Manganese oxides have always attracted great interest due to their multiple applications and unique properties in catalysis. Among these oxides, Hausmannite (Mn₃O₄) is one of the stable phases, which is characterized by its high stability due to its spinel structure and multiple valences making it a perfect candidate for multiple applications such as water treatment, catalysis, electrochemistry, adsorption, among others. Unfortunately, the synthesis routes of this oxide are sometimes not the best due to the use of surfactants and organic solvents or even the final product is just a powder difficult to handle for real applications. In this study, a successful hydrothermal synthesis method of octahedral Hausmannite nanocrystals supported on the surface of a manganese oxide layer-Nafion membrane was developed, which avoids the problem of using organic solvents and conforms to an environmentally friendly synthesis by being water-based, which also achieves a hybrid system that works satisfactorily as a working electrode in OER reaction.
The Hausmannite-Nafion hybrid was synthesized based on manganese(II) acetate, Nafion membrane N115, potassium nitrate and deionized water by conventional heating in autoclave reactor. OER reaction test was carried out in a three electrode system with 1M KOH as electrolyte, Hg/HgO as reference electrode and platinum as counter electrode. In terms of material properties, a noticeable increase in the thermal stability of the material has been appreciated as the break point of the ionic clusters of the nafion has been improved by at least 100 °C. In terms of electrocatalytic performance for OER, current densities above 75 mA/cm² and a stability of more than 12 hours have been obtained. In addition, its application as a “primer” to extend these hybrid systems to other oxides such as ZnO, SnO₂ and TiO₂ was demonstrated. Finally, this research has shown promising results to consider changing the approach to the synthesis of conventional inorganic oxides, considering the idea of making functional and scalable materials in one-step process.

Sebastian Noguera Ruiz

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