Proton-exchange membrane (PEM) water electrolysis holds significant promise for “green” hydrogen production, but broader adoption hinges on reducing dependence on costly platinum-group metals, such as iridium. A new production method for ultra-thin nanoporous layers developed by VSParticle B.V. (VSP; Delft, the Netherlands; www.vsparticle.com) looks to decrease iridium loading by as much as 90% using electrical sparks to break up solid iridium into extremely small, stackable nanoparticles.
“Nanoporous layers are essential to drive better unit economics in electrolysis because higher surface area means more catalytic reactions, leading to improved performance and durability. However, until now, no one has developed an optimal manufacturing technology for porous thin films,” says Aaike van Vugt, CEO of VSP. Many established methods for thin-film production, such as chemical vapor deposition and atomic layer deposition, focus on solid films without any porosity, but VSP’s technology fills that gap by enabling ultra-thin films with highly tunable nanoporosity using spark-ablation technology.
The technology depends on the formation of electrical sparks between two conductive electrodes in the presence of iridium, where localized temperatures can reach 20,000ºC or higher. At these temperatures, a small volume of metal is ablated, forming a vapor that condenses. “Initially, there are loose atoms in the gas phase, and then when we turn off the spark, the system goes back to normal room temperature. All the loose atoms then start to collide, and when they hit each other, they will stick, so they will start forming bigger atomic clusters, and they will keep on growing in size till they have what we call a primary particle size, which is around 2–3 nm in size,” explains van Vugt. Following spark ablation, the resulting nanoparticle aerosol is printed onto a surface, where the nanoparticles subsequently self-assemble to form stackable nanoporous layers.
The ability to synthesize such tiny nanoparticles is unique, he notes, because at typical atmospheric pressures and temperatures, particles that are smaller than 2–3 nm are not stable, meaning that they instantly merge with other particles. VSP’s spark ablation technology only requires electricity and an inert carrier gas (argon or nitrogen), and eliminates the need for chemical binders, solvents or other reagents, aiding in process economics and scalability. “Because we only use these extremely small particles, and we don’t have any chemicals mixed into the nanoporous iridium that are able to block the active sites of the iridium, we are able to use dramatically less iridium and still have a similar performance compared to state-of-the-art coatings today,” according to van Vugt.
The technology’s nanoparticle production capacity depends on how fast the system can generate electrical sparks. VSP is currently developing its second-generation system, which can produce thousands of sparks per second, representing a hundred-fold increase over the first model. “From a chemical engineering perspective, every spark is a batch process in which we make a certain amount of nanoparticles. This system can handle hundreds or thousands of batch processes per second, so even though it’s a batch process, we do so many, it feels almost like a continuous process. Simply increasing the frequency of sparks helps us to scale up massively in output,” says van Vugt.
Beyond PEM processes, other applications for the technology include CO2 electrolysis, electrochemical hydrogen compression, anion-exchange membranes and printable gas sensors. The company has recently partnered with global manufacturer Heraeus Precious Metals (Hanau, Germany) to explore the integration of VSP’s technology into the larger PEM supply chain.