Visualization and Measurement of Water Distribution in Through-Plane Direction of Polymer Electrolyte Fuel Cell during Start-Up by Using Neutron Radiography

Hideki Murakawa,Katsumi Sugimoto,Nobuki Kitamura,Nobuyuki Takenaka,Hitoshi Asano,Yasushi Saito

doi:10.4236/jfcmv.2015.33012

Hideki Murakawa, Katsumi Sugimoto + Show 4 more

Open Access

https://doi.org/10.4236/jfcmv.2015.33012

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Abstract

Water management in a polymer electrolyte fuel cell (PEFC) is a key topic for PEFC operation. A microporous layer (MPL) has been recently used to improve the water flooding in the gas diffusion layer (GDL) around the catalyst layer. However, the mechanisms of this MPL are not completely understood because of the difficulty of measuring the water distribution during operation. To clarify the water-accumulation phenomena with the MPL, visualization and measurement of the water distribution in the through-plane direction of a small fuel cell is carried out by using neutron radiography. The parallelism of the neutron flux is optimized by using a collimator to observe the transient change in the water distributions, and two-dimensional water distributions in the through-plane direction of the PEFC can be obtained every 60 s. The differences in the water accumulation processes in the GDL without and with the MPL under the lands and channels are compared. It is observed that the water accumulation in the GDL under the land is greater than that under the channel during the period of early PEFC operation. Water evacuation from the GDL to the channel mainly occurs around the land corners. Furthermore, one-dimensional water distributions are calculated from the visualized water distributions, and the results without and with the MPL in the cathode are compared. The water thickness in the through-plane direction attains its maximum value around the boundary between the catalyst layer and the GDL without the MPL, whereas it is attained between the MPL and the GDL with the MPL. The maximum water accumulation in the GDL under the land without the MPL is higher than that with the MPL.

Highlights

Our goal is to investigate the transient change in the water distribution in an operating polymer electrolyte fuel cell (PEFC) and the effect of the microporous layer (MPL) on the water transport and cell performance using neutron radiography
Two-dimensional water distributions in the through-plane direction are visualized every 60 s during start-up, and it is shown that neutron radiography is effective for observing the transient change in the water distribution in the PEFC during start-up
It is observed that the water accumulation in the gas diffusion layer (GDL) under the lands is greater than that under the channels during the early period of PEFC operation

Summary

Introduction

Fuel gas (hydrogen gas) and oxidant gas (air) are supplied to the PEFC from the gas channels. Condensation may be occurred on the cathode side because the vapor is supersaturated by the fuel-cell reactions. When condensed water exists in the GDL, gas diffusion is depressed as flooding. A larger amount of water in the gas channels may prevent the gas supply in the channel, and the cell performance decreases because oxygen is prevented from reaching the cathode reaction site. Water management is significantly important for PEFC performance, and clarification of the water-transport mechanisms between the PEM, GDL, and gas channels is of great concern. Many investigations on water management have been carried out concerning water movement inside the PEM, water flooding in the GDL, and water plugging in the channel [1]-[3]

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