Tuesday, December 5, 2023

Producing green hydrogen directly from untreated seawater

As climate change progresses, researchers worldwide continue to search for clean, sustainable replacements for fossil fuels. One promising alternative is hydrogen, which produces near-zero greenhouse gas emissions when burned.

However, producing hydrogen from renewable resources through electrolysis requires vast amounts of high-purity water. This may aggravate the shortage of freshwater resources, which has already become an urgent problem globally.

Seawater is abundant but must be desalinated before use in commercial electrolyzers.

Now, a team of researchers from China, Australia, and the U.S. has developed a new process that splits seawater without pre-treatment to produce green hydrogen.

The international team was led by the University of Adelaide’s Professor Shizhang Qiao and Associate Professor Yao Zheng from the School of Chemical Engineering.

In the electrolysis of water, an electric charge splits water molecules into hydrogen and oxygen. Current electrolyzers are operated with highly purified water electrolytes.

It is always necessary to treat impure water to a level of water purity for conventional electrolyzers, including desalination and deionization and also the addition of materials such as alkalis. This increases the operation and maintenance costs of the processes.

Additionally, the process relies on expensive noble metal components such as platinum and iridium, the preferred catalysts for producing hydrogen through electrolysis at scale.

In this new effort, the researchers provide a solution to directly utilize seawater without pre-treatment systems and alkali addition. Instead of treating the seawater, the team simply filtered it to remove microorganisms and solids.

Also, they used a non-precious-metal catalyst – a transition metal coated with a layer of chromium oxide.

During experiments, the researchers found that their process showed similar performance as that of current systems that require pre-treatment of water and expensive catalysts.

“We have split natural seawater into oxygen and hydrogen with nearly 100% efficiency to produce green hydrogen by electrolysis, using a non-precious and cheap catalyst in a commercial electrolyzer,” said Professor Qiao.

Although the new method looks promising, more work is required to make sure there are no side reactions occurring over larger spans of time. The team will also work on scaling up the system by using a larger electrolyzer so that it can be used in commercial processes such as hydrogen generation for fuel cells and ammonia synthesis.

Journal reference:

  1. Jiaxin Guo, Yao Zheng, Zhenpeng Hu, Caiyan Zheng, Jing Mao, Kun Du, Mietek Jaroniec, Shi-Zhang Qiao and Tao Ling. Direct seawater electrolysis by adjusting the local reaction environment of a catalyst. Nature Energy, 2023; DOI: 10.1038/s41560-023-01195-x