指導教授 : 王聖璋 博士演 講 者 : 林恩賢 日 期 :2011/06/08

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Outline

• Introduction

• Experimental section

• Results and discussion

• Conclusions

• Future work

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Introduction

• Unitized regenerative fuel cells(URFCs) can potentially be used in different energy management systems for transport , domestic and space applications.

• The structure and composition of electrocatalytic layers in URFCs are of particular importance and strongly impact current–voltage performances and cell efficiencies.

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Introduction(2)

• Potentially , there are two different ways to operate a URFC cell.

A-type B-type

Advantage Simpler management of gases Use of conventional GDL

Drawback Corrosion of the electrode Water management 4

Experimental section Catalysts synthesis

Cathode catalystAnode catalyst 5

Preparation of reversible membrane electrode assemblies

• The reference MEA for water electrolysis:

• Anode metallic iridium (1.5 mg cm2),

• Cathode Pt40/Vulcan XC-72 (0.35 mg Pt cm2).

• The reference MEA for fuel cell:

• Both side used Pt40/VulcanXC-72 (0.35 mg Pt cm2)

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Results and discussion XRD spectrum measured

• An average diameter of 2.5-3.5 nm is measured, in accordance with data of Fig. 2.

• The position of diffraction peaks , characteristic of the face-centered cubic lattice of Pt, confirm the successful reduction of Pt-precursors to the metallic state.

Pt,d=2.5-3.5 nm

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SEM image

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A highly porous structure is obtained.

ca. 15µm

ca. 5µm

A thicker catalytic layer (ca. 15 mm) is required to increase the area of the gas–electrolyte interface.

Cyclic voltammograms

• The electrochemical active surface area (EAS)

• Qh is coulombic charge with hydrogen-adatoms desorption .

• QHo is the amount of electricity per unit surface area.

• (for polycrystalline platinumQHo = 0.21 mC cm-2 )

• GMe is the weight, corresponding to the metal fraction in the catalyst.

Iridium powder is ca. 55 m2g-1

Pt40/VulcanXC-72,is close to 70 m2g-1

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Polarization curve of OER(Oxygen Evolution Reaction)

• As can be seen from Fig. 7, the higher the platinum content, the lower the performances.

• Prove Ir have a good performance of water electrolysis.

eHOOH 222

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Polarization curve of HOR(Hydrogen Oxidation Reaction)

• The difference between the different catalysts is less significant than for the OER.

• At high over-voltages where transport limitations appear, significantly different catalytic efficiencies are observed as a function of the iridium content.

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• Ref. electrolyser:

• Anode metallic iridium (1.5 mg cm2),

• Cathode Pt40/Vulcan XC-72 (0.35 mg Pt cm2).

• Ref. Fuel cell:

• Cathode Pt40/Vulcan XC-72 (0.35 mg Pt cm2).

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Voltages measured on the reversible cell

• Two ways to sprays the catalysts on membrane B and C.

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BET surfaces measured

• True Pt–Ir mixtures with different weight ratios and separate Pt and Ir layers.

• As a result, surface area of the mixtures is proportional to the composition.

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Stability tests

• The cell was switched off at night time.

• Voltage fluctuations are mostly due to temperature changes.

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Conclusions

• The best current-voltage performances are obtained using Ir 0.5 Pt 0.5 at the anode and Pt/Vulcan XC-72 at the cathode.

• Electrochemical performances are close to those measured on conventional water electrolysis and H2 /O2 fuel cells with the same noble metal loadings and similar operating conditions.

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Future work

• 通入 CO氣體測試觸媒抗 CO能力。

• 製作 MEA時可分兩段式塗佈。

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