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Anode Negative post of the fuel cell. Conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit. Etched channels disperse hydrogen gas over the surface of catalyst. Cathode Positive post of the fuel cell Etched channels distribute oxygen to the surface of the catalyst.
Chương PIN NHIÊN LIỆU PEM Fuel Cell Parts of a Fuel Cell Anode Negative post of the fuel cell Conducts the electrons that are freed from the hydrogen molecules so that they can be used in an external circuit Etched channels disperse hydrogen gas over the surface of catalyst Cathode Positive post of the fuel cell Etched channels distribute oxygen to the surface of the catalyst Conducts electrons back from the external circuit to the catalyst Recombine with the hydrogen ions and oxygen to form water Electrolyte Proton exchange membrane Specially treated material, only conducts positively charged ions Membrane blocks electrons Catalyst Special material that facilitates reaction of oxygen and hydrogen Usually platinum powder very thinly coated onto carbon paper or cloth Rough & porous maximizes surface area exposed to hydrogen or oxygen The platinum-coated side of the catalyst faces the PEM Proton-Exchange Membrane Cell (1) When H2 molecule comes contacts platinum catalyst, it splits into two H+ ions and two electrons (e-) (2) Make their way through the external circuit (doing useful work such as turning a motor) and return to the cathode side of the fuel cell (3) O2 forms two oxygen atoms, each with a strong negative charge Negative charge attracts the two H+ ions through the membrane Combine with an oxygen atom and two electrons from the external circuit to form a water molecule (H2O) http://www.news.cornell.edu/releases/Nov03/Fuelcell.institute.deb.html Electrochemical reactions involved in DMFC Anodic reaction(Oxidation): CH3OH + H2O 0.03 V CO2 + 6H + + 6e- Cathodic reaction (Reduction): 1.22 V 3/2 O2 + 6H+ + 6e3H2O Overall reaction: CH3OH + 3/2 O2 (Silva at al 2005) 1.19 V CO2 + 2H2O Direct Methanol Fuel Cell Pt catalyst have highest activity for MeOH oxidation thus far Ru enhances MeOH catalytic activity OH- forms at lower voltage CO blocks sites on Pt surface, Ru helps oxidize to CO2 Direct Methanol Membrane Fuel Cell Advantages: Direct fuel conversion – no reformer needed, all positive aspects of PEMFC CH3OH – natural gas or biomass Existing infastructure for transporting petrol can be converted to MeOH Problems: High catalyst loading (1-3mg/cm2 v 0.1-0.3 mg/cm2) CH3OH hazardous Low efficiency (MeOH crossover – lowers potential) Direct Methanol Membrane Fuel Cell Solving the Crossover Dilemma Alter thickness of polymer membrane Thinner = decreases ion flow resistance Thicker = decreases MeOH crossover Cs+ doped membranes Tricolli, University of Pisa, 1998 Lower affinity for H2O MeOH tolerant cathodes Mo2Ru5S5 – N Alonso-Vante, O Solorza-Feria Higher oxygen reduction activity in presence of MeOH (Fe-TMPP)2O – S Gupta, Case Western, 1997 High oxygen reduction, insensitive to MeOH