Cobalt-based hydroxide nanoparticles @ N-doping carbonic frameworks core–shell structures as highly efficient bifunctional electrocatalysts for oxygen evolution and oxygen reduction reactions (original) (raw)
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Scientific reports, 2017
A series of nanocomposites of cobalt embedded in N-doped nanoporous carbons, carbon nanotubes or hollow carbon onions have been synthesized by a one-step carbonization of metal-organic-framework ZIF-67. The effect of the carbonization temperature on the structural evolution of the resulting nanocomposites has been investigated in detail. Among the as-synthesized materials, the cobalt/nanoporous N-doped carbon composites have demonstrated excellent electrocatalytic activities and durability towards oxygen reduction reaction in alkaline medium. Compared to the benchmark Pt/C catalyst, the optimized Co@C-800 (carbonized at 800 °C) exhibited high oxygen reduction reaction activity with an onset potential of 0.92 V, and a half-wave potential of 0.82 V. Moreover, the optimized Co@C-800 also showed enhanced electrocatalytic activity towards oxygen evolution reaction from water splitting, with a low onset potential of 1.43 V and a potential of 1.61 V at 10 mA cm(-2) current density. This wo...
Chemistry - A European Journal, 2017
There has been growing interest in the synthesis of efficient reversible oxygen electrodes for both the oxygen reduction reaction (ORR) and the oxygen evolution reactions (OER) for their potential use in a variety of renewable energy technologies such as regenerative fuel cells and metal-air batteries. Here, we report a bifunctional electrocatalyst derived from a novel dicyanamide based nitrogen rich MOF {[Co(bpe)2(N(CN)2)](N(CN)2)(5H2O)}n [Co-MOF-1, bpe = 1,2-bis(4-pyridyl)ethane, N(CN)2 − = dicyanamide] under different pyrolysis conditions. Pyrolysis of the Co-MOF-1 under Ar atmosphere (at 800 C) yielded a Co nanoparticles embedded Ndoped carbon nanotube matrix (Co/NCNT-Ar) while pyrolysis under a reductive H2/Ar atmosphere (at 800 C) and further mild calcination yielded Co3O4@Co core-shell nanoparticles encapsulated N-doped carbon nanotubes (Co3O4@Co/NCNT). Both catalysts show bifunctional activity towards ORR and OER, however, the core-shell Co3O4@Co/NCNT nanostructure exhibited superior electrocatalytic activity for both the ORR with a potential of 0.88 V at a current density of-1 mA cm-2 and the OER with a potential of 1.61 V at 10 mA cm-2 , which is competitive with the most active bi-functional catalysts reported previously.
Journal of Electronic Materials, 2019
Fuel cells and metal-air batteries have been comprehensively investigated in recent years because of their high energy capacity, good efficiency and environmental friendly nature. Slow kinetics of oxygen reduction reaction (ORR), one of the main processes in fuel cells and metal-air batteries, is improved with platinum catalysts that confine the prevalent utilization of such electrochemical devices with increasing worth for them. However, platinum catalysts after long time usage exhibit weak operations due to the crossover effect and agglomeration. Metal-organic frameworks (MOFs), the porous crystalline materials, consisting of metal centers coordinated to organic ligands, are appropriate catalysts due to their superior properties such as high surface area and carbon content, tunable pore size and diverse metal nodes. In this review, we summarize the recent progress in synthesis and design of MOFderived ORR electrocatalysts in acidic and alkaline fuel cells. Our focus is on the different methods developed for improving the activity and stability of MOF based ORR electrocatalysts.
ACS Applied Materials & Interfaces, 2019
The synthesis of a new microporous metal− organic framework (MOF) based on two secondary building units, with dinuclear cobalt centers, has been developed. The employment of a well-defined cobalt cluster results in an unusual topology of the Co 2-MOF, where one of the cobalt centers has three open coordination positions, which has no precedent in MOF materials based on cobalt. Adsorption isotherms have revealed that Co 2-MOF is in the range of best CO 2 adsorbents among the carbon materials, with very high CO 2 /CH 4 selectivity. On the other hand, dispersion of Co 2-MOF in an alcoholic solution of Nafion gives rise to a composite (Co 2-MOF@Nafion) with great resistance to hydrolysis in aqueous media and good adherence to graphite electrodes. In fact, it exhibits high electrocatalytic activity and robustness for the oxygen evolution reaction (OER), with a turnover frequency number value superior to those reported for similar electrocatalysts. Overall, this work has provided the basis for the rational design of new cobalt OER catalysts and related materials employing well-defined metal clusters as directing agents of the MOF structure.
ACS Nano, 2019
Developing cost-effective, efficient bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is the heart of metal-air batteries as a renewable-energy technology. Herein, well-distributed nanopolyhedron (NP) Co 3 O 4 grown on iron (Fe) encapsulated in graphitic layers on a nitrogenated, porous two-dimensional (2D) structure, namely, a C 2 N matrix, (NP Co 3 O 4 /Fe@C 2 N), presents an outstanding bifunctional catalytic activity with a comparable overpotential and Tafel slope to those of benchmark Pt/C and IrO 2. The rationally designed atomic configuration of Co 3 O 4 on the C 2 N matrix has a well-controlled NP morphology with (111) plane, leading to bifunctional activities for the ORR and OER. Interestingly, the specific interaction between the NP Co 3 O 4 nanoparticles and the C 2 N matrix introduces synergistic coupling and changes the electronic configuration of Co atoms and the C 2 N framework. Benefiting from the synergistic coupling of Co 3 O 4 with the C 2 N matrix, the NP Co 3 O 4 /Fe@C 2 N electrocatalyst exhibits exceptionally high stability and an even lower charge-discharge overpotential gap of 0.85 V at 15 mA cm −2 than that of the Pt/C+IrO 2 catalyst (1.01 V) in Zn-air batteries. This work provides insights into the rational design of a metal oxide on a C 2 N matrix for bifunctional, low-cost electrochemical catalysts.
Advanced materials (Deerfield Beach, Fla.), 2017
The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are cornerstone reactions for many renewable energy technologies. Developing cheap yet durable substitutes of precious-metal catalysts, especially the bifunctional electrocatalysts with high activity for both ORR and OER reactions and their streamlined coupling process, are highly desirable to reduce the processing cost and complexity of renewable energy systems. Here, a facile strategy is reported for synthesizing double-shelled hybrid nanocages with outer shells of Co-N-doped graphitic carbon (Co-NGC) and inner shells of N-doped microporous carbon (NC) by templating against core-shell metal-organic frameworks. The double-shelled NC@Co-NGC nanocages well integrate the high activity of Co-NGC shells into the robust NC hollow framework with enhanced diffusion kinetics, exhibiting superior electrocatalytic properties to Pt and RuO2 as a bifunctional electrocatalyst for ORR and OER, and hold a promise as efficient ...
ChemPhysChem, 2016
Efficient, low‐cost, non‐precious metal‐based, and stable bifunctional electrocatalysts are key to various energy storage and conversion devices such as regenerative fuel cells and metal‐air batteries. In this work, we report cobalt nanoparticle‐embedded porous carbon nanofibers with inherent N‐ and F‐doping as binder‐free bifunctional electrocatalysts with excellent activity for both the oxygen reduction and oxygen evolution reaction (ORR/OER) in an alkaline medium. Single‐step electrospinning of a solution of the polymer mixture (carbon precursor) and the cobalt precursor followed by controlled pyrolysis with an intermediate reduction step in H2 (to reduce cobalt oxides to cobalt) was utilized to synthesize an integrated freestanding catalyst. The fabricated catalyst with effective structural and electronic interaction between the cobalt metal nanoparticles and the N‐ and F‐doped carbon defect sites showed enhanced catalytic properties compared to the benchmark catalysts for ORR a...
ACS Applied Energy Materials
Oxygen reduction reaction (ORR), essential in many energy conversion devices, takes particular relevance in facing the increasing global demand for clean energy sources and vectors. In this context, desirable features for ORR-based electrochemical cells are operability under environmentally friendly conditions, such as pH 7 biocompatible electrolytes, and the usage of relatively low electrocatalyst loadings. On the other hand, the improvement of the cathode performance in neutral solutions is commonly focused on the development of electrocatalyzers for reducing the ORR overpotential. In this work, we took advantage of the possibilities brought by a novel strategy toward construction of complex interfacial architectures, the so-called "nanoarchitectonics" approach. In order to achieve enhanced ORR currents and reduced overpotentials, we combined three different building blocks with defined functionalities: a conducting polymer (CP) nanofilm (the connecting electroactive matrix), well dispersed Pt-nanoparticles (the electrocatalyzer), and a layer of a Zn-based metal−organic framework (MOF) nanocrystals (the in situ oxygen reservoir). The sequential synthetic procedure includes the electrosynthesis of a polyaniline-like electroactive film, the synthesis of Pt nanoparticles within this film, and the deposition of a layer of MOF nanocrystals, which adds micro/mesoporosity to the assembly. The incorporation of the MOF nanocrystals layer incorporates two fundamental aspects: it allows for the ionic transport through its interparticle interstices, and also selectively promotes the O 2 preconcentration, which is then available for the ORR on the embedded catalytically active metallic nanoparticles. The rational integration of these blocks yields a functional interfacial architecture for enhanced ORR currents in eco-friendly neutral pH KCl solutions.