Article Dans Une Revue Inorganic Chemistry Année : 2025

Crystallization of Manganese(V) Oxides by Hydroflux Synthesis: Control of Anisotropic Growth and Electrochemical Stability

Résumé

Despite intriguing optical, magnetic, and redox properties, inorganic materials containing pentavalent manganese (Mn V ) are rare and could never be designed as shape-controlled crystals, which limits the ability to tune properties. Herein, we explore alkali hydroxide mixtures with controlled water content, namely, hydrofluxes, to demonstrate phase, shape, and nanostruc-ture control of Mn(V) oxides. We demonstrate speciation among KSrMn V O 4 , Sr 5 (Mn V O 4 ) 3 OH, and SrMn IV O 3 with the water and strontium content and the nature of the alkali cation of the hydroxide salt. We then provide evidence of the key role of water in enabling shape and nanostructure control, which we relate to the preferential interaction of water with specific c rystal f acets o f the hydroxyapatite Sr 5 (Mn V O 4 ) 3 OH, and to the impact of water on precursor solubility in water-poor hydrofluxes. We then show that nanostructured Mn(V) hydroxyapatite possesses an acid-base redox stability window, enabling electrochemical operation in strongly oxidative conditions. By correlating the fundamental knowledge of hydrofluxes with crystallization mechanisms, this work sheds light on the possibilities offered by hydrofluxes for crystal shape, size, and property control.

Manganese can be found in various oxidation states in solidstate materials from 0 to +7. 1 Despite its low stability and scarcity, pentavalent manganese(V) is the origin of important properties. It can be used to design colorful blue or green pigments. 2,3 Mn(V) compounds have been considered as laser materials 4 and also raise interest due to intriguing magnetic properties. 5,6 Mn(V) is also involved in the oxygen-evolving complex for the production of dioxygen during photosynthesis. 7,8 This suggests that Mn(V) compounds could find interest for use in water oxidation electrocatalysis provided that they can be used in conditions where the oxidation state and structural features are maintained. To date, the electrochemical properties of Mn(V) compounds, especially their pH-potential stability window, have not been evaluated, so the feasibility of using Mn(V) compounds for electrochemical applications remains an open question.

Inorganic compounds containing pentavalent manganese (Mn V ) are scarce due to their low stability. 9 Currently reported manganese oxides built on Mn(V) are Ba

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hal-04979052 , version 1 (05-03-2025)

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Carlos Inocêncio, Almudena Torres-Pardo, David Montero, Lucien Roach, Pierre-Olivier Autran, et al.. Crystallization of Manganese(V) Oxides by Hydroflux Synthesis: Control of Anisotropic Growth and Electrochemical Stability. Inorganic Chemistry, 2025, 64 (10), pp.5122-5131. ⟨10.1021/acs.inorgchem.4c05439⟩. ⟨hal-04979052⟩
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