RESUMO
High-power phosphor-converted white light-emitting diodes (hp-WLEDs) have been widely involved in modern society as outdoor lighting sources. In these devices, due to the Joule effect, the high applied currents cause high operation temperatures (>500 K). Under these conditions, most phosphors lose their emission, an effect known as thermal quenching (TQ). Here, we introduce a zero-dimensional (0D) metal halide, Rb3InCl6:xSb3+, as a suitable anti-TQ phosphor offering robust anti-TQ behavior up to 500 K. We ascribe this behavior of the metal halide to two factors: (1) a compensation process via thermally activated energy transfer from structural defects to emissive centers and (2) an intrinsic structural rigidity of the isolated octahedra in the 0D structure. The anti-TQ phosphor-based WLEDs can stably work at a current of 2000 mA. The low synthesis cost and nontoxic composition reported here can herald a new generation of anti-TQ phosphors for hp-WLED.
RESUMO
The development of efficient and highly durable materials for renewable energy conversion devices is crucial to the future of clean energy demand. Herein, cage-like quasihexagonal structured platinum nanodendrites decorated over the transition metal chalcogenide core (CoS2 )-N-doped graphene oxide (PtNDs@CoS2 -NrGO) through optimized shape engineering and structural control technology are fabricated. The prepared electrocatalyst of PtNDs@CoS2 -NrGO is effectively used as anodic catalyst for alcohol oxidation in direct liquid alcohol fuel cells. Notably, the prepared PtNDs@CoS2 -NrGO exhibits superior electrocatalytic performance toward alcohol oxidation with higher oxidation peak current densities of 491.31, 440.25, and 438.12 mA mgpt -1 for (methanol) C1, (ethylene glycol) C2, and (glycerol) C3 fuel electrolytes, respectively, as compared to state-of-the-art Pt-C in acidic medium. The electro-oxidation durability of PtNDs@CoS2 -NrGO is investigated through cyclic voltammetry and chronoamperometry tests, which demonstrate excellent stability of the electrocatalyst toward various alcohols. Furthermore, the surface and adsorption energies of PtNDs and CoS2 are calculated using density functional theory along with the detailed bonding analysis. Overall, the obtained results emphasize the advances in effective precious material utilization and fabricating techniques of active electrocatalysts for direct alcohol oxidation fuel cell applications.
RESUMO
The tug-of-war between the thermoelectric power factor and the figure-of-merit complicates thermoelectric material selection, particularly for mid-to-high temperature thermoelectric materials. Approaches to reduce lattice thermal conductivity while maintaining a high-power factor are crucial in thermoelectric applications. Using strain engineering, we comprehensively investigated the microscopic mechanisms influencing the lattice thermal conductivity in this study. Scandium nitride (ScN) was chosen for this purpose since it has recently been discovered to be a potential mid-to-high temperature thermoelectric material. Our precise DFT+U calculations showed the exact electronic direct and indirect band gaps in ScN, which was subsequently subjected to compressive and tensile volume strain (up to 2%) within the crystal structure. Relevant thermoelectric properties such as Seebeck coefficient and electrical conductivity were obtained from both strained and unstrained ScN, whilst incorporating three key scattering sources, namely, ionized impurity (IMP), acoustic deformation potential (ADP), and polar optical phonon (POP). Based on the calculated scattering rates, we found that a POP scattering source is the dominant scattering mechanism that has a significant impact on transport properties at high temperatures. Our study revealed that modifying this POP scattering mechanism through strain in ScN has a considerable impact on the variation of lattice thermal conductivity without much reduction in the thermoelectric power factor values. A detailed description was provided with a focus on understanding the effects of strain on the scattering rates and thermoelectric properties of ScN.
