Revealing the H2O/Na environments in Hydrated Manganese Iron Prussian White: a D/H exchange and machine-learning-assisted MD simulation study
Year: 2026
Type: preprint
Abstract: Manganese-iron Prussian blue analogs (MnFePBA) are promising sodium-ion battery positive electrodes, offering capacities comparable to LiFePO4 while avoiding critical metals such as cobalt and nickel. Despite their promise, the role of water in the PBA framework remains a central point of contention: some studies report severe first-cycle capacity loss and electrolyte decomposition driven by water co-extraction during cycling, while others show that hydration stabilizes a monoclinic phase capable of smooth, solid-solution sodiation which delivers superior long-term cycling stability. This disagreement is compounded by unresolved structural ambiguity of hydrated PBAs—conventional XRD cannot reliably distinguish sodium from water due to their similar electron densities, and existing neutron diffraction and computational studies disagree on where each species resides within the framework. Here, we address this gap by characterizing deuterated/hydrated (D/H) samples with neutron powder diffraction (NPD) and solid-state 2H/1H NMR to achieve improved contrast and spectral resolution between sodium and water environments, alongside machine-learned interatomic potential molecular dynamics (MLIP-MD) simulations that capture finite-temperature dynamics and configurational sampling beyond the reach of static DFT. NMR confirms consistent local environments across isotopically exchanged samples and resolves distinct signals for interstitial and coordinated water. Contrary to the prevailing XRD-based consensus, our combined NPD and MLIP-MD analysis reveals that water occupies body-center sites while sodium resides at face-center and off-face-center positions—the reverse of the commonly accepted structural model. These findings offer a revised atomic-scale picture of hydrated MnFePBA and establish a methodology for systematically probing hydration effects across the broader PBA family.
Source: ChemRxiv
Institutions: Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Laboratoire d’Innovation pour les Technologies des Énergies Nouvelles et les nanomatériaux, CEA Grenoble, Institut de Recherche Interdisciplinaire de Grenoble, Université Grenoble Alpes, Institut polytechnique de Grenoble, Centre National de la Recherche Scientifique, Institut Laue-Langevin
Language: English
Subfield: Electrical and Electronic Engineering
Field: Engineering
Domain: Physical Sciences
Open Access status: green
Funder: Agence Nationale de la Recherche
OpenAlex ID: W7204753317