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Seawater electrolysis ignites new hope for affordable green hydrogen

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The writer is a science commentator

Hydrogen has long been viewed as a miracle fuel of the future. It does not appear on its own in nature but is partnered with other elements in compounds such as water and methane. The flammable element, which produces water when burnt, is touted as a potential clean energy source for heating, industrial and agricultural use, and long-distance transport where electrification is difficult.

One way of harvesting it is via electrolysis, which uses electricity to split water into its constituent elements, hydrogen and oxygen. Now researchers in China claim to have produced hydrogen by splitting seawater without the need to desalinate or purify it first, according to a report in Chemistry World.

Since seawater accounts for more than 96 per cent of the world’s water, this could be a significant step on the path to making green hydrogen (that is produced using renewable energy) affordably. “What they’ve done is really quite challenging from a chemistry perspective,” explains Professor Alex Cowan, who researches sustainable fuels at Liverpool University in the UK, and who last year co-authored a cost-benefit analysis on direct seawater electrolysis. “This technology hits a potential niche market that hasn’t been addressed before.”

Splitting water using electrolysis is relatively straightforward, and is already done in some hydrogen-generating facilities with access to a conventional water supply. The process, which takes place in an electrolyser, electrically separates hydrogen from oxygen and allows the hydrogen to be siphoned off. But with seawater this is more complicated because salt and other impurities can effectively destroy the electrolyser.

One option is to desalinate and purify seawater before processing it — but in some settings that can add cost. Another option is to treat the electrolyser components chemically to avoid corrosion, but that is viewed as impractical.

Now Heping Xie at Shenzhen University and Zongping Shao at Nanjing Tech University have come up with a workaround. They kept the electrolyser separate from the seawater with a waterproof, breathable membrane. A bit like a sieve, the membrane keeps anything other than pure water vapour from entering the electrolyser. As the water vapour is drawn in and converted to hydrogen, more is pulled in from the seawater to take its place. It is, they reported recently in the journal Nature, a self-sustaining system.

The scientists installed a prototype in China’s Shenzhen Bay, and produced more than 1mn litres of hydrogen over 133 days without any reported deterioration. “Running it for more than 3,000 hours sets a new benchmark in stability,” Cowan says.

One potential application could be for offshore wind to power seawater electrolysers, with the resulting hydrogen being transported back to land. A similar idea lies behind the Gigastack project in the Humber estuary, off the northern English coast: offshore wind is being used to power electrolysers, with the hydrogen being used at the Humber refinery.

Hydrogen, which accounts for about 2 per cent of the global energy market, is undergoing something of a renaissance, having been subjected to the same cycle of hope and hype that has characterised research into nuclear fusion. That latter technology is progressing at speed, emphasised by Tuesday’s announcement from the Lawrence Livermore National Laboratory confirming a milestone in energy output.

Unlike fusion, however, commercial hydrogen production already exists, mostly using fossil fuels, such as extraction from methane. The big challenges lie in scaling up, cutting cost and lowering the carbon footprint. Current electrolysers, for example, work at the megawatt, rather than gigawatt, level. The UK’s hydrogen strategy seeks to double the target for low-carbon hydrogen output to 10GW by 2030, as an intermediate step to net zero.

The bid to green the hydrogen industry is leading to strategic bets elsewhere. The Hydrogen Shot initiative was launched in the US last year to bring down the cost of green hydrogen to $1 per kilogramme in a decade. The EU, as part of its hydrogen strategy, has a 10-year plan to build hydrogen infrastructure, including transport networks and fuelling station. The bloc also hopes green hydrogen can replace natural gas in polluting industries like steel production.

Most important, perhaps, the cost of renewable energy needed to produce green hydrogen is falling. It may take another decade to separate the hope from the hype but, for now, the flame for a cleaner, hydrogen-fuelled future has a healthy glow.

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