Oxygen and chlorine evolution without noble metals: Electrode potential transforms MXene surfaces

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MXenes are a class of two-dimensional materials that were discovered in 2011. Theoretical studies previously predicted that they would not be catalytically active in anodic processes. Researchers led by Prof. Dr. Kai S. Exner, head of the Department of Theoretical Catalysis and Electrochemistry at the University of Duisburg-Essen (UDE), have now disproved this theory using multiscale modeling.

The scientists discovered that when an electrode potential is applied, the MXene surface changes into a brush-like structure. Atoms of non-noble metals migrate out and form so-called "SAC-like structures" (single atom catalyst-like). These catalysts mediate two important reactions, namely the oxygen evolution and chlorine evolution reactions.

The result is a material whose surface has catalytically active sites without the addition of precious metals. "We concluded that MXenes behave similarly to enzymes in an electrochemical environment. By applying an electrode potential, their active sites are created directly in the process," explains Exner. The research is published in the Journal of the American Chemical Society.

The team was also able to show that the resulting SAC-like structures are selective—if water and chloride ions are in the reaction environment at the same time, only gaseous chlorine is formed. The formation of this base chemical is a key process in the chemical industry, which produces more than 70 million tons of gaseous chlorine (Cl₂) per year. Cl₂ is required for the production of pharmaceuticals, plastics, batteries, and for water treatment.

However, when only water is available in the electrolyte, the active MXene surface facilitates the production of gaseous oxygen (O₂) by means of oxygen evolution—an important step in the formation of green hydrogen in an electrolyzer.

This discovery can greatly simplify the production of single-atom catalysts. The elimination of expensive precious metals also reduces costs and dependencies.

More information: Samad Razzaq et al, MXenes Spontaneously Form Active and Selective Single-Atom Centers under Anodic Polarization Conditions, Journal of the American Chemical Society (2024). DOI: 10.1021/jacs.4c08518

Journal information: Journal of the American Chemical Society

Provided by University of Duisburg-Essen