Jun 18^th 2025, COB1 Room at 11:00 am

Seminar: “Photoelectrochemical water splitting on hematite: Mechanistic insights from machinelearning-interatomic-potentials MD and microkinetic modeling“

Dr. Simone Piccinin.
Consiglio Nazionale delle Ricerche, Istituto Officina dei Materiali, Trieste, Italy

The oxygen evolution reaction (OER) plays a crucial role in (photo)electrochemical devices that use renewable energy to produce synthetic fuels. While the mechanism of this reaction is still debated, recent measurements on semiconducting oxides [1,2] have shown that the dependence of the rate of OER on the surface hole density is a power law, suggesting a multihole mechanism via surface hole accumulation. This is reminiscent of the mechanism for OER promoted by the oxygen evolving complex in Photosystem II and in stark contrast with metallic oxides like IrO2 [3], where the dependence is exponential. Modeling this reaction requires all-atom simulations to capture the e7ects of the H-bond network of the solvent on the reactants, long molecular dynamics simulations to sample accurately the solvent degrees of freedom and enhanced sampling to model activated process like O-O bond formation. We have used machine learning interatomic potentials (MLIP) trained on DFT energy and forces to achieve this goal. In contrast to what was previously assumed, we find that the reaction proceeds via direct coupling of oxygen adsorbates, triggered by the oxidation of terminal oxygen sites. This process is considerably faster than competing mechanisms like the nucleophilic attack of a water molecule or hydroxide ion. We tested the accuracy of these MLIP predictions, validating the kinetics of this process with DFT calculations. Microkinetic modeling was then used to predict the overall rate of the catalytic process and to relate the photocurrent so the surface charge accumulation. We find a power-law with a third order dependence, in agreement with experiments, and we assign its origin to the facile formation of the superoxo intermediate, a step whose activation energy is weakly dependent on the surface hole coverage. 

1. H. N. Nong, L. J. Falling, A. Bergmann, M. Klingenhof, H. P. Tran, C. Spöri, R. Mom, J. Timoshenko, G. Zichittella, A. Knop-Gericke, S. Piccinin, J. Pérez-Ramírez, B. Roldan Cuenya, R. Schlögl, P. Strasser, D. Teschner, T. E. Jones, Key role of chemistry versus bias in electrocatalytic oxygen evolution, Nature 2020, 587, 408–413 
2. Camilo A. Mesa, Laia Francàs, Ke R. Yang, Pablo Garrido-Barros, Ernest Pastor, Yimeng Ma, Andreas Kafizas, Timothy E. Rosser, Matthew T. Mayer, Erwin Reisner, Michael Grätzel, Victor S. Batista & James R. Durrant, Multihole water oxidation catalysis on haematite photoanodes revealed by operando spectroelectrochemistry and DFT, Nature Chemistry, 12, 82–89 (2020)
3. G. Righi, J. Plescher, F.-P. Schmidt, R. Kramer Campen, S. Fabris, A. Knop-Gericke, R. Schlögl, D. Teschner, T. E. Jones, S. Piccinin, On the origin of multihole oxygen evolution in hematite photoanodes, Nature Catalysis 2022, 5, 888–899