Directly Electrospun Carbon Nanofibers Incorporated with Mn3O4 Nanoparticles as Bending-Resistant Cathode for Flexible Al-Air Batteries

Hausmannite-Carbon Nanofiber Composite Electrocatalyst for High Areal-Discharge Energy Rechargeable Zinc-Air Battery

Rechargeable zinc-air batteries (RZABs) have been described as one of the most viable next-generation battery technologies, especially due to their low cost, high capacity, and being environmental-friendly. In this work, hausmannite Mn3O4 nanoparticles, obtained from low-cost commercial electrolytic manganese dioxide, were dispersed on conductive multiwalled carbon nanotubes (CNTs) and carbon nanofibers (CNFs) and investigated for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in an alkaline medium and then applied in RZAB cell. The high performance of the CNFs (in terms of electron transfer kinetics) over the CNTs has been associated with its inherent defects and nitrogen content. Density functional theory (DFT) calculations predict that CNF give higher partial density of states (PDOS, i.e., 67 eV vs 51 eV for CNT) and can allow for a more favorable distribution of the d-electrons of the Mn and enhanced synergistic effect with Mn3O4 for weaker adsorption energies and p-band centers of the oxygen intermediates (O*, OH*, and OOH*). In a proof-of-concept, Mn3O4 + CNF was investigated as the air cathode for RZAB in a micro-3D-printed cell configuration. The RZAB showed good performance in terms of open circuit voltage (OCV = 1.77 V), areal-discharge energy (≥40 mW h/cm2 geometric) and cycling stability (∼25 cycles at 8 h per cycle for 140 h at 10 mA cm-2; and ∼17 cycles at 16 h per cycle for 270 h at 5 mA cm-2) better than 100 catalysts used in RZAB cells in recent articles including the state-of-the-art Pt/C-IrO2 catalysts. The findings here provide fresh physicochemical perspectives on the future design and utility of CNFs for developing Mn-based RZABs that meet or even outperform the new literature-recommended benchmark areal-discharge energy density of 35 mW h/cm2 geometric at 10 mA cm-2 current loading for any possible application in real devices.

Irreversible and Self-Healing Electrically Conductive Hydrogels Made of Bio-Based Polymers

Electrically conductive materials that are fabricated based on natural polymers have seen significant interest in numerous applications, especially when advanced properties such as self-healing are introduced. In this article review, the hydrogels that are based on natural polymers containing electrically conductive medium were covered, while both irreversible and reversible cross-links are presented. Among the conductive media, a special focus was put on conductive polymers, such as polyaniline, polypyrrole, polyacetylene, and polythiophenes, which can be potentially synthesized from renewable resources. Preparation methods of the conductive irreversible hydrogels that are based on these conductive polymers were reported observing their electrical conductivity values by Siemens per centimeter (S/cm). Additionally, the self-healing systems that were already applied or applicable in electrically conductive hydrogels that are based on natural polymers were presented and classified based on non-covalent or covalent cross-links. The real-time healing, mechanical stability, and electrically conductive values were highlighted.