Computational criteria for hydrogen evolution reaction activity in Au25-based nanoclusters Laura Laverdure 1 , Omar López-Estrada 1 , Nisha Mammen 1 , Marko M.Melander 1 , Hannu Häkkinen 1,2 , Karoliina Honkala 1 1 Department of Chemistry, Nanoscience Centre, University of Jyväskylä, Jyväskylä, Finland 2 Department of Physics, Nanoscience Centre, University of Jyväskylä, Jyväskylä, Finland The hydrogen evolution reaction (HER) is a critical reaction in addressing climate change, however, it requires catalysts to be generated on an industrial scale. Nanomaterials such as nanoclusters belong to the “every atom counts” region which allows efficient use of catalytically active but expensive elements. Similarly, another advantage over conventional HER catalysts is the possibility of atomic precision in tailoring the intrinsic activity. Ligand-protected metal clusters, such as the thiolate-protected MAu 24 (SR) 18 (M = Au, Cu, Pd), are of particular interest as not only are they electrocatalytically active towards HER, but the charge state and composition can be precisely tuned through ligand substitution and doping. Here, we present a comprehensive computational study examining how the charge state and dopants affect the catalytic activity of [MAu 24 (SCH 3 ) 18 ] q (q = -2, -1, 0, +1, +2) towards the Volmer step of the HER. According to the Sabatier principle, an ideal HER catalyst should have nearly thermoneutral H adsorption energy. In addition to H adsorption energies, we have computed the nanoclusters’ redox potentials and kinetic barriers for the Volmer step under acidic conditions. We identified -2 / -1 and -1 / 0 redox pairs as relevant for M = Au, Cu, and Pd as well as the 0 / +1 pair for Au and Cu. Hydrogen adsorption on these charge pairs is thermoneutral or energetically favoured. Despite thermoneutral adsorption energies, the kinetic barriers are high for M = Au, Cu and q = 0 / +1. The kinetic barrier remains high for CuAu 24 (SR) 18 until the -2 / -1 redox pair which is achieved at -1.48 V. For the -1 / 0 redox pair of Au 25 (SR) 18 , which occurs at -0.30V,the barrier is sufficiently lowered but the H adsorption is no longer thermoneutral thus implying the rate of reaction would be controlled by H 2 desorption. In contrast, for PdAu 24 (SR) 18 , the q = -1 / 0 redox pair occurs at 0.38V, has thermoneutral H adsorption and a low kinetic barrier. These criteria combined suggest thatPdAu 24 (SR) 18 should have the highest catalytic activity and would be comparable even to Pt(111). We can thus explain the relative activity of MAu 24 (SR) 18 (M = Au, Cu, Pd) clusters reported by Kumar et al. Our results show that adsorption energies alone are an insufficient criterion to identify a promising catalytic material; kinetic barriers and experimentally relevant redox potentials should also be considered. A more thorough computational approach that includes charge and potential is therefore required to understand and screen electrocatalytically active nanoclusters. References 1. Lopez-Estrada, O., et al. Computational Criteria for Hydrogen Evolution Activity on Ligand-protected Au25-based Nanoclusters. ChemRxiv. Cambridge: Cambridge Open Engage; 2023. 2. Sabatier, P. Hydrogénations et déshydrogénations par catalyse. Ber. Dtsch. Chem. Ges.1911, 44, 1984–2001. 3. Kumar, B. et al. Gold nanoclusters as electrocatalysts: size, ligands, heteroatom doping, andcharge dependences. Nanoscale, 2020,12, 9969-9979.
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