Researchers create hydrogen fuel from seawater
Image credit: Debra Tosca | Dreamstime.com
A team from Stanford University have created a way to generate hydrogen fuel using solar power, electrodes and saltwater from San Francisco Bay.
Existing water-splitting methods rely on highly purified water, which is a precious resource and costly to produce. To overcome this issue, the Stanford-led team demonstrated a new way of separating hydrogen and oxygen gas from seawater via electricity.
According to Hongjie Dai, J G Jackson, and C J Wood – a professor in chemistry in Stanford’s School of Humanities and Sciences – theoretically, to power cities and cars, “you need so much hydrogen it is not conceivable to use purified water.”
“We barely have enough water for our current needs in California,” the paper added.
Dai also said that hydrogen is an appealing option for fuel because when it burns it doesn’t emit carbon dioxide but only produces water, so its use should ease worsening climate change problems.
As a concept, splitting water into hydrogen and oxygen with electricity – better known as electrolysis – is a simple and old idea: a power source connects to two electrodes placed in water.
When power turns on, hydrogen gas bubbles out of the negative end – called the cathode – and breathable oxygen emerges at the positive end – the anode.
However, negatively charged chloride ions from the salt in seawater can corrode the positive end, limiting the system’s lifespan.
To prevent this from happening, Dai and his team aimed to find a way to stop the seawater components from breaking down the submerged anodes.
The researchers discovered that if they coated the anode with layers that were rich in negative charges, the layers repelled chloride and slowed down the decay of the underlying metal.
They layered nickel-iron hydroxide on top of nickel sulphide, which covers a nickel foam core. This core acts as a conductor – transporting electricity from the power source – and the nickel-iron hydroxide sparks the electrolysis, separating water into oxygen and hydrogen
During electrolysis, the nickel sulphide evolves into a negatively charged layer that protects the anode – and just as the negative ends of the two magnets push against one another, the negatively charged layer repels chloride and prevents it from reaching the core metal.
According to Michael Kenney, a graduate student in the Dai lab, without the negatively charged coating, the anode only works for approximately 12 hours in sea water.
“The whole electrode falls apart into a crumble,” Kenney said. “But with this layer, it is able to go more than a thousand hours.”
Previous studies attempting to split seawater for hydrogen fuel had run low amounts of electric current, because corrosion occurs at higher currents.
However, Dai, Kenney and their colleagues were able to conduct up to 10 times more electricity through their multi-layer device, which helps it generate hydrogen from seawater at a faster rate.
“I think we set a record on the current to split seawater,” Dai said.
The team members conducted most of their tests in controlled laboratory conditions, where they could regulate the amount of electricity entering the system. But they also designed a solar-powered demonstration machine that produced hydrogen and oxygen gas from seawater collected from San Francisco Bay.
Without the risk of corrosion from salts, the device matched current technologies that use purified water. “The impressive thing about this study was that we were able to operate at electrical currents that are the same as what is used in industry today,” Kenney said.
The findings were published on 18 March in Proceedings of the National Academy of Sciences.
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