In this article,
the effect of a porous material’s flexibility
on the dynamic reversibility of a nonwetting liquid intrusion was
explored experimentally. For this purpose, high-pressure water intrusion
together with high-pressure in situ small-angle neutron scattering
were applied for superhydrophobic grafted silica and two metal–organic
frameworks (MOFs) with different flexibility [ZIF-8 and Cu2(tebpz) (tebpz = 3,3′,5,5′tetraethyl-4,4′-bipyrazolate)].
These results established the relation between the pressurization
rate, water intrusion–extrusion hysteresis, and porous materials’
flexibility. It was demonstrated that the dynamic hysteresis of water
intrusion into superhydrophobic nanopores can be controlled by the
flexibility of a porous material. This opens a new area of applications
for flexible MOFs, namely, a smart pressure-transmitting fluid, capable
of dissipating undesired vibrations depending on their frequency.
Finally, nanotriboelectric experiments were conducted and the results
showed that a porous material’s topology is important for electricity
generation while not affecting the dynamic hysteresis at any speed.
Heat-storage
technologies are well suited to improve the energy
efficiency of power plants and the recovery of process heat. A good
option for high storage capacities, especially at high temperatures,
is storing thermal energy by reversible thermochemical reactions.
In particular, the Co3O4/CoO and Mn2O3/Mn3O4 redox-active couples are
known to be very promising systems. However, cost and toxicity issues
for Co oxides and the sluggish oxidation rate (leading to poor reversibility)
for Mn oxide hinder the applicability of these single oxides. Considering,
instead, binary Co–Mn oxide mixtures could mitigate the above-mentioned
shortcomings. To examine this in detail, here, we combine first-principles
atomistic calculations and experiments to provide a structural characterization
and observe the thermal behavior of novel mixed-metal oxides based
on cobalt/manganese metals with the spinel structure Co3–x
Mn
x
O4. We
show that novel Co3–x
Mn
x
O4 phases indeed enhance the enthalpy
of the redox reactions, facilitate reversibility, and mitigate energy
losses when compared to pure metal oxide systems. Our results expand
therefore the limited list of currently available thermochemical heat-storage
materials and pave the way toward the implementation of tunable redox
temperature materials for practical applications.
On-demand access
to renewable and environmentally friendly energy
sources is critical to address current and future energy needs. To
achieve this, the development of new mechanisms of efficient thermal
energy storage (TES) is important to improve the overall energy storage
capacity. Demonstrated here is the ideal concept that the thermal
effect of developing a solid–liquid interface between a non-wetting
liquid and hydrophobic nanoporous material can store heat to supplement
current TES technologies. The fundamental macroscopic property of
a liquid’s surface entropy and its relationship to its solid
surface are one of the keys to predict the magnitude of the thermal
effect by the development of the liquid–solid interface in
a nanoscale environment—driven through applied pressure. Demonstrated
here is this correlation of these properties with the direct measurement
of the thermal effect of non-wetting liquids intruding into hydrophobic
nanoporous materials. It is shown that the model can resonably predict
the heat of intrusion into rigid mesoporous silica and some microporous
zeolite when the temperature dependence of the contact angle is applied.
Conversely, intrusion into flexible microporous metal–organic
frameworks requires further improvement. The reported results with
further development have the potential to lead to the development
of a new supplementary method and mechanim for TES.
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