Search

Manganese oxides (MnOx) have become an increasingly popular electrode material for supercapacitors due to their low cost, abundance, and environmentally-friendly nature. One important factor that enhances their electrochemical properties is the manganese valence. Mn3+ is particularly useful as it exhibits two redox couples (Mn2+/Mn3+ and Mn3+/Mn4+), which maximize the redox reaction and result in excellent electrochemical performance. This study focused on regulating the manganese valence using a facile pyrolysis method, resulting in a Mn3+-rich MnOx/rGO composite (rGO denotes reduced graphene oxide) at a pyrolysis temperature of 400 °C. The composite demonstrated a high specific capacitance of 304 F g−1. Additionally, asymmetric supercapacitors (MnOx/rGO//activated carbon) were assembled with aqueous and quasi-solid electrolytes respectively, and they demonstrated similar performance. The supercapacitor device also showed good capacitance retention of 82% after 10,000 charge/discharge cycles at a current density of 10 A g−1. Furthermore, the variation of the energy storage mechanism for MnOx/rGO with the change of manganese valence was discussed. Overall, this work highlights the importance of controllable synthesis of MnOx-based electrode materials for high-performance supercapacitors, and could pave the way for future developments in the field. [ABSTRACT FROM AUTHOR]

With the increasing demand for high‐performance energy storage devices, single materials of ordinary structures for electrode materials have become increasingly difficult to meet people's needs. Therefore, composites of inimitable structures have drawn considerable attention. In this work, nitrogen‐doped porous graphene coated with Fe3O4 nanoparticles (NPGF) is prepared by an efficient and green pyrolysis method. Structural and compositional characterizations confirm that the NPGF nanohybrids possess uniformly distributed pore structure and quite pure composition which is free of any impurities. In addition, electrochemical characterization verifies the excellent electrochemical performance, such as high‐specific capacitance (713 F g−1 at 1 A g−1), prominent rate capability (capacitance retention of 77.3% and 67.9% when the current density is increased respectively from 1 to 10 and 20 A g−1), and outstanding cycling stability (capacitance retention of 94.3% after 3000 cycles). Such promising results suggest that the NPGF nanohybrids have great application prospects in future high‐performance supercapacitors. [ABSTRACT FROM AUTHOR]

BaSrTiO (BST), 5 mol% Mn-doped BST (Mn-BST) and bilayered Mn-BST/BST films with a thickness of about 100 nm were fabricated by using pulsed laser deposition technique on MgO single crystal substrates, and their microwave dielectric properties were comparatively investigated. It was confirmed that all the BST-based films were crystallized in pure single-oriented perovskite phase. There appeared nanosized pores in the BST film; after addition of Mn, however, the film surface morphology became denser while exhibiting an increased roughness, and ultimately, a smooth and dense morphology was achieved by the design of bilayered Mn-BST/BST film. Coherently, the microwave dielectric properties of BST films were enhanced by Mn doping and more significantly enhanced in the bilayered Mn-BST/BST film. As a result, for the bilayered film, a very low loss tangent of 0.017-0.007 and a high dielectric tunability of 70.9% under E = 36 V/μm were simultaneously obtained at 79 K and L-band frequency (1-2 GHz), thereby resulting in an extremely high commutation quality factor of 14492. The excellent microwave dielectric properties obtained in the Mn-BST/BST bilayered film originate not only from the Mn-doping effect, but are also ascribed to the pre-deposition of BST layer, which serves as a good template for the growth of Mn-BST film. [ABSTRACT FROM AUTHOR]