The air transport market requires both high specific power and high energy density

Sunday, June 7th, 2020

Existing lithium batteries have a low energy density, while existing fuel cells have low specific power. The air transport market requires both high specific power and high energy density:

Forecasting that suitable lithium battery technology might be as much as 15 years away, the HyPoint team began focusing its efforts on a fuel cell design specifically targeted at eVTOLs. To keep things lightweight, it would have to be an air-cooled design; liquid-cooled fuel cells, says Ivanenko, work well in the automotive world, but the associated coolant tanks and pumps add parasitic mass that literally isn’t going to fly in the aviation world.

But today’s available air-cooled fuel cells, he says, have limited power capacity and lifespan, and they only work in temperatures between -5 and 30 °C (23 and 86 °F). So the HyPoint team set out to develop something faster and hardier, and came up with what they call the “turbo air-cooled fuel cell.”

“We boost the power of the fuel cell stack by placing it inside an air duct, where pressurized, humidified and thermally stabilized air is circulated by fans,” says Ivanenko. “The compression of air is maintained about 3 bars inside by a compression system, and the air with reduced oxygen content is charged through a control valve, and replaced with fresh compressed air with normal oxygen content.”

The extra oxygen on the cathode side of the fuel cell stack, in conjunction with a new High Temperature Proton Exchange Membrane (HTPEM) technology HyPoint has developed, allows you to force three times as much hydrogen through the fuel cell as a traditional design, tripling its specific power output without adding any parasitic cooling mass that might weigh a VTOL aircraft down.

With the entire system taken into account, the HyPoint system delivers 2,000 watts of power per kilogram of mass. The best of the liquid-cooled fuel cells deliver between 150-800 W/kg, and other air-cooled fuel cells sit at about 800 W/kg.

The energy density of the full system comes in at around 960 Wh/kg, where lithium batteries typically sit at about a third of that figure and other air- and liquid-cooled fuel cell systems come in a little over half – all according to HyPoint’s own figures.

The system has some other huge benefits as well, says Ivanenko; it accepts “dirty” hydrogen that’s only 99 percent pure, which is a fraction of the cost of the 99.999 percent purified hydrogen you need for an LPTEM system. “That’s a huge decrease in a significant operational parameter for a commercial eVTOL operation,” he adds.

It works at more or less any real-world temperature, from -50 to +50 °C (-58 to 122 °F) and beyond. And while it’s still in the lab at this stage, the team projects these fuel cells will last some 20,000 hours without maintenance, where LTPEM systems typically last around 5,000 hours – another very significant factor for a commercial operator.


  1. Crosbie says:

    Not explained in the article is why we would use fuel cells producing 2,000 W/kg when the current gas turbine solution can produce over 8,000 W/kg.

  2. Bob Sykes says:

    The entire article is asinine. Watts per kg!!!??? For how long? A nanosecond? This is a scam.

    There are countless scams being run in the energy production business. Renewables, solar, new mysterious electric batteries, and now this.

    The electrochemical series was determined a century ago. Every possible reaction and its energy can be calculated on paper. Tere are engineering details to be worked out for each reaction, but the reality is that batteries and hydrogen fuel cells have not much improved since the days of Volta and Galvani.

    Everyone avoids the comparison with kerosene, jet fuel. Tell me when you can beat 46 MJ/kg (20,000 Btu/lbm).

  3. Wang Wei Lin says:

    Anything is possible in labs and corporate offices. It will never scale up in the real world. Dense portable carbon based fuels will always win in the long run.

  4. Gavin Longmuir says:

    As a thought experiment, let’s assume that these fuel cells as described really perform, and even get better. Let’s assume that fuel cell planes start to capture a big part of the aircraft market. Then what?

    Where will the hydrogen fuel come from?

    Since the closest natural source of hydrogen is the Sun — and there are certain problems with collecting hydrogen there — the hydrogen will have to be manufactured here on Earth, which will take energy. The optimists say that energy will come from so-called “renewables” — but wind & solar plants take a lot of energy to build, probably more than they produce over their relatively short life.

    So we will be back to either continued use of fossil fuels to create the hydrogen, or vastly expanded nuclear power generation.

    If we consider the total system, it is highly likely that continued use of refined oil for aircraft fuel will be the most economic & practical choice for the foreseeable future.

  5. TRX says:

    I’ve been reading about innovative fuel cell technologies since the early 1970s. Also batteries of miraculous storage capacity.

    Almost 50 years now, and for some reason they’re all still two or three years from going to market…

    Why pine for batteries? Just wait for cold fusion!

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