FFAE

By utilising the energy potential of the pressure difference between the pressure tank and the hydrogen consumer (e.g. the fuel cell), heat can be pumped or cold generated in a targeted manner. This is made possible by using the metal hydride refrigeration machine. The hydrogen is not consumed, but is completely returned to the fuel cell.

When the hydrogen is fed from the tank into the metal hydride reactor, the gaseous hydrogen combines with the metal and the reactor heats up. The hydrogen is then released to the fuel cell at a low pressure level, which extracts heat from the system and generates cold. This principle enables quasi-continuous cooling through the use of two reactors. The system can also be switched over in winter to create an additional heating benefit.

One focus of the work is the development of high-performance reactors as the core of the system. These will be manufactured as lightweight components, taking into account subsequent series production using additive manufacturing. As a result, three times the specific output is achieved compared to the state of the art.

In collaboration with the DLR Institute of Vehicle Technology, the integration of the system in various vehicle applications for road and rail is being investigated using simulations and a hardware-in-the-loop system. The results show increases in range of up to 20%. Current work is focussing on integration in lorries with refrigerated trailers and demonstration in a rail vehicle with 5 kW refrigeration at TRL6 in 2026.

Bidirectional temperature stabilisation to increase the service life of fuel cells

The service life of fuel cells is negatively affected by any deviation in temperature from the optimum operating temperature. On the one hand, these can be temperature fluctuations of the coolant during operation due to ascents and descents. On the other hand, strong temperature deviations occur during a cold start.

As part of the project, a temperature control unit (TCU) based on metal hydrides is being developed to improve both situations.

For temperature stabilisation, the TCU is integrated into the coolant circuit as a bidirectional "thermal capacitor" based on metal hydrides. This system enables efficient stabilisation of the operating temperature by storing or releasing heat as required. Relevant temperature profiles for fuel cells are determined and the temperature stabilisation demonstrated in cross-institute collaboration. The data obtained experimentally is used for simulations to show the potential for improvement in terms of the ageing of the fuel cell under the specific load profiles.

The TCU can also act as a thermal booster in so-called frost start scenarios. The reaction between metal hydride and hydrogen can take place in just a few seconds at temperatures as low as -40 °C and is also highly exothermic. By combining these two unique properties, it is possible to develop an energy-efficient heater that works at temperatures below -20 °C. This is a unique selling point. This is a unique selling point compared to conventional electric heaters and the catalytic combustion of hydrogen. Experiments have demonstrated power densities of 3 kW/kgMH at -40 °C and 8 bar hydrogen pressure. In collaboration with the DLR Institute of Vehicle Concepts, the reactors were integrated into an overall system with a fuel cell in order to demonstrate the significant effects on reduced ice formation and thus an increase in service life.

Thermal control component for adaptive insulation

Thermal management in the vehicle not only includes the active heating or cooling of the cabin or components, but also the integration of existing heat flows. This requires thermal control components, such as adaptive insulation panels. Thanks to their adjustable insulation effect, these can significantly reduce the need for active technologies and thus save energy. One example being considered as part of the FFAE project is the adaptive insulation of a vehicle battery.

This type of adaptive insulation enables the battery to be enclosed, which may or may not dissipate heat depending on the temperature of the battery and heat development. On the one hand, this concept can improve the optimum temperature control of the battery. On the other hand, excess heat can be channelled into the cabin as required, thus making an efficient contribution to passenger comfort in a similar way to underfloor heating.

A central component of this approach is the development of a dynamic hydrogen pressure regulator based on metal hydride, which enables precise adjustment of the gas pressure in the range of 1 and 1000 mbar in an open-pored insulation panel. This allows the thermal conductivity to be actively adjusted and regulated by a factor of more than 10 as required. In collaboration with the DLR Institute of Materials Research, the synthesis of an aerogel-based insulating core with defined pore sizes is being driven forward in order to increase efficiency and dynamics. In the ReVaD project, the functional principle is being used in the building sector for adaptive façades and targeted thermal component activation.

Ceramic heat accumulators for greater range

In severe frost, the range of electric vehicles is reduced by up to half. This is because electric vehicles are also heated using electricity from the vehicle battery. Using heat accumulators instead of electric heaters has a major advantage: instead of simply installing larger vehicle batteries for more heating power, heat accumulators can store more energy for the same size and thus increase the efficiency of electric vehicles. In addition, heat storage systems are cost-effective, the materials used can be recycled in an environmentally friendly way and the heat storage systems themselves are very scalable.

The heat accumulators are heated electrically before the journey in order to warm the interior while travelling. Ceramics can be used as a storage medium: the heat accumulator inside heats up to 900 °C. The heat is contained in a honeycomb-shaped ceramic structure with many millimetre-sized tubes. The heat is stored in a honeycomb-shaped ceramic structure with many millimetre-sized tubes. A powerful resistance heater heats the heat accumulator in less than 20 minutes. A controlled air flow through the fine tubes then transports the heat into the vehicle interior during discharge. This allows the heat output and temperature to be adjusted as required during the journey.