Synthesis and Optimization of Zeolitic Imidazolate Frameworks for the Oxygen Evolution Reaction

Metal–organic frameworks/zeolitic imidazolate frameworks (MOFs/ZIFs) and their post‐synthesis modified nanostructures, such as oxides, hydroxides, and carbons have generated significant interest for electrocatalytic reactions. In this work, a high and durable oxygen evolution reaction (OER) performance directly from bimetallic Zn100−xCox‐ZIF samples is reported, without carrying out high‐temperature calcination and/or carbonization. ZIFs can be reproducibly and readily synthesized in large scale at ambient conditions. The bimetallic ZIFs show a systematic and gradually improved OER activity with increasing cobalt concentration. A further increase in OER activity is evidenced in ZIF‐67 polyhedrons with controlled particle size of 50 %, OER activity is obtained with ZIF‐67/carbon black, which shows a low overpotential of approximately 320 mV in 1.0 m KOH electrolyte. Such activity is comparable to or better than numerous MOF/ZIF‐derived electrocatalysts. The optimized ZIF‐67 sample also exhibits increased activity and durability over 24 h, which is attributed to an in situ developed active cobalt oxide/oxyhydroxide related nanophase

Influence of hydrogen absorption on structural and electrical transport properties of Ho1−xMmxCo2 alloys

The structural and electrical transport properties of Ho1−xMmxCo2Ho1−xMmxCo2 (x=0x=0, 0.1, 0.2, 0.3, and 0.4 and Mm=mischmetalMm=mischmetal) alloys and their hydrides in the hydrogen concentration (y)(y) range of 0⩽y⩽3.60⩽y⩽3.6 have been determined through the powder x-ray diffraction (XRD) and temperature dependence of electrical resistivity [ρ(T)][ρ(T)] measurements. At room temperature, these compounds crystallize in MgCu2MgCu2-type (C15) structure. The crystalline nature and lattice expansion of hydrogenated alloys have been studied using the hydrogen concentration dependence of XRD peak analysis indicating the coexistence of two hydride phases at intermediate hydrogen concentrations. The temperature dependence of the electrical resistivity of alloys has been discussed based on the conduction electron scattering and spin fluctuation scattering mechanisms. The changes in magnetic ordering and transition temperature upon Mm substitution and at different concentrations of hydrogen loadings have been discussed. Furthermore, the transformation from metalliclike conductivity to thermally activated conduction mechanism and different conduction regimes of temperature dependent resistivity upon increasing H concentration have been well described by Kondo-type and electron-electron scattering effects

Switching effective oxygen reduction and evolution performance by controlled graphitization of a cobalt-nitrogen-carbon framework system

We report a purposely designed route for the synthesis of a promising carbon-based electrocatalyst for both ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) from zeolitic imidazolate frameworks (ZIFs). Firstly, precursor ZIFs are rationally designed with a blend of volatile zinc to induce porosity and stable cobalt to induce graphitic domains. Secondly, the self-modulated cobalt–nitrogen–carbon system (SCNCS) is shown to be an effective ORR catalyst after graphitization at mild temperatures. Finally, the best OER catalyst is developed by enhancing graphitization of the SCNCS. For the first time, solely by switching the graphitization conditions of SCNCS, excellent ORR or OER performance is realized. This approach not only opens up a simple protocol for simultaneous optimization of nitrogen doping and graphitization at controlled cobalt concentrations, but also provide a facile method of developing such active catalysts without the use of extensive synthesis procedures

Graphene-based materials: synthesis and gas sorption, storage and separation

Graphene-based materials have generated tremendous interest in a wide range of research activities. A wide variety of graphene related materials have been synthesized for potential applications in electronics, energy storage, catalysis, and gas sorption, storage, separation and sensing. Recently, gas sorption, storage and separation in porous nanocarbons and metal-organic frameworks have received increasing attention. In particular, the tuneable porosity, surface area and functionality of the lightweight and stable graphene-based materials open up great scope for those applications. Such structural features can be achieved by the design and control of the synthesis routes. Here, we highlight recent progresses and challenges in the syntheses of graphene-based materials with hierarchical pore structures, tuneable high surface area, chemical doping and surface functionalization for gas (H2, CH4, CO2, N2, NH3, NO2, H2S, SO2, etc.) sorption, storage and separation

Postsynthesis Annealing of MOF-5 Remarkably Enhances the Framework Structural Stability and CO2 Uptake

Structural stability and porosity characteristics of metal–organic frameworks (MOFs) are of great importance for practical applications, such as gas sorption/storage and catalytic support. By means of a simple and effective method of postsynthesis thermal annealing below its framework decomposition temperature, the annealed MOF-5 shows unexpectedly high CO2 uptake up to 2 mmol g–1 at 25 °C and 1 bar, which is more than double the capacity of the untreated counterpart (0.8 mmol g–1). Structural characterizations reveal that the annealed MOFs are very active with local vacancy sites due to partial decomposition of the bridging carboxylates of the framework linker. The annealed MOFs also show high stability for cyclic CO2 uptake and air/moisture. Such an approach may be effectively applied to other MOF structures or MOF based membranes to enhance their gas uptake or separation

Tuning of ZIF-Derived Carbon with High Activity, Nitrogen Functionality, and Yield - A Case for Superior CO2 Capture.

A highly effective and facile synthesis route is developed to create and tailor metal-decorated and nitrogen-functionalized active microporous carbon materials from ZIF-8. Clear metal- and pyrrolic-N-induced enhancements of the cyclic CO2 uptake capacities and binding energies are achieved, particularly at a much lower carbonization temperature of 700 °C than those often reported (1000 °C). The high-temperature carbonization can enhance the porosity but only at the expense of considerable losses of sample yield and metal and N functional sites. The findings are comparatively discussed with carbons derived from metal-organic frameworks (MOFs) reported previously. Furthermore, the porosity of the MOF-derived carbon is critically dependent on the structure of the precursor MOF and the crystal growth. The current strategy offers a new and effective route for the creation and tuning of highly active and functionalized carbon structures in high yields and with low energy consumption

An Ultrahigh Pore Volume Drives Up the Amine Stability and Cyclic CO2 Capacity of a Solid-Amine@Carbon Sorbent

Carbon monoliths of ultrahigh pore volume (5.35 cm(3) g(-1) ) and high surface area (2700 m(2) g(-1) ) accommodate a record high level of amine(tetraethylenepentamine), up to 5 g g(-1) within its hierarchically networked micro-/mesopores over a wide range. Thus, this solid-amine@carbon shows exceptional CO2 sorption and stable cyclic capacities at simulated flue-gas conditions

Graphitic nanostructures in a porous carbon framework significantly enhance electrocatalytic oxygen evolution

A hybrid structure, a graphitic nanostructures@porous carbon framework, is developed by utilizing the bimetallic zeolitic imidazolate framework-8 (ZIF-8) as a solid precursor, simultaneously templating porous carbon and growing graphitic nanocarbon in a simplified chemical vapor deposition (CVD) fashion. A ligand, 2-methylimidazolate (2MIM), in the ZIF-8 decomposes above 600 °C to yield active carbon/hydrocarbon radicals/vapour. With the idea of using the high catalytic activity of nickel to grow graphitic nanostructures in a CVD process from gaseous carbon feedstocks, a precursor, bimetallic ZIF-8, is synthesized by partial substitution of zinc metal centres by nickel. Such nickel centres thus act as nanocatalysts to grow graphitic nanostructures from the carbon radicals arising from the partly decomposed ligand of the framework during the carbonization step. These hybrid structures show a highly enhanced electrocatalytic activity for the water splitting oxygen evolution reaction (OER). Furthermore the catalytic activity for the oxygen reduction and hydrogen evolution reactions (ORR and HER), and gas uptake capacities for H2 and CO2 are enhanced with respect to the increased porosity and nitrogen doping in the samples. We also show that not all the MOF-based precursors with nickel metal centres are suitable for producing nanographitic structures. Our further investigation suggests that the graphitization in the samples plays a critical role in enhancing the catalytic activities

Nanoconfined ammonia borane in a flexible metal-organic framework Fe-MIL-53: clean hydrogen release with fast kinetics

We demonstrated the dehydrogenation behaviour of nanoconfined ammonia borane (AB) in Fe–MIL-53, a flexible metal–organic framework (MOF) by solid state thermolysis. We observed clean hydrogen release with fast kinetics at reduced temperatures

High-Performance Zinc–Air Batteries with Scalable Metal–Organic Frameworks and Platinum Carbon Black Bifunctional Catalysts

Metal-organic framework (MOF)-related derivatives have generated significant interest in numerous energy conversion and storage applications, such as adsorption, catalysis, and batteries. However, such materials' real-world applicability is hindered because of scalability and reproducibility issues as they are produced by multistep postsynthesis modification of MOFs, often with high-temperature carbonization and/or calcination. In this process, MOFs act as self-sacrificial templates to develop functional materials at the expense of severe mass loss, and the resultant materials exhibit complex process-performance relationships. In this work, we report the direct applicability of a readily synthesized and commercially available MOF, a zeolitic imidazolate framework (ZIF-8), in a rechargeable zinc-air battery. The composite of cobalt-based ZIF-8 and platinum carbon black (ZIF-67@Pt/CB) prepared via facile solution mixing shows a promising bifunctional electrocatalytic activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), the key charge and discharge mechanisms in a battery. ZIF-67@Pt/CB exhibits long OER/ORR activity durability, notably, a significantly enhanced ORR stability compared to Pt/CB, 85 versus 52%. Interestingly, a ZIF-67@Pt/CB-based battery delivers high performance with a power density of >150 mW cm-2 and long stability for 100 h of charge-discharge cyclic test runs. Such remarkable activities from as-produced ZIF-67 are attributed to the electrochemically driven in situ development of an active cobalt-(oxy)hydroxide nanophase and interfacial interaction with platinum nanoparticles. This work shows commercial feasibility of zinc-air batteries as MOF-cathode materials can be reproducibly synthesized in mass scale and applied as produced