(229g) A Novel Microporous Graphite Bipolar Plate Design for Effective Water Management in PEM Fuel Cells

Proton exchange membrane (PEM) fuel cell is an attractive clean-energy technology, that could be a viable alternative to the colossal burning of fossil fuels in vehicles powered by internal combustion engines [1, 2]. The bipolar plates, which are critical components of a PEM fuel cell stack, are associated with several functions. They provide cell-to-cell electrical contact in the stack, generate uniform flow fields for hydrogen and air, act as heat transfer surfaces, and prevent leakage of gases and coolant. Bipolar plates also significantly contribute to nearly 80 % of the total weight and 45 % of the total cost of the fuel cell stack [3]. Hence, there is significant interest in finding new materials for bipolar plates. Current bipolar plates are either metal-based or graphite-based. Metal-based bipolar plates are prone to chemical attack in the corrosive environment of the fuel cell (pH of 2-4 and temperatures around 80 °C). Electrocatalyst poisoning, ion-exchange of the dissolved metal ions with the membrane, and formation of a high impedance oxide surface layer are some of the problems associated with metal plates. Graphite plates have better chemical stability than metals but are brittle. Carbon-based composite bipolar plates, on the other hand, have improved flexural strength (albeit at the cost of lower electrical conductivity) than pure graphite plates. Other characteristics such as lower density and a relatively facile manufacturing process make carbon-based polymer composites promising alternatives to metallic or purely graphite plates.

Water management is an important consideration for the effective operation of a PEM fuel cell [4]. The PEM must be sufficiently hydrated to sustain high ionic conductivity. Conversely, excessive accumulation of water, referred to as flooding of the fuel cell, is a significant problem that needs to be appropriately tackled. Water is produced at the cathode of the fuel cell due to the oxygen reduction reaction. Water is also formed by condensation from humidified reactant gas feeds. Additionally, the protons transferred from the anode to the cathode bring along their water of hydration. Because of water accumulation by these processes, the gas flow channels, feeding oxygen to the cathode, get flooded with water. Oxygen transport to the fuel cell is blocked, which results in intermittent power losses. The presence of water in the gas flow channels or the gas diffusion layer can result in the inhomogeneous and discontinuous distribution of reactants over the active catalyst area, which not only affects the performance of an individual cell but also leads to cell-to-cell performance variations within a stack. Thus, water management is a critical issue in PEM fuel cell technology.

The work reported herein focuses on the production and properties of novel graphite-polymer composite plates designed to address the water management problem [5]. Microporous plates, whose porosity was tailored for the desired up-take of water produced during fuel cell operation through capillarity, while offering sufficient resistance to permeability and leakage of gaseous fuel, were synthesized using graphite, water-based resins, and pore-forming additives. Bipolar plate properties such as water-uptake by wicking and suction (vacuum fill), the pressure required to force gas through the water seal in the plates, through-plane, and in-plane electrical conductivities, and flexural strength of the plates were measured and correlated with plate composition. Bipolar plates that met or exceeded the US Department of Energy (DOE) 2020 requirements were obtained [6]. The synthesis and properties of these new bipolar plates will be presented in this talk.

References:

1. D.F. Dominković, I. Bačeković, A.S. Pedersen, G. Krajačić, The Future of Transportation in Sustainable Energy Systems: Opportunities and Barriers in a Clean Energy Transition, Renewable and Sustainable Energy Reviews, 82 (2018) 1823-1838. doi: 10.1016/j.rser.2017.06.117
2. A. Albarbar, M. Alrweq, Proton Exchange Membrane Fuel Cells: Review, in: A. Albarbar, M. Alrweq (Eds.) Proton Exchange Membrane Fuel Cells: Design, Modelling and Performance Assessment Techniques, Springer International Publishing, Cham, 2018, pp. 9-29. doi: 10.1007/978-3-319-70727-3_2
3. R.A. Antunes, M.C.L. Oliveira, G. Ett, V. Ett, Corrosion of Metal Bipolar Plates for PEM Fuel Cells: A Review, International Journal of Hydrogen Energy, 35 (2010) 3632-3647. doi: 10.1016/j.ijhydene.2010.01.059
4. O.S. Ijaodola, Z. El- Hassan, E. Ogungbemi, F.N. Khatib, T. Wilberforce, J. Thompson, A.G. Olabi, Energy Efficiency Improvements by Investigating the Water Flooding Management on Proton Exchange Membrane Fuel Cell (PEMFC), Energy, 179 (2019) 246-267. doi: 10.1016/j.energy.2019.04.074
5. S. Krishnan, M. Harrington, A.P. Pitchiya, Z. Putnam, D. Orlowski, Material Compositions and Methods for Porous Graphite-Polymer Composite Bipolar Plates, U.S. Patent Appl. 62/726,245 (2018)
6. A.P. Pitchiya, Microporous Graphite Bipolar Plates for Proton Exchange Membrane Fuel Cells, M.S. Thesis, Department of Chemical and Biomolecular Engineering, Clarkson University (2018).