Upload
trinhkhanh
View
226
Download
0
Embed Size (px)
Citation preview
OPTIMIZATION OF THE MEMBRANE ELECTRODE ASSEMBLY (MEA) FABRICATION FACTORS BY DESIGN
OF EXPERIMENT (DOE) METHOD
U.A. Hasran1, S.K. Kamarudin1,2, W.R.W. Daud1, B.Y. Majlis3, A.B. Mohamad2, A.A.H. Kadhum2, M.M. Ahmad4
1Fuel Cell Institute, Universiti Kebangsaan Malaysia, Malaysia2Department of Chemical And Process Engineering, Universiti Kebangsaan
Malaysia, Malaysia3Institute of Microengineering and Nanoelectronics, Universiti Kebangsaan
Malaysia, Malaysia4School of Bioprocess Engineering, Universiti Malaysia Perlis, Malaysia
email: [email protected]
INTRODUCTION
MEA
Perspex frame
Silicone rubber
Stainless steel mesh
Methanol
Bolt
Cathode
Anode
Micro Direct Methanol Fuel Cell (DMFC)
Membrane Electrode Assembly (MEA)
Polymer Electrolyte Membrane (PEM)
MEA
Electrode area = 1 cm2
+
Catalyst
+
Gas Diffusion Layer (GDL)
HOT PRESSING PROCESS
MEA COMPONENTS
PROBLEM STATEMENT
The current method typically used to optimize the critical hotpressing process for the fabrication of MEA is time-consuming,costly and only capable of estimating the importance of eachinput parameter/factor but not the interactions between themon the chosen response.
OBJECTIVES
� To investigate the effect each hot pressing factor has on theMEA fabrication by observing the performance� To observe the interactions between the input factors on thechosen response� To optimize the hot pressing process
METHODOLOGY
� Fabrication of the MEA components
� Hot pressing process
� Pre-treatment of the MEA
� Performance testing with the One-Factor-At-a-Time (OFAT)
method to obtain the levels of the hot pressing factors in this study
� Performance testing with the Design of Experiment (DOE)
method to optimize the hot pressing factors
OFAT: Effect of Hot Press Pressure
3.125 kgf/cm2
9.375 kgf/cm2
18.75 kgf/cm2
Power (mW/cm2)
Current (mA/cm2)
@Hot pressing temperature = 120C:
•power density decreases as pressure is
increased
•highest peak power density at lowest
pressure value of 3.125 kgf/cm2
@Hot pressing pressure = 9.375 kgf/cm2:
•power density increases as temperature
is increased
•highest peak power density at highest
temperature value of 140C
92.8C
100C
120C
Power (mW/cm2)
Current (mA/cm2)
140C
OFAT: Effect of Hot Press Temperature
PARAMETER RANGE
Pressure (kgf/cm2)
[ ]
Temperature (°C) Duration (min)
Time/duration: •Value fixed at 3 min
Pressure: •Range chosen = 6 – 16 kgf/cm2
•Temperature: •Range chosen = 100 - 135C
Time/durationPressureTemperature
Factor Units Low Level (-1) High Level (+1)
A: Compression pressure kgf/cm2 6 16B: Hot pressing temperature °C 100 135
DOE METHOD
� Software Design-Expert 8.0.7.1
� Response surface methodology (RSM):
•objective: optimizing the response variable(s)
•regression analysis used for modeling and analysis of problems
� Central Composite Design (CCD):
•to study the correlation between the factors and the response
•designed to estimate the coefficients of a quadratic model
•no need for detailed reaction mechanism
•blocking effect was of no interest in this work
� Normal probability plot of
the studentized residuals
Nor
mal
% P
rob
abil
ity
Internally Studentized Residuals
GRAPHICAL ANALYSIS
� Plot of the residuals
against predicted response
Inte
rnal
ly S
tud
enti
zed
Res
idu
als
Predicted
� Perturbation plot for the
micro DMFC performance
Pea
k P
ower
Den
sity
(m
W/c
m2)
Deviation from Reference Point (Coded Units)
EMPIRICAL MODEL
� Final empirical model:
Y = 5.18 - 1.46*A + 0.35*B - 1.07*AB + 0.048*A2 - 0.95*B2
� The coefficients of the model for the response show that:
•negative effect implies that A should be minimized
•positive effect implies that B should be maximized
•excessive increase is less desirable for temperature compared to pressure
A: Pressure ResidualsB: Temperature
Pea
k P
ower
Den
sity
(m
W/c
m2)
NUMERICAL OPTIMIZATION
� Desired goal for factor A and B is ‘within range’ and the response is ‘maximize’
� 3D response surface:
� By a potential expanded design space, optimum peak power density = 8.69 mW/cm2
� Max power density
= 7.23 mW/cm2
� Porous media:•electrodes - the gas diffusion layer and the catalyst layer.•PEM
� Over-pressure: •considerable decrease in size or collapse•transport of reactants suffers
•therefore, excessive hot press pressure may result in decreasing fuel cell performance
THE EFFECT OF HOT PRESS PRESSURE
� Glass transition temperature (Tg) for Nafion 117:•132C just before hot-pressing•99C when fully hydrated
� @ temperatures below Tg:•rigidity during hot-pressing•an increase in ohmic loss and a decrease in long-term stability
� @ temperatures above Tg:•softened during hot-pressing •however, it will undergo a micro-structural change and an irreversible water uptake loss at temperatures much higher than Tg
THE EFFECT OF HOT PRESS TEMPERATURE
� OFAT method: changes in compression pressure have a bigger effect on
the electrodes whereas varying the compression temperature affects the
PEM more
� DOE method: the optimum hot pressing factors expected to deliver the
maximum response were predicted using the RSM with central composite
design.
� The model chosen from the ANOVA analysis to predict the desired
response is the Quadratic model.
� The predicted net peak of 7.23 mW/cm2 was obtained from the studied
design space and an optimum performance of 8.69 mW/cm2 was obtained
from the potential expanded design space.
CONCLUSIONS
� Apply the optimum hot press settings in an active micro DMFC system
� Study more input factors with more than one response
FUTURE WORK