Flexible Nanogenerators Based on Enhanced Flexoelectricity in Mn₃O₄ Membranes

Abstract Atomically thin, few‐layered membranes of oxides show unique physical and chemical properties compared to their bulk forms. Manganese oxide (Mn₃O₄) membranes are exfoliated from the naturally occurring mineral Hausmannite and used to make flexible, high‐performance nanogenerators (NGs). An enhanced power density in the membrane NG is observed with the best‐performing device showing a power density of 7.99 mW m⁻² compared to 1.04 µW m⁻² in bulk Mn₃O₄. A sensitivity of 108 mV kPa⁻¹ for applied forces <10 N in the membrane NG is observed. The improved performance of these NGs is attributed to enhanced flexoelectric response in a few layers of Mn₃O₄. Using first‐principles calculations, the flexoelectric coefficients of monolayer and bilayer Mn₃O₄ are found to be 50–100 times larger than other 2D transition metal dichalcogenides (TMDCs). Using a model based on classical beam theory, an increasing activation of the bending mode with decreasing thickness of the oxide membranes is observed, which in turn leads to a large flexoelectric response. As a proof‐of‐concept, flexible NGs using exfoliated Mn₃O₄ membranes are made and used in self‐powered paper‐based devices. This research paves the way for the exploration of few‐layered membranes of other centrosymmetric oxides for application as energy harvesters.