60 Using hydrogen fuel cells reduces demand for battery power. Project 821 stores 543 kW hours of energy in batteries, compared with Feadship’s first diesel-electric hybrid, the 83.50 m Savannah, which was launched in 2015, and stored 1 MW. Next year, two long-route Norwegian passenger and car ferries will enter into service using the marine fuel cells developed by PowerCell Group for Project 821. The company is also supplying two 100 kW marine fuel-cell systems to retrofit the The Prince Madog, a research vessel co-owned by Bangor University. Big trucks Honda and General Motors (GM) in the US have been working on fuel-cell systems for big trucks over the last decade, and have now shown a large, Class 8 truck. The truck uses a new generation of fuel-cell and system design that has been developed from the ground up over the last eight years to improve energy density and cut costs by two-thirds. The Honda system uses a solid, polymer membrane and each cell consists of an electrode assembly, where a solid, polymer membrane is sandwiched between a hydrogen electrode and an air electrode. This is combined with bipolar plates that act as separators to form the flow paths for hydrogen, air and coolant. Each cell functions as generation unit and fuel-cell stack, consisting of layers of individual cells. The development team revamped the whole fuel-cell system, starting with the cell structure. In the previous system, one cell unit consisted of three sheets of separators and two sheets of electrode assembly (MEA). In this generation, the cell structure is simplified to consist of one sheet of separator that welds two plates together and one sheet of electrode assembly (unitised electrode assembly, or UEA) per unit. A flow path for coolant is formed inside the bipolar plate, while the flow path for hydrogen and air is formed between the bipolar plate and the UEA. This structure enables the cooling of each cell, instead of cooling every two cells adopted for the previous one. Cooling performance was improved by optimising the aspect ratio of the cell, leading to increased durability. While the previous system required flow-path structures on both the separator and plastic frame of the membrane, the new system consolidates the flow-path structures on the bipolar plate, allowing the plastic frame to have a simpler structure, helping to lower costs. As coolant flows through the hollow between the two welded plates, the separators require very precise welding. A high-precision laser technology was thus co-developed by Honda and GM to weld the metal plates together. As the electrode assembly is sandwiched between two bipolar plates to create flow paths for hydrogen and air, the cell sealing is critical. The previous system used silicone rubber moulded onto a special metal plate to ensure sealing performance using the elasticity of the rubber. Now, the system uses a more common metal seal, and the elasticity of the hollow spring structure formed by the two plates is used for sealing. The micro seal is screen-printed for higher sealing performance. To ensure electrical conductivity, instead of applying gold-plating to the entire surface, a new film formation method was adopted using physical vapour deposition (PVD) coating to deposit carbon on top of a highly corrosion-resistant titanium layer. Coating titanium and carbon before stamping enables continuous processing, improving productivity and cutting costs. By consolidating the flow-path structures on the separators, it was no longer necessary to form a flow-path structure on the plastic frame of the electrode assembly. Therefore, the precision injection moulding of expensive engineering plastics was replaced with the die-cutting of plastic film as the method to form the frame. The production process of the electrolyte membrane was also reviewed. July/August 2024 | E-Mobility Engineering A fuel-cell system (Image courtesy of Powercell) The project 821 fuel-cell superyacht (Image courtesy of Feadship)
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