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What is hydrogen fuel and how does it work?


Recent news about state hydrogen stategies brings this potential fuel solution back into the foreground. But what is hydrogen and why does it matter?

Hydrogen is set to accelerate as a fuel source over the next decade, but we need to watch where it’s used, according to a Cosmos Briefing on the 11th of March 2021.

Jessica Allen, a chemical engineer at the University of Newcastle, and Adam Osseiran, an electrical engineer at Edith Cowan University, discussed the chemistry and the future of hydrogen in the energy industry.

The session was hosted by the Royal Institution of Australia’s lead scientist, Alan Duffy.

Chemistry of hydrogen

Hydrogen is one of the best-studied elements in the world. In pure form, it’s a gas, and the most abundant element in the universe.

Pure hydrogen has been used in industry for decades. But the current interest in hydrogen is driven principally as a source of energy and electricity. Hydrogen gas can be combusted to create water vapour and energy or electricity: a potentially clean energy source. The catch? It also takes energy to make.

Allen characterises hydrogen in this context as “almost a battery. So you charge it by making the hydrogen and then you discharge it by using the hydrogen”.

Production and carbon emissions

Pure hydrogen doesn’t exist in large amounts on the earth’s surface. “It’s the most abundant element in the universe, it’s actually limitless …[but] as just gas, we have to make it,” says Osseiran.

There are a number of ways to make hydrogen, with varying levels of emissions. At the moment, hydrogen production is carbon-intensive.

“Mostly it comes from natural gas. So methane,” says Allen. 

“And when we make hydrogen in this way, because we start off with a bit of carbon to begin with, we’re also going to make some CO2. So that’s not a low-emission pathway for hydrogen generation, unless we also capture and store that carbon dioxide. The other way to make hydrogen is through electrolysis, and water splitting. Again, we can make that in a way that still has carbon emissions, if the electricity for electrolysis comes from coal-fired power or the grid. Or we can do it in a green way using solar and wind energy for the water splitting process.”

Osseiran says there are ways of labelling hydrogen gas by its production. “We gave it names, we gave it colour.”

“Brown hydrogen is produced by using fossil fuels such as coal and natural gas…grey hydrogen is obtained from again our fossil fuels.”

“Blue hydrogen is a similar process to the grey… except that we capture the CO2 and put it somewhere out of reach…to get it out of the atmosphere.”

White hydrogen is made from plastic, creating carbon monoxide in the process. Green hydrogen – made from water by electrolysis – is the only genuinely carbon-free version.

Usage

“There’s quite a few things we can do with hydrogen once we’ve made it,” says Allen. “If we’re talking about electricity and energy, the best way to get electricity from hydrogen is to put it through a fuel cell. That’s the most efficient technology.”

“In electrolysis, we put in electricity and water and we get out hydrogen and oxygen. In a fuel cell, we put in hydrogen, and we get out electricity and water.”

While it has potential in other areas, both Allen and Osseiran agree that the most immediate application of hydrogen fuel is in small amounts – such as fuel cells in vehicles.

That said, there are applications of hydrogen across the board. “It is easy to get caught up thinking about energy as electricity,” says Allen. “But if you’re a chemical engineer, we know that there are a lot of different manufacturing processes that need energy input that’s not necessarily electrical energy input.”

Scaling up

“How can hydrogen compete? How can it be scaled up? It’s an economic exercise,” says Osseiran.

He adds that because it’s so abundant, we will not run out of hydrogen like we do other resources. The question is not whether it can be produced, but whether enough industries are willing to use it.

Storage and transport

So why aren’t we all using hydrogen already? There are challenges with keeping and moving it.

“Hydrogen is a gas, it’s a light gas that wants to spread out. And so it wants to take up a lot of room,” says Allen.

“There are plans to have hydrogen tankers similar to liquefied natural gas… That technology is new… it’s still being developed.”

Techniques to store it include compressing the gas, or reacting it with ammonia to create a liquid, “which is much easier to transport. And in fact, it’s already a commercial shipping trade”.

There are solutions, but they’re not operating commercially yet.

Environment

Beyond carbon emissions, there are environmental concerns to be considered with wide-scale hydrogen energy usage, but Osseiran and Allen are both confident these challenges are smaller than the current environmental challenges posed by the fossil fuel industry.

According to Osseiran, combusting hydrogen creates “nothing else other than water, and some heat because that’s what happens when there is any chemical reaction”.

And Allen says that there is less water vapour produced than that created by fossil fuels. “It’s much less of a concern than what we’re doing right now.”

As discussed earlier, making hydrogen often requires water. But not as much as crude oil refining: in fact, Allen says refining crude oil takes “about 10 times as much” water as creating hydrogen.

There will be other resource challenges, but none are insurmountable – Allen highlighted platinum as a potential scarcity.

“Platinum is the preferred catalyst in both electrolysis and in a fuel cell. And platinum is very expensive.”

“The platinum does have to be carefully sourced.”

But there are technologies being developed to minimise the amount of platinum required.

Future

What does the next decade hold? Large-scale hydrogen fuel is still a long way away, according to Osseiran and Allen, but smaller-scale production is moving fast.

“Maybe by the end of the decade, a household could potentially be completely energy independent and powered by hydrogen,” says Allen.

And, though small, that could have big ramifications. “There will be a paradigm shift at the geopolitical level as well, because then lots of countries are going to be totally independent of this supply chain of fossil fuel,” says Osseiran.

Related reading: Hydrogen fuel is back in the picture





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