Clean Hydrogen, Now as Green Fuel from Seawater

The search for making Hydrogen a fuel that could deliver energy at a low price continues. Splitting water into hydrogen and oxygen presents an alternative to fossil fuels, but purified water is a precious resource.  With its own energy footprint to generate it. A Stanford-led team has now developed a way to harness seawater – Earth’s most abundant source – for chemical energy.

Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. Developing cheap electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion could address the water scarcity issue.

Theoretically, to power cities and cars, “you need so much hydrogen it is not conceivable to use purified water,” said Hongjie Dai, J.G. Jackson and C.J. Wood professor in chemistry in Stanford’s School of Humanities and Sciences and co-senior author on the paper.

Researchers at Stanford University have now generated polyanion-rich passivating layers formed in the anode are responsible for chloride repelling and high corrosion resistance, leading to new directions for designing and fabricating highly sustained seawater-splitting electrodes and providing an opportunity to use the vast seawater on Earth as an energy carrier.

Researchers led by Hongjie Dai, revealed they were able to generate the fuel using solar power, electrodes, and saltwater that they took right from San Francisco Bay. The findings, published March 18 in Proceedings of the National Academy of Sciences, demonstrate a new way of separating hydrogen and oxygen gas from seawater via electricity.

This work was funded by the U.S. Department of Energy, National Science Foundation, National Science Foundation of China and the National Key Research and Development Project of China.

Tackling corrosion

As a concept, splitting water into hydrogen and oxygen with electricity – called 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.

But negatively charged chloride in seawater salt can corrode the positive end, limiting the system’s lifespan. Dai and his team wanted to find a way to stop those 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 sulfide, which covers a nickel foam core. The nickel foam 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 sulfide evolves into a negatively charged layer that protects the anode. Just as the negative ends of two magnets push against one another, the negatively charged layer repels chloride and prevents it from reaching the core metal.

Without the negatively charged coating, the anode only works for around 12 hours in seawater, according to Michael Kenney, a graduate student in the Dai lab and co-lead author on the paper. “The whole electrode falls apart into a crumble,” Kenney said. “But with this layer, it is able to go more than a thousand hours.”

Green Hydrogen Potential

This finding follows another recent hydrogen breakthrough from Belgian scientists, who presented a way to develop hydrogen gas from air moisture. Researchers from KU Leuven have succeeded in developing a special solar panel that produces hydrogen gas from the moisture in the air. After 10 years of development, the efficiency of one panel has been increased to 250 liters per day, a world record according to the researchers.

The scientists are preparing a field prototype of their special panels to be used on a house.

These are two new ways of developing hydrogen from renewable sources. Though both methods are in their early stages, they offer plenty of promise.