Hydrogen shows a lot of promise as a powerful, clean fuel source – as long as the process that creates it is also green. A new report shows how tough it might be to get to truly green hydrogen, while a new study removes a barrier to its creation.
According to a paper published today in the journal Nature Energy, by researcher Kiane de Kleijne from Radboud University and Eindhoven University of Technology in the Netherlands, the production of hydrogen more often than not leads to gains in atmospheric carbon dioxide (CO2). That's only in part because some of it comes from natural gas production.
There are greener ways to produce hydrogen such as using solar or wind to power the process that splits it off from water molecules, but De Kleijne argues that in such cases, the carbon footprint of creating those facilities needs to be considered. So does the fact that green power is most effective in places with lots of sun and wind like Africa or Brazil, which means that hydrogen produced there then needs to be transported to the rest of the world for use, which again, raises its carbon footprint.
"If you look at the entire life cycle in this way, green hydrogen often, but certainly not always, leads to CO2 gains," De Kliejne said. "CO2 gains are usually higher when using wind power rather than solar power. This will improve further in the future as more renewable energy will be used to manufacture the wind turbines, solar panels and steel for the electrolyzer, for example.”
Aquatic elephant in the room
Until that time, a new breakthrough in a popular hydrogen-production process called a proton-exchange-membrane (PEM) may help.
PEM is a water electrolysis process that splits off hydrogen from water molecules. Aside from the carbon cost of the electricity that powers the process, PEM is considered a green technology because its only output is oxygen, rather than carbon dioxide. The problem is that iridium is one of the only elements that can stand up to the harsh acidic environment in which water molecules are sheared apart. And iridium is very hard to find, as it's one of the rarest metals on Earth, so PEM facilities are difficult to create at scale.
Enter a new study from the Institute of Photonic Sciences (ICFO) in Spain, explained in detail in the following video.
Basically, the ICFO researchers created an anode catalyst made from more common elements: cobalt and tungsten. But to protect the anode from the predicted degradation from the electrolysis process, they took a unique turn by impregnating a cobalt-tungsten oxide with water – the very substance in which it is made to operate.
“At the beginning of the project, we were intrigued about the potential role of water itself as the elephant in the room in water electrolysis”, said Ranit Ram, first author of the study. “No one before had actively tailored water and interfacial water in this way”
The result was that during the electrolysis process, as the new anode degraded by losing material, water and hydroxide – two compounds prevalent in the process – rushed in to fill the holes it left behind. The result was a kind of aqueous shield that kept the anode from degrading too quickly.
The whole periodic table
In tests using a PEM reactor, the new material performed admirably.
“We increased five times the current density, arriving to 1 A/cm2 – a very challenging landmark in the field," said leading co-author Dr. Lu Xia. "But, the key is that we also reached more than 600 hours of stability at such high density. So, we have reached the highest current density and also the highest stability for non-iridium catalysts."
While the researchers admit that the new water-impregnated alloy doesn't remain stable as long as current anodes, they say the finding makes up for it in demonstrating an efficient PEM approach that doesn't rely on scarce metals. In fact, the team says the process could even work with other materials, which is desirable because cobalt is often sourced from mines making use of child labor.
“Cobalt, being more abundant than iridium, is still a very troubling material considering from where it is obtained," said study participant and ICFO professor, García de Arquer. "That is why we are working on alternatives based on manganese, nickel and many other materials. We will go through the whole periodic table, if necessary. And we are going to explore and try with them this new strategy to design catalysts that we have reported in our study.”
The PEM study has been published in the journal Science.
