Visualization Analysis of Interrelationship between Temperature Profile and Water Distribution inside the PEFC
Authors: Shigemasa Kaito , Sato Hayate , Otsuki Yota , Kurosu Masato , Araki Takuto 
Published: February 2020

Introduction

For more spread of Polymer Electrolyte Fuel Cells (PEFCs), water management inside it is very important.
Water condensation and transportation modes are very difficult to reveal exactly, because there are many complicated phenomena inside Gas Diffusion Layer (GDL) which has fibrous structure and tiny pore diameter.
Temperature profile largely affects on water distribution inside a PEFC. Therefore, we should understand interrelationship between temperature profile and water distribution inside a PEFC to optimize water distribution.
There is a report [1] about interrelationship between them in which characteristics of heat transportation has been changed by changing type of GDL.
However, in [1], they couldn’t clarify interrelationship because the change of heat transportation characteristics was too small.
So in this report, by giving temperature gradient externally, temperature gradient inside cathode GDL of a PEFC was set. Then effects of temperature gradient in through-plane on water distribution in a PEFC is investigated.

Experimental method

X-ray CT
X-ray CT machine, TDM1000-H-Ⅱ(2K)(Yamato Scientific Corp.) was used for visualizing water distribution inside a PEFC. By using this machine, 3-D image of a sample can be got. Total shooting time was about 15 minute. Tube voltage was 30 kV and voxel size was about 2.7 µm.
Thin-Film Thermocouple (TFTC)
For local temperature measurement, original sensor was fabricated using Micro Electro Mechanical Systems (MEMS) in our laboratory. The sensor was so fine and thin that it wouldn’t disturb a reaction inside a PEFC. The thermocouple was made from Au and Ni. Its measurement point had about 30 µm width and about 6 µm thickness.
Cell Configuration
An active area of 1 cm2 PEFC cell was used, and is has five 1mm width gas channels and five 1mm width ribs with parallel flow configuration. 15 µm thick reinforces type PEM was used. TGP-H-060 (with MPL 2.0 mg/cm2) was used and in both anode and cathode side. TFTC was inserted between interface of anode CL/MPL and cathode CL/MPL.
Experimental proceed
First, conditioning of CCM was performed at 0.1 V for 30 minute. Then target temperature was set by temperature controller, and steady waiting was performed for 10 minute. Then some information of a cell (cell voltage, some temperature, and so on) was recorded. Finally, visualization by X-ray CT was performed. Wet gas was supplied to a cell, and water temperature in bubblers was set to 55 ℃.

Results and Discussion

Two experiments were performed with different temperature gradient by controlling temperature of each separator. One case is that anode temperature is high (An_high) and the another is that cathode temperature is high (Ca_high). Figure.1 shows temperature profile and visualization images inside PEFC. In Fig.1(a), temperature at interface was measured by TFTC, and boundary temperature (An_S, Ca_S) means temperature of separators and was measured by K-type thermocouples. As you can see Fig.1(a), in two temperature profile, both cCL/MPL temperature are almost same and temperature gradients are almost against. And as you can see Fig.1(b), there are some difference in water distribution although both of cCL/MPL temperature are almost same. From these results, we assume it is temperature gradient that largely affects water distribution, not absolute temperature.
Fig.1 Experimental results

Reference

[1] Sota H et al., ECS Trans., 80(8),143-153(2017)

Figure 1