The energy density of hydrogen is roughly 120 MJ/kg, which is much greater than that of chemical, fossil, and biofuels. Water is also the only byproduct when hydrogen is used to produce electricity. Electrolysis could be used to provide high-quality hydrogen gas, however, since noble metals – such as platinum and iridium – are currently needed to initiate such a reaction, the cost is unfortunately very high.
“Obviously, catalysts that are low-cost with high-activity are needed to make hydrogen energy more competitive with traditional technologies,” says Guowei Li, post-doctoral researcher at the Max Planck Institute for Chemical Physics of Solids, who studies the surface reactions of several topological materials.
“Topology may be the key to unlocking the barrier in the search for ideal catalysts,” states Professor Claudia Felser, director of the Max Planck Institute for Chemical Physics of Solids in Dresden. “We studied the surface properties of materials with topological order, from topological insulators to topological semimetals and metals; all these materials have non-trivial surface states that are protected by symmetries.”
Collaboration found a magnetic Weyl-semimetal
While searching out a perfect system that combines topological order, lost-cost, high efficiency, and high stability, the researchers found that surface states are very stable and robust against surface modifications. Finally, the team, together with colleagues from the TU Dresden and the Max Planck Institute for Microstructure Physics and Max-Planck-Institut für Kohlenforschung, Mülheim, identified a promising topological material: a magnetic Weyl semimetal, a Kagome-lattice Shandite compound.
High-quality bulk single crystals with sizes of up to centimeters can be exfoliated into thin-layers with defined crystal surfaces. The team showed that these surfaces act as superior catalysts for water splitting, even though the surface area is several orders of magnitudes smaller than today´s conventional nano-structured catalysts.
Pathway towards insights of quantum materials
During the water oxidation process, these surface states can accept electrons from reaction intermediates, acting as an electron channel whose resistance is not affected by the harsh electrochemical environment. Inspired by this strategy, the team subsequently investigated the catalytic performance of a platinum-tin based semimetal, a compound that contains a lower percentage of (expensive) platinum. These crystals showed superior electrocatalytic stability for periods of time exceeding one month.
The research aims to discover and understand new materials with unusual properties. In close cooperation, chemists and physicists use the most modern tools and methods to examine how the chemical composition and arrangement of atoms, as well as external forces, affect the magnetic, electronic, and chemical properties of the compounds.
New quantum materials, physical phenomena and materials for energy conversion are the result of this successful interdisciplinary collaboration.