That future has never quite materialised, however, due to hydrogen’s disadvantages. It’s difficult to transport, it can make metal brittle and it’s 20 times more explosive than petrol.

But in recent years, “green hydrogen” — hydrogen made without fossil fuels — has been identified as the clean energy source that could help bring the world to net-zero emissions.

Billions of dollars of investment capital and taxpayer support has flowed into the industry, and company share prices have soared.

This has accelerated in recent months, driven by the rising adoption of zero-emission vehicles, a deadline set by many countries to go carbon-free by 2050 and US President Joe Biden’s support for clean energy.

The European Union plans to scale up renewable hydrogen projects and invest a cumulative amount of 470 billion euros ($740 billion) by 2050.

In November, Western Australian mining magnate Andrew Forrest announced plans to invest billions of dollars in green hydrogen to grow his new energy business.

In the first of the ABC Boyer lectures on Friday, he focused on the potential for Australia to produce “green steel”, which uses green hydrogen in place of fossil fuels to power the iron ore blast furnaces.

“The immediate and multiplier impact on the Australian economy, if we get this right, could be nothing short of nation-building,” he said in the lecture.

So what is green hydrogen? How can it be used? And is the hype a lot of hot air?

What makes green hydrogen ‘green’?
Hydrogen is the universe’s most abundant element, but here on Earth it doesn’t appear pure in nature, and requires energy to separate.

The most common technique is to extract hydrogen from water, which is two parts hydrogen and one part oxygen (hence H2O).

Doing this is fairly simple. You can use heat and chemical reactions to release hydrogen from organic materials such as fossil fuels.

But this is enormously polluting. Worldwide hydrogen production is responsible for CO2 emissions equivalent to that of the United Kingdom and Indonesia combined. (The hydrogen is mostly used in the oil refining industry and to produce ammonia fertilisers.)

There is a cleaner way of getting hydrogen: a strong electrical current passed through a tank of water splits the molecule into its two constituent elements. This is called electrolysis.

Hydrogen atoms form hydrogen molecules (H2) and oxygen molecules pair up too. Each can then be bottled up (more on that later).

If the electricity is generated from renewable sources such as solar or wind, production of hydrogen in this way emits no greenhouse gasses.

This is how we come to all the different shades of hydrogen:

• brown hydrogen is produced using coal where the emissions are released to the air
• grey hydrogen is produced from natural gas where the associated emissions are released to the air
• blue hydrogen is produced from natural gas, where the emissions are captured using carbon capture and storage
• green hydrogen is produced from electrolysis powered by renewable electricity.

How can green hydrogen be used?
Hydrogen can be used in broadly two ways. It can be burnt to produce heat or fed into a fuel cell to make electricity.

A 2018 CSIRO report outlines several potential applications for hydrogen:

• fuel-cell hydrogen electric cars and trucks
• container ships powered by liquid ammonia made from hydrogen
• “green steel” refineries burning hydrogen as a heat source rather than coal
• hydrogen-powered electricity turbines that can generate electricity at times of peak demand to help firm the electricity grid
• as a substitute for natural gas for cooking and heating in homes.

The report foresaw an opportunity for Australia to export hydrogen to energy-hungry countries that don’t have access to cheap renewable energy.

It estimated potential demand for imported hydrogen in China, Japan, South Korea and Singapore could reach $9.5 billion by 2030.

By 2050, according to investment management firm Goldman Sachs, green hydrogen could supply up to 25 per cent of the world’s energy needs and become a US$10 trillion ($13 trillion) market.

But amid all this hype, hydrogen’s future is not yet assured.

To become a major export commodity, problems of storing and transporting hydrogen need to be overcome.