It is possible to convert seawater into hydrogen without the salt damaging the equipment. Chinese researchers have published on Wednesday in Nature.
Expectations for hydrogen are high – the Netherlands is also fully committed to this fuel. The big advantage is that hydrogen is liquid or gaseous. A surplus of sustainably generated energy, from wind or sun, can be stored in hydrogen.
The desired response
The production of hydrogen (H2) is done by water molecules (H2O) in an electrochemical cell. Such a cell consists of a positively charged and a negatively charged electrode in water, connected to a copper wire. When an electric current is applied to the cell, negatively charged electrons move towards the positive electrode. There the desired reaction takes place: positively charged hydrogen atoms from the water and electrons react to form hydrogen gas.
However, a number of issues hinder the practical application of this technique. It must become economically viable, for example by increasing its efficiency. Another problem is a limited water supply – clean water is already scarce in many places.
‘Impure’ water from the sea or sewer would be an option, but salt damages metal. And in an electric cell, more side reactions take place with seawater, which reduces efficiency. A possible solution is to first purify seawater and then use it in an electric cell. But this takes a lot of energy.
That is why the Chinese researchers tried to build something that can withstand seawater. In their electric cell they place a membrane that blocks salts and allows water to pass through. They tested their setup with freshly tapped seawater from a bay near the city of Shenzhen. It works well: 100 percent of the salts remain behind.
During a 3,200-hour demonstration, hydrogen gas was produced consistently, with low energy consumption. In a smaller test setup without a membrane, the reaction stopped after an hour due to damage to the electrodes. The authors speak of a “high potential for practical application”.
‘A smart solution’
But Gadi Rothenberg doesn’t dare go that far. He is professor of heterogeneous catalysis and sustainable chemistry at the University of Amsterdam. “It’s great work and a smart solution, but will it be the new way of electrolysis? No, I would say.” The question is always whether investors dare to bet on this method, he says. “Making the move to a very large scale almost never succeeds, because there are many risks. It’s nice that it works for three thousand hours, but does it also work for five years? And does it work with seawater from Portugal?”
The uncertainties surrounding the alternative are smaller for the time being, he thinks. “It takes a lot of energy, but purifying seawater is easy. Many countries are already doing it on a large scale, such as Japan, Israel and the United States. No matter how smart an innovation is, its application remains dependent on a complicated cost consideration.”