Jakob Praxmair

Perovskite oxynitride LaTiO₂N holds promise for visible-light-driven photocatalytic water splitting, yet its surface dynamics at the catalyst-water interface remain elusive. This study employs state-of-the-art density functional theory molecular dynamics (DFT-MD) and electrochemical measurements to unravel the intricate interplay of water arrangement and adsorption on the LaTiO₂N(100) surface. By considering explicit solvent effects, we reveal a pronounced hydrophilic character, with spontaneous water dissociation forming hydroxyl groups at undercoordinated Ti sites at the surface, stabilizing the latter and potentially enhancing the OER activity. Our simulations identify the thermodynamically stable termination and demonstrate its role in fostering robust hydrogen-bond networks that facilitate proton-coupled electron transfer. The surface Pourbaix diagram underscores hydroxylated configurations across diverse electrochemical conditions, corroborated by DFT-MD insights. These findings highlight the critical role of treating an explicit solvent environment and its dynamics at a given temperature in the modeling of LaTiO₂N, offering a blueprint for designing high-performance, sustainable water-splitting catalysts.

To improve safety and sustainability aspects of today's energy storage solutions, aqueous post-lithium-ion electrochemical cells are promising concepts. In this context, we synthesize hydrated vanadium oxide (V₃O₇·H₂O) via a hydrothermal process and investigate its electrochemical properties as a cathode in aqueous post-lithium-ion hybrid cells. This active material exhibits an excellent initial specific capacity of 404 mAh·g^-1 at a practical current density of 100 mA·g^-1 and a promising stability of 123 mAh·g^-1 at a current density of 1 A·g^-1 after 500 cycles upon Mg²⁺ and Na⁺ cointercalation. The insertion characteristics of this hybrid cell are investigated by cyclovoltammetry, operando XRD, and post-mortem transmission electron microscopy measurements. The results suggest that Na⁺ is inserted preferentially at lower potentials and that its effect fades quickly, while the Mg²⁺ contribution enables stable cycling, resulting in a competitive capacity retention of 73% after 500 cycles. In addition, we find that the charge transfer resistances are about one hundred times smaller in aqueous than in pure organic electrolyte as measured by electrochemical impedance spectroscopy. These results demonstrate that V₃O₇·H₂O is a suitable cathode material for aqueous Mg²⁺/Na⁺ hybrid cells, enabling a performance that is comparable to cathodes in less sustainable and less safe organic electrolytes with respect to capacity and stability and is superior in transport-related properties.