Cobalt-doped Mn3O4 nanocrystals embedded in graphene nanosheets as a high-performance bifunctional oxygen electrocatalyst for rechargeable Zn–Air batteries (original) (raw)
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CoMn 2 O 4 nanoparticles supported on N-doped reduced graphene oxide (CoMn 2 O 4 /N-rGO), for rechargeable zinc-air battery were prepared by a hydrothermal method. The CoMn 2 O 4 supported on nitrogen-doped graphene oxide showed better oxygen electrode potential compared with CoMn 2 O 4 dispersed on graphene oxide. The zinc-air battery can be reversibly charged/discharged for hundred cycles with a good cycle performance. The improved battery performance of CoMn 2 O 4 /N-rGO can be attributed to the synergistic effect of covalently coupling between the nitrogen-doped graphene sheets and spinel cobalt manganese oxide.
Nano Energy, 2016
Development of efficient bifunctional electrocatalysts from earth abundant elements, simultaneously active for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), remains to be a grand challenge for electrocatalysis. Herein we firstly synthesized a new type of bifunctional catalyst (NCNT/Co x Mn 1-x O) consisting of non-spinel cobalt-manganese oxide supported on N-doped carbon nanotubes through a simple non-surfactant assistant hydrothermal method. This hybrid catalyst exhibits much higher OER activity than that of IrO 2 , and comparable ORR activity to Pt/C with identical onset potential (0.96 V) in alkaline media. Furthermore, the NCNT/Co x Mn 1-x O catalyst was studied as a cathode in both primary and rechargeable zinc-air batteries demonstrating similar performance to commercial Pt/C or (Pt/C+IrO 2), respectively. Primary zinc-air battery tests show a gravimetric energy density of 695 Wh kg zn-1 , and the rechargeable battery exhibits a high round-trip efficiency evidenced by a low discharge-charge voltage gap (0.57 V) at a current density of 7 mA cm-2 .
Carbon, 2018
Highly efficient and low-cost nanomaterials with multifunctions for oxygen evolution reaction (OER), hydrogen evolution reaction (OER) and oxygen reduction reaction (ORR) have been attracted tremendous attentions that play significant roles in energy storage and conversion. Herein, a facile strategy is developed to synthesize metal alloys (NiCo, CoFe) with their oxides supported on nitrogen-doped graphene (N-rGO/NiCo-NiO-CoO, N-rGO/CoFe-Co 2 FeO 4). The obtained nanomaterials exhibit outstanding tri-functional performances for the above mentioned three kinds of reactions. Furthermore, the prepared composites, assembled in air cathodes, present excellent performance that are similar with Pt/C or Pt/ C þ IrO 2 in primary and rechargeable zinc-air batteries. The prepared N-rGO/NiCo-NiO-CoO and N-rGO/ CoFe-Co 2 FeO 4 exhibit the specific capacities of 734 and 711 mA h g Zn À1 at the current density of 20 mA cm À2 , respectively. The rechargeable zinc-air batteries maintain excellent durability after cycling 33 h.
Oxygen evolution (OER) and oxygen reduction (ORR) reactions are the key electrocatalytic redox couple for advanced energy storage/conversion, including rechargeable metal-air batteries and regenerative fuel cells. Heteroatom doped carbon catalysts propose a promising candidate for such purposes along with the superior durability and cost-effectiveness. Unfortunately, exact identification of the catalytic site as well as the critical role of dopants is still controversial in the catalytic mechanism. Here we present bifunctional catalytic site of nitrogen pair-doped graphene nanoribbons for precisely switchable OER and ORR. Pyrazolated N 2-edges of graphene nanoribbon serve as switchable dual-functional active sites for OER/ORR with efficient activities and extraordinary durability. Theoretical calculation reveals genuine catalytic mechanism originating from the electrochemical potential-dependent molecular absorption and conversion at the atomic level dopant site. This judiciously controllable bifunctional electrocatalytic activity of dopant catalyst fundamentally addresses the interference between ORR and OER and attains highly stable rechargeable metal-air battery with long-term stability.
Scientific reports, 2015
Rechargeable metal-air batteries are considered a promising energy storage solution owing to their high theoretical energy density. The major obstacles to realising this technology include the slow kinetics of oxygen reduction and evolution on the cathode (air electrode) upon battery discharging and charging, respectively. Here, we report non-precious metal oxide catalysts based on spinel-type manganese-cobalt oxide nanofibres fabricated by an electrospinning technique. The spinel oxide nanofibres exhibit high catalytic activity towards both oxygen reduction and evolution in an alkaline electrolyte. When incorporated as cathode catalysts in Zn-air batteries, the fibrous spinel oxides considerably reduce the discharge-charge voltage gaps (improve the round-trip efficiency) in comparison to the catalyst-free cathode. Moreover, the nanofibre catalysts remain stable over the course of repeated discharge-charge cycling; however, carbon corrosion in the catalyst/carbon composite cathode d...
Nano letters, 2017
For the promotion of lithium-oxygen batteries available for practical applications, the development of advanced cathode catalysts with low-cost, high activity, and stable structural properties is demanded. Such development is rooted on certain intelligent catalyst-electrode design that fundamentally facilitates electronic and ionic transport and improves oxygen diffusivity in a porous environment. Here we design a biphasic nitrogen-doped cobalt@graphene multiple-capsule heterostructure, combined with a flexible, stable porous electrode architecture, and apply it as promising cathodes for lithium-oxygen cells. The biphasic nitrogen-doping feature improves the electric conductivity and catalytic activity; the multiple-nanocapsule configuration makes high/uniform electroactive zones possible; furthermore, the colander-like porous electrode facilitates the oxygen diffusion, catalytic reaction, and stable deposition of discharge products. As a result, the electrode exhibits much improved...
Applied Catalysis B: Environmental, 2020
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Improving the Performance of Zn-Air Batteries with N-Doped Electroexfoliated Graphene
Materials
The constantly growing demand for active, durable, and low-cost electrocatalysts usable in energy storage devices, such as supercapacitors or electrodes in metal-air batteries, has triggered the rapid development of heteroatom-doped carbon materials, which would, among other things, exhibit high catalytic activity in the oxygen reduction reaction (ORR). In this article, a method of synthesizing nitrogen-doped graphene is proposed. Few-layered graphene sheets (FL-graphene) were prepared by electrochemical exfoliation of commercial graphite in a Na2SO4 electrolyte with added calcium carbonate as a separator of newly-exfoliated FL-graphene sheets. Exfoliated FL-graphene was impregnated with a suspension of green algae used as a nitrogen carrier. Impregnated FL-graphene was carbonized at a high temperature under the flow of nitrogen. The N-doped FL-graphene was characterized through instrumental methods: high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy,...
ACS applied materials & interfaces, 2017
N-doped graphene (NDG) was investigated for oxygen reduction reaction (ORR) and used as air-electrode catalyst for Zn-air batteries. Electrochemical results revealed a slightly lower kinetic activity but a much larger rate capability for the NDG than commercial 20% Pt/C catalyst. The maximum power density for a Zn-air cell with NDG air cathode reached up to 218 mW cm(-2), which is nearly 1.5 times that of its counterpart with the Pt/C (155 mW cm(-2)). The equivalent diffusion coefficient (DE) of oxygen from electrolyte solution to the reactive sites of NDG was evaluated as about 1.5 times the liquid-phase diffusion coefficient (DL) of oxygen within bulk electrolyte solution. Combined with experiments and ab initio calculations, this seems counterintuitive reverse ORR of NDG versus Pt/C can be rationalized by a spontaneous adsorption and fast solid-state diffusion of O2 on ultralarge graphene surface of NDG to enhance effective ORR on N-doped-catalytic-centers and to achieve high-rat...