Hierarchical porous carbon nanoshells with about 40 nm cavities are synthesized by using CdS@mSiO 2 core−shell structured materials as hard templates and 4,4′-bipyridine and FeCl 3 •6H 2 O as nitrogen, carbon, and iron sources. CdS@mSiO 2 denotes a CdS nanoparticle core and mesoporous SiO 2 (mSiO 2 ) shell. The obtained porous and hollow carbon nanoshells demonstrate excellent electrocatalytic activity for oxygen reduction reaction (ORR). Both the onset potential (0.98 V) and half-wave potential (0.85 V) are more positive than that of commercial Pt/C in alkaline conditions with the same catalyst loading (0.1 mg cm −2 ). In acidic conditions, the onset and halfwave potentials of carbon-nanoshell electrodes are only 30 and 20 mV less than that of commercial Pt/C, respectively. The outstanding stability and electrocatalytic activity for ORR of these novel carbon nanoshells can be attributed to the use of a Fe−N x containing precursor, hierarchical porous structural features, and perhaps most importantly the hollow shell design. Such hollow carbon nanoshells exhibit high performance as electrocatalysts for ORR; also this synthetic approach represents a versatile, new route toward the preparation of efficient materials with hierarchical porous and hollow structural features.
Metal-organic polyhedra (MOPs) or frameworks (MOFs) based on Cr(3+) are notoriously difficult to synthesize, especially as crystals large enough to be suitable for characterization of the structure or properties. It is now shown that the co-existence of In(3+) and Cr(3+) induces a rapid crystal growth of large single crystals of heterometallic In-Cr-MOPs with the [M8L12] (M=In/Cr, L=dinegative 4,5-imidazole-dicarboxylate) cubane-like structure. With a high concentration of protons from 12 carboxyl groups decorating every edge of the cube and an extensive H-bonded network between cubes and surrounding H2O molecules, the newly synthesized In-Cr-MOPs exhibit an exceptionally high proton conductivity (up to 5.8×10(-2) S cm(-1) at 22.5 °C and 98% relative humidity, single crystal).
Introduction of pore partition agents into hexagonal channels of MIL‐88 type (acs topology) endows materials with high tunability in gas sorption. Here, we report a strategy to partition acs framework into pacs (partitioned acs) crystalline porous materials (CPM). This strategy is based on insertion of in situ synthesized 4,4′‐dipyridylsulfide (dps) ligands. One third of open metal sites in the acs net are retained in pacs MOFs; two thirds are used for pore‐space partition. The Co2V‐pacs MOFs exhibit near or at record high uptake capacities for C2H2, C2H4, C2H6, and CO2 among MOFs. The storage capacity of C2H2 is 234 cm3 g−1 (298 K) and 330 cm3 g−1 (273 K) at 1 atm for CPM‐733‐dps (the Co2V‐BDC form, BDC=1,4‐benzenedicarboxylate). These high uptake capacities are accomplished with low heat of adsorption, a feature desirable for low‐energy‐cost adsorbent regeneration. CPM‐733‐dps is stable and shows no loss of C2H2 adsorption capacity following multiple adsorption–desorption cycles.
The development of novel photocatalysts usually centers on features such as band structures, various nano‐, micro‐, or macro‐forms, and composites in efforts to tune their light absorption and charge separation efficiency. In comparison, the selectivity of photocatalysts with respect to features of reactants such as size and charge has received much less attention, in part due to the difficulty in designing semiconducting photocatalysts with uniform pore size. Here, we use crystalline porous chalcogenides as a platform to probe reactant selectivity in photocatalytic processes. The 3‐in‐1 integration of high surface area, uniform porosity, and favorable band structures in such chalcogenides makes them excellent candidates for efficient and selective photocatalytic processes. We show that their photocatalytic activity and selectivity are closely related to their differing affinity and selectivity for different guest species. In particular, unlike common solid‐state photocatalysts with neutral framework, the anionic nature of the porous chalcogenide framework used here endows them with a high degree of selectivity for cationic species in both guest exchange and closely coupled photocatalytic transformation of such guests. Another interesting discovery is the observation of an unusual ion exchange process involving a transient state of over‐saturation of exchanged ions, which can be explained by a transition from an initially kinetically controlled process to a subsequent thermodynamically controlled one. This work is part of ongoing efforts to contribute to the development of a new generation of crystalline porous photocatalysts with custom‐designed selectivity for various reactants or products.
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