Catalysts for the oxygen reduction reaction (ORR) play an important role in fuel cells. Alternative non-precious metal catalysts with comparable ORR activity to Pt-based catalysts are highly desirable for the development of fuel cells. In this work, we report for the first time a spinel MnCo 2 O 4 /C ORR catalyst consisting of uniform MnCo 2 O 4 nanoparticles cross-linked with two-dimensional (2D) porous carbon nanosheets (abbreviated as porous MnCo 2 O 4 /C nanosheets), in which glucose is used as the carbon source and NaCl as the template. The obtained porous MnCo 2 O 4 /C nanosheets present the combined properties of an interconnected porous architecture and a large surface area (175.3 m 2 ·g −1 ), as well as good electrical conductivity (1.15 10 2 S·cm −1 ). Thus, the as-prepared MnCo 2 O 4 /C nanosheets efficiently facilitate electrolyte diffusion and offer an expedite transport path for reactants and electrons during the ORR. As a result, the as-prepared porous MnCo 2 O 4 /C nanosheet catalyst exhibits enhanced ORR activity with a higher onset potential and current density than those of its counterparts, including pure MnCo 2 O 4 , carbon nanosheets, and Vulcan XC-72R carbon. More importantly, the porous MnCo 2 O 4 /C nanosheets exhibit a comparable electrocatalytic activity but superior stability and tolerance toward methanol crossover effects than a high-performance Pt/C catalyst in alkaline medium. The synthetic strategy outlined here can be extended to other nonprecious metal catalysts for application in electrochemical energy conversion.
Considerable lithium-driven volume changes and loss of crystallinity on cycling have impeded the sustainable use of transition metal oxides (MOs) as attractive anode materials for advanced lithium-ion batteries that have almost six times the capacity of carbon per unit volume. Herein, Co3 O4 was used as a model MO in a facile process involving two pyrolysis steps for in situ encapsulation of nanosized MO in porous two-dimensional graphitic carbon nanosheets (2D-GCNs) with high surface areas and abundant active sites to overcome the above-mentioned problems. The proposed method is inexpensive, industrially scalable, and easy to operate with a high yield. TEM revealed that the encaged Co3 O4 is well separated and uniformly dispersed with surrounding onionlike graphitic layers. By taking advantage of the high electronic conductivity and confinement effect of the surrounding 2D-GCNs, a hierarchical GCNs-coated Co3 O4 (Co3 O4 @GCNs) anode with 43.5 wt % entrapped active nanoparticles delivered a remarkable initial specific capacity of 1816 mAh g(-1) at a current density of 100 mA g(-1) . After 50 cycles, the retained capacity is as high as 987 mAh g(-1) . When the current density was increased to 1000 mA g(-1) , the anode showed a capacity retention of 416 mAh g(-1) . Enhanced reversible rate capability and prolonged cycling stability were found for Co3 O4 @GCN compared to pure GCNs and Co3 O4 . The Co3 O4 @GCNs hybrid holds promise as an efficient candidate material for anodes due to its low cost, environmentally friendly nature, high capacity, and stability.
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