RESUMEN

Electrocatalysis plays a critical role in future technologies for energy storage and sustainable synthesis, but the scope of reactions achievable using electricity remains limited. Here, we demonstrate an electrocatalytic approach to cleave the C(sp3)-C(sp3) bond in ethane at room temperature over a nanoporous Pt catalyst. This reaction is enabled by time-dependent electrode potential sequences, combined with monolayer-sensitive in situ analysis, which allows us to gain independent control over ethane adsorption, oxidative C-C bond fragmentation, and reductive methane desorption. Importantly, our approach allows us to vary the electrode potential to promote the fragmentation of ethane after it is bound to the catalyst surface, resulting in unprecedented control over the selectivity of this alkane transformation reaction. Steering the transformation of intermediates after adsorption constitutes an underexplored lever of control in catalysis. As such, our findings widen the parameter space for catalytic reaction engineering and open the door to future sustainable synthesis and electrocatalytic energy storage technologies.

RESUMEN

Nanopore blockade sensors were developed to address the challenges of sensitivity and selectivity for conventional nanopore sensors. To date, the parameters affecting the current of the sensor have not been elucidated. Herein, the impacts of nanopore size and charge and the shape, size, surface charge, and aggregation state of magnetic nanoparticles were assessed. The sensor was tolerant to all parameters contrary to predictions from electronic or geometric arguments on the current change. Theoretical models showed the greater importance of the polymers around nanoparticles and the access resistance of nanopores to the current, when compared with translocation-based nanopore sensors. The signal magnitude was dominated by the change in access resistance of ∼4.25 MΩ for all parameters, resulting in a robust system. The findings provide understandings of changes in current when nanopores are blocked, like in RNA trapping or nanopore blockade sensors, and are important for designing sensors based on nanopore blockades.

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RESUMEN

Controlling which facets are exposed in nanocrystals is crucial to understanding different activity between ordered and disordered alloy electrocatalysts. We modify the degree of ordering of Pt3Sn nanocubes, while maintaining the shape and size, to enable a direct evaluation of the effect of the order on ORR catalytic activity. We demonstrate a 2.3-fold enhancement in specific activity by 60- and 30%-ordered Pt3Sn nanocubes compared to 95%-ordered. This was shown to be likely due to surface vacancies in the less-ordered particles. The greater order, however, results in higher stability of the electrocatalyst, with the more disordered nanoparticles showing the dissolution of tin and platinum species during electrocatalysis.

RESUMEN

Recent studies on the electrical conductivity and photocatalytic activity properties of semiconductor nanocrystals such as Cu2O, Ag2O, TiO2, PbS, and Ag3PO4 exposing well-defined surfaces have revealed strong facet effects. For example, the electrical conductivity of Cu2O crystals can vary from highly conductive to nonconductive, and they can be highly photocatalytically active or inactive depending on the exposed faces. The crystal surfaces can even tune their light absorption wavelengths. Our understanding is that the emergence of these unusual phenomena can be explained in terms of the presence of an ultrathin surface layer having different band structures and degrees of band bending for different surfaces, which affects charge transport and photons into and out of the crystals. This review uses primarily results from our research on this frontier area of semiconductor properties to illustrate the existence of semiconductor facet effects. A simple adjustment to normal semiconductor band diagram allows good understanding of the observed phenomena. Recognizing that facet-dependent behaviors are intrinsic semiconductor properties, we should pay attention to their influence in the explanation of the measured photocatalytic properties, and consider ways to enhance photocatalytic efficiency or design electrical components utilizing the facet effects. There should be many opportunities to advance applications of semiconductor nanocrystals and nanostructures with continued research on the facet-dependent properties of various semiconductor materials.

RESUMEN

A one-pot synthesis for the growth of PbS nanocubes and octahedra has been developed by heating an aqueous mixture of cetyltrimethylammonium bromide (CTAB), thioacetamide (TAA), lead acetate, and nitric acid at 90 °C for 3 h. The method allows for direct large-scale production of small and uniform PbS nanocubes. The PbS cubes and octahedra exhibit different surface properties, as evidenced by zeta potential measurements and stability tests in methyl orange and methylene blue solutions. Examination of the reagent introduction sequence indicates that early or late addition of nitric acid to tune the initial solution pH can strongly influence crystal growth rate and result in the formation of PbS crystals with different sizes and shapes. Remarkably, the use of pre-formed PbS nanocubes for further crystal growth under low TAA concentration can transform the cubes into large octahedra through a series of particle shape evolution.