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.

Abstract

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.