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Uso de la técnica de interrupción de corriente para la caracterización de una celda de combustible no humidificada con membrana de intercambio protónico
Ruiz Román, Jessica M.
Ruiz Román, Jessica M.
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Abstract
Due to the energetic crisis, the US government has promoted the development of
alternatives resources for the generation of electricity. Fuel Cells have emerged as one of
the most promising technologies for the power source of the future. A fuel cell is an
electrochemical reactor where the energy of a chemical reaction (hydrogen and oxygen)
is converted directly into electricity using a proton exchange membrane. The Proton
exchange membrane (PEM) has some inefficiencies that can be measured using a current
interruption technique with hydrogen and oxygen as raw materials. The current
interruption method instantaneously stops the current through the membrane. The
response of the membrane during this change is used to characterize it. A Tektronix TDS
3032 oscilloscope was used to measure the voltage drop of the system. Three different
fluxes of hydrogen and oxygen at stoichiometric rates were studied in this work (8.5, 5.3
and 2.7ml/min for hydrogen flow). The results are presented using two graphical
approaches: one for open and another for the closed circuit. The graphs were classified
according to regions. Region 1 is attributed to kinetics effects. Region 2 was attributed to
kinetics and mass transfer effects. Region 3 was attributed to equilibrium phase. The
information obtained with current interruption technique was used to find an equation
that describe the open circuit and close circuit behavior. An exponential equation
describe the closed circuit and a sixth order polinomial equation describe the open circuit
graphs. Also, was find an equivalent circuit of the cathode region using Micro Sim®
simulation program. Micro Sim® permits to find an equivalent circuit that simulates the
current signal and open circuit voltage response. The equivalent circuit describes the
region 1 and 3 behavior for the closed circuit using one resistance of 0.8Ω to simulate
region 1 and other resistance of 0.8Ω and 250mF capacitor to simulate region 3. Region
2 was not possible to simulate because the system exhibited two contributions (charge
and mass transfer effects) that convert this region in a non-linear second order behavior.
This non-linear behavior could lead to postulate a reaction mechanism with the transfer
of protons through the membrane as the rate-limiting step. In conclusion, the current
interruption technique allowed for the action of offering a graphical represenation of fuel
cell membrane equipment. For future works is recommended to repeat the same series of
experiments for anode that will permit to find an equivalent representative circuit of the
total PEM fuel cell.
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Date
2005
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Keywords
Membrana de intercambio protónico (PEM), Técnica de interrupción de corriente