The goal of this project is to achieve a deep understanding of the properties of new bi-functional 2D biomimetic catalyzers for rechargeable metal-air (e.g., Zn-air) batteries. Such batteries require effective catalyzers at the air electrode for both the oxygen evolution reaction (during charge) and for the oxygen reduction reaction (during discharge). This is typically achieved using catalyzer that are bi-phasic, that is, composed of two different materials, each one suitable for one reaction. An alternative and more appealing perspective is to use bi-functional catalyzers, composed of a single phase, containing two different transition-metal atoms acting as active sites. The challenge is to fabricate and tune these materials to achieve optimal catalyzing activity towards both reactions. Promising systems are composed of flat organic molecules, such as porphyrins or phtalocyanines, with a transition-metal atom at the center of the ring, self-assembled on a 2D substrate into a metal-organic framework, bound by other transition-metal atoms.

This project, conducted in the framework of PRIN 2022 2DOrNotToBe, will focus on the theoretical modellization of the most likely  bi-functional catalyzer candidates: M1TPyP-M2 (TetraPyridylPorphyrins, with M1,M2 = Co, Ni, Mn ...) on graphene layers, grown on an Iridium substrate. This project will be performed in close collaboration with the experimental UniTs (Trieste University) unit, led by Prof. Erik Vesselli, that provides fabrication and spectroscopic data for these new materials. Collaboration is also envisaged with theoreticians in UniTs, led by Prof. Maria Peressi, who have already investigates similar materials.

The specific work consists in the numerical simulations of the mentioned materials, using first-principle techniques (density functional theory, DFT, and beyond), as a first step. The further steps will deal with the study of the interactions of the catalyzing active sites with small molecules (mainly oxygen but also water) and the tayloring of the catalytic properties via chemical changes, doping, the surface trans effect, etc.. The analysis and rationalization of the results will be performed. Some experience with DFT calculations on high-performance computers, preferably with the Quantum ESPRESSO suite, is required.

The simulation protocol: level of theory, size of the cell, computational requirements, etc., will be first established, building upon previous experience in the UniTs group. Hubbard-corrected functionals (DFT+U) are expected to yield an acceptable quality of simulations.  The expected results include i) the detailed geometric and electronic characterization of the materials, ii) the characterization of the effects of doping, achievable through the surface trans-effect, iii) the understanding of the adsorption and activation mechanism of small molecules (oxygen, water) on the single-atom reaction centres, iv) the comparison of the theoretical results with experimental ones and the understanding and resolution of discrepancies.

References:

Single Metal Atom Catalysts and ORR: H‑Bonding, Solvation, and the Elusive Hydroperoxyl Intermediate, F. Armillotta et al.,  ACS Catal. 2022, 12, 7950−7959

Spectroscopic fingerprints of iron-coordinated cobalt and iron porphyrin layers on graphene, F. Armillotta et al., Cell Reports Physical Science 4, 101378, May 17, 2023