They are highly selective and can be easily separated from the reaction mixture: Single-atom catalysts combine the advantages of homogeneous and heterogeneous catalysis. Researchers have now succeeded in producing them in a novel way - independently and without precious metals, as the University of Duisburg-Essen reports. Their findings open up new avenues for the simpler, more sustainable production of catalytically active materials.
MXenes are a class of two-dimensional materials that were only discovered in 2011. Theoretical studies previously predicted that they are not catalytically active in anodic processes. Researchers led by Prof. Dr. Kai S. Exner, Head of Theoretical Catalysis and Electrochemistry at the University of Duisburg-Essen, have now been able to disprove this theory using multiscale modeling.
Electrical potential changes MXenes
The new finding If an electrical potential is applied to MXenes, their surface changes into a brush-like structure: atoms of base metals migrate out and form so-called "SAC-like structures" (single atom catalysts-like). These mediate two important reactions, the development of oxygen and chlorine gas.
The result is a material whose surface has catalytically active sites without the addition of precious metals. "We were able to conclude that MXenes behave similarly to enzymes in an electrochemical environment. By applying an electrical potential, their active sites are created directly in the process," explains Exner.
Production of only chlorine or only oxygen possible
The team was also able to show that the structures work selectively: If water and chloride ions are in the reaction environment at the same time, only chlorine gas generation takes place. This is a central process in the chemical industry, which supplies over 70 million tons of chlorine gas (Cl2) worldwide every year. Chlorine is required for the production of medicines, plastics and batteries as well as for the treatment of water. If only water is available to the active MXene surface, however, it releases oxygen (O2) - an important step for the formation of green hydrogen in an electrolyzer.
This discovery can significantly simplify the production of single-atom catalysts. The elimination of expensive precious metals also reduces costs and dependencies.