Search

Abstract: Noble‐metal‐free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal–air batteries, and electrolyzers. However, much of the structure–activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen‐doped multiwalled carbon nanotube hybrids (MnxCo3−xO4@NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst–support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, MnxCo3−xO4@NCNTs. Nanocrystalline MnCo2O4@NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm−2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long‐term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale. [ABSTRACT FROM AUTHOR]

We propose a new synthetic route towards nanoporous functional carbon materials based on salt templating with pore-padding approach (STPP). STPP relies on the use of a pore-padding agent that undergoes an initial polymerisation/ condensation process prior to the formation of a solid carbon framework. The pore-padding agent allows tailoring hierarchically the pore-size distribution and controlling the amount of heteroatom (nitrogen in this case) functionalities as well as the type of nitrogen (graphitic, pyridinic, oxides of nitrogen) incorporated within the carbon framework in a single-step-process. Our newly developed STPP method offers a unique pathway and new design principle to create simultaneously high surface area, microporosity, functionality and pore hierarchy. The functional carbon materials produced by STPP showed a remarkable CO2/N2 selectivity. At 273 K, a carbon with only micropores offered an exceptionally high CO2 adsorption capacity whereas a carbon with only mesopores showed promising CO2-philicity with high CO2/N2 selectivity in the range of 46-60 %, making them excellent candidates for CO2 capture from flue gas or for CO2 storage. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Structural stabilityand porosity characteristics of metal–organicframeworks (MOFs) are of great importance for practical applications,such as gas sorption/storage and catalytic support. By means of asimple and effective method of postsynthesis thermal annealing belowits framework decomposition temperature, the annealed MOF-5 showsunexpectedly high CO2uptake up to 2 mmol g–1at 25 °C and 1 bar, which is more than double the capacityof the untreated counterpart (0.8 mmol g–1). Structuralcharacterizations reveal that the annealed MOFs are very active withlocal vacancy sites due to partial decomposition of the bridging carboxylatesof the framework linker. The annealed MOFs also show high stabilityfor cyclic CO2uptake and air/moisture. Such an approachmay be effectively applied to other MOF structures or MOF based membranesto enhance their gas uptake or separation. [ABSTRACT FROM AUTHOR]

We report the first two examples of borohydride ammonia borane complexes: Li2(BH4)2NH3BH3and Ca(BH4)2(NH3BH3)2. Their structures are successfully determined using a combination of X-ray diffraction and first-principles calculations. Both structures are composed of alternating layers of borohydride and ammonia borane. Examination of bond lengths indicates that this arrangement is stabilized viadihydrogen bonding between ammonia borane and their surrounding BH4−, and the interactions between ammonia borane ligands and cations. Our experimental results show that more than 10 wt% and 11 wt% hydrogen can be released from Li2(BH4)2NH3BH3and Ca(BH4)2(NH3BH3)2, respectively. Negligible ammonia was detected compared to ammonia borane and its ammidoborane derivatives. Further improvements are needed to reduce borazine emission. Cycling studies show that decomposed Li2(BH4)2NH3BH3and Ca(BH4)2(NH3BH3)2can be partially hydrogenated under hydrogen pressures at high temperatures. [ABSTRACT FROM AUTHOR]

The authors have identified a typographical error in their manuscript on page 3591. The inter planar spacing for the (101) plane of anatase TiO SB 2 sb is stated to be measured as 0.32 nm; however, it should be 0.35 nm. The authors apologize for this oversight and for any inconvenience caused.... Further characterization with HR-TEM revealed that the metal salt modifications did not induce any changes in the inter planar spacing as it was measured to be B 0.35 nm b corresponding to the (101) plane of the anatase TiO2 (insets of Figure 1 (b), (d) and (f) respectively). [Extracted from the article]

The room temperature synthesis of perovskite nanocrystals (NCs) is typically achieved by employing a ligand‐assisted reprecipitation (LARP) method, which can be handled in air, and its products are comparable to what is obtained using the traditional hot‐injection method. However, the LARP method typically requires the use of coordinating polar solvents such as dimethylformamide, which are not appropriate for large‐scale production due to toxicity concerns and can also degrade or form defective perovskite NCs. Herein, an amine and oleic‐acid‐free room temperature synthesis of lead bromide perovskite NCs is reported that uses a combination of trioctylphosphine oxide and diisooctylphosphinic acid ligands. This combination of ligands provides a stable platform for the polar‐solvent‐free synthesis in air of fully inorganic CsPbBr3 (fwhm ≈ 14 nm, emission = 519 nm) and hybrid organic‐inorganic FAPbBr3 (fwhm ≈ 19 nm) NCs with photoluminescence emission between 530 and 535 nm, which is in line with the Rec. 2020 color standards. In addition, it is shown that compared to a traditionally used ligand combination, phosphine ligands can be easily removed from the surface of the NCs, which is important for the future development of this technology in optoelectronic devices. [ABSTRACT FROM AUTHOR]

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 Zn 100-x Co x -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 <200 nm among samples of different sizes between 50 nm and 2 μm. Building on this, a significantly enhanced, >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., (© 2020 Wiley-VCH GmbH.)

Noble-metal-free electrocatalysts are attractive for cathodic oxygen catalysis in alkaline membrane fuel cells, metal-air batteries, and electrolyzers. However, much of the structure-activity relationship is poorly understood. Herein, the comprehensive development of manganese cobalt oxide/nitrogen-doped multiwalled carbon nanotube hybrids (Mn x Co 3-x O 4 @NCNTs) is reported for highly reversible oxygen reduction and evolution reactions (ORR and OER, respectively). The hybrid structures are rationally designed by fine control of surface chemistry and synthesis conditions, including tuning of functional groups at surfaces, congruent growth of nanocrystals with controllable phases and particle sizes, and ensuring strong coupling across catalyst-support interfaces. Electrochemical tests reveal distinctly different oxygen catalytic activities among the hybrids, Mn x Co 3-x O 4 @NCNTs. Nanocrystalline MnCo 2 O 4 @NCNTs (MCO@NCNTs) hybrids show superior ORR activity, with a favorable potential to reach 3 mA cm -2 and a high current density response, equivalent to that of the commercial Pt/C standard. Moreover, the hybrid structure exhibits tunable and durable catalytic activities for both ORR and OER, with a lowest overall potential of 0.93 V. It is clear that the long-term electrochemical activities can be ensured by rational design of hybrid structures from the nanoscale., (© 2018 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

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., (© 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)