Developing novel protocols for hydrogen (H) loading is crucial for furthering the investigation of hydrides as potential high-temperature superconductors at lower pressures compared to recent discoveries. Ionic gating-induced protonation (IGP) has emerged as a promising technique for H loading due to its inherent simplicity, but it can be limited in the maximum density of injected H when ionic liquids are used as a gating medium. Additionally, most ionic liquids are limited by high production costs, complex synthesis, and potential toxicity. Here, we demonstrate that large H concentrations can be successfully injected in both palladium (Pd) bulk foils and thin films (up to a stoichiometry PdH0.89) by using a deep eutectic solvent (DES) choline chloride-glycerol 1:3 as gate electrolyte and applying gate voltages in excess of the cathodic stability limit. The attained H concentrations are large enough to induce superconductivity in Pd, albeit with an incomplete resistive transition which suggests a strongly inhomogeneous H incorporation in the Pd matrix. This DES-based IGP protocol can be used as a guideline for maximizing H loading in different materials, although specific details of the applied voltage profile might require adjustments based on the material under investigation.
@article{arxiv.2410.15452,
title = {Facile synthesis of palladium hydride via ionic gate-driven protonation using a deep eutectic solvent},
author = {Gaia Gavello and Giorgio Tofani and Domenico De Fazio and Stefania Lettieri and Andrea Mezzetta and Lorenzo Guazzelli and Christian S. Pomelli and Renato S. Gonnelli and Erik Piatti and Dario Daghero},
journal= {arXiv preprint arXiv:2410.15452},
year = {2025}
}