Electrocatalyst of RuO2 decorating TiO2 nanowire arrays for acidic oxygen evolution

Oxygen evolution reaction (OER) at the anode limits the efficiency of hydrogen production from water electrolysis substantially. A novel electrocatalyst of RuO₂ decorating TiO₂ nanowire arrays for OER was successfully prepared using a cyclic voltammetric method with electrodeposition of RuO₂ nanoparticles on the TiO₂ nanowire (TNW) arrays synthesized hydrothermally. Even though the electrodes with the composite electrocatalyst have a lower loading of RuO₂, they have higher electrocatalytic activity and stability for acidic oxygen evolution than the Ti/RuO₂ electrode prepared by conventional thermal decomposition method. The core-shell structure of the TNW@RuO₂ electrocatalyst not only increases the specific surface area of the electrodes, but also inhibits the adverse effect of the poor conductivity of TiO₂. This novel OER electrocatalyst can improve the efficiency and reduce the cost of hydrogen production from electrolytic water splitting.     

Enhanced thermometry sensitivity in upconversion nanoparticles via near-field manipulation

Recently, nanoscale thermometry has attracted extensive attention. Here, we present an innovative approach to enhance the sensitivity of upconversion nanoparticles for thermometry through near-field manipulation. This method involves a composite structure consisting of photonic crystals and upconversion nanoparticles, with the near-field of the nanoparticles manipulated by tuning the absorption of the photonic crystals. The fluorescence intensity ratio (540nm/520 nm) of ⁴H_11/2 and⁴S_3/2 states of upconversion nanoparticles doped with Er³⁺ ions is sensitive to temperature change and employed as a temperature indicator that satisfies Boltzmann thermal equilibrium. The composite structure exhibited a relative thermometry sensitivity of 21.9 × 10⁻³ K⁻¹ at 298 K, representing a significant improvement over pure core-shell upconversion nanoparticles with a 63.43% increase in relative sensitivity and a 675% increase in absolute sensitivity. This finding demonstrates the potential of our approach for advancing nanoscale thermometry.     

Nucleation and growth of SiC at the interface between molten Si and graphite

In the present work, the evolution of the SiC layer formed at the interface between liquid silicon and solid carbon is studied using a diffusion couple configuration. Reaction conditions were isothermal, with a temperature of 1450 °C maintained from 2 min to 4 h. The rapid heating and cooling of the Si–C diffusion couple specimens were achieved using a Pulse-Electric Current Sintering system. Crystallographic, compositional, and phase distribution data obtained after different reaction times were used to develop a two-stage model for SiC growth at the interface between molten Si and C. Initially, the formation of SiC at the interface is governed by diffusion of C into the molten Si and dissolution/reprecipitation of formed SiC nuclei. These nuclei further grow into larger SiC grains at the Si–C interface and this initial stage is successfully modeled using the Johnson-Mehl-Avrami-Kolmogorov model. Once a continuous SiC layer forms at the Si–C interface, the growth of SiC is controlled by the diffusion of C through the SiC layer, which can be modeled using a power rate law. However, the nature of this diffusion is difficult to determine with certainty since the rate laws for both grain boundary and bulk diffusion fit experimental data equally well.     

Improving small unmanned aerial vehicle flight endurance with cryo-compressed hydrogen vessels

Detailed analysis indicates that substantial increases (22–43%) in flight endurance of small unmanned aerial vehicles (UAVs) powered by liquid hydrogen (LH₂) are possible by increasing the maximum allowable pressure of the cryogenic storage vessel beyond the critical point to contain evaporated hydrogen (H₂) and mitigate vent losses to the environment. Taking an existing UAV (US Naval Research Laboratory's “Ion Tiger”) as a baseline, we consider the effect of increasing Dewar maximum allowable pressure on flight endurance, under two different scenarios. In Case 1, the weight of the H₂ storage system (including H₂) is kept equal to the baseline design to maintain flight conditions unchanged. In Case 2, the external volume of the Dewar is kept equal to the baseline design, and the weight of the Dewar (and UAV) increases when the maximum allowable pressure increases, with the result that the propulsion power for the heavier UAV increases.The results are favorable. Although the modified Dewars have smaller inner volume (Case 1) or greater weight (Case 2) than the original Ion Tiger, flight endurance increases by 22% (Case 1) and 43% (Case 2), because the large H₂ vent losses (39%) of the original design are reduced to only 1.6% (Case 1) and 1% (Case 2). The much higher utilization efficiency of the H₂ stored in these modified Dewars compensates for their volume and weight disadvantages, resulting in UAVs with superior endurance.     

Nucleation and growth of L12-Al3RE particles in aluminum alloys:A first-principles study

The internal mechanisms of nucleation and growth of L1₂-AI₃RE(RE=Sc,Y,La-Lu) second phases in Al alloys were investigated by combining first-principles calculations with quasi-harmonic approximation(QHA).The calculated results show that the diffusion rate D_s and chemical potential AG_V increase with the increase of temperature.With the increase of atomic number,the D_s and the strain energy ΔE_CSincrease firstly from Sc to La,and the...     

Highly active and robust biomimetic ceramic catalyst for oxygen reduction reaction: Inspired by plant leaves

Structural instability under working conditions is critical issue that restricts applications of perovskite O₂ catalysts in the field of solid oxide fuel cells. Inspired by plant leaves, a biomimetic ceramic catalyst with PrBaCo₂O_5+δ ‘mesophyll’ and Gd_0.1Ce_0.9O_1.95 ‘epidermis’ and ‘vein’ was successfully engineered in this work. The ‘epidermis’ reduces the polarization resistance of O₂ reduction reaction on catalyst surface by ∼24%, and the ‘vein’ reduces resistance of O²⁻ transport through cathode layer by ∼65%. Moreover, this biomimetic catalyst increases output power density of the cell by 79% and reverses rapid decay trend of the cell with a 23% increase in power density during first 20 h followed by stabilization at 0.91 W cm⁻² (at 750 °C and 0.7 V). This discovery provides new avenue for the development of high-performance O₂ catalysts with practical applications and enriches the scientific understanding of catalysis.     

Tuning structure and magnetic properties of table-like magnetocaloric effect in Er6MnSb2 by zirconium substitution

In this study,zirconium(Zr) successfully substituted for erbium(Er) in Er_6-xZr_xMnSb₂(x=0,0.5,1,1.5) of the Fe₂P type,with comprehensive characterizations on crystal structure,electronic structure and magnetic properties.According to synchrotron powder X-ray diffraction data analysis and density functional theory calculation,Zr does not randomly but preferentially occupy during the doping process and results in weaker magnetic exchange interactions and ...