Bimetallic Mn–Co Oxide Nanoparticles Anchored on Carbon Nanofibers Wrapped in Nitrogen-Doped Carbon for Application in Zn–Air Batteries and Supercapacitors

Abstract

The exploration and rational design of cost-effective, highly active, and durable catalysts for oxygen electrochemical reaction is crucial to actualize the prospective technologies such as metal−air batteries and fuel cells. Herein manganese cobalt oxide nanoparticles anchored on carbon nanofibers and wrapped in a nitrogen-doped carbon shell (MCO/ CNFs@NC) is successfully prepared. Benefiting from the synergistic effect between the core nanoparticles and nitrogen-doped carbon shell, MCO/CNFs@NC catalyst exhibits oxygen reduction reaction (ORR) activity with comparable onset potential (1.00 V vs RHE) and half-wave potential (0.76 V vs RHE) which is only about 40 mV lower than that of the state of art Pt/C catalyst. Furthermore, the MCO/CNFs@NC catalyst exceeds the Pt/C catalyst by a great margin in terms of stability in alkaline media. Additionally, MCO/CNFs@NC catalyst is strongly tolerant to methanol crossover, promising its applicability as cathode catalyst in alcohol fuel cells. Moreover, MCO/CNFs@NC catalyst exhibits the oxygen evolution reaction (OER) activity with low overpotential of 0.41 V at the current density of 10 mA cm −2 and ORR/OER potential gap (ΔE) as low as 0.88 V, suggesting its strong bifunctionality. The Zn−air battery based on MCO/CNFs@NC catalyst is found to deliver a specific capacity of 695 mA h g −1 Zn and an energy density of 778 W h kg −1 Zn at a current density of 20 mA cm −2 . The mechanically rechargeable Zn−air battery based on MCO/CNFs@NC catalyst is also found to function continually by only reloading the consumed Zn anode and electrolyte. Furthermore, the electrically rechargeable battery based on MCO/CNFs@NC catalyst is found to function for more than 220 cycles with negligible loss of voltaic efficiency. Moreover, MCO/CNFs@NC is found to display a supercapacitive nature with a good discharge capacity of 478 F g −1 at a discharge current density of 1 A g −1 .

Low-temperature synthesis of ultrasmall spinel Mn Co3-O4 nanoparticles for efficient oxygen reduction

“…As shown in Figure 3a and Table S2, Mn1.5Co1.5O4/C has much better ORR activity than Mn3O4/C and Co3O4/C. The half-wave potential (E1/2) and diffusion limiting current density (jL) of Mn1.5Co1.5O4/C are 0.820 V vs RHE and 5.6 mA cm -2 , respectively, which are comparable to those of commercial 20 wt% Pt/C (0.814 V vs RHE, 5.6 mA cm -2 ) used here and in the literature [25,34,35]. It is worth noting that the polarization curve of Mn3O4/C is steeper than that of Co3O4/C in the kinetic control zone (1.00.85 V vs RHE).…”

“…Raman Shift (cm -1 ) scan rate of 10 mV s -1 , which is commonly used in the literature [25,27,34]. As shown in Figure 3a and Table S2, Mn1.5Co1.5O4/C has much better ORR activity than Mn3O4/C and Co3O4/C.…”

Pt‐Like Oxygen Reduction Activity Induced by Cost‐Effective MnFeO2/N‐Carbon

“…No additional diffraction peaks in the XRD pattern (Figure S9 b in the Supporting Information) are detected after the stability test, indicating minimal dissolution of MnFeO 2 during the ORR. The MnFeO 2 particles that firmly embedded in the porous carbon aerogel can effectively inhibit the self‐aggregation and dissolution of the active component, leading to an improved stability . The resistance of the ORR catalysts to methanol crossover is also of particular importance in practical applications.…”

Carbon‐based cathode materials for rechargeable zinc‐air batteries: From current collectors to bifunctional integrated air electrodes

“…Synergistic effects have been widely reported in N‐doped carbon hybrid catalysts cooperated with metallic components, such as metal nanoparticles, 93 metal oxides, 94 metal sulfides, 95 and metal phosphates, 96 indicating that strong interactions of metallic components and carbon or nitrogen are generated. Among them, the positive effects of metal‐support interaction and active components interaction on the electrochemical performance of catalysts have been confirmed, which enlighten us to design high‐performance bifunctional catalysts in air cathodes based on carbon materials.…”