Two separate developments in the field of chemistry have been looking at sea water. One is centred on creating a green hydrogen fuel without the need to desalinate the water; the second concerns extracting carbon dioxide from seawater as part of carbon reduction measures.
Green hydrogen production
Hydrogen as a fuel is seen by many environmentalists as the necessary step towards a clean future. This is particularly for those economic sectors that are more challenging to decarbonise, including manufacturing, aviation and shipping.
Currently most hydrogen is derived from fossil fuels, contributing 830 million tonnes of carbon dioxide a year. The alternative proposed by environmentalists is an emissions-free ‘green’ hydrogen, created by splitting water.
The main obstacle to realising this green alternative is the cost, which places methods devised hitherto as commercially. The issue of unaffordability is now set to change.
Scientists have developed a way to make hydrogen straight from seawater with no desalination required. The development comes from RMIT University, and it appears to be an important step towards a viable green hydrogen industry.
The new method splits the seawater directly into hydrogen and oxygen. By avoiding the need for desalination this saves on cost, energy consumption and carbon emissions.
The method to produce hydrogen straight from seawater is said to be scalable, paving the way for further investment in the technology.
The technology involves the use of an electrolyser to send an electric current through water to split it into its component elements of hydrogen and oxygen. The process omits carbon dioxide, and it also has no chlorine production. Central to this is a special type of catalyst developed to work specifically with seawater.
The research appears in the journal Small, titled “Nitrogen‐Doped Porous Nickel Molybdenum Phosphide Sheets for Efficient Seawater Splitting.”
Carbon extraction
In the second development, researchers at the Massachusetts Institute of Technology have found the key to a truly efficient and inexpensive mechanism for removing carbon dioxide from seawater. The method could be far more efficient than existing systems for removing the greenhouse gas from the air.
The technology is described as a reversible process consisting of membrane-free electrochemical cells. Reactive electrodes are used to release protons to the seawater fed to the cells, driving the release of the dissolved carbon dioxide from the water.
The process is cyclic: It first acidifies the water to convert dissolved inorganic bicarbonates to molecular carbon dioxide, which is collected as a gas under vacuum. Then, the water is fed to a second set of cells with a reversed voltage, to recover the protons and turn the acidic water back to alkaline before releasing it back to the sea. Periodically, the roles of the two cells are reversed once one set of electrodes is depleted of protons (during acidification) and the other has been regenerated during alkalization.
This innovation is described in the journal Energy & Environmental Science, headed “Asymmetric chloride-mediated electrochemical process for CO2 removal from oceanwater.”
