MnCo₂O₄ Nanowires Anchored on Reduced Graphene Oxide Sheets as Effective Bifunctional Catalysts for Li–O₂ Battery Cathodes

Abstract

A hybrid composite system of MnCo2 O4 nanowires (MCO NWs) anchored on reduced graphene oxide (RGO) nanosheets was prepared as the bifunctional catalyst of a Li-O2 battery cathode. The catalysts can be obtained from the hybridization of one-dimensional MCO NWs and two-dimensional RGO nanosheets. As O2 -cathode catalysts for Li-O2 cells, the MCO@RGO composites showed a high initial discharge capacity (ca. 11092.1 mAh gcarbon (-1) ) with a high rate performance. The Li-O2 cells could run for more than 35 cycles with high reversibility under a limited specific capacity of 1000 mAh gcarbon (-1) with a low potential polarization of 1.36 V, as compared with those of pure Ketjenblack and MCO NWs. The high cycling stability, low potential polarization, and rate capability suggest that the MCO@RGO composites prepared here are promising catalyst candidates for highly reversible Li-O2 battery cathodes.

Spinel MnCo2O4 nanoparticles cross-linked with two-dimensional porous carbon nanosheets as a high-efficiency oxygen reduction electrocatalyst

“…The Co 2p spectrum was fitted with the Gaussian fitting method considering the two spin-orbit doublet characteristic of Co 2+ and Co 3+ ions. The binding-energy separation between the two main peaks is about 15.2 eV, in line with previous reports [40,43,44]. Similarly, the Mn 2p3/2 and Mn 2p1/2 peaks at 642.00 and 653.51 eV, respectively, can be Nano Res.…”

“…The calculated I G /I D ratio for the MnCo 2 O 4 /C hybrid is 1.15, while that of Vulcan XC-72R carbon is 0.86. The higher I G /I D ratio is a clear indication of a larger number of graphene layers [38][39][40]. Moreover, the appearance of the characteristic peaks for the Mn-O and Co-O bonds also confirms that high-quality MnCo 2 O 4 spinel has been successfully prepared in this study.…”

“…1(b)). Generally, the peak intensity ratio between the G and D bands (I G /I D ) provides an important index for the assessment of the graphitization degree of carbon materials [38][39][40]. The calculated I G /I D ratio for the MnCo 2 O 4 /C hybrid is 1.15, while that of Vulcan XC-72R carbon is 0.86.…”

“…2016, 9(7): 2110-2122 resolved into four peak components (Fig. 4(c)): The two peaks at binding energies of 641.8 and 653.3 eV are attributed to Mn 3+ ions, whereas the other two peaks at binding energies of 644.2 and 654.7 eV are assigned to Mn 4+ ions [40,43,44]. These results show that the solid-state redox couples Co 3+ /Co 2+ and Mn 4+ / Mn 3+ coexist in spinel MnCo 2 O 4 .…”

“…Overall, the as-prepared MnCo 2 O 4 /C nanosheets present the combined properties of an interconnected porous structure and a large surface area, as well as good conductivity. Thus, the MnCo 2 O 4 /C nanosheets can offer structural advantages as O 2 electrode catalysts: (i) The interconnected porous structure provides abundant catalytically active sites for the transmission of the reactant and resultant molecules throughout the catalyst and, accordingly, the inner catalysts can efficiently participate in electrocatalytic reactions; and (ii) the existence of graphitic carbon in the composites can satisfactorily overcome the poor electrical conductivity of MnCo 2 O 4 as a result of the high conductivity of graphitic carbon and, accordingly, the MnCo 2 O 4 /C nanosheets display the required electrical conductivity from an electrocatalyst to promote oxidation reduction reactions [23,40,45].…”