指導教授 : 王聖璋 博士 演 講 者 : 林恩賢 日 期 :2011/06/08 1

Outline Introduction Experimental section Results and discussion Conclusions Future work 2

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. 3

Introduction(2) Potentially, there are two different ways to operate a URFC cell. A-typeB-type AdvantageSimpler management of gasesUse of conventional GDL DrawbackCorrosion of the electrodeWater management 4

Experimental section Catalysts synthesis Cathode catalyst Anode catalyst 5

Preparation of reversible membrane electrode assemblies The reference MEA for water electrolysis: Anode metallic iridium (1.5 mg cm 2 ), Cathode Pt40/Vulcan XC- 72 (0.35 mg Pt cm 2 ). The reference MEA for fuel cell: Both side used Pt40/VulcanXC- 72 (0.35 mg Pt cm 2 ) 6

Results and discussion XRD spectrum measured An average diameter of 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= nm 7

SEM image 8 A highly porous structure is obtained. ca. 15 µm ca. 5 µ m 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) Q h is coulombic charge with hydrogen-adatoms desorption. Q Ho is the amount of electricity per unit surface area. (for polycrystalline platinumQ Ho = 0.21 mC cm -2 ) G Me is the weight, corresponding to the metal fraction in the catalyst. Iridium powder is ca. 55 m 2 g -1 Pt40/VulcanXC-72,is close to 70 m 2 g -1 9

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. 10

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. 11

Ref. electrolyser: Anode metallic iridium (1.5 mg cm 2 ), Cathode Pt40/Vulcan XC- 72 (0.35 mg Pt cm 2 ). Ref. Fuel cell: Cathode Pt40/Vulcan XC- 72 (0.35 mg Pt cm 2 ). 12

Voltages measured on the reversible cell Two ways to sprays the catalysts on membrane B and C. 13

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. 14

Stability tests The cell was switched off at night time. Voltage fluctuations are mostly due to temperature changes. 15

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 H 2 /O 2 fuel cells with the same noble metal loadings and similar operating conditions. 16

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。 17