The need to prolong the life of proton-exchange membrane fuel cell has of late accelerated. Researchers have realized that water management in the fuel cell has a major influence in the cell and stack performance. More so, it directly affects the durability of the cell components. Normally, the quantity of water generated at the cathode is directly proportional to the current density, therefore, the water removal capability of the cathode is a critical parameter for ensuring ultimate fuel cell performance.
Additionally, an appropriate water balance in the cell is crucial for durability purposes. Water evolution and build up during the start-up of proton-exchange membrane fuel cell is equally important, especially, since the relative humidity conditions around the electrodes are prone to variations. Therefore, to strike this balance, a technique that enables both the quantification and visualization of the local water content within the cell during operation, would be crucial. Besides, most of the two-phase flow studies found in literature center on the steady state behavior of water in the proton-exchange membrane fuel cell, whereas relatively few works address the transient behavior of the water build-up and evolution.
Alfredo Iranzo and colleagues proposed a study on water build-up and evolution during the start-up of a proton-exchange membrane fuel cell: Visualization by means of Neutron Imaging – a technique that allows visualization and quantification of local water content in the cell during operation simultaneously. Their main objective was to further look into the water build up and evolution during the start-up the cell, for a set of different anode and cathode relative humidity conditions. Their research work is published in International Journal of Hydrogen Energy.
Briefly, the empirical procedure involved operating a commercial 50 cm2 proton-exchange membrane fuel cell with serpentine flow fields at 2.0 bars and 60 C with varying relative humidity values for the inlet reactants. Between each tests, the team ensured that the cell was decompressed and the liquid water was thus flushed out. They then utilized Neutron Imaging to record the liquid water build up and the time evolution during each experiment. Eventually, they conducted a qualitative and quantitative analysis using the recorded data.
The research team mainly observed that the dynamics of the water build up comprises of three main stages, where the main difference is the local liquid water accumulation rate. They noted that the onset location for the water appearance in the flow field channels was determined by the flow field design, gravity and gas flow direction along the serpentine path. Eventually, they analyzed the time evolution of the water progressive accumulation along the flow field channels and cell active area.
Herein, a comprehensive experimental investigation of channel liquid water distributions in a 50 cm2 Proton-exchange membrane fuel cell with serpentine flow field has been presented. Neutron radiographs have been used to determine water build-up and time evolution of the liquid water content and distributions for a set of several varying operating conditions of the cell. The outcomes of this study are impressive and provide crucial insight into the liquid water dynamics during cell transients that can contribute to a better understanding and optimized design of cell components and operating conditions, which should result in an optimized performance of the cell dynamics in applications such as automotive fuel cells dealing with driving cycles.
Alfredo Iranzo, Antonio Salva, Pierre Boillat, Johannes Biesdorf, Elvira Tapia, Felipe Rosa. Water build-up and evolution during the start-up of a PEMFC: Visualization by means of Neutron Imaging. International journal of hydrogen energy volume 42 (2017) pages 13839-13849.
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