For carbon-free transportation, battery EVs are racing ahead while hydrogen-fueled vehicles are stuck in first gear. One key reason: most commercial hydrogen is produced from natural gas, so it remains a fossil-fuel energy source.
There are many approaches in development (such as here, here and here) that, instead of processing natural gas, use electrolysis to separate water into hydrogen and oxygen gases. Commercial electrolyzer devices rely on a membrane, or divider, to separate the electrodes that generate H2 and O2 gas. These intricate membranes are too expensive for economic use at scale. Current research for electrolysis typically focuses on new membrane structures and materials.
A team at Columbia Engineering led by Daniel Esposito, assistant professor of chemical engineering, has created a new electrolysis device that does not need a membrane, promising to lower the cost of generating H2 and opening up an interesting approach to driving the reaction with photovoltaic solar energy.
Their electrolysis device uses a novel electrode configuration that floats in water, separating and collecting the gases using the buoyancy of bubbles in water, instead of a membrane. According to the announcement by the university:
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 percent.
The device uses asymmetric electrodes that are coated with a catalyst on just one side, deriving gaseous H2 and O2 on only their outer surfaces. Then the H2 and O2 bubbles rise in the water: H2 bubbles are harvested within the interior of the device as they float upwards, while O2 is vented to the atmosphere. See here in this video:
Eliminating the membrane is the key to low-cost, high-quality hydrogen gas: membranes are prone to degradation and failure, and so work reliability only in pure water. Without a membrane, this device works with almost any water, including seawater.
This is where the researchers put the “sustainability” into the concept. Esposito imagines the device working at scale as a sort of “solar fuels rig,” anchored in the ocean like a deep-sea oil rig, but producing hydrogen fuel from sunlight and water instead of extracting oil from the ocean floor. The hydrogen could then be piped or shipped back to shore in containers. This idea makes it possible to situate solar fuel production close to coastal cities without requiring land area for the photovoltaic panels.
Having shown success using aqueous electrolytes in the lab, the team is now refining the design for more efficient operation in real seawater. They also plan to develop modular designs that are suitable for larger, scaled-up systems.