Insights into Amorphous Low-Density Hydrous Ruo2 for Supercapacitors Using Ab Initio Molecular Dynamics Simulations

Hydrated ruthenium dioxide (RuO2) 2 ) stands out as the archetype of pseudocapacitive materials, renowned for its outstanding capacitance and remarkable stability for supercapacitor applications. Herein, we introduce a model of amorphous low-density hydrous RuO2 2 for supercapacitors, achieving 2.2 g cm-3 -3 density, utilizing a combined approach of ab initio molecular dynamics simulations (AIMD) and static calculations using the Nudged Elastic Band (NEB) technique, within the frame of density functional theory (DFT), making the first instance of such an approach. Starting from an anhydrous amorphous structure, we systematically increase hydration levels within the model. It is found that full hydration exhibits both the presence of more than one OH group per Ru atom in the structure and molecular water loading into RuO2 2 pores. Hydrogen diffusion is estimated at 7.05 . 05 x 10 -6 cm2 2 s-1 , -1 , which is further correlated with the specific presence of OH species located at non-bridging oxygen sites. They are shown to almost annihilate local hydrogen migration barriers (0.06 eV), while non dissociated water molecules insures hydrogen migration from distant sites via Grotthuss type of mechanisms (0.3-0.4 eV activation range). These findings provide valuable insights into the behavior of hydrated RuO2 2 in supercapacitors, shedding light on the statistical interplay between hydration and hydrogen motion for enhanced energy storage applications.