The ability to achieve an understanding of the correlations between chemical synthesis, doping mechanism and properties of aluminium-doped zinc oxide (ZnO:Al) nanocrystals is of great importance to evaluate the potential of ZnO:Al nanocrystals as optimal building blocks for solution deposited
A combined experimental and first-principles study is performed to study the origin of conductivity in ZnO:Al nanoparticles synthesized under controlled conditions via a reflux route using benzylamine as a solvent. The experimental characterization of the samples by Raman, nuclear magnetic resonance (NMR) and conductivity measurements indicates that upon annealing in nitrogen, the Al atoms at interstitial positions migrate to the substitutional positions, creating at the same time Zn interstitials. We provide evidence for the fact that the formed complex of Al and Zn corresponds to the origin of the Knight shifted peak (KS) we observe in Al NMR. As far as we know, the role of this complex has not been discussed in the literature to date. However, our first-principles calculations show that such a complex is indeed energetically favoured over the isolated Al interstitial positions. In our calculations we also address the charge state of the Al interstitials. Further, Zn interstitials can migrate from Al and possibly also form Zn clusters, leading to the observed increased conductivity.
Methane, which has a high energy
storage density and is safely
stored and transported in our existing infrastructure, can be produced
through conversion of the undesired energy carrier H
2
with
CO
2
. Methane production with standard transition-metal
catalysts requires high-temperature activation (300–500 °C).
Alternatively, semiconductor metal oxide photocatalysts can be used,
but they require high-intensity UV light. Here, we report a Ru metal
catalyst that facilitates methanation below 250 °C using sunlight
as an energy source. Although at low solar intensity (1 sun) the activity
of the Ru catalyst is mainly attributed to thermal effects, we identified
a large nonthermal contribution at slightly elevated intensities (5.7
and 8.5 sun) resulting in a high photon-to-methane efficiency of up
to 55% over the whole solar spectrum. We attribute the excellent sunlight-harvesting
ability of the catalyst and the high photon-to-methane efficiency
to its UV–vis–NIR plasmonic absorption. Our highly efficient
conversion of H
2
to methane is a promising technology to
simultaneously accelerate the energy transition and reduce CO
2
emissions.
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