Design and development of large-scale flow fields and bipolar plates for PEM fuel cells in aircraft applications

Kurzfassung

Keeping the rise in average global temperature well below 2 °C above pre-industrial levels, coupled with other factors, has brought hydrogen back into the scene. This energy carrier is widely available and can be produced and used with virtually no greenhouse gas (GHG) emissions, playing an important role in the electrification and decarbonisation of key segments of the economy. A fuel cell can convert the chemical energy contained in hydrogen and use it to produce electricity, with water and heat as by-products. From the 5 major types of fuel cells, Proton Exchange Membrane Fuel Cells (PEMFCs) present some interesting features which makes them popular on the transportation sector. The performance of such a device depends on how the reactants are fed and distributed across the cell. The design of the so-called flow field is, therefore, not only a vital part of the bipolar plate (BPP) but also for the functioning of the fuel cell. The present work aims to support the development of a BPP for a fuel cell with an active area of 900 to 1200 cm2. This study is part of the Project BALIS, which ultimately aims to develop and test a fuel cell powertrain for a regional aircraft with an output of approximately 1.5 MW. This is significantly above any of the most powerful fuel cell stacks existing on the market and, therefore, is a bold and complex task. For this purpose, the fundamentals of fuel cells are detailed and the importance of the BPP and the flow field is highlighted. Then, a thorough investigation is made about the most powerful PEMFCs stacks on the market (especially within the automotive sector), followed by a literature study on the most important aspects of flow field design for PEMFCs and their influence on the performance (including a review on the typical flow field patterns and the most recent state-of-knowledge). Subsequently, a brief analysis of the implications of a stack of such a magnitude, concerning the active area and number of cells, is provided. With all this background, the first design attempts are made and improved until, eventually, a final sketch of a flow field is proposed. This idea is supported with some experimental and computational data from other studies conducted at DLR. Finally, all the steps for the creation of the ultimate design in a computer-aided design (CAD) software are described and the end product unveiled.