Nitrogen-doped graphitic porous carbons (NGPCs) have been synthesized by using a zeolite-type nanoscale metal-organic framework (NMOF) as a self-sacrificing template, which simultaneously acts as both the carbon and nitrogen sources in a facile carbonization process. The NGPCs not only retain the nanopolyhedral morphology of the parent NMOF, but also possess rich nitrogen, high surface area and hierarchical porosity with well-conducting networks. The promising potential of NGPCs as metal-free electrocatalysts for oxygen reduction reactions (ORR) in fuel cells is demonstrated. Compared with commercial Pt/C, the optimized NGPC-1000-10 (carbonized at 1000 C for 10 h) catalyst exhibits comparable electrocatalytic activity via an efficient four-electron-dominant ORR process coupled with superior methanol tolerance as well as cycling stability in alkaline media. Furthermore, the controlled experiments reveal that the optimum activity of NGPC-1000-10 can be attributed to the synergetic contributions of the abundant active sites with high graphitic-N portion, high surface area and porosity, and the high degree of graphitization. Our findings suggest that solely MOF-derived heteroatom-doped carbon materials can be a promising alternative for Pt-based catalysts in fuel cells.

No abstract

No abstract

The polymerization and decomposition of acetaldehyde (CH3CHO) on Ru(001) was studied by high-resolution electron energy loss spectroscopy (HREELS), static secondary ion mass spectrometry (SSIMS), and temperature-programmed desorption (TPD). Evidence is presented that low exposures (<0.4 langmuir) of CH3CHO on Ru(001) at 110 K polymerize across the surface in two dimensions upon adsorption. p'(0) CH3CHO, which is the proposed intermediate in surface polymerization, is stable only at exposures approaching saturation of the first layer (0.4-0.6 langmuir). This species incorporates into the surface polymer after heating above 150 K. Exposures above 0.6 langmuir result in multilayer CH3CHO, which desorbs in TPD at 148 K. A second CH3CHO state appears in TPD at 250 K for CH3CHO exposures above 2 langmuir and is attributed to decomposition of polymerized CH3CHO in three dimensions above the surface. Ions from this polymer, containing at least monomer units, are detected in +SSIMS. The surface polymer decomposes to rj1 2(C,0) CH3CHO after heating above 250 K. Decomposition of the latter species at 315 K evolves H2 in TPD and leaves CO and small amounts of C^H and p2(C,0) CH3CO on the surface.

Block polymers offer unparalleled opportunities for designing materials with enhanced functionalities and properties. Hence, we report a synthetic strategy for diblock polyesters through bridging two distinct reactions between ring-opening polymerization of lactide (LA) and ring-opening copolymerization of epoxides with anhydrides by using a binary catalyst. Specifically, in the terpolymerization of LA, epichlorohydrin (ECH), and phthalic anhydride (PA), spectroscopy indicated that this process occurs first by ECH/PA copolymerization and then homopolymerization of LA, forming diblock polyester. Density functional theory (DFT) calculations revealed that coupling of ECH/PA was more favorable than LA homopolymerization in the presence of PA, while an incorporation of LA into the ECH−PA sequence was also possible owing to the competitive energy barriers and thermodynamic priority. It was also computationally found that LA homopolymerization occurred after consumption of PA to achieve diblock polyester, as experimentally observed. Furthermore, the diblock polyester architectures could be extended and modified by introducing various monomers.

The switchable catalysis using a commercial salenMn catalyst was firstly developed and applied in the one‐pot selective copolymerization from anhydrides, epoxides, CO2 and ϵ‐caprolactone (ϵ‐CL) mixtures for the precise synthesis of AB, ABA and novel ABC block copolymers. The observed unique double switch process comprising three different polymerization cycles was rationalized by theoretical calculations. Surprisingly, the first block turned out to be an efficient macromolecular initiator for the consecutive introduction of carbonate linkages into copolymers, albeit with dominant cyclization with the catalyst alone. Further, through the selective reaction on different epoxides, the switchable copolymerization of up to five monomers was achieved yielding well‐defined multi‐block copolymers with structural diversity and functionality.

No abstract

Switchable polymerization is an attractive strategy to enable the sequential selectivity of multi‐block polyesters. Besides, these well‐defined multi‐block polyesters could enable further modification for wider applications. Herein, based on the reversible insertion of CO2 by Salen‐MnIII, a new monomer controlled self‐switchable polymerization route was developed. Chemoselective ring opening copolymerization of O‐carboxyanhydrides (OCAs) and lactide (LA) was explored without cocatalyst. The sequential conversion of OCAs and LA into the polymer chain could form multi‐block polyesters. Based on this strategy, a series of multi‐block polyesters with different pendant groups were synthesized. Furthermore, by modifying the propargyl‐containing copolymers with quaternary ammonium groups, we have realized antibacterial functionalization of PLA. These results imply the potential application of this strategy for the fabrication of functional polymers for biomedical applications.