As a new class of crystalline porous organic materials, covalent organic frameworks (COFs) have attracted considerable attention for proton conduction owing to their regular channels and tailored functionality. However, most COFs are insoluble and unprocessable, which makes membrane preparation for practical use a challenge. In this study, we used surface‐initiated condensation polymerization of a trialdehyde and a phenylenediamine for the synthesis of sulfonic COF (SCOF) coatings. The COF layer thickness could be finely tuned from 10 to 100 nm by controlling the polymerization time. Moreover, free‐standing COF membranes were obtained by sacrificing the bridging layer without any decomposition of the COF structure. Benefiting from the abundant sulfonic acid groups in the COF channels, the proton conductivity of the SCOF membrane reached 0.54 S cm−1 at 80 °C in pure water. To our knowledge, this is one of the highest values for a pristine COF membrane in the absence of additional additives.

Molybdenum carbides are considered as one type of privileged noble-metal-free electrocatalysts for hydrogen evolution reactions (HER) due to their d-band electron structure, which is similar to Pt. Especially, the electronic structure of such materials can be further adjusted by elemental doping to improve their electrocatalytic activity. Herein, we selected the Anderson-type polyoxometalates (POMs) (NH4)n[TMMo6O24H6]·5H2O (TM = Ni2+, Co2+, n = 4; TM = Fe3+, Cr3+, n = 3) as precursors to prepare new transition-metal-doped Mo2C materials. When these POMs were mixed with dicyandiamide (DCA) by solid grinding, and carbonized at a high temperature, a series of Ni-, Co-, Fe-, and Cr-doped Mo2C composite nanoparticles covered by few-layer graphitic carbon shells (abbr. TM-Mo2C@C) were obtained. All these nanoparticles possess a similar size, morphology, and TM/Mo component ratio, and thus it is feasible to systematically investigate the influence of different TM dopants on the electrocatalytic activity of Mo2C for HER. Both electrocatalytic experiments and DFT calculations reveal that TM dopants have a significant effect on the hydrogen binding energy (ΔGH*) and the catalytic activity of Mo2C. The sequence of HER electrocatalytic activity is as follows: Ni-Mo2C > Co-Mo2C > Fe-Mo2C > Cr-Mo2C. As a result, Ni-Mo2C@C possesses the best HER performance, which required an overpotential of 72 mV at a current density of 10 mA cm-2 and the Tafel slope is 65.8 mV dec-1. This work suggests a shortcut to reasonably investigate the effects of elemental doping on molybdenum carbides and explore new high-efficient and low-cost electrocatalysts for HER.

No abstract

The reasonable construction of heterojunction photocatalysts with clear nanostructures and a good interface contact especially the one-dimensional/two-dimensional (1D/2D) composite heterojunction with unique morphology is considered one of the most effective strategies for designing highly efficient photocatalysts. Herein, a series of the 1D β-keto-enamine-based covalent organic framework (COF)/2D g-C3N4 composite materials COF–CN (1:x; where 1:x represents the mass ratio of COF and g-C3N4, x = 2.5, 5, 10, 15, 20) is prepared through the in situ reaction of 2,4,6-triformylphloroglucinol (Tp) and benzidine (BD) in stripped g-C3N4 suspension. A series of characterizations, such as X-ray diffraction (XRD), Fourier transform infrared (FT-IR), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), have verified their 1D/2D heterojunction structure. With the introduction of 1D COF nanobelts, the absorption of the composite is largely extended to 560 nm. Photocatalytic experiments reveal that the composite COF/CN shows evidently superior photocatalytic performance than individual COF and g-C3N4. The optimized COF–CN (1:10) exhibits a H2 production rate of 12.8 mmol g–1·h–1 under visible-light (λ ≥ 420 nm) irradiation, which is about 62 and 284 times higher than those of COF and g-C3N4, respectively. The apparent quantum efficiency (AQE) of COF–CN (1:10) is about 15.09% under 500 nm light irradiation, which is one of the highest among previous COF- or g-C3N4-based materials. This work provides important strategies for designing and constructing high-efficiency heterojunction photocatalysts with multidimensional features.

Polymer brushes have emerged as one of the most important means of surface modification. We summarise efficient methods for the fabrication of polymer brushes. In addition, we highlight the topology and potential applications of polymer brushes.