Active Area Determination for Porous Pt-Electrodes used in PEM Fuel Cells - Temperature And Humidity Effects

To achieve optimal performance of proton exchange membrane (PEM) fuel cells, effective water management is crucial. Cells need to be fabricated to operate over wide ranges of current density and cell temperature. To investigate these design and operational conditions, the present experiment utilized neutron radiography for measurement of in-situ water volumes of operating PEM fuel cells under varying operating conditions. Fuel cell performance was found to be generally inversely correlated to liquid water volume in the active area. High water concentrations restrict narrow flow field channels, limiting the reactant flow, and causing the development of performance-reducing liquid water blockages (slugs). The analysis was performed both quantitatively and qualitatively to compare the overall liquid water volume within the cell to the flow field geometry. The neutron image analysis results revealed interesting trends related to water volume as a function of time. At temperatures greater than 25°C, the total liquid water volume at start-up in the active area was the lowest at 1.5 A/cm2. At 25°C, 0.1 A/cm2 performed with the least amount of liquid water accumulation. However, as the reaction progressed at temperatures above 25°C, there was a crossover point where 0.1 A/cm2 accumulated less water than 1.5 A/cm2. The higher the temperature, the longer the time required to reach this crossover point. Results from the current density analysis showed a minimization of water slugs at 1.5 A/cm2, while the temperature analysis showed unexpectedly that, independent of current density, the condition with lowest water volume was always 35°C.

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Non-active area water mitigation in PEM fuel cells via bipolar plate surface energy modification

International Journal of Hydrogen Energy ◽

10.1016/j.ijhydene.2017.11.018 ◽

2018 ◽

Vol 43 (2) ◽

pp. 908-920 ◽

Cited By ~ 3

Author(s):

Xuan Liu ◽

Thomas A. Trabold

Keyword(s):

Fuel Cells ◽

Surface Energy ◽

Bipolar Plate ◽

Pem Fuel Cells ◽

Active Area ◽

Plate Surface

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The Role of Channel Plurality in Two-Phase Flow Instabilities in PEM Cathode Channels

ASME 2011 9th International Conference on Fuel Cell Science, Engineering and Technology ◽

10.1115/fuelcell2011-54408 ◽

2011 ◽

Author(s):

Nicholas Siefert ◽

Colin O’Shea ◽

Shawn Litster

Keyword(s):

Fuel Cells ◽

Two Phase Flow ◽

Pem Fuel Cells ◽

Flow Instabilities ◽

Active Area ◽

Phase Flow ◽

Constant Number ◽

Two Phase ◽

Voltage Loss ◽

Dimensional Parameters

Water management is a critical issue in the development of proton exchange membrane (PEM) fuel cells with robust operation. Liquid water can accumulate and flood the gas delivery microchannels and the porous electrodes within PEM fuel cells and deteriorate performance. Since the liquid distribution fluctuates in time for two-phase flow, the rate of oxygen transport to the cathode catalyst layer also fluctuates, resulting in unstable power density and efficiency. In previous research into measuring the voltage loss and voltage fluctuation due to two-phase flow instabilities in the cathode channels of PEM fuel cells, we investigated the effect of the number of parallel channels covering the active area by studying flow fields with varying numbers of parallel channels (4 to 25) while keeping the active area constant at 5 cm2. The resulting voltage loss and fluctuation measurements were expressed as functions of two non-dimensional parameters: channel plurality and the air flow stoichiometric ratio. Channel plurality is a flow field design parameter that defines the number of channels per unit of active area, which is non-dimensionalized by the cross-sectional area of the channels. In this paper, we expand upon our prior studies by studying cathode flow field designs of varying active area, from 5 cm2 to 25 cm2, with a constant number of 25 channels. By increasing the active area with a constant number of channels, we are reducing the channel plurality value. The new results are mapped back to the non-dimensional parameters to extract empirical scaling rules for voltage loss and fluctuation. Furthermore, we compare this data to our prior work with constant active area and identify the significance of the fuel cell size in the scaling relationships. Finally, a refined scaling is presented for generalizing the results for fuel cells having different active area and number of channels.

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