Bjorn’s Corner: The challenges of hydrogen. Part 22. Hydrogen fuel cells

By Bjorn Fehrm

January 29, 2021, ©. Leeham News: Over the last weeks, we looked at Center of Gravity (CG) problems with rear fuselage liquid hydrogen tanks as used in Airbus’ ZEROe turbofan airliner concept. We can conclude that the CG shift is manageable for a short-range aircraft (range below 2,000nm).

Now we spend the next Corners diving into hydrogen fuel cell technology and how it can benefit a hydrogen-fueled airliner.

Figure 1, The principle of a hydrogen fuel cell. Source: Airbus.

Hydrogen fuel cells as an energy source

Fuel cells use an electrochemical process to release the energy stored in hydrogen instead of the combustion (oxidation) process in gas turbines. How do fuel cells work?

Here a description from Airbus, released in connection with  their ZEROe concepts:

Composed of two electrodes (an anode and a cathode) separated by an electrolyte membrane (Figure 1), a typical hydrogen fuel cell works in the following way:

Hydrogen enters the fuel cell via the anode. Here, hydrogen atoms react with a catalyst and split into electrons and protons. Oxygen from the ambient air enters on the other side through the cathode.

The positively charged protons pass through the porous electrolyte membrane to the cathode. The negatively charged electrons flow out of the cell and generate an electric current, which can be used, for example, to power an electric or hybrid-electric propulsion system. 

In the cathode, the protons and oxygen then combine to produce water.

A PEM, Proton Exchange Membrane cell uses hydrogen gas and oxygen gas as fuel.

Because there are no moving parts in a fuel cell, they are reliable and silent. The technology is often used to produce electric power in delicate situations, as the end products are electricity and water with no harmful emissions. Examples are inhouse forklift trucks (no extra ventilation systems needed) and the US Apollo space program where fuel cells generated energy for the capsule and drinking water for the crew on space flights.

Use is now increasing for zero carbon emission in mobility applications like trucks, buses, cars, and other applications where low emissions are wanted. Hydrogen fuel cell technology gives vehicles a longer range than battery-based solutions and once the energy in the hydrogen tanks is consumed it refills faster than a battery re-charges.

The problem for aeronautical applications has been the power level required and the power density in weight and volume of a hydrogen fuel cell. Experimental fuel cells are now coming within 50% to 70% of the values for gas turbine engines. But this is for the fuel cell alone. As we add the components to form a complete system the density can decrease.

The application to replace the APU in an airliner requires no inverter and motor to generate shaft power to drive a fan or propeller. Here the fuel cells’ electric power can be compared to the electric power from an APU with a generator/alternator. In applications where we need a power output on a shaft, it’s more problematic.

Over the next Corners, we will design different fuel cell solutions for airliners and look at the total system weight and volumes compared to today’s solutions. We use the present state of the art for fuel cells and look at their development curve to understand where we will be in 10 to 20 years.

22 Comments on “Bjorn’s Corner: The challenges of hydrogen. Part 22. Hydrogen fuel cells

    • Hmm, my fading memory is that Boeing evaluated something different for the 737 APU, using a retired WestJet 737 in the BCIT aviation education facility at YVR.

      Problem with fuel cells is still AFAIK that they don’t handled liquid fuels. There has been work on ‘reformers’ but AFAIK not very successful despite much effort by Ballard etc. in Vancouver BC and partnering automotive companies.

      Bjorn’s something of course uses hydrogen as main engine fuel so does not need ‘reformers’.

      Whether or not people like Airbus know what they are doing is a question, certainly good PR from them. But hey! a famous novel featured getting electricity out of the air. (Great ideas about humans in the novel Atlas Shrugged, but the electricity part was fiction.)

      • Does propane count as a liquid? Propane has been a focus because it can flow thought the reactor as a gas, is easily stored in liquid form and there is a global infrastructure for it.

        Propane fuels cells are now available as backups to solar panels for yachts and other small “off grid” applications. They claim fairly good “full-system” efficiency’s. Power density is still low (though not far from that of a small diesel get-set).

        • Propane is readily available, but has the hazard of being heavier than air so can collect in places where it could ignite.

          Natural gas is safer in that it is lighter than air, but it requires much more compression than propane thus bulkier and heavier tanks. Unless there is some magic substance that can absorb it inside a tank.

          • That magic substance is ammonia it will absorb the hydrogen I work in a scrapyard and I’ve been experimenting a little with my own feul cell and was talking with afreind about cryo freezing my hydrogen ammonia solution in a small cryotank to see what kind of runtime I could get off my torch plus a couple other little science projects if I ever get time to play

      • There are already methanol fuel cells available on the consumer market. Google e.g. efoy.
        I guess the problem is even less energy output per weight than for normal fuel cells.

    • And where does the energy for their electrolyzer come from?

      In BC, PQ, and Labrador from hydro-electric. In ON from nuclear, which eco-activists do not like. But in AB from coal. Etc.

  1. The in production 2:nd gen Toyota Mirai fuel cell engine is in the APU power range. For the 787 with its electrical driven cabin compressors can be fuel cell powered with engines off. Other aircrafts with compressed air offtake from the APU will need an additional engine driven compressor. Another advantage with fuel cells is that many airlines fire up the APU while truck taxing aircrafts around to have AC on and lights on, this can the fuel cell handle.

      • The Mirai engine has the Toyota FC Stack with a maximum output of 114 kW (153 hp), all electrical power.
        The old Honeywell/Garrett APU family names are named for power in hp. GTCP131-XX has 131 shp if I remeber right, the old GTCP85-xx had 85 shp. So for narrowbodies they are in the similar power range. These APU’s of cause can mix shaft hp to the gearbox and generator power and bleed air offtake power.

        • Yes, we have to count the complete power produced by the APU, both shaft power to Generator/Alternator, hydraulic power to pump and bleed power to air start and ECS. All this is replaced by the electric power delivered from a fuel cell.

  2. Bjorn,

    are you also going to write an article about palladium based storage devices and their advantages/disadvantages.

      • The enlighten part is the problem. What i know is that palladium can store big amounts of Hydrogen. Up to 1 Hydrogen atom can be absorped for every Palladium atom. I think that comes down to a higher H2 density than liquid H2. And that all under a reasonable temperature and pressure which would allow much easier packaging. Also the release of the absorped H is seen as reasonably fast. But is that also fast enough for a big energy user like a plane?

        ps the obvious problem is that palladium is price like gold and production is not big. But other metals also absorp hydrogen so it is more storage devices like palladium.

  3. Keep in mind that hydrogen is not a source of energy, it is only a means of transporting energy.

    Similarly the batteries in electric cars are not a source of energy, only a storage medium.

    Fossil fuels are an energy source, in storage in the ground. They can be used directly, or to convert into another form such as electricity or hydrogen.

    So the fundamental question for Bjorn, since his interest is in ‘saving the climate’ is “How do you plan to obtain the hydrogen?”, preceded by “Why?”.

    German voters don’t like nuclear generation, and building nuclear plants is very costly.

    Hydro-electric power is only available in some areas, with some ability to transport it to elsewhere.

    How to generate electricity in other locations? C o a l.

    Lots of it in the world, including some parts of Canada and the US – Fernie and Tumbler Ridge BC, the Powder River Basin, etc.

    Or can hydrogen be efficiently be generated some other way?

    • The long-term goal is renewable electricity to be used for electrolysis of water. That renewable capacity doesn’t exist yet. The short-term plan is reformation of methane. Which will have a carbon footprint until replaced, for awhile yet.

    • In countries that already have a sizable wind energy segment, excess capacity (e.g. on windy nights) can be (and is being – Germany) used to generate hydrogen by electrolysis.

  4. Check out SunHydrogen. They already have the amazing technology to produce hydrogen. Their demonstration plans in Colorado and Germany in early Q2 will show the world a clean green way to fuel our homes, cars and airplanes.

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