Designing High-Quality Electrocatalysts Based on CoO:MnO₂@C Supported on Carbon Cloth Fibers as Bifunctional Air Cathodes for Application in Rechargeable Zn–Air Battery

To achieve the requirements of rechargeable Zn–air batteries (ZABs), designing efficient, bifunctional, stable, and cost-effective electrocatalysts is vital for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which still are struggling with unsolved challenges. The present research provides a concept based on the nanoscale composites which were engineered by using MnO2@C, CoO@C, and CoO:MnO2@C bifunctional electrocatalysts for fabrication of uniform carbon cloth (CC)-based electrodes. The CoO:MnO2@C electrocatalyst represented more efficient electrochemical properties through ORR and OER processes with superior positive half-wave potential (E1/2 = 0.78 V) and better limiting current density (i = 1.10 mA cm–2) in comparison with MnO2@C (E1/2 = 0.71 V, i = 0.92 mA cm–2) and CoO@C (E1/2 = 0.69 V, i = 0.86 mA cm–2) electrocatalysts. For the rechargeable ZABs fabricated by using CoO:MnO2@C–CC as an O2-breathing cathode, the specific capacity (SC), peak power density (P), open-circuit voltage (EOCV), and gap of charge/discharge voltage resulted in values of 520 mAh gZn–1, 210.0 mW cm–2, and 1.45 and 0.45 V, respectively, that afforded greater electrochemical characters than what was obtained for ZABs based on MnO2@C–CC (410 mAh gZn–1, 195.0 mW cm–2, 1.38 and 0.44 V) and CoO@C–CC (440 mAh gZn–1, 165.0 mW cm–2, 1.15 and 0.54 V). At the same time, lower Ei=10 (= 1.45 V) implied a more efficient OER in alkaline electrolyte solution for CoO:MnO2@C than MnO2@C (Ei=10 = 1.50 V) and CoO@C (Ei=10 = 1.39 V). Based on cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), linear sweep voltammetry (LSV), and X-ray photoelectron spectroscopy (XPS) results, it could be stated that the CoO:MnO2@C catalytic surface could experience 30 and 32% lower charge transfer resistance (Rct = 13.9 Ω) than MnO2@C (Rct = 20.1 Ω) and CoO@C (Rct = 29.7 Ω), respectively, which empowers an enhancement in ORR/OER performance. Prominently, the design concept of proposed electrocatalysts could suggest clear horizon for the synthesis and development paradigms of bifunctional catalysts for energy storage materials and devices

Biological Applications of Bacterial Nano-Surface Layers : A Brief Overview

Surface layer as the outer protective coverage of bacteria and archaea are two-dimensional crystalline and symmetrical arrays of proteins that recently attract a lot of attention for biologist scientists. The surface layers of bacteria are usually 5 to 10 nm in diameter and represent highly porous protein lattices with uniform size and morphology with the pore sizes of 2 to 8 nm. The crucial and most prominent property of this protein-based layer is the regular morphology and suitable chemical composition for different biological applications. Although the formation mechanism of surface layers is different from one type of cell to another once, the surface layer protein molecular compositions almost are same for all types. Recently, the biological application of surface layers opens a prominent research fields in surface biological science such as nano-biotechnology adhesion, vaccination, pharmaceutical, biosensors, bioremediation and mineralization application. In this mini review, we discussed about the main application of this nano-layer in biological systems