Fuel cell focus | The potential of PEM
Rolls-Royce Power Systems sees PEM (proton exchange membrane) fuel cells as a key part of its mtu-brand portfolio in the coming years. Key attractions of low-temperature PEM technology include high power density, good load following, high electrical efficiency (especially at part load), as well as technical and market maturity. Applications envisaged include emergency power, eg for data centres, and provision of demand response for the grid. A 250 kW PEM demonstrator is nearing completion at the Rolls-Royce Power Systems Friedrichshafen site
Michele Bozzolo*, Georg Fink**, Dr Philippe Gorse***, Benjamin Oszfolk**** Rolls-Royce Power Systems, Friedrichshafen, Germany
Since 2015, Rolls-Royce Power Systems has been investing specifically in future solutions aiming at less CO2
, reduced pollutant
emissions and lower consumption of energy and raw materials via its Green and High- Tech programme. The company has recently established a new Sustainable Power Solutions business unit, which focuses intensively on innovative technologies for more climate- and environmentally friendly propulsion and energy systems. This also includes the generation and use of synthetic fuels, the conversion of internal combustion engines to alternative fuels and the development of alternative energy and drive systems. Rolls-Royce Power Systems has sufficiently reliable data to be able to define a science-based interim target to reduce by 35% the lifetime emissions of new products sold by the business by 2030.
With this in mind, it is only logical for Rolls- Royce Power Systems to grow its mtu portfolio to include fuel cells, and to gradually extend its development activities to include a variety of application areas. The potential of fuel cell technology is convincing, as is hydrogen as a storage medium within an overall energy system. Strong arguments for using and promoting this technology are high reliability, scalability and the ability to use renewable
energy sources. With their modular design, fuel cell systems are easily adaptable to match output with demand, and their low maintenance requirements and low running costs also make them attractive. Futhermore fuel cell technology is ready to be brought to market and suitable for commercial use. The rapidly developing market offers good growth opportunities for zero-emissions fuel cell technology. Unlike combustion engines, fuel cells convert the chemical energy contained in a fuel directly into electricity, which can then be used to drive a growing number of electrified systems. This conversion is more efficient than with combustion engines, as the intermediate thermo-mechanical steps required with conventional energy converters (heat engines) are eliminated. The greatest plus point arises when the fuel used is hydrogen produced from renewable energy sources because it allows polluting and climate-damaging gas emissions to be reduced to zero. In this way, fuel cells have an enormous potential to become an essential technology component for decarbonising propulsion and energy systems.
The case for PEM
We think that the low-temperature proton exchange membrane fuel cell or PEM
(sometimes called polymer electrolyte membrane fuel cell) currently represents the most suitable technology for developing and growing the Rolls-Royce Power Systems portfolio.
This low-temperature fuel cell has a high- power density enabling even small units to achieve sizeable outputs. Low-temperature fuel cells have operating temperatures of up to around 100°Celsius, posing minimal hazards to both materials and people, while high- temperature fuel cells reach 250 to 1000°C. The PEM has good load following characteristics as opposed to other types, allowing it to respond to changes of power requirement within seconds. Another advantage of the compact PEM fuel cell is its very high electrical efficiency, especially at part load. PEM fuel cells typically run on a hydrogen fuel source however they can operate on a wide variety of hydrocarbon fuels (eg, methanol, diesel or natural gas). This is achieved by using well known reforming techniques to convert them into hydrogen. This gives PEM fuel cells a very wide-ranging field of application. As the name “polymer electrolyte membrane fuel cell” indicates, the membrane is a key feature of this type of fuel cell. The membrane is usually made of plastic and is similar to Teflon. The water-saturated polymer membrane, which
How a PEM fuel cell works
O2– H+
Anode
The fuel cell is a galvanic cell that electrochemically reacts fuel and an oxidant (usually air) to produce electricity and exhaust products. It works quietly and without much in the way of vibration. Similar to batteries, fuel cells also generate direct current voltage. However, unlike batteries fuel cells require a constant inflow of fuel and oxidant. With a PEM fuel cell, a chemical process takes place between the electrodes (anode and cathode) in which the positive ions (protons) migrate from anode to the cathode, and the electrons are conducted externally from the anode to the cathode via an electrical conductor. The product of this process is electrical power that can be withdrawn and used. The electrodes are coated with a platinum or palladium catalyst and separated from each other by an electrolyte. Without the catalyst, hydrogen and oxygen would not react to produce heat and electricity. The electrolyte consists of an ion-conducting membrane, and it is important for this membrane to be permeable for protons and impermeable to electrons.
*System engineer, fuel cell solutions **System engineer, fuel cell solutions ***Head of fuel cell solutions ****System engineer, fuel cell solutions 14 | July/August 2021 |
www.modernpowersystems.com
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