Hiệu suất của pin nhiên liệu methanol lỏng

Hdi nghi Khoa hgc ky niem 35 ndm Viin Khoa hgc vd Cdng nghi Viet Nam - Hd Ndi 10/2010<br /> <br /> <br /> HIEU S U A T CUA PIN NHIEN LIEU METHANOL LONG<br /> <br /> Nguyen Lu-dng Lam, Nguyin Trong TTnh<br /> Institute of Applied Physics and Scientific Instmment<br /> 18 - Hoang Qudc Viet, Ciu Giiy, Ha Ndi<br /> Email: nllaml95(a),vahoo.com<br /> Tom tat:<br /> Pin nhien lieu Methanol Idng (DMFC) Id mot thiit bi diin hda, nd cd thi<br /> chuyin hda true tiip ndng lugng hda hoc (d ddy Id ndng lugng hda hoc ciia<br /> Methanlo Idng) thdnh ndng lugng dien. Pin DMFC dugc nghien cieu trong trudng<br /> hgp ndy cd chdt xiic tdc su dung cho cue Anode Id bdt Ru-Pt khdi lugng sit dung<br /> Id 4mg/cm2. Cdn chdt xuc tdc dimg cho cue Cathode Id bdt Pt, khdi lugng sit<br /> dung Id 2mg/cm2. Mdng trao ddi Proton dugc sit dung cho Pin DMFC Id mdng<br /> Naflon 117. Hiiu sudt cita Pin DMFC dugc ddnh gid thdng qua cdc diiu kiin nhu<br /> ndng do cita Methanol vd nhiet do cita Pin.<br /> Key words: DMFC, Ru-Pt, Pt, Naflon 117<br /> Abstract:<br /> Direct Methanol Fuel Cell (DMFC) is an electrochemical device that can<br /> converts Methanol chemical energy to electrical energy directly. DMFC was<br /> studied in this case as Catalyst for anode is Ruthenium-Platinum powders and<br /> catalyst loading is 4mg/cm^. Catalyst for cathode is Platinum powder; catalyst<br /> loading is 2mg/cm . In this case proton membrane is Naflon 117. Performance<br /> will be discussed in terms of Methanol concentration and cell temperature.<br /> <br /> <br /> \. INTRODUCTION<br /> At the beginning of the 21'' century, the conversion of chemical energy into electrical<br /> energy became more important due to the increase in the use of electricity. One of the major<br /> factors that have influenced the development of fiiel cells has been the increasing concern<br /> about the environmental consequences of fossil fuel in production of electricity and for the<br /> propulsion of vehicles. The dependence of the industrialized countries on oil became apparent<br /> in the oil crises. One type of fiiel cells as a Direct Methanol Fuel Cells may help to reduce our<br /> dependence on fossil fuel and diminish poisonous emissions into the atmosphere, since they<br /> have higher electrical efficiencies compared to heat engines.<br /> A Direct Methanol Fuel Cell (DMFC) is defined as an electrochemical device that can<br /> continuously convert chemical energy (Methanol) into electrical energy directly. Much like a<br /> battery, a fiiel cell produces electrical energy. However, unlike battery, reactants eire supplied<br /> continuously and products are continuously removed.<br /> The Direct Methanol Fuel Cell (DMFC) has been studied due to many merits: Methanol is<br /> a high energy fuel; a clean power is produced at low operating temperatures; membranes last<br /> longer due to operating in aqueous environment; reactant humidification is not required; the<br /> DMFC system has faster response and is smaller in volume [1-2].<br /> <br /> <br /> 407<br /> Tiiu ban: Mdi tru&ng vd Ndng hcgng ISBN: 978-604-913-013-7<br /> <br /> <br /> In a direct methanol fuel cell (DMFC), methanol is oxidized at the anode and oxygen<br /> (usually in air) is reduced at the cathode [1]. The electrochemical oxidation of methanol (in<br /> acid electrolyte) occurs as follows:<br /> Anode reaction: CH3OH + H2O => CO2 +6H^ + 6e"<br /> Cathode reaction: 3/2O2 + 6H"' +6e" => 3H2O<br /> Overall cell reaction: CH3OH +3/2O2 => CO2 + 2H2O<br /> In this report, we present of performance of the direct methanol fuel cells have 5 cm active<br /> areas. An anode catalyst is commercial Ru-Pt powders and a cathode catalyst is commercial<br /> Pt powder.<br /> <br /> <br /> 2. EXPERIMENTAL<br /> Preparation of diffusion layers: A carbon paper was used as a diffusion layer. Thickness of<br /> carbon paper is 0.2 mm. The dimensions are 2.23cmx2.23cm (5cm activity area). The<br /> diffusion processes facilitated a role of catalysts adhered on its surface.<br /> Preparation of anode catalyst: a catalyst material for anodes in this work that is PtRu black<br /> powder (50:50 atom ratios, Johnson Matthey Corp.). The catalyst was well-dispersed with 5%<br /> Nafion solution (Dupont) for 30 minutes, leading to a solution, namely, a catalyst ink. The<br /> catalyst ink was painted into a surface of a 5cm^ carbon paper (dimensions 2.23x2.23cm) with<br /> the catalyst loading of about 4mg/cm^. The catalyst/carbon paper was dried at room<br /> temperature before being assembled to a MEA (membrane electrolyte assembly).<br /> Preparation of cathode catalyst as same the way of anode but a catalyst for cathode only Pt<br /> powder and the catalyst loading is 2mg/cm^ (Johnson Matthey Corp.).<br /> Treatment of Nafion 117 membrane: a membrane is very crucial to the DMFCs electrode.<br /> It is called a heart of electrode because the membrane is a proton-conducting polymer. A<br /> commercial Nafion membrane used in this work was Nafion 117(Dupont, Fuel Cell Store). A<br /> membrane sheet was cut into several pieces of 4.28cm x 4.28cm. Pre-treatment of Nafion 117<br /> membrane was accomplished by heating membrane at 80 C in distilled water, 3% H2O2,<br /> distilled water, 0.5M H2SO4 and distilled water three times again, for 1 hour each step. After<br /> the treatment, the membrane was dried at room temperature for 2 hours and then stored in an<br /> oven at 80''C for 2 hours.<br /> A MEA (membrane electrolyte assembly) consists of anode, Nafion membrane and<br /> cathode. Assembly of electrodes is a finial step in preparation of the MEA. A detailed<br /> structure of MEA used in this work was anode (carbon paper/anode catalyst layer)/ Nafion<br /> 117 membrane/cathode (cathode catalyst layer/carbon paper). In the MEA preparation, anode,<br /> Nafion membrane and cathode were hot-pressed at 130 C and 250kgcm"^ for 2 minutes and<br /> then cooled down by water to room temperature. More details on this MEA fabrication<br /> procedure have been given in Lu and Wang [3]<br /> Performances of the MEA have been measured by an electronic load following the<br /> diagram below:<br /> <br /> <br /> <br /> <br /> 408<br />  Hoi nghi Khoa hoc ky niem 35 ndm Vien Khoa hoc va Cong nghe Viet Nam - Ha Noi 10/2010<br /> <br /> <br /> Out put: ( Oj.lljO. CO<br /> <br /> <br /> Switch valve<br /> I Kotamctcr<br /> lumidilier<br /> <br /> Oj / Air<br /> <br /> Pump<br /> OulI put: II^O<br /> II.O Heating Koiai^cter<br /> un-.'Sr;<br /> <br /> <br /> <br /> <br /> ClljOnC Liquid)!<br /> <br /> <br /> <br /> <br /> Fig. 1: Schematic of an experimental setup<br /> <br /> <br /> 3. RESULT AND DISCUSSION<br /> After the hot press process, we have achieved a MEA that has performance test following the<br /> schematic infig.2.A direct methanol fuel cell's performance characteristics are shown in fig.3:<br /> <br /> <br /> Oprerating temperatures<br /> • 90°C<br /> • 80°C<br /> A 65°C<br /> <br /> <br /> <br /> <br /> 0,00 0,05 0,10 0,15 0,20 0,25<br /> Current density (A/cm^)<br /> <br /> <br /> Fig. 2: Temperature dependency of performance of MEA at IM<br /> In fig.3 the MEA size is ~5cm^; electrolyte: Nafion 117: Anode: PtRu black powder<br /> (~4mgcm"^ loading); Cathode: Pt (~2mg cm"^ loading). Feed rate of MeOH of IM (ImL/min),<br /> flow rate of O2: 0.5L/min. The fig.3 shows that the maximum current densities at IM<br /> methanol solution at 90*'C are 0.18 A/cm^. This indicates that the cell performance is affected<br /> by the cell temperature that the performances decrease from temperature 90°C to 45°C.<br /> <br /> <br /> <br /> <br /> 409<br /> Tieu ban: Mdi truang vd Ndng lugng ISBN: 978-604-913-013-7.<br /> <br /> <br /> <br /> <br /> — I ' 1 '—<br /> Oprerating temperatures:<br /> —•—so'c<br /> - « - 80°C<br /> .„.&_ 65°C<br /> --r-5S°c<br /> • 45°C<br /> <br /> <br /> <br /> <br /> 0,10 0,15 0,20 0,25<br /> Current density (A/cm')<br /> <br /> Fig. 3: Temperature dependency of performance of MEA at 2M<br /> Fig.4, the MEA size is ~5cm^; electrolyte: Nafion 117: Anode: PtRu black powder<br /> (~4mgcm"'^ loading); Cathode: Pt (~2mg cm"^ loading). Feed rate of MeOH of 2M (ImL/min),<br /> flow rate of O2: 0.5L/min. The fig.4 shows the performance of the MEA that the maximum<br /> current densities at 2M methanol solution at 90*^0 are 0.22 Aleve?. This indicates that the cell<br /> performance is affected by the cell temperature that the performances decrease from<br /> temperature 90''C to 45''C. When compared to the performance using IM methanol solution<br /> shovm in fig.3, the open circuit voltage with 2M solution shown in fig.4 drop somewhat due<br /> to the stronger methanol crossover effect. The MEA with 2M solution shovm better<br /> performance than IM solution.<br /> The MEA was fabricated that the type of the MEA using Nafion 117, made with the<br /> carbon paper have been investigated for its polarization characteristics at different methanol<br /> concentration and temperature cell. The performances depend on cell temperature and<br /> methanol concentration.<br /> <br /> <br /> 4. ACKNOWLEDGMENTS<br /> This work was supported by Institute of Applied Physics and Scientific Instrument's<br /> fundamental research.<br /> <br /> <br /> REFERENCES<br /> 1. Thomas S. and Zalbowits M., "Fuel Cell-Green Power, Los Alamos National<br /> Laboratory", LA-UR-99-3231 (1999).<br /> 2. J.H Hirschenhofer, D.B. Stauffer, R.R Engleman, "In Fuel Cells: A Handbook<br /> (Revision 3) ", DOE/METC -94/10006,1994<br /> 3. G.Q. Lu, C.Y. Wan, Jumal Power Sources 35,134 (2004).<br /> <br /> <br /> <br /> <br /> 410<br />