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Flow accelerated organic coating degradation has been received attention, but the degradation mechanism is still not completely understood. In this study, we focus on investigating the influence of fluid shear on the degradation of organic coatings. A commercially available epoxy based clear coating was exposed to the laminar flow, and a 3.5 wt% NaCl solution was employed as the working fluid with a variety of flow rates. The change in the composition of the working fluid during the coating immersion was characterized by Fourier Transform Infrared Spectrometer (FTIR) and conductivity measurement. The effect of fluid shear is also demonstrated by the change in coating thickness. The barrier properties of organic coatings were monitored inline by Electrochemical Impedance Spectroscopy (EIS) measurement. The time evolution of coating resistance, capacitance, and permittivity obtained from the equivalent circuit model was studied to demonstrate the internal composition change of the coatings due to the flowing fluid. In this study, the experiments and analysis confirmed that flowing fluid promotes the release of coating materials from the coating into the surrounding working fluid while it accelerates the transport of water and ions into the coating. [ABSTRACT FROM AUTHOR]

Bubble dynamic behaviors from photoelectrochemical water splitting are key issues in the interfacial mass transport on photocatalyst surface. To date, the interaction between gas bubbles and photocatalyst surfaces has received limited attention, especially bubble bouncing behaviors during photoelectrochemical process have rarely been discussed in the literature. In this study, a visualization method by external chopping disturbance was proposed to regulate bubble dynamic behaviors on the TiO 2 photoelectrode surface during photoelectrochemical reaction. Under continuous irradiation, the dominant physics in each bubble growth phase were inertia-controlled, the transition from diffusion-controlled to chemical reaction-controlled and the chemical reaction-controlled. Under rhythmically chopping, the bouncing bubble grew only while in contact with the photoelectrode and its trajectory was approximately to a spiral shape. The proportion of the acceleration stage was very small during the overall rising process, and the bubble rise velocity can be approximately as constant. The main reason for the bubble no longer return is that the rising distance is too far to feel the Marangoni attraction force. • A method to regulate bubble dynamic behaviors by chopping is proposed. • Single bubble evolution is controlled by different dominant physics in each phase. • Bouncing bubbles keep spherical and grow only while in contact with photoelectrode. • The motion trajectory of bouncing bubble is approximately to a spiral shape. • Main reason for no longer return is the bubbles rise too far to feel attraction. [ABSTRACT FROM AUTHOR]

In this article we report a facile method to create a polyaniline (PANI) nanorod/carbon nanoparticle (CNP) composite structure that is suitable for supercapacitor use. A network of CNPs was conveniently produced on the surface of a nickel foam by collecting candle soot above a burning candle. The PANI nanorods were then electrochemically deposited on the CNP network, forming a star-like interconnected 3D structure. As a comparison, MnO 2 particles were also deposited on the CNP network to produce a broccoli-like structure. The electrochemical properties of these two composites were examined using cyclic voltammetry, cyclic charge-discharge, and electrochemical impedance spectroscopy. The two electrodes exhibited different electrochemical behaviors: high capacitance at low current densities and marked deterioration at high ones for CNPs/PANI and relatively low but stable capacitance for CNPs/MnO 2 . The reasons for this distinction were discussed based on the structures and material properties of the electrodes. [ABSTRACT FROM AUTHOR]

This paper presents a study on single bubble photogenerated by 376 nm laser light at TiO 2 nanorod-array electrode during photoelectrochemical (PEC) conversion. The surface properties of TiO 2 nanorod-array electrode were investigated at first for a better understanding of the three-phase contact line behavior. The results indicate the light-induced hydrophilic effect of TiO 2 nanorod-array electrode under illumination, which makes bubble tend to be pseudo-sphere shape during attaching on electrode. The experimental investigation on photogenerated bubble at TiO 2 nanorod-array electrode shows that there is a linear relationship between cubic root of time and bubble radius, demonstrating the gas products from the surface reaction transferring into bubble through bubble bottom according to the analysis of the relative size between bubble and effective solid surface. Furthermore, the coupling effects between bubble and irradiance were discussed. The bubble scatter effect on light causes a local light intensity increase at electrode surface area on both sides of bubble, and leads to photocurrent increase especially at small bubble size. While the increase of irradiance causes the parameters of bubble evolution period, dissolved gas concentration for nucleation and departure diameter increase, but leads to bubble evolution rate and incident photon conversion efficiency (IPCE) decrease. These results suggest a lower irradiance is preferred for a higher PEC conversion efficiency from the aspects of IPCE and bubble evolution rate. [ABSTRACT FROM AUTHOR]

Bubble evolution from photo(electro)catalytic water splitting plays a vital role in the interfacial mass transport on photocatalyst surface. However, little success has been achieved to optimize this process, restricted by the poor understanding. Herein, taking photoelectrochemical (PEC) water splitting over a titanium dioxide (TiO 2 ) nanorod-array electrode as a model system, experiments were performed to study single oxygen bubble dynamics by combining electrochemical measurement and high-speed microscopic imaging. The experimental results indicate that the departure of bubble from photoelectrode is retarded by light irradiation, but the traditional bubble departure criterions fail to predict the bubble departure diameters especially in high light intensity. Additional analysis reveals that the light irradiation causes the Marangoni force acting on the evolving bubble, because it induces temperature rise and generates dissolved gas. A modified force balance model for bubble departure from photoelectrode was developed by adding Marangoni force. This modified model that takes account of the light-induced temperature rise and the dissolved gas, agrees well with the experimental data and can be extended to other photo(electro)catalytic reactions. [ABSTRACT FROM AUTHOR]

• An expression for single bubble coverage on the photoelectrode surface is proposed. • The mass transfer is dominated by single-phase free convection in low current density. • The mass transfer coefficient peaks in the inertia-controlled bubble growth phase. • Periodic illumination accelerates bubble detachment and enhances mass transfer. The limitation of the transfer of gas products within the photocatalytic system is the key to the efficiency of the water splitting, which is directly influenced by the bubble evolution process on the catalyst surface. In this study, the entire process of bubble evolution on the surface of a superhydrophilic TiO 2 photoelectrode was simultaneously measured visually and electrochemically. The bubble growth and detachment characteristics were investigated under different laser powers and constant bias voltages. An expression for the bubble coverage characterized by the bubble radius and photocurrent, which is applicable to the photoelectrocatalytic water splitting, was proposed to accurately obtain the mass transfer coefficient during bubble evolution. The mass transfer mechanism of gas product transfer in the low current density range dominated by single-phase free convection was revealed. The mass transfer coefficient was found to increase in the inertia-controlled phase and decrease in the chemical reaction-controlled phase of bubble growth. Furthermore, a method to accelerate bubble detachment from the photoelectrode surface by periodic illumination was proposed, which could significantly enhance the gas product transfer process. [Display omitted] [ABSTRACT FROM AUTHOR]