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Toyota developing regenerative fuel cell system for Lunar Cruiser with an eye to Earth

Toyota is developing a regenerative fuel cell for the manned pressurized rover (nicknamed the “Lunar Cruiser”) for the lunar polar exploration mission (LUPEX), part of projects led by the Japan Aerospace Exploration Agency (JAXA). (Earlier post.)


During an update on the development status, Ken Yamashita, Project Head for the Lunar Exploration Mobility Works Project, noted that the technologies under development and being fine-tuned for the lunar rover will be applied back on Earth. One of those is the regenerative fuel cell (RFC) system. (Others are off-road driving performance, automated off-road driving, and the user experience.)

A regenerative fuel cell has the ability to function as a fuel cell that converts hydrogen and oxygen into electricity and water, and as an electrolyzer that produces hydrogen and oxygen through the application of electrical energy. This dual-mode operation allows the fuel cell to switch between being an energy generator and an energy storage device.

One of the key challenges for the Lunar Cruiser is making it through the lunar night (14 days) without sunlight. Toyota is looking to the RFC to produce hydrogen and oxygen during daylight hours and then use the fuel cell to supply electricity at night.


There are a number of technology issues to solve for this application, including lightweight storage for both hydrogen and water. Toyota is partnering with Mitsubishi Heavy (MHI) on marine electrolysis technology for that aspect of the RFC, and leveraging its own fuel cell work as well.


Yamashita said that the development of RFC technology could enable high-efficiency hydrogen production using sunlight, making it compact and lightweight enough to be mounted in vehicles. Overall, Toyota sees RFC technology as contributing to global circular living and carbon neutrality.



Here is the cutting edge for hydrogen from solar:

' Rice University engineers can turn sunlight into hydrogen with record-breaking efficiency thanks to a device that combines next-generation halide perovskite semiconductors with electrocatalysts in a single, durable, cost-effective and scalable device. '

Of course this has implications way beyond powering a moon rover, and with an efficiency of 20% can potentially enable far more economic hydrogen production.

The bit that caught my eye was 'durable' which is all the difference between a laboratory curiosity and real world production.


And here is news on storing the hydrogen once produced:

' Flexible spheres of the biomolecule chitosan, made from shrimp waste, can be used for catalysts that generate hydrogen gas from borohydride salts. A research team now shows how the spheres can 'breathe out' hydrogen bubbles without breaking. This is an important step towards practical and safe hydrogen storage and release units. '

This is very much 'early days' lab work, and I won't be investing imminently in sending shrimp shells to the moon! ;-)

But at up to 18% by weight borohydrides are an interesting storage solution, for as the article says:

' As an alternative, alkali borohydrides can provide a safe source ofhydrogen, binding it chemically as a solid salt. A reaction with water releases the hydrogen, and the resulting metaborate salt by-product can be reprocessed and repurposed for hydrogen storage.'


I meant to add to my first post on hydrogen from solar, but forgot, that I have no idea even what the challenges are for making the halide perovskites reversible so that they can operate as fuel cells as well as electrolysers for applications including the projected moon rover!


I suppose the question is - is it one device that can "run backwards", or two devices packaged up and called one device ?
Not that it matters - they just have to build a reversable system that runs on solar and can work on a 14 day on and 14 day off cycle (sounds tricky/heavy?) and can be sent to the moon on a rocket.
How do they do it in submarines - nuclear ? - + submarine gear can be heavy and reasonably bulky.


Hi Jim.

A 14 day cycle for fuel cells/electrolysers is not really a problem, as what they are not so keen on is starting up and switching off repeatedly, and a longer cycle means that the advantages of electrolysers coupled with hydrogen storage over batteries are more pronounced due to the superior energy density,

If it were a matter of a few hours rather than days, then batteries would do the job better.

Reversible fuel cells are just that, not an electrolyser and a separate fuel cell in combination.

They can be done with either PEM or SOFC technology, although that is a long way from saying that they are fully developed and ready to go in a commercial environment.

Here is a discussion of reversible fuel cells in the context of space flight:


Thanks Dave. From looking at your paper, it is two devices packaged up, rather than one reversible one. (Which is fine, just the title is a little misleading).
As far as I can see it is:
fuel cells: (H2+O2 -> electricity+water) +
hydrolyzers+ (electricity+water -> H2 + O2).
Which they call a reversible fuel cell.
(+ storage for H2 and O2)

"Overall, Toyota sees RFC technology as contributing to global circular living and carbon neutrality."

I'm not sure about that. We have abundant oxygen and water on earth, not like the moon. We have a 24 hour day and wind.
It isn't a good template for living on earth.
I suppose the big thing you want is a way to store electricity on a daily to yearly scale, which could be H2 from electrolysis.

If you only use solar, you'll need multi-month level storage to get you through winter. If you use solar + wind, you could probably get away with 1-2 week storage, or much less (maybe 8 hours - 1-2 days) if you allow "emergency" gas usage for winter lulls.


Interesting; chitosan is also used in the novel zinc battery presented this year, which has really good specs.
It seems there are advances lately in using organic components for electrochemical devices.


Seems like Toyota is having a Mid-Life Crisis.



You have rather caught me with my hand in the cookie jar.
It ain't what we don't know that is the problem, its what we think we know which just ain't so.

I thought that reversible fuel cells did just that, rather than being two units stuck together, and when I came across that link in a space application which was directly relevant to your question simply posted it, without studying it.

I don't know if essentially using two units is peculiar to this application, or if it is normal in 'reversible' fuel cells, so will have to look into it in more depth to see whether my previous understanding was correct.

Many thanks for the correction!


You can see why Toyota might have the heebie-jeebies as the market is in a state of flux while moving to electrification.
Huge decisions have to be taken - do you go HEV, EV, hydrogen, phev, etc.
You can wait till the direction becomes clear, but it may be too late by then.
VW bit the bullet and went all in on BEV, but they were "helped" by their diesel scandal and had to put some clear air between the past and the future.
Toyota's HEV approach didn't hit any rocks so there was no crisis to force change.
But the Chinese are snapping at their heels and threatening to eat their (and everyone's) lunches with BEVs.



It looks as though I was not totally out to lunch in my previous understanding of how reversible fuel cells work being just one integated unit which can switch:

Dunno why they are not using that in space applications, I will have to have another look at the reference, when I am feeling studious!


' VW bit the bullet'

And swallowing it has not done them much good.

The VAG group and Toyota used to be level pegging on sales, last year they sold 8.26 million., against Toyota's 10.48 million ( Statistica )

Driving to all electric is one thing for a specialist producer of premium cars, quite another for a mass market producer who needs to cover all segments and price points, which Toyota has stayed focussed on.

According to Stellantis, production of BEVs still costs around 40% more than an ICE.

Where the market is growing in the less well off countries, there just is not the money to throw around when you are struggling to get basic transport for your family.

Toyota has been at the forefront of electrification since its foundation, and as soon as they have something really able to do the job at the right cost, will do so.

In my view VAGs drive to electrification with no alternatives is demonstrably a massive failing.

Interestingly the 'party line' at VAG means that their heavy goods vehicle subsidiary Mann is just about the only heavy goods manufacturer, not counting Tesla as they are not a subatantial player, not to include hydrogen as part of their plans.

The party line at VAG gave us 'clean diesel' with the engineers forced to fake figures to tow the line.

Their management remains just as one-eyed and ill advised.

It is not about being first, it is about getting the timing right.

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