursors. Iron and nitrogen codoped carbon (Fe???N/C) catalysts have emerged as the most promising electrocatalysts for the ORR among various classes of NPMCs. A growing body of literature suggests that Fe???Nx species are major active sites in a Fe???N/C catalyst. Chapter 3 presents a general ???silica-protective-layer-assisted??? approach that can preferentially generate the catalytically active Fe???Nx sites in Fe???N/C catalysts while suppressing the formation of less-active large Fe-based particles. The catalyst preparation consisted of the adsorption of iron porphyrin precursor on CNT, silica layer overcoating, high-temperature pyrolysis, and silica layer etching, which yielded CNTs coated with thin layers of porphyrinic carbon (CNT/PC) catalysts. We found that the silica-coating step plays a decisive role in preferentially generating catalytically active Fe???Nx coordination sites, as revealed by temperature-controlled in situ X-ray absorption spectroscopy (XAS). The CNT/PC catalyst contained higher concentration of active Fe???Nx sites compared to the CNT/PC prepared without silica coating. The CNT/PC showed very high ORR activity and excellent stability in alkaline media. Importantly, an alkaline AEMFC with a CNT/PC-based cathode exhibited the highest current and power densities among NPMC-based AEMFCs. In addition, a CNT/PC-based cathode exhibited a high volumetric current density of 320 A cm???3 in acidic proton exchange membrane fuel cell. We also demonstrated the general applicability of this synthetic strategy to other carbon supports. Chapter 4 describes the investigation of active site structures of bifunctional oxygen electrode catalysts based on cobalt oxide (CoOx) under reaction conditions. Size-controlled (3???10 nm) cobalt oxide nanoparticles (CoOx NPs) supported on CNT were prepared, and served as model catalysts. Electrochemical in situ XAS suggested that the initial Co3O4 or CoO phase was transformed to Co3O4???CoOOH core???shell structures under the ORR and OER conditions regardless of particle sizes. Combined with the in situ XAS, cyclic voltammetry study revealed that Co2+/Co3+ and Co3+/Co4+ redox transitions are involved in the ORR and OER, respectively. We further examined the size-dependent electrocatalytic activities. The OER activity increased with decreasing NP size, which correlated to the larger amount of Co(III) species and larger surface area in smaller NPs. For the ORR, no particle size dependence was foundthe CoOx NPs mainly played an auxiliary role, promoting the reduction or disproportionation of peroxide generated from the two-electron reduction of O2 by CNT. In Chapter 5, we investigated the active site structure of NPMC comprising cobalt- and nitrogen-codoped carbon supported on CNT for the HER. For this purpose, CNT hybridized with cobalt phthalocyanic carbons (CNT/Co-PcC) were prepared via the silica coating strategy. A suite of Co???N/C catalysts that contain different concentrations of cobalt-based species (Co???Nx and Co@C) were prepared by controlling experimental parameters. The catalytic role of two Co-based sites for the HER in both acidic and alkaline media was investigated, which revealed that the HER activity in both media was linearly increased with the portion of the Co???Nx sites. This structure???activity relationship suggests that the Co???Nx sites are the major active sites while Co@C species have a minimal catalytic effect for the HER. In addition, reaction kinetics study over the CNT/Co-PcC catalyst allowed us to acquire a better understanding of the Co???Nx active sites for the HER.ope

Simple coordination complex-derived three-dimensional mesoporous graphene as an efficient bifunctional oxygen electrocatalyst

3D mesoporous graphene (mesoG) was synthesized from [Ni<inf>2</inf>(EDTA)] (EDTA = ethylenediaminetetraacetate). The material is comprised of interconnected 4 nm-sized hollow carbon shells composed of 3-4 layers of graphene and exhibits high bifunctional electrocatalytic activity as well as high durability for use in oxygen evolution and reduction reactions. This journal is ??? 2015 The Royal Society of Chemistryopen11

Catalyst design, measurement guidelines, and device integration for H2O2 electrosynthesis from oxygen reduction

The electrosynthesis of H2O2 via a two-electron pathway oxygen reduction reaction (2e??? ORR) has emerged as a promising way of carbon-free and on-site production of H2O2. Active and selective electrocatalysts for the 2e??? ORR are essential for achieving high O2-to-H2O2 conversion efficiency. In this review, we present the recent progress in the development of 2e??? ORR electrocatalysts including Pt-group-metal (PGM) and non-PGM atomically dispersed catalysts and metal-free heteroatom-doped carbons. The impact of the active sites and interface structures on the electrocatalytic process is summarized. Benchmarking of the electrocatalytic activities in terms of O2-to-H2O2 mass activity and site-normalized activity is presented to understand the current status of advancement and to provide an insight into possible future research directions. In addition, some guidelines and pitfalls in typical laboratory measurements for assessing 2e??? ORR performance are proposed. Finally, recent advances in high-current-density H2O2 electrosynthesis reactors and devices that exploit electrosynthesized H2O2 are introduced

Umbilical Arterial Blood Gas and Perinatal Outcome in the Second Twin according to the Planned Mode of Delivery

Purpose: To compare umbilical arterial gas parameters in the second twin of twin pregnancies according to the mode of deliver

Oxygen-deficient triple perovskites as highly active and durable bifunctional electrocatalysts for oxygen electrode reactions

Highly active and durable bifunctional oxygen electrocatalysts have been of pivotal importance for renewable energy conversion and storage devices, such as unitized regenerative fuel cells and metal-air batteries. Perovskite-based oxygen electrocatalysts have emerged as promising nonprecious metal bifunctional electrocatalysts, yet their catalytic activity and stability still remain to be improved. We report a high-performance oxygen electrocatalyst based on a triple perovskite, Nd1.5Ba1.5CoFeMnO9-delta (NBCFM), which shows superior activity and durability for oxygen electrode reactions to single and double perovskites. When hybridized with nitrogen-doped reduced graphene oxide (N-rGO), the resulting NBCFM/N-rGO catalyst shows further boosted bifunctional oxygen electrode activity (0.698 V), which surpasses that of Pt/C (0.801 V) and Ir/C (0.769 V) catalysts and which, among the perovskite-based electrocatalysts, is the best activity reported to date. The superior catalytic performances of NBCFM could be correlated to its oxygen defect rich structure, lower charge transfer resistance, and smaller hybridization strength between O 2p and Co 3d orbitals

Ordered mesoporous Co3O4 spinels as stable, bifunctional, noble metal-free oxygen electrocatalysts

We report the use of noble metal-free ordered mesoporous Co 3O4 spinels (meso-Co3O4), templated from KIT-6 mesoporous silica, as highly active and stable bifunctional electrocatalysts for both oxygen evolution and reduction reactions (OER and ORR, respectively). The meso-Co3O4 nanostructures showed high activity for OER in an alkaline medium (0.1 M KOH), which makes them comparable to the most active Ir/C catalyst and better than Co3O4 nanoparticles (NPs) and the Pt/C catalyst. Furthermore, meso-Co 3O4 exhibited enhanced stability, compared to Co 3O4 NPs. The enhanced activity and stability of meso-Co3O4 over Co3O4 NPs could be attributed to its high surface area and structural stability of the gyroid network structure in the meso-Co3O4 catalysts. The meso-Co3O4 nanostructures also showed promising activity for ORR and exhibited a methanol-tolerance superior to the Pt/C catalyst. The total overpotential of meso-Co3O4 for OER (at 10 mA cm-2) and ORR (at -3 mA cm-2) was 1.034 V, which is on a par with noble metal-based catalysts. This work demonstrates that directing metal oxides into mesostructures is a promising means of preparing highly active, stable, bifunctional oxygen electrocatalysts that can potentially replace expensive noble metal-based catalysts. This design strategy can be extended to other reactions relevant to energy conversion and storage applications.close17

Ordered mesoporous porphyrinic carbons with very high electrocatalytic activity for the oxygen reduction reaction

The high cost of the platinum-based cathode catalysts for the oxygen reduction reaction (ORR) has impeded the widespread application of polymer electrolyte fuel cells. We report on a new family of non-precious metal catalysts based on ordered mesoporous porphyrinic carbons (M-OMPC; M = Fe, Co, or FeCo) with high surface areas and tunable pore structures, which were prepared by nanocasting mesoporous silica templates with metalloporphyrin precursors. The FeCo-OMPC catalyst exhibited an excellent ORR activity in an acidic medium, higher than other non-precious metal catalysts. It showed higher kinetic current at 0.9a�...V than Pt/C catalysts, as well as superior long-term durability and MeOH-tolerance. Density functional theory calculations in combination with extended X-ray absorption fine structure analysis revealed a weakening of the interaction between oxygen atom and FeCo-OMPC compared to Pt/C. This effect and high surface area of FeCo-OMPC appear responsible for its significantly high ORR activity.open251

A case of isolated metastatic hepatocellular carcinoma arising from the pelvic bone

Reports of metastatic hepatocellular carcinoma (HCC) without a primary liver tumor are rare. Here we present a case of isolated HCC that had metastasized to the pelvic bone without a primary focus. A 73-year-old man presented with severe back and right-leg pain. Radiological examinations, including computed tomography (CT) and magnetic resonance imaging (MRI), revealed a huge mass on the pelvic bone (13×10 cm). He underwent an incisional biopsy, and the results of the subsequent histological examination were consistent with metastatic hepatocellular carcinoma. The tumor cells were positive for cytokeratin (AE1/AE3), hepatocyte paraffin 1, and glypican-3, and negative for CD56, chromogranin A, and synaptophysin on immunohistochemical staining. Examination of the liver by CT, MRI, positron-emission tomography scan, and angiography produced no evidence of a primary tumor. Radiotherapy and transarterial chemoembolization were performed on the pelvic bone, followed by systemic chemotherapy. These combination treatments resulted in tumor regression with necrotic changes. However, multiple lung metastases developed 1 year after the treatment, and the patient was treated with additional systemic chemotherapy