Advances in Single-Atom-Polaron Catalysis
Wider research context:
The catalytic properties of single-atom catalysts (SACs) differ fundamentally from those of nanoparticles. The electronic structure and local environment of a single atom determine its properties, and these are closely linked. As such, SACs resemble the coordination complexes utilized in homogeneous catalysis, and it is hoped that SACs can reach similar levels of activity and selectivity. Changing the atom coordination alters the number of free ligands available to adsorb reactants, but this also changes the electronic structure, and thus the binding strength of reactants. Both considerations must be simultaneously satisfied consistent with the Sabatier principle, which stipulates that reactants must be neither too well, nor too loosely bound. Since the beginning of the SAC field, hematite has been a support of choice. However, I recently encountered severe computational issues when dealing with atoms deposited on its surface. The current state-of-the-art DFT framework is insufficient to reproduce any of the experimental observations made. However, experimental and preliminary computational results indicate that the hematite support accumulates electron polarons (quasiparticles where charge carriers are trapped within the atomic lattice) at its surface. These strongly affect the system and especially the single atom’s catalytic properties. The important aspect is the breaking of scaling relations between the single atom’s electronic structure and its atomic environment, with the addition of polarons originating from the support.
Research questions:
Can we accurately account for the polarons at the surface of hematite? Are polarons ultimately responsible for the experiment-theory discrepancies observed up to now? Can we establish how polarons interact with single atoms and reactants?, and can we use this knowledge to utilize these phenomena to design better SACs?
Approach:
Using already existing experimental results as benchmark, polarons are considered in the DFT framework and their interplay with single atoms is investigated. As a probe, I will use the adsorption of small molecules such as H2O or CO on the pristine surface and on single atoms. I intend to tune the amount of polarons in the support, by using dopants, to further enhance the understanding of their role on catalytic properties.
Level of originality:
The decoupling of the single atoms’s electronic structure from its atomic environment will provide new possibilities in designing catalytic active sites. These will move the field further away from costly transition metals, more so than can be done by single-atom catalysis alone.
