Mathias Gerard

Ripple Current Effects on PEMFC Aging Test by Experimental and Modeling

Polymer electrolyte membrane fuel cells’ (PEMFCs) systems usually require power conditioning by a dc-dc boost converter to increase the output fuel cell voltage, especially for automotive applications and stationary applications. The output fuel cell current is then submitted to the high frequency switching leading to a current ripple. The ripple current effects on fuel cell are studied by experimental ripple current aging test on a five cell stack (membrane electrode assembly (MEA) surface of 220 cm2) and compared with a reference aging test. The stack is run in nominal conditions but an ac component is added to the dc load. The ac component is a 5 kHz triangle, amplitude of which is ±20% of the dc component, in order to simulate a boost waveform. Fuel cell characterizations (polarization curves, impedance spectra, and voltammetry) provide information on the PEMFC aging and the performance evolution. Local conditions are computed through a dynamic stack model. The model takes into account transport phenomena, heat transfer, and semi-empirical electrochemical reactions and includes a meshing to calculate local conditions on the MEA surface (gas reactant pressures, local temperature, gas molar fractions, water activity, and local electronic current density). The consequences about performance and aging during high frequency ripple current are explained.

Ripple Current Effects on PEMFC Ageing Test by Experimental and Modeling

PEMFCs’ systems usually require power conditioning by a DC/DC boost converter to increase the output fuel cell voltage, especially for automotive applications and stationary applications. The output fuel cell current is then submitted to the high frequency switching leading to a current ripple. The ripple current effects on fuel cell are studied by experimental ripple current ageing test on a 5 cell stack (MEA surface of 220 cm2 ) and compare to a reference ageing test. The stack is run in nominal conditions but an AC component is added to the DC current load. The AC component is a 5 kHz triangle which amplitude is ±20% of the DC component in order to simulate a boost waveform. Fuel cell characterizations (polarization curves, impedance spectra and voltammetry) provide information on the PEMFC ageing and the performance evolution. Local conditions are computed through a dynamic stack model. The model takes into account transport phenomena, heat transfer, and semi-empirical electrochemical reactions and includes a meshing to calculate local conditions on the MEA surface (gas reactant pressures, local temperature, gas molar fractions, water activity, and local electronic current density). The consequences about performance and ageing during high frequency ripple current are explained.Copyright

Distribution Study of Species and Current Density During Oxygen Starvation

In a fuel cell system the stack is strongly coupled with the main system components, among which the compressor is one of the most important. Malfunction of this auxiliary device (delay during peak power, low stoichiometry operation, emergency stop, etc.) is directly responsible for bad oxygen distribution in the cathode (substoichiometry reactants feeding). This phenomenon is usually called oxygen starvation. In this study we want to identify the consequences of oxygen starvation on the performance and durability of polymer electrolyte membrane fuel cell stacks, and more particularly, on the current distribution along the cell. The oxygen concentration decreases along the channel and induces a change in the local electrochemical response; it means that the local current density on the cell is redistributed on the surface. This bad distribution of reactive gas (in a transient time or long time) decreases the performance but may also have an effect on cathode degradation such as carbon corrosion and platinum dissolution/oxidation. The current distribution along the cell is studied by two approaches (modeling and experiments). The 3D model using serpentine bipolar plate meshing is adapted to dynamically compute for the catalyst layer local conditions (local current, temperature, gases partial pressure, and water activity). It is able to reproduce the conditions of low or high oxygen concentration in the cathode side. The experiments are performed with a bi-cell stack developed by CEA with specific design for the magnetic sensors (the local current is computed by measuring the local induced magnetic field and using the Maxwell equations).

Hybrid Electric System for an Hydrogen Fuel Cell Vehicle and its Energy Management

Fuel cell vehicles, (FCV) are characterized by the utilization on the same electric bus of an hydrogen fuel cell (FC) as a primary energy source and of storage elements like batteries as a secondary source. In our project, the fuel cell is a Polymer Electrolyte Membrane (PEM), which is well adapted for transport field applications. A Lithium rechargeable battery, more specifically a LiFePO4, is used to supplement the FC over the driving cycle. According to the requirements of the drive cycle of the vehicle, a 30 kW PEM FC system and a 4.5 kWh LiFePO4 battery is considered here.