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In this work, nanorods like bimetallic Zn/Mn metal–organic-frameworks (MOFs) are proposed as the precursor for preparing MnxOy/porous carbon composite as a high-performance catalyst. The synthesis conditions, including the ratio of Zn:Mn and reaction time, are systematically investigated. The optimized sample has nanorods like morphology with a length of 200 nm and a diameter of 50 nm. Electrochemical tests show that the initial potential of the optimized MnxOy/porous carbon composite is 0.896 V(vs. reversible hydrogen electrode, RHE), the half-wave potential is 0.763 V (vs. RHE), and the kinetic current is 0.962 mA cm−2 (0.8 V). It has higher stability and selectivity than commercial Pt/C. The results reveal that the existence of Zn grain refinement occurs in MnxOy/carbon nanomaterials and increases its pore structure. The obtained material possesses a large electrochemical active area, indicating the higher exposed active sites and enhanced catalytic performance. Besides, the assembled Zn-air battery with MnxOy/porous carbon composite as cathode catalyst exhibits a power density of 0.14 W cm−2, close to that of commercial Pt/C. This work provides adequate data for further study of bimetallic MOF-derived materials as high-performance ORR catalysts. [ABSTRACT FROM AUTHOR]

Reasonable design of the porous metal-organic frameworks (MOFs) to convert a burgeoning carbon-based catalysts with high oxygen reduction reaction (ORR) activity are still challenging in energy conversion, storage and transport. Herein, Fe 7 C 3 -doped in-situ grown carbon nanotubes and N-doped hollow carbon (Fe x -CNT@NHC) are prepared by using a simple and robust preparation method, which is used cubic ZIF-8-derived zinc oxide cubes as a template for secondary MOFs re-growth followed by the final carbonization. In the 0.1 M KOH, the as-pyrolyzed Fe 0.1 -CNT@NHC electrocatalyst displays the value of half-wave potential is 0.92 V and the value of diffusion-limited current density is 6.08 mA cm−2, respectively, which are close to the corresponding electrochemical values of the standard commercial Pt/C (0.89 V and 5.89 mA cm−2). Meanwhile, the material has passed relevant tests on its long-term stability and methanol tolerance in alkaline media, showing that it has excellent ORR activity and efficient stability under electrocatalysis. Furthermore, the Fe 0.1 -CNT@NHC materials catalyze a Zn-air battery that delivers a performed peak power density of 105.9 mW cm−2. The impressive catalytic activity of Fe 0.1 -CNT@NHC stems from the effective synergy between efficient Fe and N co-doping, large specific surface area, and high electrical conductivity. This preparation route for carbon nanomaterials will provide a new synthetic strategy to synthesize high-performance non-noble metal carbon-based ORR catalysts for practical energy-related applications. Image 1 • Nano Fe 7 C 3 with in situ grown CNT on N doped hollow carbon cube is proposed as new ORR catalyst. • The contained hollow structure of meso-macropores facilitates the transfer of O 2 and electron. • The in situ grown CNT greatly increases its conductivity to enhance its ORR activity. • The optimized Fe 0.1 -CNT/NHC has superior ORR performance and methanol tolerance. [ABSTRACT FROM AUTHOR]

The non-platinum metal-nitrogen-carbon (M-NC) system is a class of highly active oxygen reduction reaction (ORR) electrocatalysts that are well known and widely used in fuel cell applications. Herein, one simple synthesizing method of efficient M-NC electrocatalysts is proposed by the direct pyrolysis of a pretreated core-shell structure of ZnO@ZIF-8 containing metal-ammonia complex (MAC, [M(NH 3) x n+) from the polydisperse self-sacrificing MOF-5 cubes. The as-pyrolyzed M-NC (M = Co, Ag, Cu, and Ni) electrocatalysts showcase high electrocatalytic ORR activity in an alkaline medium. Among them, Co-NC catalyst exhibits an excellent ORR performance where its E 1/2 = 0.80 V, J L = 5.88 mA cm−2, as well as Tafel slope of 67.0 mV dec−1 are close to commercial Pt/C and Ag-NC, better than the other two catalysts of Cu-NC and Ni-NC. Impressively, zinc-O 2 batteries assembled with M-NC materials exhibit the better discharge performance, and have great potential in the practical energy conversion and storage. The experimental demonstration of metal-based nanoparticles and active M-N sites in the carbonaceous matrix can be efficiently used to promote the ORR activity, which is derived from a synergistic contribution of its particular hollow structure, large specific surface area, rich M-N active sites, and high degree of graphitization. This attractive preparation approach provides us a powerful contribution to the construction of high-performance carbon-based ORR electrocatalysts. Herein, a series of high-performance non-precious TM-based M-NC catalyst for ORR are successfully obtained by direct pyrolysis of a MAC-impregnated core-shell structure synthesized from the self-sacrificing cube-shaped MOF-5 precursors. The as-pyrolyzed M-NC (M = Co, Ag, Cu, and Ni) electrocatalysts showcase a high electrocatalytic ORR activity in an alkaline medium due to metal-based nanoparticles and active M-N sites in the carbonaceous matrix. Image 1 [ABSTRACT FROM AUTHOR]

In energy conversion systems, energy can be efficiently converted from one form to another form with catalysts, of which the design and synthesis are of great importance. Based on the remarkable traits of metal-organic frameworks, we have tuned the InOF-1 morphology by adding different amounts of the CTAB surfactant. Subsequently, as the rod-like InOF-1 with the highest adsorption capacity can encapsulate more metal ions, it is selected as the precursor to absorb the [Co(NH 3) 6 3+ ions and further calcined at high temperature to form N-doped carbon nanosheets containing Co NPs (Co-NCS). The resultant carbon nanomaterial shows a satisfying ORR performance (E onset of 0.92 V vs. RHE, E 1/2 of 0.83 V vs. RHE and the J L of 5.05 mA cm−2) and electrochemical stability (97.26% after 10 h) due to its hierarchical porosity, large specific surface area, abundant active sites and appropriate N-doping. Finally, an outstanding oxygen reduction property of the Co-NCS catalyst can be achieved to substitute the commercial Pt/C as the cathode catalyst for the Zn-air battery. This work would be expected to instructive in understanding ORR catalytic reaction and supplement a pathway to prepare MOFs-derived carbon nanomaterials for energy conversion and storage. In this work, we have tuned the InOF-1 morphology by adding different amounts of the CTAB surfactant. Subsequently, as the rod-like InOF-1 with the highest adsorption capacity can encapsulate more metal ions, it is selected as the precursor to absorb the functional [Co(NH 3) 6 3+ ions and further calcined at high temperature to form N-doped carbon nanosheets containing Co NPs, denoted as Co-NCS. The resultant carbon nanomaterial of Co-NCS shows a satisfying ORR performance and electrochemical stability, its derived Zn-air battery. Image 1 • A rod-like indium-based framework of InOF-1 is synthesized by the surfactant-assisted approach. • Hierarchically porous Co/N-doped carbon nanosheets (Co-NCS) can be achieved. • The obtained Co-NCS exhibits large surface area, abundant active sites and high graphitization. • The Co-NCS compound shows a satisfying ORR and practical applicability for Zn-air battery. [ABSTRACT FROM AUTHOR]

Exploiting non-noble metal bifunctional electrocatalysts for efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is a feasible approach for developing clean energy. Herein, we synthesize a transition metal coordinating nitrogen (Fe/Ni-N) doped carbon material (FeNi-MNC) with unique morphology combining external diverging carbon nanotubes and internal carbon matrix with ordered macropore alignments. With the co-catalysis of Fe and Ni species and the space limiting of SiO 2 template in carbonation, the obtained FeNi-MNC shows high Fe/Ni-N contents. Profiting from the hierarchical morphology and abundant active sites, the catalyst exhibits excellent activity for ORR in 0.1 M KOH with a half-wave potential of 0.834 V and a Tafel slope of 53.1 mv dec−1 being superior to Pt/C. Moreover, it only needs an overpotential of 298 mV reaching 10 mA cm−2 for OER in 1.0 M KOH. Our work constructs a 3-dimensional porous carbon matrix integrated with 1-dimensional carbon nanotubes and 2-dimensional carbon nanosheets to enhance the catalytic performance. Image 1 • Abundant nanotube coated ordered macroporous carbon matrix FeNi-MNC is prepared. • FeNi-MNC remains ultrahigh Fe/Ni-N contents by the co-catalysis of Fe and Ni species. • FeNi-MNC is active both for OER (η = 298 mV) and ORR (E1/2 = 0.834 V). [ABSTRACT FROM AUTHOR]

2-dimensional Co nanoparticles embedded in N-doped carbon nanosheets (NCNS) are derived from indium-based frameworks which are impregnated with discrete [Co(NH 3) 6 ]3+ ions by high-temperature pyrolysis as a new approach to convert a 3-dimensional porous metal-organic frameworks (CPM-5) to 2-dimensional functional nanosheets. The as-made porous Co, N-doped carbon nanosheets (NCNS–Co 0.5 In 0.5) perform the excellent ORR catalytic activity with a half wave potential of 0.82 V in comparison with the commercial Pt/C. Meanwhile, it also owns good stability and methanol tolerance as a suitable catalyst for zinc-air batteries with a high power density of 132.2 mW cm−2. This method can easily be extended to other In-based MOFs, including QMOF-2, In-MIL-68, InOF-1 , in which all the corresponding derived materials exhibit efficient ORR performance. Especially, the porous Co, N-doped carbon nanosheets annealed from InOF-1 (InOF-1-Co-800) display an E onset of 0.93 V, a half-wave potential of 0.85V, and a diffusion-limited current of 5.40 mA cm−2 density. Our work provides a new path to tune the morphology and catalytic performance of MOF derivatives. Image 1 • ·A general method to transform 3D In-based MOFs into 2D Co,N-doped carbon nanosheets. • The Introduction of [Co(NH 3) 6 ]Cl 3 complex into MOFs brings in Co and N sources. • ·The pore-making effect and evaporation of CoIn 2 lead to hierarchically porous carbon. • ·The Co,N-doped carbon nanosheets show an excellent ORR activity for Zn-air battery. [ABSTRACT FROM AUTHOR]

It is of great importance to find non-precious metal based oxygen reduction reaction (ORR) catalysts with high stability, high performance and low cost. In this context, hierarchically porous carbon-based nanomaterials doped with heteroatoms are regarded as one of promising catalysts for ORR. Herein, a bottom-up approach is proposed by using the initial MOF-derived CoO@ZIF-67 core-shell structure as a template to obtain hollow cobalt-anchored N-doped carbon material followed by acid etching (A-CoNC). It exhibits a type of hollow porous nitrogen-carbon network anchored by well-dispersed atomic Co-N x sites with high activity and stable catalytic performance. The as-obtained A-CoNC shows high electrocatalytic ORR activity, good reaction selectivity with the low Tafel slope of 55.5 mV dec−1, large limited current density of 5.37 mA cm−2 and excellent long-term stability (retention = 96.1%, time = 10 h). Furthermore, A-CoNC can also be serving as efficient electrocatalysts for zinc-air battery with a high power density of 144.0 mW cm−2. Our synthetic strategy from the MOF-derived core-shell structure to ORR electrocatalyst provides new pathway for the design and preparation of highly efficient electro-/photo-catalysts stemmed from MOFs materials. [Display omitted] • A bottom-up method is proposed to prepare hollow porous Co,N-doped carbon materials. • The obtained MOF-derived core-shell structure is endowed with decent surface area. • The nitrogen-carbon network anchored by rich dispersed Co-N x sites is obtained. • The Co,N-doped carbon materials show an excellent ORR activity for Zn-air battery. [ABSTRACT FROM AUTHOR]