Green Hydrogen Breakthrough Edges Clean Energy Closer to Reality

Scientists managed to significantly boost the production of green hydrogen using sound waves in a clean energy breakthrough.

The "exciting" study combined high-frequency sound waves with less expensive green hydrogen production techniques to get 14 times more output.

The development could have important implications as the world tries to wean itself off fossil fuels and transition to cleaner energy sources, the research team, led by Amgad Rezk, a lecturer in the School of Engineering at RMIT University, Melbourne, said.

Rezk told Newsweek green hydrogen will likely have a "major role" to play as an energy source of the future and that the latest findings, which have been documented in the journal Advanced Energy Materials, could contribute to making this eco-friendlier fuel more widely available.

"Electrifying and decarbonizing the economy are the obvious next steps but there are sectors such as heavy-machinery and shipping where it will be difficult to electrify—green hydrogen is then a possible substitute," he said.

"Considering only about four percent of global hydrogen is considered 'green' there is more that could be done to decarbonize the existing hydrogen demand," he said. "But a lot of this comes down to economics and there is still more research to be done in reducing the cost and improving the scalability. That's where innovative strategies like sound waves could make the difference."

Hydrogen is the most abundant element in the universe and can be considered a renewable energy source. But not all hydrogen fuels have the same environmental impact. Green hydrogen, produced by splitting water in a process known as electrolysis, is the cleanest option as it emits practically zero greenhouse gases.

Blue hydrogen, on the other hand, is made by splitting natural gas into hydrogen and the byproduct carbon dioxide—a process that can emit greenhouse gases into the atmosphere. Currently, most hydrogen fuel around the world is produced in this way.

"Hydrogen could be a major player in the transition to green energy because via water-splitting it produces only oxygen as the byproduct," Rezk said.

"But at the moment, the process is limited by the need to use highly corrosive—i.e. very acidic or alkaline—electrolytes and expensive, scarce electrode materials, such as platinum and iridium.

"Ideally, water-splitting would be conducted with neutral electrolytes while avoiding expensive electrode materials," Rezk added.

The problem with carrying out electrolysis using an electrolyte solution with a neutral or near-neutral pH is that this usually results in hydrogen production levels that are much lower than with a very acidic or alkaline solution.

In an attempt to address this challenge, Rezk and his colleagues designed a setup comprising a standard electrochemical cell—the apparatus used in electrolysis—incorporated with a device that emitted high-frequency sound waves.

"The term 'sound waves' may be misleading because in fact the frequency is so high that it is above our hearing range," Rezk said—around 10 megahertz.

In a standard electrochemistry cell you would have two electrodes—one with a positive voltage bias and the other negative—to complete a circuit and split water into hydrogen and oxygen.

The researchers took this basic setup but pumped high-frequency sound waves through the electrode and electrolyte as the process was running, creating an effect that improved the hydrogen production rate by 14 times compared with experiments in which no sound waves were used.

"We found that by using high-frequency sound waves the hydrogen bond lattice can be disrupted—we call this 'frustration.' This 'frustration' process essentially weakens the water bonds and this makes it easy to retrieve hydrogen from water," Rezk said. "As an analogy, this is like squeezing more juice out of lemon."

This is a potentially significant development when it comes to lowering the cost of green hydrogen production, Rezk said. The lead author also said there was an estimated 27 percent net energy reduction when the scientists used the sound waves compared to not using them. This was despite the fact that adding the sound waves consumed energy.

"The study showed that in the lab it was possible to reduce the net energy required to run the reaction and therefore reduce the cost to produce hydrogen in a neutral [pH] system," Rezk said. "This could have ramifications in the hydrogen economy where the hydrogen production cost is reduced."

While the innovation is promising and proves there is scope for more studies in this area, Rezk said there are significant challenges to overcome when it comes to scaling up the technology involved.

"We're looking for people in industry to help us take and scale this work from the lab into the real world," he said.