The MXene class of materials has many talents. A world team led by HZB chemist Michelle Browne has now demonstrated that MXenes, properly functionalised, are excellent catalysts for the oxygen evolution response in electrolytic water splitting. They’re more stable and efficient than the very best metal oxide catalysts currently available. The team is now extensively characterising these MXene catalysts for water splitting on the Berlin X-ray source BESSY II and Soleil Synchrotron in France.
Green hydrogen is seen as one among the energy storage solutions of the longer term. The gas could be produced in a climate-neutral way using electricity from the sun or wind by electrolytic water splitting. While hydrogen molecules are produced at one electrode, oxygen molecules are formed at the opposite. This oxygen evolution response (OER) is one among the limiting aspects in electrolysis. Special catalysts are needed to facilitate this response. Amongst the very best candidates for OER catalysts are, for instance, nickel oxides, that are inexpensive and widely available. Nevertheless, they corrode quickly within the alkaline water of an electrolyser and their conductivity also leaves much to be desired. That is currently stopping the event of low-cost, high-performance electrolysers.
MXene as catalysts
A brand new class of materials could offer an alternate: MXenes, layered materials made from metals, reminiscent of titanium or vanadium, combined with carbon and/or nitrogen. These MXenes have an enormous internal surface area that could be put to implausible use, whether for storing charges or as catalysts.
A world team led by Dr Michelle Browne has now investigated the usage of MXenes as catalysts for the oxygen evolution response. PhD student Bastian Schmiedecke chemically ‘functionalised’ the MXenes by docking copper and cobalt hydroxides onto their surfaces. In preliminary tests, the catalysts produced in this manner proved to be significantly more efficient than the pure metal oxide compounds. What’s more, the catalysts showed no degradation and even improved efficiency in continuous operation.
Measurements at BESSY II
Measurements on the BESSY II X-ray source, with Namrata Sharma and Tristan Petit, showed why this works so well: “We were in a position to use the Maxymus beamline there to learn the way the outer surfaces of the MXene samples differ from the within,” explains Schmiedecke. The researchers combined scanning electron microscopy (SEM/TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray transmission microscopy (STXM) and X-ray absorption near-edge structure (XANES) to realize further insights into the fabric.
Outlook: statement under continuous load
“We’ve got been in a position to show that MXenes have great potential to be used as catalysts in electrolysers,” says Michelle Browne. The collaboration with partner teams from Trinity College, Dublin, Ireland, and the University of Chemistry and Technology, Prague will proceed. Along with further chemical variations of MXene catalysts, the team also plans to check such catalysts in conventional electrolysers in continuous operation.
