scholarly journals Microscopic Observations of Freezing Phenomena in PEM Fuel Cell at Cold Starts

2011 ◽  
Author(s):  
Takemi Chikahisa
Keyword(s):  
Water Transport ◽  
Porous Layer ◽  
High Current Density ◽  
Transport Phenomena ◽  
Catalyst Layer ◽  
Optical Microscope ◽  
Gas Diffusion ◽  
Ice Formation ◽  
Micro Channels ◽  
Cold Starts

In Polymer electrolyte membrane fuel cells (PEMFCs), the generated water transfers from the catalyst layer to the gas channel through micro channels of different scales in a two phase flow. It is important to know details of the water transport phenomena to realize better cell performance, as the water causes flooding in the high current density conditions and start up problem under freezing temperatures. The keynote speech presents specifics of the ice formation characteristics in the catalyst layer and in the gas diffusion layer (GDL) with photos taken with an optical microscope and a CRYO-SEM. The observation results show that cold starts at −10°C results in ice formation at the interface between the catalyst layer and the micro porous layer (MPL) of GDL, at −20°C most of the ice is formed in the catalyst layer. Water transport phenomena through the micro porous layer and GDL are also a matter of interest, because the role of the MPL is not well understood from the water management angle. The speech will discuss the difference in the water distribution at the interface between the catalyst layer and the GDL arising from the presence of such a micro porous layer.

Microscopic Observation of Ice Distribution in PEM Fuel Cell at Cold Start

2011 ◽  
Author(s):  
Yutaka Tabe ◽  
Masataka Saito ◽  
Ryosuke Ichikawa ◽  
Takemi Chikahisa
Keyword(s):  
Produced Water ◽  
Polymer Electrolyte Membrane ◽  
Catalyst Layer ◽  
Cold Start ◽  
Optical Microscope ◽  
Gas Diffusion ◽  
Ice Formation ◽  
Electrolyte Membrane ◽  
Cathode Catalyst Layer ◽  
Observation Results

In Polymer electrolyte membrane fuel cells (PEFCs), freezing of produced water induces the extreme deterioration of cell performance below zero. This phenomenon is a serious problem in cold regions and is needed to be solved to achieve the practical use of PEFCs. In this study, we investigated ice distribution at the cold start in a PEFC using an optical microscope and a CRYO-SEM to clarify the freezing mechanism. The observation results showed that the cold start at −10°C makes ice at the interface between the cathode catalyst layer (CL) and the micro porous layer of gas diffusion layer. Little ice was, however, observed in the cold start at −20°C, which indicated the ice formation inside the CL. The CRYO-SEM observation was conducted at −20°C to investigate the ice formation inside the CL, and this identified the effects of the current density and the cathode gas species on the ice distribution.

In-Situ Observation of the Water Distribution in Porous Layers of PEMFCs by Soft X-Ray Radiography

2010 ◽  
Author(s):  
Takashi Sasabe ◽  
Shohji Tsushima ◽  
Shuichiro Hirai
Keyword(s):  
Water Transport ◽  
Temporal Resolution ◽  
Liquid Water ◽  
Water Distribution ◽  
Transport Phenomena ◽  
Catalyst Layer ◽  
In Situ Observation ◽  
X Ray ◽  
Porous Layers ◽  
Liquid Water Transport

To observe the liquid water distribution in porous layers of an operational Proton Exchange Membrane Fuel Cell (PEMFC) with high spatial and temporal resolution, Laboratory-based soft X-ray microscopy has developed. This system can generate low energy X-ray in the soft X-ray range, and maximum sensitivity towards water is achieved. A point X-ray source with a diameter of less than 1.0 μm and the improved detector optics contribute to realize a spatial resolution of 500 nm and a temporal resolution of 1.0 sec/frame. In addition, in-plane and through-plane observations of an operational PEMFC were carried out. In the in-plane observation test, non-uniform distribution of liquid water in the plane of the catalyst layer was observed, and the importance of appropriate design of the catalyst layer to liquid water transport phenomena was suggested. In the through-plane observation test, liquid water discharge behavior near under the rib area was observed, and the importance of channel wall wettability to liquid water transport phenomena was also suggested.

Water Transport in a PEMFC Based on the Difference in Capillary Pressure Between the Cathode Catalyst Layer and Microporous Layer

2015 ◽  
Vol 12 (5) ◽  
Author(s):  
Enju Nishiyama ◽  
Masaya Hara ◽  
Toshiaki Murahashi ◽  
Kazushige Nakao
Keyword(s):  
Capillary Pressure ◽  
Water Transport ◽  
Proton Exchange Membrane ◽  
Effective Diffusivity ◽  
Catalyst Layer ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Diffusion Resistance ◽  
Cathode Catalyst ◽  
Cathode Catalyst Layer

The water transport behavior of the cathode catalyst layer (CCL) in a proton exchange membrane fuel cell (PEMFC) was investigated by comparing the performance of several cells containing different microporous layers (MPLs). The capillary pressure and effective diffusivity of the cathode gas diffusion layer (GDL) and the CCL play an important role in the transport of water generated in the PEMFC. Experimental data for various inlet humidities and air stoichiometries were evaluated using the modified water vapor activity with the capillary pressure of the MPL. The capillary pressures in the MPLs and CCL are approximated using a polynomial function of liquid saturation. There was a significant increase in the diffusion resistance of oxygen in the CCL, while that in the MPLs and CCL was moderate, which indicates that the CCL is susceptible to flooding.

Modeling Carbon Black Aggregate Structure and Ionomer Coat for Optimum Design of PEFC Catalyst Layer

2011 ◽  
Author(s):  
Gen Inoue ◽  
Yun Peng Fan ◽  
Takahiro Matsuoka ◽  
Yosuke Matsukuma ◽  
Masaki Minemoto
Keyword(s):  
Carbon Black ◽  
High Current Density ◽  
Transport Phenomena ◽  
Computer Calculation ◽  
Catalyst Layer ◽  
Polymer Electrolyte Fuel Cell ◽  
Void Space ◽  
Aggregate Structure ◽  
Porous Catalyst ◽  
Reaction Field

In present Polymer Electrolyte Fuel Cell (PEFC), the cathode oxygen reduction reaction (ORR) is dominant at high current density condition. In order to accelerate this reaction, oxygen, proton and electron, which move in void space, ionomer and carbon black (CB) or CNT respectively, have to be transferred at Pt surface smoothly. Accordingly, it is very important to know the transport phenomena in catalyst layer (CL) to design the optimum structure and to develop new materials. In order to investigate the transport phenomena in CL by applying calculation technique, in this study, heterogeneous CB aggregate structure was simulated by computer calculation as the first examination. In addition, ionomer coating condition and proton conductivity were examined. Furthermore oxygen, proton and electron transfer in 3D porous catalyst layer were calculated, and the effective reaction field was examined in various structure and ionomer condition.

The Analysis of Mass Transport Phenomena in Micro Porous Layer for High Current Density Operation in PEMFC for Automobile Application

2013 ◽  
Author(s):  
Toshikazu Kotaka ◽  
Koichiro Aotani ◽  
Yuichiro Tabuchi ◽  
Partha Mukherjee
Keyword(s):  
Contact Resistance ◽  
Porous Layer ◽  
Oxygen Transport ◽  
Current Density ◽  
High Current Density ◽  
Transport Phenomena ◽  
Dominant Factor ◽  
High Current ◽  
Micro Structure ◽  
Carbon Particles

Cost reduction is the most important issue for commercialization of Fuel Cell Electric Vehicle (FCEV). High current density operation is one of the solutions for it. In order to realize high current density operation, it is necessary to reduce both of electron and oxygen transport resistance in the porous materials such as gas diffusion layer (GDL) and micro porous layer (MPL). However, the impacts of MPL microstructure on their properties are not fully understood yet compared with GDL because of the necessity of higher spatial resolution. In previous study, the transport analysis on the micro-structure which were visualized by Nano X-ray CT and FIB-SEM were conducted for it. However, it was not enough to understand both of the electron and oxygen transport phenomena and find the dominant factors, because there is no study which focused on the comparison of the numerical and experimental results on both of the electron and oxygen transport. In this study, the comprehensive analysis on both of electron and oxygen transport phenomena in GDL and MPL was conducted with experimental and numerical study based on the three-dimensional (3D) micro structure data. As a result, it was found that pore structure, such as a local porosity and/or tortuosity significantly affected the oxygen transport phenomena. On the other hands, especially in the case of electron transport phenomena in MPL, our results suggested that the dominant factor is not the solid structure such as local solid fraction and/or tortuosity but the contact resistance between carbon particles. This fact revealed that it is effective way to reduce the contact resistance between carbon particles and/or the number of contact points in unit length of a transport path in order to improve electrical transport of MPL.

Effect of Wettability of Micro-Porous Layer on Microscopic Water Transport Phenomena in PEFC

2014 ◽  
Vol 64 (3) ◽  
pp. 527-535 ◽  
Author(s):  
Y. Aoyama ◽  
K. Suzuki ◽  
Y. Tabe ◽  
T. Chikahisa ◽  
T. Tanuma
Keyword(s):  
Water Transport ◽  
Porous Layer ◽  
Transport Phenomena
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