Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Thermal characteristics of an air-cooled open-cathode proton exchange membrane fuel cell stack via numerical investigation

In light of stricter emissions regulations and depleting fossil fuel reserves, fuel cell vehicles (FCVs) are one of the leading alternatives for powering future vehicles. An open-cathode, air-cooled proton exchange membrane fuel cell (PEMFC) stack provides a relatively simple electric generation system for a vehicle in terms of system complexity and number of components. The temperature within a PEMFC stack is critical to its level of performance and the electrochemical efficiency. Previously created computational models to study and predict the stack temperature have been limited in their scale and the inaccurate assumption that temperature is uniform throughout. The present work details the creation of a numerical model to study the temperature distribution of an 80-cell Ballard 1020ACS stack by simulating the cooling airflow across the stack. Using computational fluid dynamics, a steady-state airflow simulation was performed using experimental data to form boundary conditions where possible. Additionally, a parametric study was performed to investigate the effect of the distance between the stack and cooling fan on stack performance. Model validation was performed against published results. The temperature distribution across the stack was identical for the central 70% of the cells, with eccentric temperatures observed at the stack extremities, while the difference between coolant and bipolar plate temperatures was approximately 10°C at the cooling channel outlets. The results of the parametric study showed that the fan-stack distance has a negligible effect on stack performance. The assumptions regarding stack temperature uniformity and measurement were challenged. Lastly, the hypothesis regarding the negligible effect of fan-stack distance on stack performance was confirmed.     

The role of microstructural evolution during spark plasma sintering on the soft magnetic and electronic properties of a CoFe–Al2O3 soft magnetic composite

Journal of Materials Science - For transformers and inductors to meet the world’s growing demand for electrical power, more efficient soft magnetic materials with high saturation magnetic...     

Color–concept associations: A cross‐occupational and ‐cultural study and comparison

This study used a questionnaire survey to examine color–concept associations in two occupational groups from Hebei Province in China: steel workers (n = 139) and managerial staff (n = 74). The color stereotypes held by these two groups were also compared to those held by three other cultural groups studied elsewhere (Hong Kong Chinese, Yunnan Chinese, and Americans). The participants were presented with 16 concepts and asked to choose one of 10 colors to represent each concept. The chi‐square test results showed that each concept was significantly associated with at least one color. Both the steel workers and the managerial staff primarily associated green with “go” and “safe” and red with “stop” and “danger.” The cross‐group comparisons indicated that the steel workers and the managerial staff produced stronger color associations than those produced by the Yunnan Chinese and the Hong Kong Chinese subjects, but weaker than those produced by the US subjects. Our findings build on existing knowledge of population stereotypes for color–concept associations and provide guidelines for the design of color displays and products for global users. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 630–635, 2014     

Energy and technology lessons since Rio

The 1992 Framework Convention on Climate Change created the basic international architecture for addressing climate change. That treaty was negotiated at a time when the research literature examining emissions mitigation and the role of energy technology was relatively limited. In the two subsequent decades a great deal has been learned. The problem of stabilizing the concentration of greenhouse gases in the atmosphere has proved far more difficult than envisioned in 1992 and the role of technology appears even more important when emissions mitigation strategies are co-developed in the context of multiple competing ends.     

Photodegradation of phenol using TiO<Subscript>2</Subscript>, ZnO and TiO<Subscript>2</Subscript>/ZnO catalysts in an annular reactor

In recent years the incorporation of ZnO as a semiconductor into other catalysts, for enhancing photodegradation processes, has gained attention. This paper describes the synthesis of a blend of metal oxide (TiO₂/ZnO) photocatalyst and subsequent testing of the catalyst for the degradation of phenol in an annular photoreactor. The concentration of phenol before and after degradation was determined using Ultra-Violet-Spectroscopy (UV-Vis). Calcined TiO₂/ZnO composite material with a mass loading ratio of 1: 1 exhibited the highest percentage phenol removal compared to the unblended TiO₂ and ZnO systems at pH 7.2 and temperature of 25°C. It was shown that about 98% phenol degradation could be achieved at initial phenol concentration of 10; 20 and 50 ppm, except for 100 ppm which gave less than 50% degradation. Thus, TiO₂/ZnO blend as photocatalyst can be used for degradation of phenol in water. The pseudo-first order reaction kinetics fitted well the Langmuir-Hinshelwood model in almost all concentration ranges tested.