Dangerous and dirty: 7 myths about hydrogen power debunked

By Marco Alverá

Published: Thursday, 18 November 2021 at 12:00 am

Hydrogen’s story goes back 13.7 billion years, to a time when the Universe was new-born, and very hot.

Hydrogen emerged from that primordial furnace in far larger quantities than any other element, and even today it dominates the cosmos. It is the main ingredient of stars, including over 90 per cent of our Sun, and a thin mist of it is scattered through space. About 60 per cent of the atoms in our bodies are hydrogen, and of course it is one of the two key ingredients in water.

Hydrogen is the simplest atom: just a single proton orbited by a single electron. It is odourless, colourless and very energetic.

Hydrogen makes an excellent fuel. You can heat your home or cook a meal by burning hydrogen, the same way many homes burn natural gas. One kilogram of hydrogen can release enough energy to drive a typical car for 130km or provide two days of heating for an average household. And of course, when hydrogen is burned in air, the only emission is water.

Or you can convert its energy into electricity, in what’s called a fuel cell. It performs essentially the same chemistry as a flame: combining hydrogen with oxygen to make water and release energy; except that in a fuel cell the energy goes into electricity instead of heat.

A big bonus for fuel cells is that they are typically very efficient. About 60 per cent of the energy in hydrogen can be converted to electricity to drive a car, compared to only 20 per cent of the energy in petrol. So, hydrogen vehicles can be three times more efficient.

Hydrogen is now set to play a crucial role helping us to tackle the climate crisis and wean the world off greenhouse gas emissions. In a net-zero CO₂ world, studies estimate that hydrogen could account for up to a quarter of our overall energy needs. Yet, despite its central role in our carbon-free future, a number of myths about hydrogen persist.

Myth #1: Hydrogen is too dangerous to ever be used on a large scale

The Hindenburg airship disaster and the explosive power of the hydrogen bomb (also known as the H-Bomb) have done little for hydrogen’s public safety image; but it’s an unwarranted reputation.

The 1937 Hindenburg disaster, in which an airship lifted by hydrogen gas caught fire, killing 36 people, is still held up as an example of the element’s explosive properties.

Whether the airship’s hydrogen supply was the source of the fire or not remains controversial – there are several forensic examinations of the live pictures which show the fabric cover of the airship burning for about half a minute as the airship descended slowly to the ground, not the hydrogen exploding. All this is somewhat beside the point: nobody today is talking about flying around using giant bags of hydrogen gas.

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Neither is today’s push for hydrogen power linked to the blast of the H-Bomb.

The H-bomb is based on nuclear fusion, the process that powers the Sun. This is only achieved under extreme temperature and pressure many thousands of times higher than anything that will ever happen in your car.

Like any technology, hydrogen is not and never will be completely risk-free. Hydrogen can ignite anywhere between 4 per cent and 74 per cent concentration, giving it the widest flammability range of any fuel. Hydrogen can also detonate into an explosion (where the flame travels at supersonic speed) at concentrations of 18 to 59 per cent. And it doesn’t need much of a spark. At its most flammable concentration, of 28 per cent, a tiny spark with just 0.02 millijoules of energy is enough to ignite the stuff. Its flame, which is invisible, propagates very quickly.

The good news with hydrogen is that it disperses quickly. If it leaks into the open air, it rises (being much lighter than air) and its concentration very rapidly falls below the explosive level.

In a hydrogen-powered car, the type of tanks being developed to store the fuel are virtually indestructible. And even if the tank is pierced, hydrogen dissipates almost immediately.

This means that hydrogen, carefully managed, need be no more risky than the fuels we use today.

Myth #2: Hydrogen is a dirty fuel that is part of the problem, not the solution

This myth comes from a misunderstanding. Proponents of this theory look at how hydrogen is traditionally produced, rather than the green technology that is beginning to take off.

Most hydrogen today is produced using a process called steam methane reforming, which combines methane and water to produce hydrogen and carbon dioxide (CO₂), a powerful greenhouse gas. The product is known as grey hydrogen. But that is changing.

Instead of using fossil methane as our hydrogen source, we can use electricity to break down water (H₂O) into hydrogen (H₂) and oxygen (O₂). If the electricity comes from a renewable or low-carbon source, then this is clean ‘green hydrogen’, with essentially zero carbon emissions.

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Green hydrogen is becoming an increasingly attractive option because the cost of renewable energy is plummeting. Ten years ago, renewables such as wind and solar were expensive, at around £400 per megawatt hour. In 2021, a solar auction was won in Saudi Arabia, for the equivalent of around £7.30 per megawatt hour.

At the same time, the machines (electrolysers) used to make green hydrogen will become much cheaper as the industry grows in size, and develops more efficient equipment, or larger equipment with economies of scale. Green hydrogen can soon be cheaper than grey.

There are some other colourful options in the mix, too.

Blue hydrogen is made using methane (CH₄) in a similar way to grey hydrogen, but instead of releasing the CO₂ into the atmosphere, this is captured and buried underground or, even better, turned into new products such as plastic and construction materials. Blue hydrogen has low CO₂ emissions provided the natural gas used to make it does not leak when it is produced and transported, and that a high proportion of the CO₂ can be captured.

Next up is turquoise, which uses a process called pyrolysis to heat up methane in the absence of oxygen, leaving hydrogen and the carbon as a solid material that can be used for construction, as well as making tyres.

The rainbow is completed by pink hydrogen, which uses electricity powered by nuclear energy to split water into hydrogen and oxygen using the electrolysis process.

Myth #3: Hydrogen is inefficient and not economically viable

Of course, using renewable electricity directly is more energy-efficient than first converting it to hydrogen, then using that for power.

But for many things, direct electrification is impossible or unfeasible. Heavy industry such as steelmaking needs chemical inputs, and green hydrogen can replace CO2-emitting metallurgical coal or fossil-fuel based chemicals. Many industries also need high temperatures, which are expensive to produce with electrical heating. Long-range transport such as trains or shipping, and winter heating in many temperate areas such as the UK, have such huge energy demands than it is impractical to store enough electrical energy; but hydrogen is easy to store in pressurised tanks, or large caverns excavated in rock salt deep underground.