博士論文審査報告書 Doctor Thesis Screening Results Reports
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(2) C o u p l i n g e l e c t r o c h e m i c a l r e a c t i o n s t o r e n e w a b l e e n e r g y s o u r c e s ( e . g . s o l a r, w i n d , geothermal, etc.) is a realistic pathway toward a closed -loop economy where energy and materials can be recycled indefinitely without any of the negative si de eff ects of f oss il fuel s . El ectr ochemi cal water split ti ng i s a reli abl e met hod t o t r a n s f o r m w a t e r i n t o o x y g e n a n d h y d r o g e n f u e l s . H o w e v e r, e l e c t r o c h e m i c a l water splitting method tends to rely on expensive precious metal catalysts like p l a t i n u m ( P t ) w h i c h l i m i t s i t s s c a l a b i l i t y a s a v i a b l e e n e r g y s u p p l y t e c h n o l o g y. This. thesis. describes. the. design. of. nanoporous. transiti on. metal. sulfide. e l e c t r o d e s f o r e f f i c i e n t e l e c t r o c h e m i c a l w a t e r s p l i t t i n g . Tr a n s i t i o n m e t a l s u l f i d e s have unique physical and chemical properties that enable them to catalyze the full water splitting reaction from the hydrogen evolution reaction (HER) to the oxygen evolution reaction (OER) in a bifunctional electrode setup . In addition, these transition metal sulfide materials are far more Earth -abundant and can generate hydrogen at a lower economic cost . Chapter 1 introduces recent development s in the application of transition metal sulfides in electrochemical water splitting. Chapter 2 describes the preparation of a bifunctional electrocatalyst for both HER and OER. A metal-organic framework called ZIF-67 is used as a morphological template and. c o b a l t p r e c u r s o r. T h i s. work creates. a hollow. core -shell heterostructure composed of inner Co 3S4 and outer MoS2 using a hydrot her mal pr oces s. T he Co3S4 i s an effi ci ent OER cat al yst that has poor s t a b i l i t y, w h i l e t h e M o S 2 i s a g o o d H E R c a t a l y s t w i t h p o o r O E R p e r f o r m a n c e . The s ynergis ti c and pr ot ecti ve eff ect s bet ween t he cor e of Co 3S4 and s hell of MoS2 allow these Co3S4@MoS2 materials to have. outstanding bifunctional. catalytic performances for both HER and OER in acidic and alkaline media. The strategy developed here opens new avenues in the design and fabrication of hi ghl y eff ecti ve bif uncti onal el ect ro catal ys ts . Chapter 3 demonstrates the synthesis of a hollow cubic Co 3S4@MoS2 bifunctional catalyst using a Co -Fe Prussian blue analogue (PBA) precursor. The hollow Co3S4 nanoboxes are formed initially based on an ion exchange reaction b e t w e e n F e ( C N ) 6 3 - o f C o - F e P B A a n d S 2 - . S u b s e q u e n t l y, M o S 2 n a n o s h e e t s a r e grown on the surface of the Co3S4 nanoboxes. Again this work demonstrates the str ong s ynergis ti c eff ects f ost er ed by the combi nati on of M oS2 and Co 3S4, providing. more. evidence. that. this. material. system. generates. enhanced. b i f u n c t i o n a l c a t a l y t i c p e r f o r m a n c e . C o n s e q u e n t l y, t h e C o 3 S 4 @ M o S 2 s h o w s a l o w cell voltage of 1.58 V when it is used as both cathodic and anodic electr odes in a w a t e r s p l i t t i n g e l e c t r o l y z e r. T h i s a p p r o a c h i s w i d e l y a p p l i c a b l e t o o t h e r P B A s with. different. compositions.. We l l - d e s i g n e d 1. architectures. with. optimal.
(3) compositions will improve the performance of these electrodes in practical applications. Chapter. 4. extends. the. above. synthetic. strategy. to. generate. hollow. heterometallic phosphide nanocubes via one-step phosphidization of trimetallic NiCoFe PBA. Modulating the Ni content in the PBA precursors enables various heter ometall ic phos phi des wit h di ff er ent mo r phologi es and co mposit i ons t o be synthesized. There is an optimal composition that exhibit s increased active sites a n d i m p r o v e s e l e c t r i c a l c o n d u c t i v i t y, w h i c h m a k e s i t a g o o d c a t a l y s t f o r b o t h HER and OER. This work highlights a new strategy for preparing low-cost, efficient, and stable catalysts for overall water splitting. Chapter. 5. describes. the. preparation. of. mesoporous. metal. sulfides.. P o l y s t y r e n e - b l o c k - p o l y ( a c r y l i c a c i d ) ( P S - b - PA A ) p o l y m e r m i c e l l e s a r e u s e d a s pore-directing agents and as sacrificial templates. The electrostatic interactions between negatively charged micelles and positively charged metal species play a c r i t i c a l r o l e i n t h e f o r m a t i o n o f m e s o s t r u c t u r e d p r e c u r s o r. D i t h i o o x a m i d e ( D T O , NH2C(S)C(S)NH2) is added to the synthetic process so that it combines with the cationic metal (e.g., Zn2+, Co2+, Ni2+) by strong covalent bonding and with the Mo. source. material. by. electrostatic. generates. interactions,. spherical. CoMo. r e s p e c t i v e l y.. sulfides. Calcination. containing. of. this. mesopores.. The. mes o por ous net wor k pr omot e s di ff usi on of r eact ant s and products wit h in t he spheres, leading to enhanced catalytic kinetics for both the HER and OER. Chapter 6 extends the soft -templating method described earlier for the construction of mesoporous N -doped carbon containing ultrafine molybdenum carbide. (Mo2C). nanoparticles.. Another. amphi philic. diblock. copolymer. polystyrene-block -polyethylene oxide (PS -b-PEO) is used as the pore -forming agent.. The. complexation. between. d opamine. hydrochloride. (DA,. (HO)2C6H3CH2CH2NH2·HCl) and the Mo source on the PS-b-PEO micelles results in. the. formation. of. mesostructured. p r e c u r s o r.. After. carbonization. of. the. precursor under N2 atmosphere, mesoporous Mo 2C/N-doped carbon is obtained with high surface area. In this catalyst, the Mo2C is responsible for enhanc ing oxygen reduction reaction (ORR) performance, while the N-doped carbon matrix can help to further improve the conductivity and prevent the aggregation of the Mo2C nanoparticles. This chapter shows the wide applicability of the polymeric micelle. strategy. to. generate. various. kinds. of. mesoporous. materials. with. di ff er ent el ectr ocat al yt ic pr operti es . Chapter 7 describes the general conclusion s of the thesis and proposes future. prospects.. splitting. are. Highly. obtained. efficient. through. bifunctional. various 2. electrocatalysts. strategies ,. including. for. water. morphological.
(4) control, construction of heterostructures, and heteroatom doping. Perhaps more i m p o r t a n t l y, t h e s t r a t e g i e s d e v e l o p e d i n t h i s t h e s i s w i l l p r o v i d e a g e n e r a l r o u t e to s ynthes i ze ot her ki nds of eff icient electr ocatal ys ts f or energy s torage and conversion systems in the future. Therefore, we believe this work is sufficient to warrant a degree of Doctor of Engineering.. January 2019 審査員 （主査） 早稲田大学客員准教授 博 士 (工 学 ) 早 稲 田 大 学. 山内 悠輔. 早稲田大学教授 工学博士（早稲田大学）. 菅原 義之. 早稲田大学教授 博 士 (理 学 ) 早 稲 田 大 学. 朝日 透. China University of Geosciences 教 授 PhD (China University of Geosciences). 物 質 ･材 料 研 究 機 構 主 任 研 究 員 PhD (Northwestern University). 王 圣平. Joel Henzie. 3.
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