Monitoring an Electrode Flooding Through the Back Pressure in a Proton Exchange Membrane (PEM) Fuel Cell

Abstract

For proton exchange membrane (PEM) fuel cells, proper water management is important to obtain maximum performance. In understanding the water process within the fuel cell, the exhaust back pressure was found to be a useful indicator of the water content within the cell. Measured back pressure at the exhaust is an indication of how much water content is in the membrane during the electrochemical reaction. From these experiments, the measured back pressure shows when the fuel cell suffered from flooding because of generated water. When humidified inlet gases are supplied to the fuel cell, maintaining back pressure at the exhaust is an indication that the produced water is removed properly by the supplying gas. For the cases of dry operation, the average back pressure at the anode side continued to increase due to the back diffusion. This back diffusion was a result of the water concentration gradient between the anode and the cathode. INTRODUCTIONA fuel cell is an energy conversion device that converts the chemical energy of a reaction directly into electrical energy without any intermediate thermal or mechanical processes. The basic structure of a fuel cell consists of an electrolyte layer in contact with a porous anode and cathode on each side. The anode is made of a substance that easily releases electrons, and the cathode is made of a substance that readily accepts electrons. In contrast to a fuel cell, a battery converts chemical energy stored in the chemical bonds of the reactants to electrical work in a closed system. A fuel cell, on the other hand, is an energy conversion device that has the capability of producing electrical energy for as long as the fuel and oxidant are supplied to the electrodes as an open system. In a proton exchange membrane (PEM) fuel cell, a gaseous fuel, typically hydrogen, is fed to the anode and an oxidant is fed to the cathode. This leads to the electrochemical reactions taking place at the electrodes to produce an electric current.The effect of water throughout the fuel cell needs to be investigated in terms of fuel cell performance. To be a promising power source for portable devices, transportation, and stationary systems, the proton exchange membrane fuel cell needs to overcome some critical issues. One of the most important remaining challenges is to maintain the membrane electrode assembly (MEA) water balance, since proton conductivity is dependent on water content.There are two processes to explain water transport in a PEM fuel cell: electro-osmotic drag and back diffusion. Electro-osmotic drag refers to the fact that as a proton is transported from anode to cathode, it can ''drag'' water molecules. The number of water molecules conducted through the membrane per proton is called the electro-osmotic drag coefficient. Since the inlet gases may include humidification and water is formed at the cathode as well, a water concentration gradient across the membrane may exist, which results in ''back diffusion'' of water molecules. Insufficient humidified inlet gases lead to water...

Modeling of liquid water transport in a proton exchange membrane fuel cell gas flow channel with dynamic wettability

“…Proton exchange membrane fuel cell (PEMFC) has high energy efficiency, zero emission, and rapid startup capability, making it a desirable clean power source for stationary, mobile, and portable applications. One of the critical issues in PEMFC is the water management because a delicate water balance is required to obtain a good cell performance and durability . Water accumulates in the cathode due to reaction and electroosmotic drag effect and is mainly removed by gas flow in the cathode gas flow channel; a good water management strategy in PEMFC hence requires the understanding of water behavior in the gas flow channel.…”

Pressure Effect on the PEMFC Performance

“…Y. H. Park and J. A. Caton found that the outlet back pressure is a useful indicator of the water content and relative humidity inside the PEMFC . With relative humidity of 100% at both anode and cathode side will result in flooding which decreases the performance of PEMFC.…”

Effects of catalyst layer structure and wettability on liquid water transport in polymer electrolyte membrane fuel cell

“…Furthermore, liquid water is one of the key factors responsible for the degradation of electrolyte membrane. Because Springer et al [9] and Bernardi and Verbrugge [10] developed a one-dimensional PEM fuel cell model including various modes of water transport, numerous research works have been focused on the analysis of water transport and management [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30]. Most of them addressed liquid water transport in the electrolyte membrane and GDL.…”