Researchers from Columbia Engineering have developed a novel photovoltaic-powered electrolysis device that can operate as a stand-alone platform that floats on open water. Daniel Esposito, assistant professor of chemical engineering, has been studying water electrolysis—the splitting of water into oxygen (O2) and hydrogen (H2) fuel—as a way to convert electricity from solar photovoltaics (PVs) into storable hydrogen fuel, a clean fuel expected to play an important role in a sustainable energy future.
The study “Floating Membraneless PV-Electrolyzer Based on Buoyancy-Driven Product Separation,” was published by International Journal of Hydrogen Energy.
As explained, in a single hour, more energy from the sun hits the Earth than all the energy used by humankind in an entire year and harnessing sun power to Earth’s energy needs, in an economical, scalable, and environmentally responsible way, has long been seen as one of the grand challenges of the 21st century.
The floating PV-electrolyzer can be thought of as a “solar fuels rig” that bears some resemblance to deep-sea oil rigs, except that it would produce hydrogen fuel from sunlight and water instead of extracting petroleum from beneath the sea floor.
The researchers’ key innovation is the method by which they separate the H2 and O2 gases produced by water electrolysis. State-of-the-art electrolyzers use expensive membranes to maintain separation of these two gases. The Columbia Engineering device relies instead on a novel electrode configuration that allows the gases to be separated and collected using the buoyancy of bubbles in water. The design enables efficient operation with high product purity and without actively pumping the electrolyte. Based on the concept of buoyancy-induced separation, the simple electrolyzer architecture produces H2 with purity as high as 99%.
“The simplicity of our PV-electrolyzer architecture—without a membrane or pumps—makes our design particularly attractive for its application to seawater electrolysis, thanks to its potential for low cost and higher durability compared to current devices that contain membranes,” says Dr. Esposito.
Commercial electrolyzer devices rely on a membrane, or divider, to separate the electrodes within the device from which H2 and O2 gas are produced. Most of the research for electrolysis devices has been focused on devices that incorporate a membrane. These membranes and dividers are prone to degradation and failure and require a high purity water source. Seawater contains impurities and microorganisms that can easily destroy these membranes.
Crucial to the operation of the PV-electrolyzer is a novel electrode configuration comprising mesh flow-through electrodes that are coated with a catalyst only on one side. These asymmetric electrodes promote the evolution of gaseous H2 and O2 products on only the outer surfaces of the electrodes where the catalysts have been deposited. When the growing H2 and O2 bubbles become large enough, their buoyancy causes them to detach from the electrode surfaces and float upwards into separate overhead collection chambers.
The team used the Columbia Clean Room to deposit platinum electrocatalyst onto the mesh electrodes and the 3D-printers in the Columbia Makerspace to make many of the reactor components. They also used a high-speed video camera to monitor transport of H2 and O2 bubbles between electrodes, a process known as “crossover.” Crossover between electrodes is undesirable because it decreases product purity, leading to safety concerns and the need for downstream separation units that make the process more expensive.
The team is refining their design for more efficient operation in real seawater, which poses additional challenges compared to the more ideal aqueous electrolytes used in their laboratory studies. They also plan to develop modular designs that they can use to build larger, scaled-up systems.
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