Corrosion studies of a copper–beryllium alloy in a simulated polymer electrolyte membrane fuel cell environment
Introduction
A fuel cell is an energy conversion device. It is an electrochemical device that converts chemical energy of fuel and oxidant into electricity. A fuel cell usually consumes chemicals, which are supplied in the form of hydrogen and oxygen to produce the electricity and thus are not exhaustible like batteries. Fuel cells find applications in vehicles, space shuttles, and various areas where electricity is needed [1].
A fuel cell is essentially an electrochemical cell consisting of two electrodes, namely anode and cathode. Hydrogen or another gaseous fuel is continuously fed to a porous anode and oxygen is continuously fed to the surface of a porous cathode. Electrochemical oxidation of the fuel takes place while oxygen is electrochemically reduced [2]. This reaction gives rise to a flow of electrons through the outer load and a flow of the ions (protons) through the electrolyte as shown in Fig. 1.
The two half cell reactions in the fuel cell are given by:
The overall reaction is thus
The fuel cell is an environmental friendly device since the only by-product of the cell reaction is water.
The bipolar plate is one of the most important components of the PEM fuel cell. It separates the individual cells in the stack. The main function of the bipolar plate is to provide a conduct for hydrogen and oxidant flow. It accounts for approximately 80% of the weight of fuel cell. Due to the critical machining requirement for gas flow fields, the bipolar plates contribute approximately 15% of the total cost of stack components [3]. Earlier various materials like graphite, SS316, molded composites were proposed and used as the bipolar plate material [4], [5], [6].
Several researchers have reported that the PEM fuel cell functions in an acidic environment (pH 3.0–5.0) due to presence of SO42−, Cl−, F−, etc. ions in the Nafion® membrane [7], [8]. The material for bipolar plate application must have good corrosion resistance and conductivity to reduce resistive losses in the acidic environment. Copper and copper alloys are well known for their good electrical and thermal conductivity. Copper–beryllium alloy (C-17200) was considered in this study because of its good conductivity, oxidation resistance, and corrosion resistance.
The corrosion behavior of copper–beryllium alloy (C-17200) in a fuel cell environment was studied using electrochemical techniques. The experimental data is essential for understanding and modifying corrosion behavior of materials in fuel cell.
Section snippets
Experimental procedure for corrosion experiments
The electrochemical experiments were carried out in a simple cell consisting of a three-electrode arrangement with a working electrode, auxiliary electrode, and a reference electrode as shown in Fig. 2. The counter electrode was platinum foil spot welded to platinum wire sealed in Pyrex, and Accumet™ saturated calomel reference electrode was fixed in the separable funnel outside the cell. The funnel was filled with saturated KCl solution. The sealed funnel was carefully attached to the cell
Experiments in 0.5 M H2SO4 electrolyte environment
Tafel extrapolation plots for various conditions in 0.5 M H2SO4 are presented in Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7.
Discussion
The corrosion results for the C-17200 alloy were compared with corrosion properties of other copper and copper alloys. Several reports have discussed the behavior of copper and its alloys in an acidic environment. Some literature has reported the change in pH of the solution due to formation and consumption of H+ ions [16], but due to very small span of experiment (<5 min for scan) this possibility can be neglected. Its long been known that copper and its alloys are prone to a higher corrosion
Conclusions
The experiments in the simulated fuel cell environment were carried out and the corrosion rates of the selected alloy at all experimental conditions were observed to be well within the DOE specified norm. The formation of a duplex type of oxide layer was observed to be formed as the corrosion product. The alloy tested can be considered as a candidate material for PEMFC bipolar/end plates. The corrosion resistance along with the high conductivity are the advantages of copper alloys over
Acknowledgments
Authors are very pleased to acknowledge the financial support given by US Department of Energy (DOE). The financial support given by Center for Advanced Vehicle Technology at the University of Alabama is also appreciated.
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