Theoretical and Experimental Aspects of Electrocatalysts for Oxygen Evolution Reaction.

Scientists are increasingly paying attention to using theoretical design as a guide combined with modern in-situ characterization techniques to develop catalysts with high activity, low cost, and long-term life. The review discusses the progress of catalyst theoretical design and corresponding experiments based on three typical oxygen evolution catalytic mechanisms, including the adsorbate evolution, lattice oxygen-mediated, and unconventional bifunctional mechanisms. This work briefly describes the commonly used tools and descriptors in theory as well as the electrochemical techniques and characterizations in experiments. Our purpose is to sort out the ways to closely integrate the theoretical method and experimental verification from the perspective of reaction mechanism, and to provide some experience reference for the future development of theoretical tools and experimental technologies.

Hierarchical nanosheet-based Ni3S2 microspheres grown on Ni foam for high-performance all-solid-state asymmetric supercapacitors.

The hierarchical nanosheet-based Ni3S2 microspheres directly grew on Ni foam using a two-step hydrothermal method. The microsphere with a diameter of ∼1 microns and a rough surface was well connected to each other without any binders to provide a larger specific surface area, shorter ion/electron diffusion paths, richer electroactive sites as a supercapacitor electrode. As a three-electrode supercapacitor, it delivers a high specific capacity of 981.8 F g-1 at 2 A g-1, an excellent rate capability of 436.4 F g-1 at 12 A g-1, and a good cycling stability of 950.9 F g-1 with 96.9% retention after 1000 cycles at 2 A g-1. Furthermore, an asymmetric supercapacitor based on Ni3S2-microsphere as a positive electrode and active carbon as a negative electrode shows a high energy density of 29.4 Wh kg-1 at 324.5 W kg-1 and a high power density of 3197.6 W kg-1 at 15.1 Wh kg-1. This work demonstrates that nanosheet-based Ni3S2 microspheres coated Ni foam can be an effective electrode for a real supercapacitor.

One-Step Solvothermal Synthesis of Black TiO2 Films for Enhanced Visible Absorption.

An economic and facile solvothermal method was reported to prepare black TiO2 films on Ti foils that possessed the property of optical absorption in the visible region. The UV-vis spectra showed that the black TiO2 samples exhibited highly enhanced visible-light absorption from 400-600 nm. The black TiO2 films were compact and uniform, composed of nanoparticles and nanosheets. Moreover, a mixed structure of anatase and rutile was present in black TiO2 films. The electron paramagnetic resonance (EPR) spectra confirmed the presence of Ti3+ in samples, which accounted for longer wavelength optical absorption. The results showed that the TiO2 films had retained their black color upon storage in ambient atmosphere for more than one month. Therefore, it was supposed that the ethylene glycol in solvothermal reaction was the key factor for the extension of the absorption spectrum.

Anti-icing potential of superhydrophobic Ti6Al4V surfaces: ice nucleation and growth.

On the basis of the icing-delay performance and ice adhesion strength, the anti-icing potential of the superhydrophobic surface has been well-investigated in the past few years. The present work mainly emphasized the investigations of ice nucleation and growth to fully explore the anti-icing potential of the superhydrophobic surface. We took the various surfaces ranging from hydrophilic to superhydrophobic as the research objects and, combining the classical nucleation theory, discussed the ice nucleation behaviors of the water droplets on these sample surfaces under the condition of supercooling. Meanwhile, the macroscopical growth processes of ice on these surfaces were analyzed on the basis of the growth mechanism of the ice nucleus. It was found that the superhydrophobic surface could greatly reduce the solid-liquid interface nucleation rate, owing to the extremely low actual solid-liquid contact area caused by the composite micro-nanoscale hierarchical structures trapping air pockets, leading to the bulk nucleation dominating the entire ice nucleation at the lower temperatures. Furthermore, ice on the superhydrophobic surface possessed a lower macroscopical growth velocity as a result of the less ice nucleation rate and the insulating action of the trapped air pockets.

Nanostructures in superhydrophobic Ti6Al4V hierarchical surfaces control wetting state transitions.

This paper mainly reports the wetting state of liquid droplets on a Ti6Al4V micro-nanoscale hierarchical structured hydrophobic surface. In this work, the detailed action mechanism of the secondary nanostructure in the hierarchical structure on the wetting-state transition (from the Wenzel state to the Cassie state) was revealed and discussed. The variation of micro-morphology of the sample surface was observed using a field emission scanning electron microscope (FE-SEM). Furthermore, the apparent contact angle and sliding angle of the droplets on the surfaces were measured via a contact angle measurement instrument. The theoretical and experimental results indicated that the one-dimensional nanowire structure, which was planted on the microstructure surface by the hydrothermal method, effectively changed the wetting state of liquid droplets on the surface from the Wenzel state to the Cassie state owing to its good size synergies with microscale structure. This process not only increased the apparent contact angle of liquid droplets on the solid surface (to 161°), but also decreased the sliding angle significantly (to 3°) and contact angle hysteresis (to ∼2°), demonstrating the robust non-wetting property.

Effect of BaTiO3 powder as an additive in perovskite films on solar cells.

Perovskite solar cells (PSCs) are considered to be ideal energy devices, where perovskite-type organic metal halides act as light-absorbing materials. In PSCs, the photoexcitons are extracted and separated to afford high photoelectric conversion efficiency under the action of the built-in electric field (E bi). However, the current challenge is that a low E bi cannot provide a sufficient driving force to separate photonic excitons, which causes the captured charges to escape from the deep energy-level defect state. Here, the ferroelectric material barium titanate (BaTiO3) was directly introduced into the perovskite precursor solution to reduce the defection density (to 8.58 × 1017 cm-3) in PSCs and promote the separation of photoexcitons. Furthermore, the addition of BaTiO3 improved the quality of the perovskite film and significantly increased the photoelectric performance after the polarization treatment. This is mainly attributed to the residual polarization electric field generated by ferroelectric polarization, which increased the E bi of the PSCs and the width of the depletion layer and inhibited the non-radiative recombination of carriers. This work provides a possibility to design and develop optoelectronic devices with high-efficiency optoelectronic response behavior.

Effect of Intrinsic Pore Distribution on Ion Diffusion Kinetics of Supercapacitor Electrode Surface.

The electrolyte ion diffusion kinetics have an important impact on electrochemical energy storage. Herein, we report the effect of the intrinsic porosity of NiCoP on accelerating electrolyte ion diffusion kinetics and accommodating volume expansion during the charge/discharge process. The pore distribution model of electrode/electrolyte was designed and optimized by the finite element simulation, demonstrating the visualization and quantitative analysis of the diffusion process of the electrode/electrolyte interface with intrinsic porous structure. When the pore area ratio reached 50.01%, the theoretical diffusion coefficient of 1.41 × 10-11 m2 s-1 would be conducive to the rapid diffusion of electrolytes. The electrode gained a specific capacity of 2805 F g-1 at a current density of 1 A g-1 based on the measured diffusion coefficient (1.79 × 10-10 m2 s-1), superior to 1.44-times that of the pristine electrode. The diffusion barriers of intrinsic porous NiCoP (3.19 eV) and conventional NiCoP (47.10 eV) were calculated by the density functional theory calculations, respectively. The intrinsic porous NiCoP was prepared by the hydrothermal treatment, annealing, and phosphating processes. The pore distribution was regulated by the concentration of NaHCO3 as a pore-forming additive. This work combines simulations and experiments to form a method to optimize diffusion kinetics at the electrode/electrolyte interface.

Reconstruct gene regulatory network using slice pattern model.

BACKGROUND: Gene expression time series array data has become a useful resource for investigating gene functions and the interactions between genes. However, the gene expression arrays are always mixed with noise, and many nonlinear regulatory relationships have been omitted in many linear models. Because of those practical limitations, inference of gene regulatory model from expression data is still far from satisfactory. RESULTS: In this study, we present a model-based computational approach, Slice Pattern Model (SPM), to identify gene regulatory network from time series gene expression array data. In order to estimate performances of stability and reliability of our model, an artificial gene network is tested by the traditional linear model and SPM. SPM can handle the multiple transcriptional time lags and more accurately reconstruct the gene network. Using SPM, a 17 time-series gene expression data in yeast cell cycle is retrieved to reconstruct the regulatory network. Under the reliability threshold, theta = 55%, 18 relationships between genes are identified and transcriptional regulatory network is reconstructed. Results from previous studies demonstrate that most of gene relationships identified by SPM are correct. CONCLUSION: With the help of pattern recognition and similarity analysis, the effect of noise has been limited in SPM method. At the same time, genetic algorithm is introduced to optimize parameters of gene network model, which is performed based on a statistic method in our experiments. The results of experiments demonstrate that the gene regulatory model reconstructed using SPM is more stable and reliable than those models coming from traditional linear model.

Rounded Cu2ZnSnS4 nanosheet networks as a cost-effective counter electrode for high-efficiency dye-sensitized solar cells.

Semi-transparent rounded Cu2ZnSnS4 (CZTS) nanosheet networks were in situ grown on a FTO glass substrate, via an effective solution method, without any post-treatments. An improved power conversion efficiency of 6.24% was obtained by applying CZTS nanosheet networks as a counter electrode for dye-sensitized solar cells. When assisted by a mirror reflection, the PCE increased to 7.12%.

Relationship between Wetting Hysteresis and Contact Time of a Bouncing Droplet on Hydrophobic Surfaces.

The contact time of impacting water droplets on superhydrophobic surfaces directly reflects the extent of thermal and energy conversions between the water droplet and the surface, which is also considered to be crucial to the practical applications. The purpose of this study was to reveal the relationship between the contact time and the wetting hysteresis. We designed and fabricated six classes of surfaces with different extent of hydrophobicity through modifying the microscale/nanoscale hierarchical textured titanium surfaces with 1H,1H,2H,2H-perfluorodecyltrimethoxysilane, and we filmed the contact process of the water droplet impacting on these surfaces using a high-speed camera. It can be concluded that wetting hysteresis played a significant role in determining how long the impacting water droplet can bounce off the surface, based on the interfacial wetting mechanism and the work done against the resistance force generated by contact angle hysteresis during the dynamic process.