“Exceptional” new catalyst cheaply splits hydrogen from seawater

According to RMIT researchers, green hydrogen is not environmentally friendly if you drink a lot of fresh water or release a lot of toxic chlorine.

Research into green hydrogen production is currently advancing rapidly as countries around the world scramble to position themselves in what is expected to be a huge global market for clean fuels. Australia’s vast renewable energy potential and export-oriented economy are well-suited to compete internationally in bulk. But as a continent dominated by deserts, we are also critically aware of water scarcity and the dangers of shipping our land’s lifeline abroad. is not suitable for mass production.

Producing green hydrogen from seawater is more difficult than from fresh water. As with many impurities and microorganisms, there is corrosion to consider. You need a coastal location close to renewable energy. Not a problem for a big and relatively empty country like Australia, but it’s definitely a factor elsewhere. Is it creating dangerous levels of salinity, or is it pumping high concentrations of toxic chlorine into the marine environment?

But the benefits are huge. Not only does using seawater make the water supply free, but when that hydrogen is burned or locally passed through a fuel cell, freshwater is released and fed across the water table to dry land. The desalinated water is one of the bonuses.

Therefore, there are many teams currently working on electrolysis technology to produce green hydrogen from seawater. In December, we examined an efficient Chinese device that uses vapor pressure differences to naturally evaporate pure water from seawater and then electrolyze it. A few weeks ago we covered an international team that discovered a surface treatment that would convert a standard electrolyser to work equally well in seawater. And in 2021, we explored very exciting ways to recover not only hydrogen but also salable quantities of chlorine and battery-grade lithium phosphate in Saudi Arabia. process.

Scientists at RMIT in Australia today unveiled another approach with great potential to produce highly efficient and low-cost green hydrogen directly from seawater without generating chlorine.

“The biggest hurdle to using seawater is chlorine, which can be generated as a by-product,” said Dr. Nasir Mahmood, principal investigator of the paper, which has just been published in the peer-reviewed Wiley journal. says. small“If we can meet the global demand for hydrogen, [using seawater] Without solving this problem first, 240 million tonnes of chlorine will be produced each year. That’s three to four times more chlorine than the world needs. It makes no sense to replace hydrogen produced by fossil fuels with hydrogen production that could otherwise damage the environment. Our process not only saves carbon dioxide, it also produces no chlorine. ”

RMIT devices are nitrogen-doped nickel molybdenum phosphide (NiMo₃P). Throughout each sheet layer are large pores designed to promote catalytic activity and mass transfer.

According to the team, nitrogen doping serves many functions, including increasing conductivity, optimizing electron density and surface chemistry, and creating new active sites for water catalysis within the sheets. Electronegative properties that occur when nitrogen binds to surface metals help prevent unwanted ions and molecules from contacting the surface of the catalyst, reducing phosphate, sulfate, nitrate, and hydroxyl ions on the surface. Presence helps to block chlorine. Prevent corrosion.

Experimentally, the team found that the catalyst exhibited excellent efficiency and completely suppressed chlorine evolution. “N Nemo₃P-sheet shows exceptional HER [hydrogen evolution reaction] Alkaline electrolyte and seawater yield overvoltage values ​​of 23 and 35 mV at 10 mA cm-2, respectively. Furthermore, complete water splitting requires only 1.52 V and 1.55 V to achieve 10 mA cm-2 in the alkaline electrolyte. electrolytes and seawater, respectively. These exceptional results demonstrate that low-cost hydrogen can be produced from seawater by tuning the structure and composition of 2D materials. ”

“These new catalysts require little energy to run and can be used at room temperature,” Mahmoud clarified in a press release. It should also be relatively cheap and easy to produce at the large scale that the green hydrogen market is expected to demand.

“To be truly sustainable, the hydrogen we use must be 100% carbon-free throughout its entire manufacturing lifecycle and not deplete the world’s precious freshwater reserves. Our method of producing hydrogen directly from seawater is simple.It is more scalable and much more cost-effective than any green hydrogen approach currently on the market.Further development will make this a thriving green hydrogen industry in Australia. We hope that we can promote the establishment of

The team will grow in size as the research progresses. The next step is to build a prototype electrolyser system running a stack of these catalyst sheets to produce large amounts of hydrogen and optimize system-level efficiency at scale. Mahmoud believes the technology will help the Australian government meet its target of green hydrogen production at his A$2/kg (US$1.40/kg).

After all, this is the key indicator. For companies to invest heavily in large-scale green hydrogen production, they need to know that they can profitably compete with other hydrogen and fuel sources. Let’s see how everything changes. But I hope some of these seawater-breaking innovations work on balance sheets just as they do in the lab.

Watch the short video below.

The article is open access in the journal small.

Source: RMIT