Localized surface plasmon absorption features arise at high doping levels in semiconductor nanocrystals, appearing in the near-infrared range. Here we show that the surface plasmons of tin-doped indium oxide nanocrystal films can be dynamically and reversibly tuned by postsynthetic electrochemical modulation of the electron concentration. Without ion intercalation and the associated material degradation, we induce a > 1200 nm shift in the plasmon wavelength and a factor of nearly three change in the carrier density.
Plasmonic nanocrystals have been attracting a lot of attention both for fundamental studies and different applications, from sensing to imaging and optoelectronic devices. Transparent conductive oxides represent an interesting class of plasmonic materials in addition to metals and vacancy-doped semiconductor quantum dots. Herein, we report a rational synthetic strategy of high-quality colloidal aluminum-doped zinc oxide nanocrystals. The presence of substitutional aluminum in the zinc oxide lattice accompanied by the generation of free electrons is proved for the first time by tunable surface plasmon absorption in the infrared region both in solution and in thin films.
Favoring the CO2 reduction reaction (CO2RR) over the hydrogen evolution reaction and controlling the selectivity towards multicarbon products are currently major scientific challenges in sustainable energy research. It is known that the morphology of the catalyst can modulate catalytic activity and selectivity, yet this remains a relatively underexplored area in electrochemical CO2 reduction. Here, we exploit the material tunability afforded by colloidal chemistry to establish unambiguous structure/property relations between Cu nanocrystals and their behavior as electrocatalysts for CO2 reduction. Our study reveals a non-monotonic size-dependence of the selectivity in cube-shaped copper nanocrystals. Among 24 nm, 44 nm and 63 nm cubes tested, the cubes with 44 nm edge length exhibited the highest selectivity towards CO2RR (80 %) and faradaic efficiency for ethylene (41 %). Statistical analysis of the surface atom density suggests the key role played by edge sites in CO2RR.
In catalysis science stability is as crucial as activity and selectivity. Understanding the degradation pathways occurring during operation and developing mitigation strategies will eventually improve catalyst design, thus facilitating the translation of basic science to technological applications. Herein, we reveal the unique and general degradation mechanism of metallic nanocatalysts during electrochemical CO2 reduction, exemplified by different sized copper nanocubes. We follow their morphological evolution during operation and correlate it with the electrocatalytic performance. In contrast with the most common coalescence and dissolution/precipitation mechanisms, we find a potential-driven nanoclustering to be the predominant degradation pathway. Grand-potential density functional theory calculations confirm the role of the negative potential applied to reduce CO2 as the main driving force for the clustering. This study offers a novel outlook on future investigations of stability and degradation reaction mechanisms of nanocatalysts in electrochemical CO2 reduction and, more generally, in electroreduction reactions.
Synthetic
control over inorganic nanocrystals has made dramatic
strides so that a great number of binary and a few ternary or more
complex compounds can now be prepared with good control over size
and physical properties. Recently, chemists have tackled the long-standing
challenge of introducing dopant atoms into nanocrystals, and strategies
that apply across diverse compositions are beginning to emerge. In
this review, we first briefly summarize the array of characterization
methods used to assess doping efficacy for reference throughout the
discussion. We then enumerate chemical strategies for doping with
illustrative examples from the literature. A key concept is that the
reactions leading to growth of the host crystal and to deposition
of dopant ions must be balanced to succeed in incorporating dopants
during crystal growth. This challenge has been met through various
chemical strategies, and new methods, such as postsynthetic diffusion
of dopant ions, continue to be developed. The opportunity to deliver
new functionality by doping nanocrystals is great, particularly as
characterization methods and synthetic control over introduction of
multiple dopants advance.
Despite substantial progress in the electrochemical conversion of CO 2 into value-added chemicals, the translation of fundamental studies into commercially relevant conditions requires additional efforts. Here, we study the catalytic properties of tailored Cu nanocatalysts under commercially relevant current densities in a gas-fed flow cell. We demonstrate that their facet-dependent selectivity is retained in this device configuration with the advantage of further suppressing hydrogen production and increasing the faradaic efficiencies toward the CO 2 reduction products compared to a conventional H-cell. The combined catalyst and system effects result in stateof-the art product selectivity at high current densities (in the range 100−300 mA/cm 2 ) and at relatively low applied potential (as low as −0.65 V vs RHE). Cu cubes reach an ethylene selectivity of up to 57% with a corresponding mass activity of 700 mA/mg, and Cu octahedra reach a methane selectivity of up to 51% with a corresponding mass activity of 1.45 A/mg in 1 M KOH.
Understanding
the structural and compositional sensitivities of
the electrochemical CO2 reduction reaction (CO2RR) is fundamentally important for developing highly efficient and
selective electrocatalysts. Here, we use Ag/Cu nanocrystals to uncover
the key role played by the Ag/Cu interface in promoting CO2RR. Nanodimers including the two constituent metals as segregated
domains sharing a tunable interface are obtained by developing a seeded
growth synthesis, wherein preformed Ag nanoparticles are used as nucleation
seeds for the Cu domain. We find that the type of metal precursor
and the strength of the reducing agent play a key role in achieving
the desired chemical and structural control. We show that tandem catalysis
and electronic effects, both enabled by the addition of Ag to Cu in
the form of segregated nanodomain within the same catalyst, synergistically
account for an enhancement in the Faradaic efficiency for C2H4 by 3.4-fold and in the partial current density for
CO2 reduction by 2-fold compared with the pure Cu counterpart.
The insights gained from this work may be beneficial for designing
efficient multicomponent catalysts for electrochemical CO2 reduction.
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