指導教授 : 王聖璋 博士 演 講 者 : 林恩賢 日 期 :2011/06/08 1. outline introduction...
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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
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Experimental section Catalysts synthesis
Cathode catalystAnode catalyst 5
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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.
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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
122
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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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