Hdi nghi Khoa hgc ky niem 35 ndm Viin Khoa hgc vd Cdng nghi Viet Nam - Hd Ndi 10/2010
HIEU
S U A T C U A P I NNHIEN LIEU METHANOL LONG
Nguyen Lu-dng Lam, Nguyin Trong TTnh Institute of Applied Physics and Scientific Instmment
18 - Hoang Qudc Viet, Ciu Giiy, Ha Ndi Email: nllaml95(a),vahoo.com Tom tat:
Pin nhien lieu Methanol Idng (DMFC) Id mot thiit bi diin hda, nd cd thi chuyin hda true tiip ndng lugng hda hoc (d ddy Id ndng lugng hda hoc ciia Methanlo Idng) thdnh ndng lugng dien. Pin DMFC dugc nghien cieu trong trudng hgp ndy cd chdt xiic tdc su dung cho cue Anode Id bdt Ru-Pt khdi lugng sit dung Id 4mg/cm2. Cdn chdt xuc tdc dimg cho cue Cathode Id bdt Pt, khdi lugng sit dung Id 2mg/cm2. Mdng trao ddi Proton dugc sit dung cho Pin DMFC Id mdng Naflon 117. Hiiu sudt cita Pin DMFC dugc ddnh gid thdng qua cdc diiu kiin nhu ndng do cita Methanol vd nhiet do cita Pin.
Key words: DMFC, Ru-Pt, Pt, Naflon 117 Abstract:
Direct Methanol Fuel Cell (DMFC) is an electrochemical device that can converts Methanol chemical energy to electrical energy directly. DMFC was studied in this case as Catalyst for anode is Ruthenium-Platinum powders and catalyst loading is 4mg/cm^. Catalyst for cathode is Platinum powder; catalyst loading is 2mg/cm . In this case proton membrane is Naflon 117. Performance will be discussed in terms of Methanol concentration and cell temperature.
\. INTRODUCTION
At the beginning of the 21'' century, the conversion of chemical energy into electrical energy became more important due to the increase in the use of electricity. One of the major factors that have influenced the development of fiiel cells has been the increasing concern about the environmental consequences of fossil fuel in production of electricity and for the propulsion of vehicles. The dependence of the industrialized countries on oil became apparent in the oil crises. One type of fiiel cells as a Direct Methanol Fuel Cells may help to reduce our dependence on fossil fuel and diminish poisonous emissions into the atmosphere, since they have higher electrical efficiencies compared to heat engines.
A Direct Methanol Fuel Cell (DMFC) is defined as an electrochemical device that can continuously convert chemical energy (Methanol) into electrical energy directly. Much like a battery, a fiiel cell produces electrical energy. However, unlike battery, reactants eire supplied continuously and products are continuously removed.
The Direct Methanol Fuel Cell (DMFC) has been studied due to many merits: Methanol is a high energy fuel; a clean power is produced at low operating temperatures; membranes last longer due to operating in aqueous environment; reactant humidification is not required; the DMFC system has faster response and is smaller in volume [1-2].
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Tiiu ban: Mdi tru&ng vd Ndng hcgng ISBN: 978-604-913-013-7
In a direct methanol fuel cell (DMFC), methanol is oxidized at the anode and oxygen (usually in air) is reduced at the cathode [1]. The electrochemical oxidation of methanol (in acid electrolyte) occurs as follows:
Anode reaction: CH3OH + H2O => CO2 +6H^ + 6e"
Cathode reaction: 3/2O2 + 6H"' +6e" => 3H2O
Overall cell reaction: CH3OH +3/2O2 => CO2 + 2H2O
In this report, we present of performance of the direct methanol fuel cells have 5 cm active areas. An anode catalyst is commercial Ru-Pt powders and a cathode catalyst is commercial Pt powder.
2. EXPERIMENTAL
Preparation of diffusion layers: A carbon paper was used as a diffusion layer. Thickness of carbon paper is 0.2 mm. The dimensions are 2.23cmx2.23cm (5cm activity area). The diffusion processes facilitated a role of catalysts adhered on its surface.
Preparation of anode catalyst: a catalyst material for anodes in this work that is PtRu black powder (50:50 atom ratios, Johnson Matthey Corp.). The catalyst was well-dispersed with 5%
Nafion solution (Dupont) for 30 minutes, leading to a solution, namely, a catalyst ink. The catalyst ink was painted into a surface of a 5cm^ carbon paper (dimensions 2.23x2.23cm) with the catalyst loading of about 4mg/cm^. The catalyst/carbon paper was dried at room temperature before being assembled to a MEA (membrane electrolyte assembly).
Preparation of cathode catalyst as same the way of anode but a catalyst for cathode only Pt powder and the catalyst loading is 2mg/cm^ (Johnson Matthey Corp.).
Treatment of Nafion 117 membrane: a membrane is very crucial to the DMFCs electrode.
It is called a heart of electrode because the membrane is a proton-conducting polymer. A commercial Nafion membrane used in this work was Nafion 117(Dupont, Fuel Cell Store). A membrane sheet was cut into several pieces of 4.28cm x 4.28cm. Pre-treatment of Nafion 117 membrane was accomplished by heating membrane at 80 C in distilled water, 3% H2O2, distilled water, 0.5M H2SO4 and distilled water three times again, for 1 hour each step. After the treatment, the membrane was dried at room temperature for 2 hours and then stored in an oven at 80''C for 2 hours.
A MEA (membrane electrolyte assembly) consists of anode, Nafion membrane and cathode. Assembly of electrodes is a finial step in preparation of the MEA. A detailed structure of MEA used in this work was anode (carbon paper/anode catalyst layer)/ Nafion 117 membrane/cathode (cathode catalyst layer/carbon paper). In the MEA preparation, anode, Nafion membrane and cathode were hot-pressed at 130 C and 250kgcm"^ for 2 minutes and then cooled down by water to room temperature. More details on this MEA fabrication procedure have been given in Lu and Wang [3]
Performances of the MEA have been measured by an electronic load following the diagram below:
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Hoi nghi Khoa hoc ky niem 35 ndm Vien Khoa hoc va Cong nghe Viet Nam - Ha Noi 10/2010
Out put: ( O j . l l j O . CO
Switch valve I Kotamctcr
lumidilier
I put: II.O Heating un-.'Sr;
Oul put: II^O Heating Koiai^cter Oj / Air
Pump
C l l j O n C Liquid)!
Fig. 1: Schematic of an experimental setup
3. RESULT AND DISCUSSION
After the hot press process, we have achieved a MEA that has performance test following the schematic in fig.2. A direct methanol fuel cell's performance characteristics are shown in fig.3:
Oprerating temperatures
• 90°C
• 80°C A 65°C
0,00 0,05 0,10 0,15 0,20 0,25
Current density (A/cm^)
Fig. 2: Temperature dependency of performance of MEA at IM In fig.3 the MEA size is ~5cm^; electrolyte: Nafion 117: Anode: PtRu black powder (~4mgcm"^ loading); Cathode: Pt (~2mg cm"^ loading). Feed rate of MeOH of IM (ImL/min), flow rate of O2: 0.5L/min. The fig.3 shows that the maximum current densities at IM
methanol solution at 90*'C are 0.18 A/cm^. This indicates that the cell performance is affected by the cell temperature that the performances decrease from temperature 90°C to 45°C.
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Tieu ban: Mdi truang vd Ndng lugng ISBN: 978-604-913-013-7.
— I ' 1 ' — Oprerating temperatures:
—•—so'c - « - 80°C .„.&_ 65°C - - r - 5 S ° c
• 45°C
0,10 0,15 0,20 Current density (A/cm')
0,25
Fig. 3: Temperature dependency of performance of MEA at 2M
Fig.4, the MEA size is ~5cm^; electrolyte: Nafion 117: Anode: PtRu black powder (~4mgcm"'^ loading); Cathode: Pt (~2mg cm"^ loading). Feed rate of MeOH of 2M (ImL/min), flow rate of O2: 0.5L/min. The fig.4 shows the performance of the MEA that the maximum current densities at 2M methanol solution at 90*^0 are 0.22 Aleve?. This indicates that the cell performance is affected by the cell temperature that the performances decrease from temperature 90''C to 45''C. When compared to the performance using IM methanol solution shovm in fig.3, the open circuit voltage with 2M solution shown in fig.4 drop somewhat due to the stronger methanol crossover effect. The MEA with 2M solution shovm better performance than IM solution.
The MEA was fabricated that the type of the MEA using Nafion 117, made with the carbon paper have been investigated for its polarization characteristics at different methanol concentration and temperature cell. The performances depend on cell temperature and methanol concentration.
4. ACKNOWLEDGMENTS
This work was supported by Institute of Applied Physics and Scientific Instrument's fundamental research.
REFERENCES
1. Thomas S. and Zalbowits M., "Fuel Cell-Green Power, Los Alamos National Laboratory", LA-UR-99-3231 (1999).
2. J.H Hirschenhofer, D.B. Stauffer, R.R Engleman, "In Fuel Cells: A Handbook (Revision 3) ", DOE/METC -94/10006,1994
3. G.Q. Lu, C.Y. Wan, Jumal Power Sources 35,134 (2004).
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