ANEMEL researchers have created a catalyst for water splitting that’s efficient and stable, without relying on scarce platinum group metals (PGMs). The study, recently published in Energy & Environmental Science, reports a high-performance PGM-free catalyst for the cathode in water electrolysis, responsible for the reaction that creates green hydrogen.
Current anion exchange membrane (AEM) water electrolyzers rely on PGMs, which are scarce and expensive. Specifically, these metals are used as catalysts at the cathode, where hydrogen is generated. However, ANEMEL AEM electrolyzers avoid PGMs, opting instead for more abundant metals such as nickel. This is essential to enable the wide adoption of electrolyzers: it helps to decrease the cost of electrolyzer components and improve their recyclability, reducing waste and providing a competitive advantage.
This requires investigating innovative ways to ensure electrolyzers perform at least as well, if not better than, those made with PGMs. After all, platinum and other metals in this group offer excellent activity and stability, especially at high current densities in electrolyzer environments, something PGM-free catalysts still don’t.
To understand the achievement, the researchers define two concepts: self-supported catalyst and electrodeposition. A self-supported catalyst is a type of catalyst formed by growing it directly on a support, known as a gas diffusion layer (GDL). The GDL allows gases to diffuse while providing a conductive pathway and can be made of various materials. These include carbon paper, and nickel foam, felt and mesh.
Electrodeposition is a widely used technique in applications such as watches and boats, anywhere a metal coating is needed. It works through electrolysis, a process that uses electrical energy to drive a chemical reaction. Two electrodes, the working electrode—where the GDL is located—and a counter electrode, are immersed in an electrically conductive solution called the electrolyte. By applying a current between the two, ions in the solution, which serve as precursors of the catalyst, migrate towards the working electrode “growing” the catalyst.
Here, ANEMEL researchers grew a catalyst made from nickel and molybdenum, both abundant metals. The novelty lies in the method and variables involved in achieving a high-performing catalyst, since this combination of metals had already been used in similar reactions before.
“I’ve been working on this catalyst for a long time now. This work has been accumulated over time—we optimized the method, the composition of the electrodeposition bath, and the substrates we are using for the GDL,” says the first author of the paper Ariana Serban, doctoral researcher at ANEMEL partner the École Polytechnique Fédérale de Lausanne (EPFL), in Switzerland.
Researchers chose carbon paper as the substrate for the GDL. This decision was made after confirming that nickel foam, felt and mesh weren’t the best options. For example, the latter created small holes in the membrane, with the consequent short circuit. Regarding the method, its novelty lies in the composition of the electrodeposition bath and the use of high-current density for deposition.
“Electrodeposition baths frequently used in the literature often include a buffering agent, such as boric acid, to stabilize the pH. We haven’t used this. That’s why the technique is special. We rely solely on an electrolyte with high conductivity. This high conductivity is crucial as it affects the electrodeposition process,” explains Serban. Such high conductivity allowed the use of a higher deposition current density, a deliberate choice to achieve a more compact and thicker electrode structure.
The result is a catalyst with remarkable activity. In particular, it enabled electrolyzers to operate stably at current densities as high as 3 A/cm² —the increased stress during high current operations can serve as a rapid assessment tool for the device’s robustness, eliminating the need for lengthy tests spanning thousands of hours.
Such performance is comparable to benchmark platinum catalysts, even with a slightly superior stability. This means ANEMEL not only developed a PGM-free HER catalyst, but also a catalyst exceeding state-of-the-art catalysts. According to Serban, this result ranks among the top 100, or even top 50, in terms of performance for non-PGM catalysts.
Characterization of the catalyst revealed a structural change during the reaction that explained the good results. “There was a reorganization of the surface, where bulk molybdenum atoms migrated to the surface, helped by distortions in the bulk,” she explains.
Some of these atoms become oxidized—they lose electrons—and these oxidized species contribute to the water-splitting process. This result brings us one step closer to large-scale green hydrogen production.
