(84bl) Understanding Proton-Coupled Electron Transfer on Polyoxovanadate Nanoclusters

Poly-Oxo-Metalates (POMs) comprise a versatile and fruitful material group, possessing tunable properties such as H–bond strength/reactivity (e.g. via heteroatom doping)¹, dynamic Proton-Coupled-Electron-Transfer (PCET), and having many applications in the field of small-molecule activation². Great promise for POMs abounds in a wide variety of applications. For example, recent electrochemical research has found interesting PCET behavior and selectivities for the Oxygen Reduction Reaction (ORR) on certain vanadium oxide nanoclusters^3,4.

In this work, we report on the investigation of the experimentally synthesized V₆O₁₉ nanoclusters via Density Functional Theory (DFT). First, we find in congruence with experimental results⁴, that the clusters' energetics of hydrogen chemisorption (PCET) are exergonic up to V₆O₁₃(OH)₆, and that the cluster Bond Dissociation Free Energies (BDFEs) follow a slight decreasing trend with increasing degree of cluster hydrogen-chemisorption, similar to our previous group findings⁵. The DFT results were in strong agreement with experimental BDFE and BDFE-trend results, especially after accounting for configurational entropies.

We found that the BDFE trend is significantly influenced by the configurational entropies of the increasingly hydrogen-chemisorbed clusters. We also found that the configurational entropies are themselves impacted by the inclusion of near-iso-energetic spin states that increase in number with increasing hydrogen chemisorption. This work rationalizes a series of experimental results on PCET processes of POM clusters and enables us to understand how cluster electronic properties and ensemble effects give rise to individual PCET steps.

1. Chakraborty, S.; Schreiber, E.; Sanchez-Lievanos, K. R.; Tariq, M.; Brennessel, W. W.; Knowles, K. E.; Matson, E. M., Modelling local structural and electronic consequences of proton and hydrogen-atom uptake in VO2 with polyoxovanadate clusters. Chemical Science 2021, 12 (38), 12744-12753.

2. Cooney, S. E.; Fertig, A. A.; Buisch, M. R.; Brennessel, W. W.; Matson, E. M., Coordination-induced bond weakening of water at the surface of an oxygen-deficient polyoxovanadate cluster. Chemical Science 2022, 13 (43), 12726-12737.

3. Chakraborty, S.; Petel, B. E.; Schreiber, E.; Matson, Ellen M., Atomically precise vanadium-oxide clusters. Nanoscale Advances 2021, 3 (5), 1293-1318.

4. Fertig, A. A.; Brennessel, W. W.; McKone, J. R.; Matson, E. M., Concerted Multiproton–Multielectron Transfer for the Reduction of O2 to H2O with a Polyoxovanadate Cluster. Journal of the American Chemical Society 2021, 143 (38), 15756-15768.

5. Miu, E.V; McKone, J.R.; Mpourmpakis, G., The Sensitivity of Metal Oxide Electrocatalysis to Bulk Hydrogen Intercalation: Hydrogen Evolution on Tungsten Oxide. Journal of the American Chemical Society 2022, 144 (14), 6420-6433.