A solution-based process was investigated for synthesizing cubic Li7La3Zr2O12 (LLZO), which is known to exhibit the unprecedented combination of fast ionic conductivity, and stability in air and against Li. Sol-gel chemistry was developed to prepare solid metal-oxide networks consisting of 10 nm cross-links that formed the cubic LLZO phase at 600 ° C. Sol-gel LLZO powders were sintered into 96% dense pellets using an induction hot press that applied pressure while heating. After sintering, the average LLZO grain size was 260 nm, which is 13 times smaller compared to LLZO prepared using a solid-state technique. The total ionic conductivity was 0.4 mS cm(-1) at 298 K, which is the same as solid-state synthesized LLZO. Interestingly, despite the same room temperature conductivity, the sol-gel LLZO total activation energy is 0.41 eV, which 1.6 times higher than that observed in solid-state LLZO (0.26 eV). We believe the nano-scale grain boundaries give rise to unique transport phenomena that are more sensitive to temperature when compared to the conventional solid-state LLZO.
Dry
reforming of methane (DRM) is an attractive route to simultaneously
consume both methane (CH4) and carbon dioxide (CO2) for the production of valuable syngas. Although nickel catalysts
are considered to be the most promising in both cost and activity,
catalysts having high stability with low coke formation are highly
coveted for commercialization. Here, we report a one-pot synthesis
for mesoporous supported nickel catalysts with high activity and stability
in a DRM reaction by using a spray pyrolysis-assisted evaporation-induced
self-assembly (EISA) method. Two different strategies were introduced
to prepare the catalysts of mesoporous alumina supports with highly
dispersed active nickel sites from one pot of precursor solutions.
One is phase segregation of nickel from alumina supports already in
the self-assembly step by using a hydrophobic nickel oleate precursor,
a hydrophilic alumina precursor, and an amphipathic triblock copolymer,
which was achievable owing to the unique characteristics of spray
pyrolysis, especially its fast drying-pyrolysis-mediated kinetic quenching,
which was used to form catalysts with highly dispersed active sites
of nickel (3 nm). The other strategy is exsolution, entailing the
release and anchoring of nickel from the bulk to the surface of the
alumina phase in the reduction step while using a hydrophilic nickel
precursor. Compared with nickel catalysts prepared by conventional
wet impregnation, the one-pot catalysts, especially the nickel oleate-based
catalyst, showed high coke resistance, maintaining conversion for
30 h with 92% CH4 conversion and 97% CO2 conversion,
which originated from the smaller well-dispersed nickel particles,
the strong metal–support interaction, and the suppressed particle
agglomeration. We envisage the development, by the one-pot processing
of multicomponent precursor solutions, of heterogeneous supported
catalysts with superior performances for a wider range of applications.
The inert annealing step during the synthesis of the Ni/MgAl2O4 catalyst induces positive changes in the catalyst substructure. The obtained catalyst displayed high catalytic activity towards steam methane reforming with low carbon deposition.
Highly efficient photothermal layers were developed based on a commercially available low-cost material, activated carbon, which demonstrates the potential for practical desalination application with upscalability.
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