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.
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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