Fixing graphene-Mn3O4 nanosheets on carbon cloth by a poles repel-assisted method to prepare flexible binder-free electrodes for supercapacitors

Resent Development of Binder-Free Electrodes of Transition Metal Oxides and Nanohybrids for High Performance Supercapacitors - A Review

The entire world is aware of the serious issue of global warming and therefore utilizing renewable energy sources is the most encouraging steps toward solving energy crises, and as a result, energy storage solutions are necessary. The supercapacitors (SCs) have a high-power density and a long cycle life, they are promising as an electrochemical conversion and storage device. In order to achieve high electrochemical performance, electrode fabrication must be implemented properly. Electrochemically inactive and insulating binders are utilized in the conventional slurry coating method of making electrodes to provide adhesion between the electrode material and the substrate. This results in an undesirable "dead mass," which lowers the overall device performance. In this review, we focused on binder-free SCs electrodes based on transition metal oxides and composites. With the best examples providing the critical aspects, the benefits of binder-free electrodes over slurry-coated electrodes are addressed. Additionally, different metal-oxides used in the fabrication of binder-free electrodes are assessed, taking into account the various synthesis methods, giving an overall picture of the work done for binder-free electrodes. The future outlook is provided along with the benefits and drawbacks of binder-free electrodes based on transition metal oxides.

MOF-Derived MnO/C Nanocomposites for High-Performance Supercapacitors

As ordered porous materials, metal-organic frameworks (MOFs) have attracted tremendous attention in the field of energy conversion and storage due to their high specific surface area, permanent porosity, and tunable pore sizes. Here, MOF-derived MnO/C nanocomposites with regular octahedral shape were synthesized using a Mn-based analogue of the MIL-100 framework (Mn-MIL-100, MIL: Matérial Institut Lavoisier) as the precursor. Using aberration-corrected environmental transmission electron microscopy (ETEM), MnO nanocages with a diameter of approximately 20 nm were recognized in the MnO/C nanocomposites fabricated, dispersed in a microporous carbon matrix homogeneously. The nanocages are composed of MnO nanoparticles with a diameter of approximately 2 nm and with a single crystal structure. The specific surface area of the as-prepared MnO/C octahedra decreases to 256 m² g^-1 from 507 m² g^-1 of the Mn-MIL-100 precursor, whereas the total pore volume increases to 0.245 cm³ g^-1, which is approximately 29% higher than that of the precursor (0.190 cm³ g^-1). Additionally, when utilized as an electrode for supercapacitors, the MOF-derived MnO/C nanocomposite demonstrates a towering specific capacitance of 421 F g^-1 at 0.5 A g^-1 and good cycle stability (94%) after 5000 cycles. Our work reveals that the MnO nanoparticles in MOF-derived MnO/C nanocomposites exhibit nanocage structure characteristics, which might be inherited from the Mn-MIL-100 precursor with analogous supertetrahedron units.

Oxygen Reduction Reaction with Manganese Oxide Nanospheres in Microbial Fuel Cells

Operating microbial fuel cells (MFCs) under extreme pH conditions offers a substantial benefit. Acidic conditions suppress the growth of undesirable methanogens and increase redox potential for oxygen reduction reactions (ORRs), and alkaline conditions increase the electrocatalytic activity. However, operating any fuel cells, including MFCs, is difficult under such extreme pH conditions. Here, we demonstrate a pH-universal ORR ink based on hollow nanospheres of manganese oxide (h-Mn3O4) anchored with multiwalled carbon nanotubes (MWCNTs) on planar and porous forms of carbon electrodes in MFCs (pH = 3-11). Nanospheres of h-Mn3O4 (diameter ∼ 31 nm, shell thickness ∼ 7 nm) on a glassy carbon electrode yielded a highly reproducible ORR activity at pH 3 and 10, based on rotating disk electrode (RDE) tests. A phenomenal ORR performance and long-term stability (∼106 days) of the ink were also observed with four different porous cathodes (carbon cloth, carbon nanofoam paper, reticulated vitreous carbon, and graphite felt) in MFCs. The ink reduced the charge transfer resistance (R ct) to the ORR by 100-fold and 45-fold under the alkaline and acidic conditions, respectively. The current study promotes ORR activity and subsequently the MFC operations under a wide range of pH conditions, including acidic and basic conditions.

Binder-free electrodes of NiMoO4/graphene oxide nanosheets: synthesis, characterization and supercapacitive behavior

In the present work we report a facile and efficient hydrothermal method to fabricate a nanocomposite of NiMoO₄ and graphene nanosheets (NiMoO₄/GNS) on a nickel foam (NF) substrate.