RESUMEN
Improving solar energy collection in aquatic environments would allow for superior environmental monitoring and remote sensing, but the identification of optimal photovoltaic technologies for such applications is challenging as evaluation requires either field deployment or access to large water tanks. Here, we present a simple bench-top characterization technique that does not require direct access to water and therefore circumvents the need for field testing during initial trials of development. Employing LEDs to simulate underwater solar spectra at various depths, we compare Si and CdTe solar cells, two commercially available technologies, with GaInP cells, a technology with a wide bandgap close to ideal for underwater solar harvesting. We use this method to show that while Si cells outperform both CdTe and GaInP cells under terrestrial AM1.5G solar irradiance, CdTe and GaInP cells outperform Si cells at depths >2 m, with GaInP cells operating with underwater efficiencies approaching 54%.
RESUMEN
Combining isolated atomic active sites with those in nanoparticles for synergizing complex multistep catalysis is being actively pursued in the design of new electrocatalyst systems. However, these novel systems have been rarely studied due to the challenges with synthesis and analysis. Herein, a synergistically catalytic performance is demonstrated with a 0.89 V (vs reversible hydrogen electrode) onset potential in the four-step oxygen reduction reaction (ORR) by localizing tungsten single atoms around tungsten nitride nanoparticles confined into nitrogen-doped carbon (W SAs/WNNC). Through density functional theory calculations, it is shown that each of the active centers in the synergistic entity feature a specific potential-determining step in their respective reaction pathway that can be merged to optimize the intermediate steps involving scaling relations on individual active centers. Impressively, the W SAs/WNNC as the air cathode in all-solid-state Zn-air and Al-air batteries demonstrate competitive durability and reversibility, despite the acknowledged low activity of W-based catalyst toward the ORR.
RESUMEN
Layer-by-layer (LbL) assembly is a nanoscale technique with great versatility, simplicity and molecular-level processing of various nanoscopic materials. Weak polyelectrolytes have been used as major building blocks for LbL assembly providing a fundamental and versatile tool to study the underlying mechanisms and practical applications of LbL assembly due to its pH-responsive charge density and molecular conformation. Because of high-density uncompensated charges and high-chain mobility, weak polyelectrolyte exponential multilayer growth is considered one of the fastest developing areas for organized molecular films. In this article, we systematically review the current status and developments of weak polyelectrolyte-based multilayers including all-weak-polyelectrolyte multilayers, weak polyelectrolytes/other components (e.g. strong polyelectrolytes, neutral polymers, and nanoparticles) multilayers, and exponentially grown weak polyelectrolyte multilayers. Several key aspects of weak polyelectrolytes are highlighted including the pH-controllable properties, the responsiveness to environmental pH, and synergetic functions obtained from weak polyelectrolyte/other component multilayers. Throughout this review, useful applications of weak polyelectrolyte-based multilayers in drug delivery, tunable biointerfaces, nanoreactors for synthesis of nanostructures, solid state electrolytes, membrane separation, and sensors are highlighted, and promising future directions in the area of weak polyelectrolyte-based multilayer assembly such as fabrication of multi-responsive materials, adoption of unique building blocks, investigation of internal molecular-level structure and mechanism of exponentially grown multilayers, and exploration of novel biomedical and energy applications are proposed.
RESUMEN
Polymer nanocomposites offer the opportunity to bridge properties of nanomaterials to the macroscale. In this work, layer-by-layer (LbL) assembly is used to demonstrate nanocomposites of 2D titanium carbide nanosheets (MXene) and clay nanoplatelets (montmorillonite) to fabricate freestanding thin films with unique multifunctional properties. These thin films can be tuned by adjusting the thickness to exhibit a tensile strength of 138 MPa-225 MPa, EMI specific shielding effectiveness normalized to thickness and density up to 24 550 dB cm2 g-1, and sheet resistance from 855 Ω sq-1-3.27 kΩ sq-1 (corresponding to a range of conductivity from 53 S m-1 to 125 S m-1). This composite is the strongest MXene-based LbL film prepared to date, in part due to the nacre-like brick-and-mortar structure. Ultra-strong, multifunctional films of this nature are desirable for many applications ranging from membranes, to structural and multifunctional composites, energy harvesting and storage, and materials for aerospace.
RESUMEN
2D graphitic carbon nitride (g-C3 N4 ) nanosheets are a promising negative electrode candidate for sodium-ion batteries (NIBs) owing to its easy scalability, low cost, chemical stability, and potentially high rate capability. However, intrinsic g-C3 N4 exhibits poor electronic conductivity, low reversible Na-storage capacity, and insufficient cyclability. DFT calculations suggest that this could be due to a large Na+ ion diffusion barrier in the innate g-C3 N4 nanosheet. A facile one-pot heating of a mixture of low-cost urea and asphalt is strategically applied to yield stacked multilayer C/g-C3 N4 composites with improved Na-storage capacity (about 2 times higher than that of g-C3 N4 , up to 254â mAh g-1 ), rate capability, and cyclability. A C/g-C3 N4 sodium-ion full cell (in which sodium rhodizonate dibasic is used as the positive electrode) demonstrates high Coulombic efficiency (ca. 99.8 %) and a negligible capacity fading over 14 000 cycles at 1 A g-1 .