A radical new way of producing hydrogen could provide renewable energy sources with the storage option they need to replace fossil fuels.
Hydrogen has long been touted as a way to store energy from renewable sources. On the surface, it has great advantages: you can make it from a widely available resource (water) and when burned you get pollution-free water back.
Unfortunately, the “hydrogen economy” has been one of those wonderful things that keep receding into the future as the challenges of hydrogen production and storage turns out to be more intractable than expected.
University of Glasgow chemists, however, have announced in Science a methodology that they say could transform the production side.
Currently, the major way to produce hydrogen is by reacting natural gas with high-temperature steam. As with coal gasification—another widely used technique—this doesn’t help wean the world off fossil fuels or stop the production of greenhouse gases.
Electrolysis, on the other hand, uses electricity to split water into hydrogen and oxygen. The oxygen can be released and the hydrogen stored for burning, or oxidation in fuel cells, when required.
However, the most popular tools for electrolysis—proton exchange membrane electrolysers (PEMEs)—require very strong electric currents to work. For a large solar plant, for example, this may be achievable during the middle of the day, but poses challenges when the sun is lower in the sky. PEMEs are also expensive to construct, needing precious metal catalysts and high-pressure containers.
Professor Leroy Cronin says that his team’s technique “uses a liquid that allows hydrogen to be locked up in a liquid-based inorganic fuel. By using a liquid sponge known as a redox mediator that can soak up electrons and acid, we've been able to create a system where hydrogen can be produced in a separate chamber without any additional energy input after the electrolysis of water takes place.”
Keeping the hydrogen and oxygen separate is essential, avoiding the effort that currently goes into stopping them from recombining. Cronin captures the protons and electrons that make up hydrogen separately, trapping them in acid. When exposed to platinum, the acid releases the particles, allowing them to combine to form hydrogen gas. This can be done in the absence of oxygen.
The result is that Cronin gets 30 times as much hydrogen per minute for the same amount of catalyst as the leading PEME, at least when both are at laboratory scale. The system also works with much lower currents, indicating that some hydrogen could be produced even at times of low wind or sunlight. Moreover, the Glasgow team avoid the degradation of PEME membranes from high gas pressure.
The potential benefits extend beyond energy storage. As Cronin points out, “Some of this hydrogen is used to make ammonia fertilizer and as such, fossil hydrogen helps feed more than half of the world's population."