Porous CoFe2O4/C NRAs supported on nickel foam@NC (denoted as NF@NC‐CoFe2O4/C NRAs) are directly fabricated by the carbonization of bimetal–organic framework NRAs grown on NF@poly‐aniline(PANI), and ...they exhibit high electrocatalytic activity, low overpotential, and high stability for the oxygen evolution reaction in alkaline media.
Electroreduction of CO2 to acetate provides a promising strategy to reduce CO2 emissions and store renewable energy, but acetate is usually a by‐product. Here, we show a stable and conductive ...two‐dimensional phthalocyanine‐based covalent‐organic framework (COF) as an electrocatalyst for reduction of CO2 to acetate with a single‐product Faradaic efficiency (FE) of 90.3(2)% at −0.8 V (vs. RHE) and a current density of 12.5 mA cm−2 in 0.1 M KHCO3 solution. No obvious degradation was observed over 80 hours of continuous operation. Combined with the comparison of the properties of other catalysts with isolated metal active sites, theoretical calculations and in situ infrared spectroscopy revealed that the isolated copper‐phthalocyanine active site with high electron density is conducive to the key step of C−C coupling of *CH3 with CO2 to produce acetate, and can avoid the coupling of *CO with *CO or *CHO to produce ethylene and ethanol.
Compared to multiple active sites, an isolated active site with high electron density may be more suitable for electroreduction of CO2 towards the C2 product acetate, and can avoid the coupling of *CO with *CO or *CHO to produce ethylene and ethanol.
A lanthanide cluster, PCC‐72, which is the second largest, with 72 Dy(III) ions assembled into an unprecedented tubular structure, is synthesized. Remarkably, PCC‐72 exhibits superionic proton ...conductivity (>10−4 S cm−1) under both ambient (with relative humidity RH < 75%) and hot (T > 90 °C, RH = 95%) conditions. Moreover, slow magnetic relaxation is observed, making PCC‐72 the largest Dy(III) cluster that is a single‐molecule magnet.
•Metal–organic frameworks are emerging as promising electrocatalysts.•MOFs can be a bridge between heterogeneous and homogeneous electrocatalyst.•Besides crystal structure, the chemical stability, ...electric conductivity, and crystal growth are also important.
Porous coordination polymers (PCPs) or metal–organic frameworks (MOFs) have been widely used as catalysts for their large porosities, uniform pore sizes/shapes, diversified/tunable pore surfaces, redox properties, and other unique structural features. Accompanying the urgent need for clean and sustainable technologies for energy storage and conversion, as well as the fast improvement of the chemical stability of these materials, MOFs and their composites are emerging as unique electrocatalysts for the hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and some other redox reactions. This review summaries representative progress and focuses on the structure–property relationships. Combining the advantages of inorganic heterogeneous and molecular homogeneous catalysts, MOFs can serve as a promising platform for achieving high electrocatalytic performances and studying the electrocatalytic mechanisms. More attention should be devoted to designing new MOFs with high chemical stability and electric conductivity, and optimizing their crystal growth on conducting substances.
Separating ethene (C2H4) from ethane (C2H6) is of paramount importance and difficulty. Here we show that C2H4 can be efficiently purified by trapping the inert C2H6 in a judiciously designed ...metal-organic framework. Under ambient conditions, passing a typical cracked gas mixture (15:1 C2H4/C2H6) through 1 litre of this C2H6 selective adsorbent directly produces 56 litres of C2H4 with 99.95%+ purity (required by the C2H4 polymerization reactor) at the outlet, with a single breakthrough operation, while other C2H6 selective materials can only produce ca. ⩽ litre, and conventional C2H4 selective adsorbents require at least four adsorption-desorption cycles to achieve the same C2H4 purity. Single-crystal X-ray diffraction and computational simulation studies showed that the exceptional C2H6 selectivity arises from the proper positioning of multiple electronegative and electropositive functional groups on the ultramicroporous pore surface, which form multiple C-H···N hydrogen bonds with C2H6 instead of the more polar competitor C2H4.
Conventional adsorbents preferentially adsorb the small, high-polarity, and unsaturated 1,3-butadiene molecule over the other C₄ hydrocarbons from which it must be separated. We show from ...single-crystal x-ray diffraction and computational simulation that a hydrophilic metal-organic framework, Zn₂(btm)₂, where H₂btm is bis(5-methyl-1H-1,2,4-triazol-3-yl)methane, has quasi-discrete pores that can induce conformational changes in the flexible guest molecules, weakening 1,3-butadiene adsorption through a large bending energy penalty. In a breakthrough operation at ambient temperature and pressure, this guest conformation–controlling adsorbent eluted 1,3-butadiene first, then butane, butene, and isobutene. Thus, 1,3-butadiene can be efficiently purified (≥99.5%) while avoiding high-temperature conditions that can lead to its undesirable polymerization.
Efficient adsorptive separation of propylene/propane (C3H6/C3H8) is highly desired and challenging. Known strategies focus on either the thermodynamic or the kinetic mechanism. Here, we report an ...interesting reactivity of a metal–organic framework that improves thermodynamic and kinetic adsorption selectivity simultaneously. When the metal–organic framework is heated under oxygen flow, half of the soft methylene bridges of the organic ligands are selectively oxidized to form the more polar and rigid carbonyl bridges. Mixture breakthrough experiments showed drastic increase of C3H6/C3H8 selectivity from 1.5 to 15. For comparison, the C3H6/C3H8 selectivities of the best‐performing metal–organic frameworks Co‐MOF‐74 and KAUST‐7 were experimentally determined to be 6.5 and 12, respectively. Gas adsorption isotherms/kinetics, single‐crystal X‐ray diffraction, and computational simulations revealed that the oxidation gives additional guest recognition sites, which improve thermodynamic selectivity, and reduces the framework flexibility, which generate kinetic selectivity.
Tailoring with O2: When a flexible metal–organic framework is heated in a flow of oxygen, half of the organic ligands are selectively oxidized, thereby adding guest recognition sites and reducing the flexibility of the pores. As a result, the thermodynamic and kinetic selectivity for propylene/propane separation improve simultaneously.
Integration of CO2 capture capability from simulated flue gas and electrochemical CO2 reduction reaction (eCO2RR) active sites into a catalyst is a promising cost‐effective strategy for carbon ...neutrality, but is of great difficulty. Herein, combining the mixed gas breakthrough experiments and eCO2RR tests, we showed that an Ag12 cluster‐based metal–organic framework (1‐NH2, aka Ag12bpy‐NH2), simultaneously possessing CO2 capture sites as “CO2 relays” and eCO2RR active sites, can not only utilize its micropores to efficiently capture CO2 from simulated flue gas (CO2 : N2=15 : 85, at 298 K), but also catalyze eCO2RR of the adsorbed CO2 into CO with an ultra‐high CO2 conversion of 60 %. More importantly, its eCO2RR performance (a Faradaic efficiency (CO) of 96 % with a commercial current density of 120 mA cm−2 at a very low cell voltage of −2.3 V for 300 hours and the full‐cell energy conversion efficiency of 56 %) under simulated flue gas atmosphere is close to that under 100 % CO2 atmosphere, and higher than those of all reported catalysts at higher potentials under 100 % CO2 atmosphere. This work bridges the gap between CO2 enrichment/capture and eCO2RR.
Electrochemical CO2 reduction reaction occurs in the pores of a porous catalyst possessing CO2 capture sites, which boosts the catalytic performance virtually independent on the CO2 concentration.
The paddle-wheel type cluster Co2(RCOO)4(LT)2 (R = substituent group, LT = terminal ligand), possessing unusual metal coordination geometry compared with other cobalt compounds, may display high ...catalytic activity but is highly unstable especially in water. Here, we show that with judicious considerations of the host/guest geometries and modular synthetic strategies, the labile dicobalt clusters can be immobilized and stabilized in a metal–organic framework (MOF) as coordinative guests. The Fe(na)4(LT) fragment in the MOF {Fe3(μ3-O)(bdc)3}4{Fe(na)4(LT)}3 (H2bdc = 1,4-benzenedicaboxylic acid, Hna = nicotinic acid) can be removed to give {Fe3(μ3-O)(bdc)3}4 with a unique framework connectivity possessing suitable distribution of open metal sites for binding the dicobalt cluster in the form of Co2(na)4(LT)2. After two-step, single-crystal to single-crystal, postsynthetic modifications, a thermal-, water-, and alkaline-stable MOF {Fe3(μ3-O)(bdc)3}4{Co2(na)4(LT)2}3 containing the desired dicobalt cluster was obtained, giving extraordinarily high electrocatalytic oxygen evolution activity in water at pH = 13 with overpotential as low as 225 mV at 10.0 mA cm–2.
Nanosized aggregations of metal ions shielded by organic ligands possessing both exquisite structural aesthetics and intriguing properties are fundamentally interesting. Three isostructural gigantic ...transition‐metal–rare‐earth heterometallic coordination cages are reported, abbreviated as {Ni64RE96} (RE=Gd, Dy, and Y) and obtained by a mixed‐ligand approach, each possessing a cuboidal framework made of 160 metal ions and a nanosized spherical cavity in the center. Along with the structural novelty, these hollow cages show highly selective adsorptions for CO2 over CH4 or N2 at ambient temperatures. Moreover, the gadolinium analogue exhibits large magnetocaloric effect at ultralow temperatures.
The highest‐nuclearity transition‐metal–rare‐earth heterometallic coordination cages {Ni64RE96} (RE=Gd, Dy, and Y) with a cuboidal porous structure have been synthesized by using a mixed‐ligand approach to control the hydrolysis of the metal ions. These giant cluster complexes exhibit high selectivity for CO2 over CH4 or N2 at ambient temperature and a large magnetocaloric effect at ultralow temperatures.
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