Transcript 下載/瀏覽Download

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-type
B-type
Advantage
Simpler management of gases
Use of conventional GDL
Drawback
Corrosion of the electrode
Water management
4
Experimental section
Catalysts synthesis
Anode catalyst
Cathode catalyst
5
Preparation of reversible
membrane electrode assemblies
• The reference MEA for
water electrolysis:
• Anode metallic iridium
(1.5 mg cm2),
• Cathode Pt40/Vulcan XC72 (0.35 mg Pt cm2).
• The reference MEA for fuel
cell:
• Both side used Pt40/VulcanXC72 (0.35 mg Pt cm2)
6
Results and discussion
XRD spectrum measured
Pt,d=2.5-3.5 nm
• 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.
7
SEM image
A highly porous structure is obtained.
ca. 5µm
ca. 15µm
A thicker catalytic layer (ca. 15 mm) is required to
increase the area of the gas–electrolyte interface.
8
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
9
Polarization curve of OER
(Oxygen Evolution Reaction)
1
H 2O  O2  2 H   2e 
2
• 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 cm2),
• Cathode Pt40/Vulcan XC72 (0.35 mg Pt cm2).
• Ref. Fuel cell:
• Cathode Pt40/Vulcan XC72 (0.35 mg Pt cm2).
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 H2 /O2
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