A systematic development of 2D alloy catalyst with synergistic performance of high lithium polysulfide (LiPS) binding energy and efficient Li+ ion/electron conduction is presented. The first section of work found that Li+ ions can flow through the percolated ion transport pathway in polycrystalline MoS2, while Na+ and K+ ions can easily flow through the percolated 1D ion channel near the grain boundaries. An unusually high ionic conductivity of extrinsic Li+, Na+, and K+ ions in 2D MoS2 film exceeding 1 S/cm was measured that is more than two orders of magnitude higher than those of conventional solid ionic materials, including 2D ionic materials. The second section of this dissertation focus on catalyzing the transformation of LiPSs to prevent the shuttle effect during the battery cycling by synthesizing 2H (semiconducting) – 1T (metallic) mixed phase 2D Mo0.5W0.5S2 alloy on CNF paper, using two step sputtering and sulfurization method. The lithium sulfur (Li-S) battery cell assembled with the 2D Mo0.5W0.5S2/CNF/S cathode shows a high specific capacity of 1228 mAh g-1 at 0.1C and much higher cyclic stability over 4 times as compared to the pristine cathodes. The high LiPSs binding energy of catalyst efficiently prevents the shuttling effect and corrosion of Li anode after long term stability test for over 400 cycles. The defect engineered MoWS catalyst on CNF showed significantly enhanced polysulfide transformation resulting in specific capacity of 1586 mAh g-1 at 0.05C for the full cell Li-S battery and much higher cyclic stability over 1000 cycles. Stacked layers of D-MoWS-CNF-S cathodes can result in an increased sulfur loading up to 10 mg cm-2 with highest achievable areal capacity of 13.5 mAh/cm2. The efficient sulfur utilization and reduced negative-to-positive capacity (N/P) ratio by D-MoWS catalyst significantly increased the gravimetric energy density to the highest reported value of 1090 Wh kg-1 w.r.t the total weight of anode and cathode.

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Dealloying refers to the partial, selective dissolution of the less noble component(s) of a binary or ternary alloy precursor, resulting in a noble-rich, porous structure that has high surface area. Such surface structure is beneficial for fuel cells (FC) because FC uses platinum (Pt), a scarce metal, to catalyze the oxygen reduction reaction (ORR) at the cathode surface. In order to characterize the benefit of the dealloying process in FC ORR catalysts with the rotating disk electrode (RDE) technique, a high surface area catalyst support, namely 3M Co’s nanostructured thin film (NSTF), was incorporated into the RDE measurements. NSTF-coated glassy carbon (GC) disks were used in RDE experiments on a Pt/Pt1-xIrx (0.05 < x < 0.3) composition spread. ORR measurements using NSTF-coated GC disks measure the catalytic properties with the same morphology, composition and surface structure as would be found in a fuel cell. A series of Pt1-xCox and Pt1-xNix (0.5 < x < 0.8) dealloy catalyst precursor films were tested using NSTF-coated GC disks in RDE studies. The value of x in Pt1-xMx (M = Ni, Co) was selected to be high in order to examine the dealloying process. The catalyst films were examined by a RDE test protocol that tracked the surface enhancement factor (SEF) and ORR current densities over a large number of test cycles. The aim was to measure the catalytic performance of the Pt-M materials as dealloying took place. The SEF of the PtCo and PtNi materials increased rapidly at the beginning and reached a plateau as high as 50 cm2/cm2 while the specific ORR activities increased as the initial M content in the catalyst precursor increased. The impact of the dealloying process on morphology was examined by completely dealloying a Pt3Ni7 precursor, deposited on mirror-polished GC disks, at a constant potential. As the dealloying process continued, the SEF of the material increased from about 1 cm2/cm2 to > 30 cm2/cm2 and resulted in the formation of whisker-like structures.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22467号 / 工博第4728号 / 新制||工||1738(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 田中 庸裕, 教授 江口 浩一, 教授 佐藤 啓文 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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