Heterogeneous catalysis is at the core of sustainable chemistry, since it allows a fine control of chemical bond forming and breaking processes. For the optimal design of catalysts, a fundamental atomic scale understanding of the structure and electronic structure of the catalytic particle, in interaction with the reactant is of utmost importance. Computational chemistry today is a key method, to reach such an understanding at the molecular level of the structure of the active site and of the elementary processes occurring during the catalytic act. Experiments on model surfaces commonly help in identifying the structural sensitivity of catalytic reactions. Nevertheless, their conclusions do not frequently lead to devising superior “real-world” catalysts. For instance, this is true for single-crystal platinum electrodes and the oxygen reduction reaction (ORR), an important reaction for sustainable energy conversion. Pt(111) is substantially enhanced by steps, reaching a maximum at short terrace lengths of 3-4 atoms. Conversely, regular platinum nanoparticles with similar undercoordinated defects are less active than Pt(111) and their activity increases alongside the terrace-to-defect ratio. We show here that a model to design ORR active sites on extended surfaces can also be used to solve this apparent contradiction and provide accurate design rules on nanoparticles. Essentially, only surfaces and nanostructures with concave defects can surpass the activity of Pt(111), whereas convex defects are inactive. A second example of material design will deal with photocatalysis, where understanding photophysical processes is crucial for developing efficient solar energy conversion systems. We showed that an enhancement by a factor of 3 in photocatalytic efficiency for the oxygen evolution reaction (OER) is obtained by adding trace amounts (~0.05 wt%) of noble metals (Rh or Ru) to a 2 wt% cobalt oxide-modified Ta3N5 photocatalyst. Density functional theory (DFT) calculations show that the effects of a second metal addition perturbs the electronic structure and redox properties in such a way that both hole transfer kinetics and electrocatalytic rates improve and hence explain the influence of the noble metal dopant.

First-principles modeling and design of catalytic materials

253rd National Meeting (2017)

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