Ultrathin Hollow Co/N/C Spheres from Hyper-Crosslinked Polymers by a New Universal Strategy with Boosted ORR Efficiency.

Porous carbon materials with hollow structure, on account of the extraordinary morphology, reveal fascinating prospects in lithium-ion batteries, electrocatalysis, etc. However, collapse in ultrathin carbon spheres due to insufficient rigidity in such thin materials obstructs further enhanced capability. Based on hyper-crosslinked polymers (HCPs) with sufficient pore structure and rigid framework, a new bottom-up strategy is proposed to construct SiO2 @HCPs directly from aromatic monomers. Heteroatom and function groups can be facilely introduced to the skeleton. The thickness of HCPs' wall can be tuned from 9 to 20 nm, which is much thinner than that of hollow sphere synthesized by the traditional method, and the sample with a thickness of 20 nm shows the highest surface area of 1633 m2 g-1 . The oxygen reduction reaction is conducted and the CoNHCS electrocatalysts with an ultrathin thickness of 5 nm display higher half-wave potential than those of bulk samples, even better than commercial Pt/C electrode. On account of the hollow structure, the relative current density loss of electrocatalysts is only 4.1% in comparison with 27.7% in Pt/C electrode during the 15 000 s test, indicating an obvious higher long-term stability. The new strategy to construct hollow HCPs may shed light on efficient chemical catalysis, drug delivery, and electrocatalysis.

Selective photocatalytic CO2 reduction in aerobic environment by microporous Pd-porphyrin-based polymers coated hollow TiO2.

Direct photocatalytic CO2 reduction from primary sources, such as flue gas and air, into fuels, is highly desired, but the thermodynamically favored O2 reduction almost completely impedes this process. Herein, we report on the efficacy of a composite photocatalyst prepared by hyper-crosslinking porphyrin-based polymers on hollow TiO2 surface and subsequent coordinating with Pd(II). Such composite exhibits high resistance against O2 inhibition, leading to 12% conversion yield of CO2 from air after 2-h UV-visible light irradiation. In contrast, the CO2 reduction over Pd/TiO2 without the polymer is severely inhibited by the presence of O2 ( ≥ 0.2 %). This study presents a feasible strategy, building Pd(II) sites into CO2-adsorptive polymers on hollow TiO2 surface, for realizing CO2 reduction with H2O in an aerobic environment by the high CO2/O2 adsorption selectivity of polymers and efficient charge separation for CO2 reduction and H2O oxidation on Pd(II) sites and hollow TiO2, respectively.

Grafting Hypercrosslinked Polymers on TiO2 Surface for Anchoring Ultrafine Pd Nanoparticles: Dramatically Enhanced Efficiency and Selectivity toward Photocatalytic Reduction of CO2 to CH4.

Metal deposition with photocatalyst is a promising way to surmount the restriction of fast e- /h+ recombination to improve the photocatalytic performance. However, the improvement remains limited by the existing strategies adopted for depositing metal particles due to the serious aggregation and large unconnected area on photocatalyst surface. Here, a strategy is proposed by directly grafting hypercrosslinked polymers (HCPs) on TiO2 surface to construct Pd-HCPs-TiO2 composite with uniform dispersion of ultrafine Pd nanoparticles on HCPs surface. This composite with surface area of 373 m2 g-1 exhibits improved photocatalytic CO2 conversion efficiency to CH4 with an evolution rate of 237.4 µmol g-1 h-1 and selectivity of more than 99.9%. The enhancement can be ascribed to the grafted porous HCPs with high surface area and N heteroatom on TiO2 surface for the stabilization of Pd nanoparticles, favoring the electron transfer and CO2 adsorption for selective CH4 production. This strategy may hold the promise for design and construction of porous organic polymer with semiconductor for efficient photocatalytic conversion.