別紙41 (課程博士(英文))Date of submission (month day, year)
Depar血entof

6th, 2023

tsunoriMatsuda

Electrical and Electronic

StudentlD Number

D153267

Information Engineerin牙
Pplicant's nameJanOSI)iaki HattoriSupervisors

KeiiC11iro Mae曾awa

Abstract (Docto,)
Title ofThesis

Development ofsolid・state ionic conductors and application to the polymer eleC廿olyte
membrane fuelceⅡS

Approx. 80o words

As a solution of the 牙10bal warmin今 Caused by the 牙reenhouse 曾ases, fuelCe11techn010套y can be considered as one ofthe promisin目 Candidates ofthe ener套yresources. Amon曾 the several kinds offuelce11, polymer electrolyte membrane fuelCeⅡ(PEFC) is main wpe of the fuel ce11S for the application to the fuelce11 Vehicle(FCV) due to the nature of pEFc such as compact,1ightweight, and high、power

density.1n general, PEFc can be considered as the proton exchan旦e type membrane fuel ceⅡ(PEMFC). However, fU11・scale market expansion of pEFC・derived techn010gy has not beenrealized yet, due to tlw scarcity of pt electrocatalysts resulting in high cost and concern about
SustainabiHty.

Variety kind of approaches were attempted to reduce amount of pt use by enhancing
Catalytic activity or to seek an alternative catalyst, to solve the problem. Yet, the impact ofmaterial development of catalysts on solving problems is Hmited.1n these circumstances, thetwo new drastic approaches, which are the changing the ion・conducting species transportino
through the electrolyte membrane to oH、 and elevating the fuel ce11 0perating temperature,
Were conducted in this study.1n other words, investigation and development of newelectrolyte membrane 、vere conducted for reaHzing these approaches. PEFcs using oH、Conducting electrolyte membrane is ca11ed anion exchange membrane fuel ceⅡ(AEMFC)、
Under the oH、 ion conduction, the reaction in the fuel ceⅡ Changed, resulting in th
Suppressed activation energy meaning that the reduced catalyst in need. As for the pEFCS
Operating under higher temperature, it is caⅡed medium temperature anhydrous pEFC
(MT・PEFC). since the conventional pEFc electrolyte, Naaon is limited to operate under
100゜c due to the necessity of humidity, the electrolyte membrane for MT、PEFc is needed.

Through the investigation on the ionic conductor and the examination of the application ofPrepared ionic conductor, the performance enhancement ofthe both AEMFc and MT、PEFC

Was confirmed. Furthermore, investigation on the composite proton conductor based on theacid・base interaction suggested that the theory to develop the proton conductor 、Nith hiσhProton conductivity helping the future studies.

In the first and second research, improvement of hydroxide ion conductivity on thegenera11y used potassium hydroxide・doped polybenzimidazole (PBD by introducing layer
double hydroxides (LDHS) showing high hydroxide ion conductivity was conducted for thePerformance enhancement of AEMFC. According to the results obtained by thePhysicochemical and electrochemical analysis, LDHs incorporation derived the improved
Water adsorbing property of the membrane, resulting in the hi8h oH、 conductivity and lessdependent on the humidity. EspeciaⅡy, PBl composite membrane with highest amount of
LDHS (50 wt.% LDHs addition) showed maximum ion conductivity of 3.ol ms cm‑1 at 60OC

and 80% RH. FinaⅡy, the prepared membrane with 30 wt.% LDHs exhibited the maximum

fuel ce11 Performance. For further improvement of AEMFc performance,1thought thatContr011ing the nano/micro structural properties of LDHs is one of the approaches to achieve
the better AEMFc performance in the aspect of the conductivity and dispersibiHty. The
hydrothermaltreatment which is the effective way to change the crysta11ine and bulk structure
Of LDHs was appHed to s01・gel synthesized LDHs with different duration of time toinvestigate the morph010gical changes in the LDHS. As a resuH of 血e xRD and sAXS

analysis, crystalHne growth has two phases before and a丑er 18h while the platelet structure
growth contentiously pursuing foe 48h.

Abovementioned studies have shown improved performance of AEMFC, but there
are Hmitations to further improving performance. Thus,1 focused medium temperature
Operation of proton exchange type pEFc as an aHernative solution.1n third research, theUnique solution that incorporation of soHd proton conductor into the catalyst layer, to reduce
the activation overvoltage of MT・PEFc was introduced.1n MT・PEFC, application of theanhydrous proton conductor to the catalyst layer to create the effective reaction mechanism isneeded. Thus, cesium hydrogen sulfate (CHS)・siHcotungstic acid (、ⅣSiA) composites which
is previously reported in our laboratory was used as the solid ionomer. Not only suppression
Of the activation overvoltage but fuel ceⅡ Performance enhancement was also conarmed
Under 150゜c anhydrous condition by the cHS・圦IsiA ionomer.1n fourth research, counter

Plan for the phosphoric acid (PA) 1eaching problem of conventiona11y used electrolyte,
PA・doped pBl for the MT・PEFc was investigated. As a solution, reduced graphene oxide
nanosheets (rGO NSS) was introduced to the pBl as a pA capturing fiⅡers. The enhanced pA

retention property was observed in the acid leaching test when 2 、Nt.% of rGo addition.
Furthermore, proton conductivity of the pBI、Nas improved probably due to the formation ofProton conductive channel established by the adsorbed pA on the rGo surfaces, resulting in
the improved power density ofMT・PEMFC.
For the further enhancement of the MT・PEFC,1 Considered that the high proton
Conductive material forthe medium temperature anhydrous operation notto depend on the pA
doping which is potentia11y leaching, is essential. Thus, the proton conductive salt material、vith chemicaⅡy fixed acid by acid・base interaction was examined.1n the fi丘h study,1investigated the poly(4・vinylpyridine) based salt material reacting with several kinds of acids(PA, sulfuric acid: SA, nitric acid: NA, hydrochloric acid: HCI, acetic acid: AA,diauoroacetic acid: DFA and triauoroacetic acid: TFA) to obtain the indicator to know

highno、N of proton conductivity of the salts.1 focused on the protonated atomic distance(PAD) which is represented as the distance between nitrogen atom in the base and oxygen
atom in the acid since the proton conduction in the salt is performed in between base and acidand calculated it using DFT.1 Confirmed that the pAD is strongly correlating with the proton
Conductivity, indicating that the pAD can be an indicator to evaluate the high/10、N of theProton conductivity.1n the sixth study,、Ne developed organic・inorganic salt proton conductor
based on the heterocycHc imidazole with double acid・base interaction. Here, hydrochloricacid (HCI) and silanol group of the si02 、vas oriented to the imidazole (1mi), then form theImiHCI・si02. xlmiHCI・(100・χ)si02 (χ=60 wt.%) exhibited maximum proton conductivity of

1.4×10‑2 S cm"1 at 130゜c anhydrous. Accordin旦 to the theoretical investioation using DFT
established in the previous part and physical characterization, promotion of proton
dissociation in the system by the acid modification is the reason for the improved proton
Conductivity. 1n addition, MT・PEFc performance enhancement by incorporating
ImiHCI・si02into pBl membrane was confirmed, achieving more than 520 mw cm、2 Which ishigh level among the relative studies.