It is of great significance to develop creative proton exchange membrane materials for proton exchange membrane fuel cells (PEMFCs). The strategy of doping metal–organic frameworks (MOFs) with guest molecules into the Nafion matrix is adopted to improve the electrochemical performance of Nafion hybrid membranes. Various and abundant hydrogen bonds can make a tremendous contribution to the proton conduction of hybrid membranes. In this work, we used high proton-conducting Zn-MOFs with the characteristics of host–guest collaborative hydrogen bonds as the filler to prepare Zn-MOF/Nafion hybrid membranes. Alternating current (AC) impedance tests show that when the doping amount of Zn-MOF is 5%, the proton conductivity reaches 7.29 × 10–3 S·cm–1, being 1.87 times that of the pure Nafion membrane at 58% relative humidity (RH) and 80 °C. In an attempt to prove the promotion effect of guest NH3 on proton conductivity of Nafion hybrid membranes, Zn-MOF-NH3 was filled into the Nafion matrix. Under the same conditions, its proton conductivity reaches the maximum value of 2.13 × 10–2 S·cm–1, which is 5.47 times that of the pure Nafion membrane. Zn-MOF-NH3/Nafion-5 was used to fabricate a proton exchange membrane for application in H2/O2 fuel cells. The maximum power density of 212 mW cm–2 and a current density of 630 mA cm–2 reveal a respectable single cell performance. This study provides a promising method for optimizing the structure of MOF proton conductors and inspires the preparation of high-performance Nafion hybrid membranes.

Photoinduced electron/energy transfer–reversible addition–fragmentation chain transfer (PET–RAFT) polymerization represents a versatile and highly efficient method for polymerizations of wide-ranging monomer variances upon solar energy harvesting. Although significant progress has been achieved, several drawbacks are still associated with existing photocatalysts, such as toxicity of transition metals, high cost, poor stability, and unavoidable purification procedures because of the photobleaching effect, to name a few. Herein, 1,4-diethynylbenzene-linked xanthene dye-conjugated porous polymers (CPPs) have been established as potential heterogenous photocatalysts of PET–RAFT polymerization. With this two-dimensional planar architecture, we demonstrate dual-stimuli toggling of RAFT polymerization using two different external physical manipulations: light “ON”/“OFF” and solution pH “LOW”/“HIGH”. In addition, these CPPs endowed radical polymerizations with various impressive features such as compatibility of diverse monomer formulations, unique oxygen tolerance, and ppm-level catalyst dosage. Demonstrations of chain extension and catalyst recycling further highlight the robustness and performance of this CPP catalyst. Through the study of structure–property relationship using the experimental analyses, we envisage that a series of xanthene dye-functionalized CPPs can be developed as visible light-absorbing organocatalysts rivaling transition-metal photocatalysts.

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In this paper, a series of organic compounds (L1–L6) with a D-π-A conjugation system were prepared. The investigations of third-order nonlinear optical (NLO) properties indicate that L1–L6 show different degrees of third-order NLO responses. It is surprising that introducing metal ions can effectively regulate their third-order NLO properties and even change the type of nonlinear absorption signal from reverse saturable absorption to saturable absorption, which can be attributed to the formation of coordination bonds between metal ions and L1–L6. It has aroused our tremendous interests in regulating third-order NLO performance. The regulation mechanisms were also discussed through the pump–probe measurements and the density functional theory. The enhancement of electron transfer efficiency is considered to be the key to improving NLO performance. Furthermore, we also obtained two coordination complexes [Cu­(L1)2­(NO3)2] (1) and [Cd­(L1)2­I2] (2) based on L1, which further proved the coordination between metal ions and L1–L6. Ligand-to-metal or metal-to-ligand charge transfer makes more electronic delocalization, leading to better third-order NLO properties. This work provides new ideas and explorations for the excogitation of third-order NLO materials.

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