A neat way to store and purify hydrogen

Hydrogen gas is going to be an increasingly important substance over the next decade, as a means of storing and transporting renewable energy.

But hydrogen itself is hard to store and transport: as a flammable, invisible gas, it could make for dangerous cargo.

And the most common method of making it at the moment produces a lot of greenhouse gas emissions.

New research, published in Science Advances, might have landed on both an easier way to store it – and a cheaper and less carbon-intensive way to make it.

The researchers, at Osaka University in Japan, have found some substances that react with hydrogen, and only hydrogen – so they can store and release the gas with ease.

Currently, most commercial hydrogen is made from steam-reforming natural (methane) gas, producing carbon dioxide and other greenhouse gases in the process.

The hydrogen made by this method is only about 70% pure: it also contains carbon monoxide, carbon dioxide, and trace amounts of other gases, each of which have to be removed individually through laborious, energy-intensive ways.

“Even a small amount of carbon monoxide can hinder hydrogen uptake,” says corresponding author Associate Professor Yoichi Hoshimoto, from Osaka University’s Department of Applied Chemistry.

“Thus, costly purification methods to isolate the hydrogen prior to storage are necessary.”

The Osaka research has found that boron-based compounds called triaryl boranes could catalyse a reaction between hydrogen and another substance called 2-methylquinoline, causing the hydrogen to stick to the 2-methylquinoline.

When heated at 200°C for three hours, the 2-methylquinoline released the hydrogen again.

The resulting method is a 99% efficient way to store hydrogen, and releases hydrogen with 99.9% purity.

This method still produces some carbon emissions in its first stage – unlike electrolysis, which can be a near zero-emissions way of making hydrogen.

But this chemical trick could help boost the industry in its nascency, and provide a neat storage method.

“The industrial value of molecular hydrogen has long been plagued by substantial quantities of carbon monoxide and other contaminants,” says Hoshimoto.

“However, in the catalytic hydrogenation method we developed, even a five-fold excess of a contaminant wasn’t a problem, and hydrogen uptake and release were each achieved without using any solvents.”

Boron is being recognised for its gas storage potential around the world – a few months ago, Australian researchers showed it could store and separate carbon-based gases too.