Researchers pull hydrogen fuel from seawater using sunlight

A floating device uses solar energy to split seawater into hydrogen and oxygen. The “solar fuels rig” reported in the International Journal of Hydrogen Energy could float like out on the open ocean, using sunlight to produce hydrogen fuel.

Hydrogen is a clean fuel for fuel-cell vehicles that only produces water when burned. But until now it is produced from natural gas using energy-intensive methods.

Scientists have been trying to come up with sustainable ways of producing hydrogen. One way is to split water into hydrogen and oxygen using electrolysis. The method involves passing electricity—preferable solar-generated—through water, and separating hydrogen and oxygen with the help of a membrane. But these membranes are expensive, fragile, and degrade unless used with pure water.

Researchers have previously made membrane-less electrolyzers, but they use special flowing liquids to separate hydrogen and oxygen. This requires pumps and valves.

The new device made by chemical engineers at Columbia University can split water without the need for a membrane. That means it can be used with seawater, which has impurities and microbes that could damage membranes.

Instead of a membrane, the device uses two electrodes made of titania mesh. Each is coated on one side with platinum. They are connected to a solar cell and placed in water with the uncoated sides facing each other.

Rendering of a hypothetical large-scale “solar fuels rig” operating on the open sea where it uses abundant sunlight to split seawater into hydrogen, which is temporarily stored on the rig before being piped or shipped back to shore.
©Justin Bui / Columbia Engineering

Hydrogen bubbles form on the negatively charged electrode and oxygen bubbles on the positive one. When the gas bubbles join and become big enough, they float up to the water surface. The hydrogen is collected while the oxygen is vented into air.

“Our challenge is to find scalable and economical technologies that convert sunlight into a useful form of energy that can also be stored for times when the sun is not shining,” says chemical engineering professor Daniel Esposito.

The new device could allow just that. The engineers say it is the first practical floating solar hydrogen-generating device to perform water electrolysis without pumps or membranes, and could lead to low-cost, sustainable hydrogen production. They are now fine-tuning the design before tests in seawater.

Source: Jonathan T. Davis et al. Floating Membraneless PV-Electrolyzer Based on Buoyancy-Driven Product Separation. International Journal of Hydrogen Energy. 2017.