...that could help end the world's dependence on fossil fuels...

....and aid the transition to net-zero emissions

But for this hydrogen revolution to take place...

...some big obstacles need to be overcome

So is the hype about hydrogen justified?

Hydrogen is the most abundant element in the universe

It's essential for life…

...the sun is mostly made of it

And it's present in almost all living things

But on Earth pure hydrogen is very scarce

Instead, it mainly exists combined with oxygen in the form of water

So how does this abundant element...

...get turned into a fuel that could help save the planet?

First hydrogen needs to be obtained

This is done by splitting molecules

Hydrogen is an energy carrier unlike, let's say, petroleum...

...which is a primary energy source

You have to make hydrogen from something

To do this requires an input of energy

You can use methane through a process called steam reforming

Or a source of electricity through electrolysis

Once you have some hydrogen you can either burn it directly...

...or mix it with oxygen in a fuel cell, which is rather like a battery

The reaction in the fuel cell produces electricity and heat...

And the only waste...

...is water

One of the benefits of hydrogen...

...in a hydrogen vehicle, let's say...

...the only emission that comes out of the tailpipe is pure, drinkable water

In contrast, of course, to the internal-combustion engine...

...which puts out loads of nasty chemicals and carcinogens

This means that, as long as the energy used to produce it is sustainable...

...hydrogen can be a truly green fuel

NASA started using hydrogen fuel cells...

...to generate electricity in its space capsules in the 1960s

Today it's not just being considered as a rocket fuel in space...

...but also for planes, trains and automobiles

As well as the industrial sector

The most likely early applications are going to be in heavy industry...

...for example, steel- and cement-making

These are heavy, heavy greenhouse-gas polluters...

...and they consume lots of energy, a lot of coal in particular

And it's very hard to replace that with electricity...

...which is probably how most of the decarbonisation...

...of the global economy will happen

This isn't the first time hydrogen has been hailed as a fuel of the future

So why has it never taken off?

Until renewables existed at scale...

...making hydrogen required vast amounts of fossil fuel, or nuclear energy...

...which made hydrogen both more expensive...

...and less efficient than other ways of storing and delivering energy...

...until climate change moved up the political agenda...

...hydrogen simply wasn't worth it

The existing fossil-fuel infrastructure has been in place for decades...

It's trillions of dollars of invested legacy equipment...

...and the companies that built it defend their assets

And so it makes it very difficult...

...for governments to force that legacy equipment to be pushed aside...

...in favour of radically new rival equipment...

...like hydrogen infrastructure or for that matter, renewable energy

The passengers look down to see the east coast of America...

...gliding by beneath them

There has also been a battle against public perception of hydrogen's safety...

...sparked by the Hindenburg disaster in 1937

Within seconds there was a terrific explosion...

...and brilliant orange flames formed the backdrop...

...for a tableau of death

Hydrogen gas is very flammable, and does need to be stored in a specific way

But fears about its safety are overblown

The Hindenburg did not explode because of the hydrogen it's been shown

That's a misperception

And what's more, industry has shown that hydrogen vehicles...

...can be safer than internal-combustion vehicle cars that use gasoline...

...which, of course, is an explosive product

Across the world, hydrogen every day is used by industry perfectly safely

One advantage hydrogen has over batteries...

...is that it's much more energy dense...

...which means that with a very high-pressure storage system...

...it takes much less space in order to make a vehicle go any distance

If you have a hydrogen tank on board a vehicle...

...you can refuel quickly compared to batteries and electric cars

But we do have issues of cost

We have issues of refuelling stations and fuelling infrastructure...

...that have to be built out

So that's another obstacle that stands in the way of hydrogen

There's also a question over how sustainable hydrogen really is

Despite some advances in the technology to generate it...

...it still requires energy-intensive processes...

...that are fuelled largely by fossil fuels or lots of electricity

The only way to make truly green hydrogen...

...is to produce it using sustainable energy

At the moment, a lot of the hydrogen that's used in the world...

...is made from natural gas...

...but that does produce some greenhouse-gas emissions

Some people see this as terrible. And other people say this could be a bridge

It can help build a market until there's enough renewable energy...

...and electrolysers become more efficient and more cost effective

But even if renewable energy is used in the electrolysis process...

...the energy content that comes out is less than what goes in

Which leads some to argue that hydrogen is just a waste of renewable energy

They have a point

There are a lot of applications...

...in which electricity is simply the best thing to use and more efficient

But there are other applications in heavy industry particularly...

...or long-distance transport, for example...

...where hydrogen could find a niche and quite a big niche

Unlike earlier waves of enthusiasm...

...hydrogen fuel could be here to stay this time

Technological advances are making hydrogen production more efficient and cheaper

And this, along with governments' commitment to decarbonise...

...is helping drive a new hydrogen economy

We see huge improvements in the vehicles...

...or the processes that use hydrogen...

...and we see much more sophistication among the companies that are using it

According to a study by McKinsey...

...there are more than 350 large-scale global projects under way right now

The projected total investment in the hydrogen sector...

...amounts to an estimated $500bn

We're seeing much more interest from venture capitalists...

...entrepreneurial activity, scientific advances, moving from the laboratories...

...to pilot plants and ultimately getting towards a marketplace...

...because they know a market that will pay for low-carbon approaches...

...or green hydrogen is coming

Germany has announced a €7bn programme

And the Chinese government wants to have 1m...

...fuel-cell-powered vehicles on its roads by 2030

When we think about the tools...

...that are needed to get to a net-zero carbon world

There's no doubt that hydrogen will play a role

In the short term, electrification is going to lead the decarbonisation charge...

...but longer term, I think there is a great potential for a real hydrogen revolution...

...that would play a big role in a decarbonised society

I'm Vijay Vaitheeswaran...

...The Economist's global energy and climate innovation editor

To keep up to date with all our climate-change coverage...

...please click on the link

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