Hydrogen is already an important source of energy. The $250 billion industry supports fertilizer production, steel manufacturing, oil refining, and dozens of other vital activities. While nearly all hydrogen produced today is created using carbon-intensive methods, researchers are racing to develop cheaper ways of producing hydrogen with a lower carbon footprint.
One of the most promising approaches is water electrolysis, a process that uses electricity to power a reactor — called an electrolyzer — to split water (H2O) molecules into hydrogen (H2) and oxygen (O2).
Electrolyzers rely on a thin membrane that blocks O2 and H2 molecules while allowing positively charged hydrogen atoms — called protons — to pass through. Today, the industry standard membrane material is Nafion, a type of per- and polyfluoroalkyl substance (PFAS). These toxic chemicals are dubbed "forever chemicals" because of their ability to persist in the environment for decades. If not manufactured and disposed of properly, these PFAS materials can create significant environmental hazards.
At Columbia Engineering, chemical engineer Dan Esposito and his team are developing an alternative to Nafion. Their work, supported by the U.S. Department of Energy and in collaboration with industrial partners Nel Hydrogen and Forge Nano, aims to replace the Nafion membranes used in conventional electrolyzers with ultra-thin, PFAS-free oxide membranes. Replacing this component eliminates upwards of 99% of the PFAS contained in an electrolyzer.
"The membrane is the heart of the electrolyzer, where it enables proton transport while keeping hydrogen and oxygen separate," said Esposito, associate professor of chemical engineering at Columbia. "If it fails, the system doesn't work, and it can even become dangerous."
In a new paper, published today in ACS Nano, Esposito's lab describes a process for manufacturing these incredibly thin membranes and solving a major impediment to implementing them safely within water electrolyzers.
A new approach
The membrane inside an electrolyzer is responsible for efficiency and safety.
"The oxygen and hydrogen have to be kept separate — otherwise it's an explosive mixture," Esposito said. "The membrane is so important because it physically separates the oxygen and the hydrogen while allowing protons to pass through."
To create a superior alternative, Esposito and his team turned to silicon dioxide, a PFAS-free material that has far lower proton conductivity than Nafion. Previous generations of researchers had viewed that quality as a drawback, but advancements in nanoscale manufacturing pointed to a new solution: use the substance to fabricate a much thinner membrane.
"These oxide materials are a little non-intuitive for this application, in part because their conductivity is orders of magnitude lower than Nafion," Esposito said. "But resistance depends not only on the conductivity, but also on thickness."
Typically, the thickness of a Nafion membrane is around 180 microns, which is about two to three times thicker than a human hair. Using atomic layer deposition, a precise manufacturing technique refined by collaborator Forge Nano, the researchers crafted dense oxide membranes less than one micron thick. That's roughly 1/100th the thickness of a human hair — and hundreds of times thinner than Nafion. Even though silicon dioxide is less conductive, the drastic reduction in thickness brings its overall resistance in line with the best commercial options.
Pushing the limits of manufacturing
Thin membranes come with a new challenge: defects. Microscopic pinholes or cracks can let hydrogen leak across to the oxygen side.
"It only takes a few pinholes per square centimeter to make the whole thing unsafe," Esposito said.
To solve this problem, the team developed a clever electrochemical method to selectively seal the defects. By applying a pulsed voltage, they triggered chemical reactions that deposited nanoscopic "plugs" only inside the holes and cracks, preserving the membrane's thinness and low resistance.
"We figured out that you have to apply a pulse of energy, rather than a continuous current," Esposito said. "If you do this as a continuous process, then you change the pH everywhere and end up depositing plug material everywhere on the front of the membrane."
Pointing towards a superior product
The results have been dramatic. In laboratory tests, the plugged membranes exhibited hydrogen crossover rates up to 100 times lower than Nafion despite having less than 1/100th of its thickness.
The work is still early-stage, but the team's industry partners, Nel Hydrogen and Forge Nano, are already helping scale the approach. The researchers are now transitioning from centimeter-scale tests to larger prototypes necessary for commercial applications.
While the immediate focus is on hydrogen production, Esposito sees broader potential. The same defect-plugging strategy could benefit fuel cells, flow batteries, and even water treatment and semiconductor applications.
For now, though, the team is excited about helping to advance technology with so much potential to make hydrogen production from water electrolysis both cost-effective and environmentally friendly.
"Right now, less than 0.1% of global hydrogen comes from electrolysis," Esposito said. "If we want to scale that up sustainably, we need membranes that are both high-performing and environmentally responsible. That's what we're working to deliver."
