Abstract
The electrocatalytic activities of the MnO2/C composites are examined in Li-O2 cells as the cathode catalysts. Hierarchically mesoporous carbon-supported manganese oxide (MnO2/C) composites are prepared using a combination of soft template and hydrothermal methods. The composites are characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, small angle X-ray scattering, The Brunauer–Emmett–Teller (BET) measurements, galvanostatic charge-discharge methods, and rotating ring-disk electrode (RRDE) measurements. The electrochemical tests indicate that the MnO2/C composites have excellent catalytic activity towards oxygen reduction reactions (ORRs) due to the larger surface area of ordered mesoporous carbon and higher catalytic activity of MnO2. The O2 solubility, diffusion rates of O2 and O2•− coefficients ( and ), the rate constant (kf) for producing O2•−, and the propylene carbonate (PC)-electrolyte decomposition rate constant (k) of the MnO2/C material were measured by RRDE experiments in the 0.1 M TBAPF6/PC electrolyte. The values of kf and k for MnO2/C are 4.29 × 10−2 cm·s−1 and 2.6 s−1, respectively. The results indicate that the MnO2/C cathode catalyst has higher electrocatalytic activity for the first step of ORR to produce O2•− and achieves a faster PC-electrolyte decomposition rate.
Highlights
Energy storage devices with high energy and power densities are being developed for use as power sources for electric vehicles (EV) and hybrid electric vehicles (HEV) [1,2,3]
The electrochemical tests indicate that the MnO2 /C composites have excellent catalytic activity towards oxygen reduction reactions (ORRs) due to the larger surface area of ordered mesoporous carbon and higher catalytic activity of MnO2
The results indicate that the MnO2 /C cathode catalyst has higher electrocatalytic activity for the first step of ORR to produce O2 ‚ ́ and achieves a faster
Summary
Energy storage devices with high energy and power densities are being developed for use as power sources for electric vehicles (EV) and hybrid electric vehicles (HEV) [1,2,3]. Rechargeable nonaqueous Li-air batteries have attracted much interest owing to their low cost, environmental friendliness, and high theoretical energy density (~3500 Whkg1 ), which is nearly equivalent to a nine-fold increase over conventional Li-ion batteries (~400 Whkg1 ) [4,5,6,7] Despite these favorable characteristics, their practical applications are still hampered by several serious challenges including limited rate capability, poor cycling stability due to the instability of the electrode and electrolyte, and low round-trip efficiency induced by the rather large polarization, resulting in a wide charge–discharge voltage gap [3,8,9,10,11,12,13,14,15]. The O2 cathode is an oxygen catalyst loaded
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