The stability, selectivity and activity of nanocatalysts depend on the electronic interactions between the metal particles and their oxide support. Understanding the nature of the electron transfer across the metal/surface interface is key to improving such catalysts. A European team has now used synchrotron radiation photoelectron spectroscopy, scanning tunneling microscopy and density functional theory to determine the charge transfer per platinum atom and how this is greatest for particles containing approximately fifty platinum atoms.
Noble metal nanoparticle catalysts on oxides are a class of the most common catalytic materials used across the chemical industry, in fuel production, as environmental catalysts, photocatalysts and electrocatalysts. Efficient use of the expensive and rare metal elements they contain is a priority, so chemists and materials scientists are constantly on the lookout for new ways to improve efficacy and efficiency. The details are controversial and have been for thirty years. What is known with certainty is that electronic structure, nanoscopic structure, structural flexibility and interaction with the support are the major factors in determining how well such catalysts function.
Writing in the journal Nature Materials, the team also showed that one electron is transferred for every ten platinum atoms from the nanoparticle to the support. By contrast, for larger particles, the charge transfer limit is established by the support whereas nucleation effects partially inhibit charge transfer in smaller particles. "These mechanistic and quantitative insights into charge transfer will help to make better use of particle size effects and electronic metal–support interactions in metal/oxide nanomaterials," the team reports.
The team comprises scientists from SISSA and CNR-IOM of Trieste, the University of Barcelona, Spain, ELETTRA Sincrotrone Trieste, Italy, Friedrich Alexander Universität Erlangen-Nürnberg, Germany and Univerzita Karlova of Prague, Czech Republic. "By combining experimental measurements and theoretical numerical simulations, we established guidelines for controlling the charge of nanoparticles and obtaining catalysts having maximum efficiency," explains team member Stefano Fabris of the CNR-IOM/SISSA. "The experimental measurements were carried out by researchers from the University of Prague at ELETTRA Sincrotrone Trieste, whereas the simulations were the result of my collaboration with the University of Barcelona."
If industrial production of methanol as feedstock for fuel cells can be scaled up sustainably, perhaps by using a light-driven system that in some ways mimics photosynthesis, then the catalysts studied by the European team could be critical in releasing the pent up energy from that methanol as electricity generated in a fuel cell.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the bestselling science book "Deceived Wisdom".