Research projects
in situ study of nanomaterials for the electrocatalytic synthesis of renewable fuels
Effective electrocatalysts are key for obtaining renewable chemical fuels (hydrogen, hydrocarbons from CO2 reduction) at a large scale. In particular, for hydrogen production, the best catalysts are rare and precious Pt group metals. The large scale deployment of renewable fuels would greatly benefit from catalysts containing only cheap and widely available elements.
We study in situ the behavior of 2D nanomaterials that have shown promise for the electrocatalytic production of H2 or the reduction of CO2. The active structure of a catalyst in situ often differs from its structure at rest or just after synthesis. In situ studies that can reveal the chemical structure of the catalyst are necessary to advance the field of electrocatalysis.
We use in situ Raman spectroscopy, a vibrational spectroscopy technique suited for the study of interfaces in aqueous solutions. More precisely, we employ surface enhanced Raman spectroscopy (SERS), a technique where a plasmonic nanostructure is used to increase the Raman signal by orders of magnitude. SERS is a very sensitive and surface specific technique, it will help us reveal how the catalysts’ surface structure relates to its activity.
in situ Raman nanospectroscopy
Raman spectroscopy is a powerful technique to investigate the structure of molecules and materials but its spatial resolution is limited by the diffraction of light, a few hundred nanometers at best in the visible. However, it is at the nanoscale that catalytic sites and the link between structure and activity can be best studied.
We are combining Raman spectroscopy with a scanning probe technique (atomic force microscopy or scanning tunneling microscopy) to perform Raman experiments with a resolution of 10 nm or better, this nanospectroscopy technique is called tip enhanced Raman spectroscopy, TERS. In TERS, a tip made of a plasmonic material is scanned on the surface of the sample, the apex of the tip acts as a nanoscale antenna, enhancing the local electromagnetic field and providing a very strong Raman signal in a nm3 volume.
We are developing TERS for in situ experiments, which will yield maps of the chemical structure at the surface with nanoscale resolution.
Plasmon triggered electrocatalysis
The use of plasmonic excitation in metallic nanostructures to generate energetic charge carrier has attracted a lot of attention to improve catalysts’ performance. In contrast with usual photocatalysis, one can use visible light to generate excited intermediates. When combined with standard heterogeneous or electrochemical catalysts, plasmon triggered charge carriers can give access to new reaction routes and change the activity as well as the specificity of a reaction.
We will use plasmonic nanostructure, that we already use for analytical purposes in SERS and TERS to improve electrocatalysts. In particular, we will study the reduction of CO2 (CO2RR), which is a complex and multistep reaction, characterized by a low selectivity on most catalysts. Copper and silver, which have a plasmonic resonance in the visible, are known catalysts for this reaction. We will study how the size and shape of their nanostructures can be changed to tune the plasmonic resonance and how it affect electrocatalytic activity. The precise control of plasmonic resonance, and the generation of charge carrier that comes with it, represent a new degree of freedom to create plasmonic catalysts that perform better than their non plasmonic counterparts.