Hydrogen is great.

It’s abundant, it’s an energy-packed fuel, and when you burn it, you get nice clean water instead of planet-destroying carbon dioxide. But while we would love to incorporate hydrogen as part of a carbon-free future, it has a dirty little secret: It’s mostly produced from polluting fossil fuels.

But there may be ways to change that. In this episode, we’ll learn about the rainbow of methods to produce hydrogen in greener and bluer ways. [♪ INTRO] Hydrogen is the lightest element on the periodic table, and out in nature, it’s typically incorporated into bigger molecules with other elements. But it can also exist as a gas, and that’s what we’re really interested in.

We use hydrogen gas in a lot of different ways, mostly in chemical processes like oil refining or making ammonia for fertilizers. But hydrogen can also be used as a fuel. There are heaters, cars, and boats that run on hydrogen, for example.

And, like I said earlier, hydrogen doesn’t produce carbon emissions when consumed, like gasoline or diesel do. Its main byproduct is water vapor. And water is fine.

We like water. This makes hydrogen a pretty appealing energy option, but annoyingly, in the real world, things are never that easy. Because even though hydrogen itself doesn’t produce carbon emissions, producing hydrogen often does.

Here’s how that works. While hydrogen gas is, well, a gas, we can’t just scoop it out of the air. It rarely exists on its own, because it’s pretty reactive – so it’s usually chemically bound to other stuff.

Instead, almost all of the hydrogen humans use today is made by taking coal or natural gas – which both contain hydrogen bonded to other elements – and blasting those fossil fuels with high pressure steam in a process called steam-reforming. This causes a chemical reaction to occur, producing hydrogen gas… but also carbon dioxide as a byproduct, which is typically then just released into the atmosphere. So it turns out, we have created this elaborate color code used to refer to different ways of making hydrogen.

This one is called black, gray, or brown hydrogen, depending on the exact type of fossil fuel used in the reaction. And this process can be pretty carbon intensive. Around 6% of the world’s supply of natural gas is used to make hydrogen, to the tune of around 800 million tonnes of carbon dioxide produced per year.

For comparison, that’s about twice of what the country of Australia produces per year. So it’s not the leading source of emissions, but it’s still a lot. But steam reforming isn’t the only way to make hydrogen.

So here’s our next color: green hydrogen. Everybody watching right now who knows one single chemical formula knows this; There’s hydrogen in water. You can also generate hydrogen through something called hydrolysis electrolysis, which is essentially basically just zapping plain old water with a bunch of electricity, and that splits the H2O into its H’s and its O’s.

And we can generate carbon-free electricity for this process using renewables like solar or wind. So if you hook up an electrolysis factory to a wind turbine, you end up with green hydrogen. This kind of hydrogen is exciting because it could sort of smooth over the bumps that come with green energy sources with limited uptime – like wind farms on days with no wind.

Instead of always feeding your wind energy directly to the grid, you make a bunch of hydrogen on blustery days and then burn it when it’s calm again. It could also be a way to, like, “renewable-ify” industrial processes like ammonia fertilizer production or to fuel things that can’t easily run on electricity, like big boats. However, there are some potential problems.

The hydrolysis process uses a lot of water, which might be needed for other things, especially in areas that are drier. But mostly, it’s just really expensive. Renewable electricity is getting cheaper, but even so, green hydrogen is still not on the level of black hydrogen or plain old diesel right now.

And to address the climate crisis, we ideally want industries to start converting their operations now, which means we have to make it make business sense for them to do that. There is a potentially cheaper, faster option though, which brings us to blue hydrogen. Blue hydrogen is made the old-fashioned way, by steaming the heck out of natural gas or coal.

But here’s the difference: blue hydrogen would use carbon capture to prevent the emissions from getting into the atmosphere. Instead that CO2 would be trapped, likely in some sort of underground reservoir where it can be injected into rock or deep, salty water. This would theoretically be cheaper and faster to bring online than green hydrogen, because we could retrofit existing hydrogen plants instead of having to build all new ones.

Blue hydrogen could be a thing all on its own, or it could help bridge the gap while we build out green hydrogen plants. However, some scientists have raised concerns about whether blue hydrogen really is any better than the black or gray stuff. Not for nothing, but not everyone agrees carbon capture tech is anywhere near ready to go.

And we’d need to factor in the energy or fuel it takes to run the plant. And if you’re using methane as a base ingredient there are fears about methane leaks, since those can also contribute to climate change. If you add all that up, some researchers end up with numbers that don’t actually look all that good in terms of limiting carbon emissions.

For instance, one paper by two researchers in 2021 suggested that in the end blue hydrogen only saved something like 10% of the greenhouse gas emissions compared to gray hydrogen, and it might be straight up worse than just burning natural gas. But other groups have taken a different look at the numbers and ended up with different estimates that make blue hydrogen look better. A group looked at that 2021 analysis, for example, and pointed out that with a few tweaked assumptions, like fewer methane leaks and a better power supply, you end up with only about 60 or 70% of the emissions of natural gas.

So still not emission-less, but better. Another criticism of blue hydrogen is that it still relies on digging up fossil fuels. And depending on who you ask, green hydrogen might fix its cost problem soon, so like why bother with blue?

So to sum up: Green hydrogen avoids carbon emissions by using renewable electricity to split up water molecules, while blue hydrogen uses the old-school natural gas or coal method, but captures the carbon before it gets into the atmosphere. If you’re wondering about the rest of the color wheel, we didn’t have time for all of it, so lightning round! None of these are as popular as the ones we’ve already talked about, but keep an eye out for: “Pink”, “purple” or “red” hydrogen produced from nuclear energy. “Turquoise” hydrogen, which uses an alternative way of treating methane that produces hydrogen and solid carbon instead of hydrogen and carbon dioxide. “Yellow” hydrogen, which refers to solar-powered hydrogen in particular, so I don’t really see how it’s different from green, but go off I guess.

And “white” hydrogen, referring to naturally-occurring hydrogen deposits underground. As to which we should choose, that’s a little above my pay grade, but a lot of smart people are looking into it. We have a lot to figure out when it comes to making hydrogen production greener, or bluer, so it’s exciting to see so many people working on this big shift in how we power the world.

Thanks as always for watching and learning with us here at Scishow. [♪ OUTRO]