Scientists have developed a new technique that doubles the amount of hydrogen produced when splitting water molecules with electricity. The method works by adding a simple organic molecule and a modified catalyst to the reactor.
The adapted method lowers energy costs by up to 40% and may offer a "promising pathway for efficient and scalable hydrogen production," the researchers said in a new study published Dec. 1 in the Chemical Engineering Journal.
Using electricity to split water into hydrogen and oxygen molecules — a method known as electrolysis — could potentially offer a way to create hydrogen with no direct carbon dioxide emissions.
This works by connecting two metal plates known as electrodes to a direct current supply and submerging the ends of the plates into water. Applying electricity to the circuit generates hydrogen at the negative electrode (anode) and oxygen at the positive one (cathode).
However, electrolysis of water is currently inefficient, expensive and uses a lot of electricity, which often comes from non-renewable sources. The main inefficiency is from producing oxygen at the anode, Heidarpour explained.
To overcome this issue, the team behind the new study adapted the standard electrolysis setup to replace the oxygen-forming reaction with one that produces hydrogen by oxidizing an organic molecule.
First, the researchers set up two chambers containing potassium hydroxide (KOH) solutions, which were separated by a thin membrane, and then connected an electrode to either chamber to form a circuit. The team added a chemical called hydroxymethylfurfural (HMF) to the anode chamber, as well as a modified copper catalyst. Heidarpour said that chromium atoms, within the surface of their specifically designed catalyst, help favor hydrogen production by stabilizing the copper atoms in their reactive state.
When the team applied electricity, electrons from the anode oxidized the aldehyde groups in the HMF molecules. This generated hydrogen and a byproduct called HMFCA, which may find use as a chemical feedstock to make bioplastics, Heidarpour said. (Aldehydes have a carbon atom doubly bonded to an oxygen atom and a single bond to a hydrogen atom.)
This adapted method effectively doubles the amount of hydrogen made in one go, when also accounting for the hydrogen created by splitting water molecules at the cathode as usual.
The reactions also ran at around 0.4 volts, which is around 1 volt lower than in conventional water electrolysis. The researchers said this helps reduce overall energy usage by up to 40%.
Heidarpour said the team is not the first to report this type of strategy but explained that they increased the overall hydrogen production rate by using a more efficient catalyst.
HMF is often made by breaking down non-food plant materials such as paper residues, making it an attractive reagent to use in these systems. However, HMF is currently an expensive material.
Other aldehyde-containing molecules such as formaldehyde could be used instead. "Where there is a surplus of low-value organic substrates, oxidizing these into more valuable chemicals with simultaneous hydrogen generation could be an attractive and environmentally-friendly way to make two feedstocks at once," Mark Symes, a professor of electrochemistry and electrochemical technology at the University of Glasgow, who was not involved in the study, told Live Science in an email.
The researchers noted that there are still ways to improve the process to make it more efficient.
For example, further work needs to be done to improve the catalyst's stability so that it "can work for thousands of hours in an industrial setting," Heidarpour said.
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