In a large meeting of energy experts organised by BP in Canada sometime around 2003, the subject of hydrogen as a fuel for the future was discussed. To nobody’s great surprise, virtually the first thing that came up was the Hindenburg disaster of May 1937. This wasn’t strictly on the agenda, of course, but the airship catastrophe seems to haunt the whole subject, not least because most people know far more about the Hindenburg than they know about the chemistry of hydrogen.

It is, after all, one of the great technical mysteries of all time and it owes its fame to the huge gathering of journalists and photographers around when it crashed, killing 35 people out of 97 on board. In fact, seven years earlier the British R101 disaster in France killed rather more including the Air Minister Lord Thomson, the head of UK Civil Aviation and the Director of Airship Development plus 45 other people on board out of 54, but nobody was around to photograph the crash. The probable explanation was low atmospheric pressure and a faulty altimeter. Either way, the experience put the British off airships for decades, not least because those in charge of their development were all dead.

The Hindenburg is another matter and controversy has raged ever since. Was its sabotage? Did a passenger do it because he hated the Nazis. Did Hitler do it because he hated the head of the Zeppelin company? Was it struck by lightning? Did an engine backfire and ignite? Was it struck by St Elmo’s fire or static electricity? Did the ‘dope’ coating the outside and containing cellulose acetate butyrate catch fire from a spark when the wet hemp ropes touched the earth? Or was it because hydrogen is an extremely dangerous gas and they were too stupid not to use inert helium?

Well, the hydrogen certainly did catch fire, but whatever it was that the press men saw burning as they created a legend, was not the hydrogen. It generates mostly ultraviolet light on combustion and may produce a very faint blue flame. It can also explode on mixtures with air and with chlorine from a spark, heat or even sunlight, but the temperatures have to be very high to auto ignite. It is also a lot lighter than air so the force of the burning is upwards.

The weight of gases is an interesting subject in its own right, not least because people tend to think that if it is a gas, it is basically weightless. However, the weight and density of gases are fundamental to their safety and use as fuel. The classic example is propane/butane or Liquid Petroleum Gas (LPG). Because this is heavier than air, when it is leaks it falls to the floor and spreads out in a thin film, mixing with air. If it hits a spark, it is in just the right mixture not merely to burn, but to detonate. Given that LPG is used as a cooking fuel in many countries where there is no supply of piped gas, it is widely regarded as the single largest global source of burns to infants and toddlers, since they are frequently on the kitchen floor.

As for density, when the first Liquid Natural Gas (LNG) was shipped into Boston Harbour, the US Coast Guard sensibly pointed out that one of these ships carrying liquid methane at -162°C and reduced to 1/600^thof its gaseous volume, had enough thermal content to blow half the city sky high. A fully loaded LNG vessel contains the thermal equivalent of 730 odd kilotonnes of TNT and only 15 kt were necessary to destroy Hiroshima. The magnificent film Syriana makes great play of this, ending the movie on a suggested Götterdämmerung as terrorists crash a small vessel into an LNG carrier.

Fears such as this forced a number of companies, most notably Shell, into a number of experiments to see if they could burn or even detonate LNG by firing artillery at it, but the absolute best they could do was to make it burn very slowly at the edges. This has not stopped fears about terrorism, but the central fact is that methane needs a ratio of air to gas of 10 to 1 to burn, let alone explode. The technical view is that the sheer density of the liquid methane and its temperature means that Syriana’s terrorists would have frozen or asphyxiated to death if they penetrated the double hull and the outcome would have been a small fire at the edges of the hole rather than detonation. Gas fires and explosions generally require air.

The density, weight and volume of fuels are thus rather important, particularly when it comes to hydrogen. After all, 1 kg of hydrogen or around 11 litres of the gas has as much energy as a gallon of gasoline, so – hurrah – our problems are over! All we need to do is to stick 500 litres of the stuff in the car and off we go, leaving behind merely water in the exhaust and no impact on the global climate from CO2. You would need a pretty big tank at atmospheric pressure. And given that one kilogram of hydrogen produces around 10 litres of water on combustion, it is not difficult to see what might happen to the local climate in, say, Los Angeles from this new way of powering cars, but who cares. California has a lot of drought problems.

There would be a weight advantage too, since hydrogen only weighs around 0.08988 grams per litre, so a tank load would weigh about the same as a fat baby. Mind you, you would have to be careful not to overfill it, or you might just take off as you accelerate onto the highway…

But enough of this facetious nonsense. Hydrogen undoubtedly does have a role to play in combating climate change. It is, after all, a primary element in all hydrocarbons and, as far as is known, the most common element in the Universe. However, extracting from its oxides without generating large amounts of CO2 requires a lot of renewable electricity. Equally it is pretty tricky to use. Because of its small molecular size, it can leak through some piping materials and corrode them.

And for a start, getting it into liquid form for ease of use requires cooling it to -235°C or some 30°C above absolute zero. As matters currently stand, this requires roughly 30% as much energy as is actually in it. Meanwhile, something this cold is rather difficult to handle, needing a lot of insulation, since air will freeze around it. Equally, any leakage will not only freeze air, but could also produce forceful outward flows leading to potential explosions and certainly fire if ignited.

Current global hydrogen liquefaction capacity is just under 12,000 tonnes a year, the bulk of it coming from either coal gasification or methane reforming, which would need carbon capture and storage to be truly green. With our newly super-green International Energy Agency (IEA) anticipating a need for 9-14 million tonnes per annum (mtpa) by 2030 and 125 to 300 mtpa by 2050, somebody, somewhere rather needs to get their skates on.

In practice, we should not really be talking about hydrogen as a substitute for gasoline for cars, although fuel cells could conceivably play a role here, at least until people realise the ever-increasing cost of lithium for batteries. In practice, such are the issues concerned with hydrogen itself that its usefulness as a fuel is currently with the big battalions. In this regard, the Swedes with their abundance of hydropower are currently in the lead tackling one of the biggest CO2 producing industries; Steel.

In Boden, northern Sweden, SSEB in combination with Vattenfall have started to produce steel using hydrogen with the aim of reaching five million tonnes by 2030. But to recognise the distance to be travelled, this is around 0.3% of Europe’s steel production. Dispiritingly, they are going to need 800 MW of hydropower to electrolyse the water to produce the hydrogen, but at least the process is circular.

Elsewhere, the Austrian engine-maker Jenbacher now has a very large collection of big engines for power production, which can run on hydrogen or indeed a mixture of gases, with very high electrical efficiency for combined heat and power plant. The problem here is getting hold of the hydrogen.

As for getting a substitute for gasoline and diesel without the cost of transforming every vehicle into a battery-powered version of Tesla, the hydrogen-based solution would be ammonia or NH3. We know it works with straight forward spark ignition (SI) or compression-based engines, because the Belgians used it that way back in 1944, when they ran out of gasoline due to the war. Meanwhile, a Marangoni Toyota GT 86 sports car was hurtling around Europe on a tank full of ammonia in 2013, giving it 111 zero emission miles on one tank.

True, the standard SI engine would need modification, but most would work on a gasoline or diesel mix with ammonia, which would save emissions, but would involve having two tanks. Nor would there be a problem in getting hold of it since around 235 million tonnes of it are produced every year to turn into ammonium nitrate (NH4NO3) for use as a fertiliser and for explosives. The trouble is that making ammonia currently produces around 1.8% of global greenhouse gases, using the Haber-Bosch process invented in 1909.

Indeed, for every one tonne of ammonia produced, three tonnes of CO2 go into the atmosphere. And there are other factors against pouring it into cars. It is corrosive, attracts water and is a very irritating gas causing damage to skin, eyes and lungs. As a fuel, it is like LPG being liquid under low pressure, but more caustic. Agriculturalists meanwhile suggest that without the fertiliser, half the global population would starve to death. In 2022, its cost grew by 66% due to shortages anyway, according to the UN Food and Agriculture Organisation. Be that as it may, the hunt is now on for finding a less carbon intensive way of producing the stuff.

And guess what? This would involve electrolysis of hydrogen from water, using electricity which to complete the cycle would need to be renewable. Siemens are experimenting with this in the UK, using wind power, while the Japanese at the Fukushima Renewable Energy Institute have been successfully using solar power since 2018 to produce the ammonia, which in turn can be burnt to produce electricity from turbines. As a peak shaving plant in a renewable-dominated power grid, this clearly could have its uses, but as a global substitute for gasoline any time soon, it rather lacks scale.

Much the same can be said about using a “reverse fuel cell” to produce ammonia, by running a current through a fuel cell full of water to produce hydrogen and mixing it with the nitrogen. Various Australian Institutions are following this path, but once again, the core of the system lies in renewable electricity, in their case from solar. All power to their elbow, but the idea does at least introduce one of the most engaging of hydrogen’s contributions to the great climate change debate; the fuel cell.

Way back sometime in the mid-1990s, a group of fuel cell enthusiasts came to London to promote the device as a clean means of electricity production and a major energy technology for the future. Perhaps because it was in England and wishing to give the technology a suitable background in history, the speaker went on at some length about its invention by a London barrister called Sir William Grove in 1838. When pausing for questions, he was visibly enraged when a voice at the back shouted: “Well if they’ve been around for over 150 years and they are so good, why the hell has nobody ever heard of them?”

If he had he been less taken aback by the unwashed journalist, he could perfectly well have said that fuel cells were fundamental to NASA’s space programme. Fuel cells are used in the space shuttle, not only providing electricity, but also potable water. They are devices that produce electricity from chemical reactions rather than a turbine and there are basically three kinds; proton-exchange membrane fuels cells (PEMFCs), solid oxide fuel cells (SOFCs) and regenerated fuel cells (RFCs).

Life is too short to go into the complexities here, but at its most basic PEMFCs and SOFCs produce electricity from mixing hydrogen with air and RFCs produce hydrogen and other things from electricity. What makes them attractive is that they involve no combustion at all. The most common type is the PEMFC, which operates at low temperatures and has a high energy density at 39.7 kW/kg. One of its disadvantages is that it uses expensive platinum as a catalyst, but we use platinum in catalytic exhaust converters in cars anyway, which explains why people steal them.

In theory, fuel cells could be used for a great many transportation uses, not least for aircraft electricity instead of batteries, being relatively light. Kings of the PEMFC are Vancouver’s Ballard. The company uses one of its fuel cells to power a bus running around Vancouver as a way to promote its activities, with full information written in capital letters on its side. Driving around and finding itself at a red light, it would conveniently sit next to any suitable sports car and when the lights change to green, the driver would hit the accelerator.

With no inconvenient gears, the powerful electric engine would roar – or rather thrust – into life leaving everything else well behind to the great amusement of any passengers and the surprise of those left behind. Naturally people seeing the bus drew the obvious conclusion that the fuel cell was the source of this incredible power. In reality, it was the fact that, like for like in size, electric engines have far more torque than gasoline ones and thus much higher acceleration. But it was not difficult to fall in love with fuel cells simply because of this trick.

However, where fuel cells can really come into their own is balancing out the supply of renewable wind and solar power. Ballard have recently won a contract from Shell and the Dutch utility Eneco’s Hollandse Kust Noord to attach a 1 MW fuel cell to their 759 MW wind farm in the North Sea. This will balance out the supply, when the wind falls. This use of hydrogen has a neat circularity, because the wind creates the hydrogen and the hydrogen makes up for the wind as it declines. Its role will be to supply around a million Dutch homes. 

Meanwhile Europe’s Airbus has been experimenting with hydrogen turbines for aircraft. But perhaps the key role of hydrogen, if we continue to warm up the planet, will be to get the very rich elsewhere in the solar system and beyond. It is after all, the primary rocket fuel!