Electricity generation and use are key considerations for renewable-energy applications. In terms of energy sources, the focus is increasingly shifting to fuel cells. That use stored hydrogen to generate clean electricity for all kinds of applications. Researchers around the world are working hard to make fuel-cell technology fit for mass production. And, by doing so, reduce the associated costs significantly.
Hydrogen-based technologies have a major part to play in the European Commission’s “European Green Deal”. It promotes “green” hydrogen as a means of storing electricity generated from renewable energy sources. Fuel cells are then required to convert the hydrogen back into usable electricity. Randy MacEwen, CEO of leading fuel cell manufacturer Ballard, sheds more light on the matter: “While governments across the planet are increasingly declaring green hydrogen to play a major role in the path towards net zero carbon. There is also a growing recognition that zero-emission fuel cell systems are well suited to decarbonising a range of drive applications. That have historically been difficult to abate.
This is true for buses, commercial trucks, trains, and marine vessels where there is a requirement for heavy payload, extended range, and rapid refuelling.” Moreover, fuel cells should become increasingly commonplace in stationary applications in the future. Such as in buildings, which they could supply with electricity and keep warm using residual heat.
Cleaner mini power stations
Fuel cells effectively work like mini power stations. Their inputs are hydrogen and oxygen, which are converted into water, electricity, and heat in a chemical reaction. To this end, hydrogen is fed to an electrode, where it is split into positively charged protons and negatively charged electrons. The electrons flow out through an external circuit, generating electric current in the process. Meanwhile, the protons pass through a membrane which only they can permeate. On the other side, they react with oxygen from the air at a second electrode coated with a catalyst, causing water vapour to be created. This is then discharged through the “exhaust”.
Different concepts, varied applications
Even though these processes are identical for all fuel cells. There still exist various designs, all of which differ in terms of operating temperatures and the electrolytes used. The design ultimately chosen depends on the application concerned. As such, fuel cells intended for mobile applications should have the highest possible energy density. That is to say, they should produce as much electricity as possible at the lowest possible weight. For stationary systems, on the other hand, more emphasis is placed on endurance. Nowadays, a service life of 50,000 hours is required. While mobile fuel cells tend to last for around 5,000 hours.
Control units ensure efficient operation
Researchers are pursuing a number of different avenues to boost fuel cells’ performance and reduce their associated costs. One such avenue of exploration is the “balance of plant” (BoP). These peripheral components – controllers, sensors, power electronics, and other systems – are all needed for the fuel cell to function. They control the system, are responsible for thermal management, or monitor the various functions. To name one example, the EU’s Inn-Balance project is developing new solutions for supplying water and oxygen in fuel cells. And also for thermal management and function monitoring in the entire fuel cell system, among other things. “These components increase the efficiency of the fuel cell and minimise hydrogen loss,” explains Consuelo Mora Gonzalez, Inn-Balance Coordinator at Fundacion Ayesa. “These advances are improving the efficiency and reliability of fuel cell vehicles, paving the way for environmentally friendly hydrogen mobility.”
Moving closer to mass production
The production of the fuel cells themselves is another area with enormous potential for optimising the technology involved. Stakeholders like the Fraunhofer Institutes for Production Technology, for Material and Beam Technology, and for Machine Tools and Forming Technology hope to put an end to fuel cell systems being substantially more expensive to manufacture than conventional, petrolpowered drive technology. In the ideal scenario, conventional 100-kilowatt fuel-cell systems for automotive applications would only cost around 5,000 euros to manufacture – less than ten per cent of the current figure. Here, the focus is primarily on components that make up the heart of the fuel cell. Bipolar plates and membrane-electrode assemblies.
Together, these form the cell in which the chemical processes take place. In turn, a stack is made up of several hundred individual cells. While the bipolar plates’ sheets, which are 50 to 100 micrometres thick, first have channels formed on them before being coated and welded together with extreme precision, various application and hot-pressing processes are required for manufacturing the membranes. Costs here should be substantially reduced through the use of new materials and more efficient production processes. Dr Ulrike Beyer, Head of the Hydrogen Task Force at the Fraunhofer Institute for Machine Tools and Forming Technology, explains further: “We will only make this happen if we break away from the painstaking manufacturing processes we currently see and into mass production – which also involves using effective technologies that enable up to four fuel cell stacks to be manufactured every minute.”