Ellen Phiddian
Hydrogen: it’s an energy-dense abundant resource, but also a gas that’s difficult to store and transport. Batteries: excellent at storing energy, but containing precious metals like lithium and cobalt.
Now researchers have combined the best of both worlds, with an experimental battery that uses hydrogen.
Their fast-charging “proton battery” is made with completely renewable resources, and operates mostly on water and activated carbon.
The researchers, based at RMIT University in Melbourne, have made a proton battery only powerful enough to run a handheld fan for a few minutes.
But by weight, these tiny batteries are already comparable with lithium-ion.
A partnership with an Italian company hopes to see a prototype big enough for home storage within a couple of years.
“The proton battery has evolved from our attempts to get a simpler, more efficient, hydrogen-based energy storage system,” says research lead Professor John Andrews, a renewable energy specialist at RMIT University.
Traditional green hydrogen fuel systems take water (H2O), and use electricity to split it into hydrogen gas (H2) and oxygen gas (O2).
But this reaction has a few more steps hidden within it: the hydrogen atoms are first converted into positively charged hydrogen ions (H+), before they pair up and become H2 gas.
Then, hydrogen is burned or reacted with oxygen again, releasing energy and water once more.
“The basic reaction that we’re using is similar to what is used in a hydrogen fuel cell-based energy storage system,” explains Andrews.
“So we start with water, we split that in a cell that’s very like an electrolyser that’s used in a hydrogen system, and then you get protons, H+.”
Hydrogen atoms mostly just have one positively charged proton and one negatively charged electron. Remove the electron, and you have an H+ ion – or, in other words, a proton.
“Protons are then passed through a membrane, same as in a fuel cell, but they then enter a porous carbon electrode that is negatively charged. The protons are then stored within this carbon matrix,” says Andrews.
“In your normal hydrogen system, those protons combine in pairs with electrons to give you hydrogen gas, and then you have to store the hydrogen gas.
“But in the proton battery, there’s no gas. We’re storing protons directly in the carbon electrode, which is part of the cell.”
Then, when it’s time to discharge the battery, those protons react with oxygen in the air, releasing energy and generating water again.
“We’ve cut out that step of producing and having to store hydrogen gas. The protons are stored directly, which is safer, and it is much more energy efficient,” says Andrews.
The electrode which stores these protons best is a type of material called activated carbon.
“Activated carbon is a carbon that’s been hollowed out, and it’s got a very high internal surface area. It’s got lots of pores and channels connecting the pores,” says Andrews.
The carbon can be made from any number of feedstocks.
“You can make it from wood and charcoal, you can make it from wheat straw, you can make it from coal,” says Andrews.
“We’re quite optimistic about the eventual economics of the device. Because the primary sources are very abundant and very cheap.
“As long as we can get a procedure to convert them to activated carbon that is very cost-effective – which, again, we’re quite optimistic about – we think that should really mean that we can get a very cost-effective proton battery.”
The RMIT researchers have partnered with automotive company Eldor Group, and are hoping to scale their technology up over the next two years.
“We’re looking to get to near a kilowatt scale by the end of this two years,” says Andrews.
This would make it on par with small home storage batteries, which is the researchers’ primary target. They’re also toying with smaller scale devices, like solar lights.
“In the future, there’s no reason why we shouldn’t be looking at applying a similar sort of proton battery to the automotive area, but we’re taking it step by step,” says Andrews.