Efficient solar vapor/steam generation is important for various applications ranging from power generation, cooling, desalination systems to compact and portable devices like drinking water purification and sterilization units. However, conventional solar steam generation techniques usually rely on costly and cumbersome optical concentration systems and have relatively low efficiency due to bulk heating of the entire liquid volume. Recently, by incorporating novel light harvesting receivers, a new class of solar steam generation systems has emerged with high vapor generation efficiency. They are categorized in two research streams: volumetric and floating solar receivers. In this paper, we review the basic principles of these solar receivers, the mechanism involving from light absorption to the vapor generation, and the associated challenges. We also highlight the two routes to produce high temperature steam using optical and thermal concentration. Finally, we propose a scalable approach to efficiently harvest solar energy using a semi-spectrally selective absorber with near-perfect visible light absorption and low thermal emittance. Our proposed approach represents a new development in thermally concentrated solar distillation systems, which is also cost-effective and easy to fabricate for rapid industrial deployment.
Cubic gauche polynitrogen (cgPN) has been very attractive because of its high energy density that is 3.5 times of the TNT energy. cgPN has been investigated theoretically in detail, but few experimental studies have been reported. In 2004, cgPN was first synthesized from nitrogen gas under extremely high temperature and high pressure conditions and the trace amount of cgPN in the high-pressure vessel decomposed once the pressure was released. Until recently, our group for the first time synthesized cgPN from an NaN 3 precursor under ambient conditions with radio-frequency plasma. Here, synthesis and stabilization of cgPN are systematically investigated both computationally and experimentally. The effects of several major factors are studied, and the possible key intermediate is explored. In addition to NaN 3 , a ZEZ N 8 precursor is also used. ZEZ N 8 was synthesized by the cyclic voltammetry method. EZE N 8 is found to be the potential intermediate for cgPN formation based on the Fourier transform infrared and Raman spectra and the fact that a higher yield of cgPN is obtained with the ZEZ N 8 precursor. Na + is shown to stabilize cgPN under ambient conditions; however, an excess of Na + has a negative effect on cgPN growth. The oxygen reduction reaction (ORR) was carried out using cgPN as the cathodic catalyst, and the result shows that it is very active for the ORR, which is comparable with a commercial Pt/carbon catalyst. Moreover, cgPN shows an excellent stability during the ORR. This work guides the rational synthesis and scaleup of cgPN and its practical applications for the ORR.
Polynitrogen (PN) deposited on multiwalled
carbon nanotubes was
synthesized by cyclic voltammetry with ultraviolet (UV) irradiation.
Compared to the sample formed without UV, a larger amount of N8
– was synthesized and was found to distribute
more uniformly on the MWNTs with 254 nm UV irradiation, indicating
that the production of more azide (N3)0 radicals
as the precursors for synthesis of N8
– by photoexcitation of azide (N3
–) ions
is a rate-limiting step for PN synthesis. An oxygen reduction reaction
kinetics study indicated a four-electron reaction pathway on N8
–, whereas a two-electron process occurs
on N3
–. Analysis by in situ shell-isolated
nanoparticle-enhanced Raman spectroscopy revealed that the side-on
and end-on O2 adsorption occurred at N8
– and N3
–, respectively,
confirming the electron transfer process. A full direct-methanol fuel
cell study shows that methanol crossover typically reduces the current
density of Pt/C by ∼40% but has very little effect on the performance
of the PN-MWNT catalyst after testing for 120 h. Moreover, the power
density from the PN-MWNT cathode is at least twice that from a Pt/C
cathode.
Polymeric nitrogen (PN) is a general family of materials containing all-nitrogen molecules or clusters. Although it is rare and challenging to synthesize PN materials, they are attracting increasing scientific attention...
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