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[Display omitted] • This study introduces positive charge to seed surfaces for controlled growth of silica rods. • Positively charged seeds promote strong adhesion of PVP, leading to high yields of decorated particles. • Tailoring seed surface chemistry allows precise control over final particle morphology. • This method enables decoration of complex materials like magnetic core-multishell particles with silica rods. • Surface charge engineering offers a new strategy for precise control of silica rod growth on seed particles. In this study, the effect of surface modification and the resulting surface charge of colloidal silica seeds on the growth of silica rods during an emulsion droplet-based process is investigated. Through electrostatic interactions between negatively charged poly(vinylpyrrolidone) (PVP) and seed surfaces, significant PVP adsorption occurs as the seed surfaces are modified with positively charged cationic substances and then aged with PVP. This surface charge-enhanced PVP adsorption promotes the anchoring of water emulsion droplets, serving as the starting point for the growth of silica rods on the seed surfaces and leading to a high yield of silica rod-decorated particles during emulsion droplet-based growth. The surface properties, including surface charge and hydrophobicity, can be further modified by applying different cationic modifiers, which influence the morphology, structural architecture, and yield of the final product. We further demonstrated the versatility of this approach by successfully generating silica rod-decorated magnetic core (Fe 3 O 4)–multishell (silica/polystyrene/titania) particles. The findings of this study highlight the critical role of surface charge engineering in controlling the structure and morphology of silica rod-decorated silica particles as well as their integration into complex multicomponent systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The pH of rinsing solution alters the structure of adsorbed water on glass surface. • Rinsing solution with different pHs only changed the topmost surface of glass. • Surface charging of glass can be correlates to the structure of adsorbed water. This study explored the effects of rinsing solutions on the surface energy and elemental composition of Corning's EAGLE-XG® display glass, as well as its water adsorption/desorption behaviors and their impact on surface charging/discharging behaviors. The study employed aqueous solutions with different pHs to immerse the glass samples for 1 min and then characterized them immediately after quick drying using various spectroscopic techniques. The results show that the surface-free energy and overall elemental composition of the glass surfaces were insensitive to the exposure to different pH values. However, the O/(Si + Al) ratio of the glass network exposed at the topmost surface was altered, and the water structure and desorption rate also varied among the samples rinsed with different pH solutions. Interestingly, it was found that the DI water treated surface appeared to discharge more slowly than the pH 1 or pH 13 solution treated surfaces, which correlated with the temporal change of water structure. Overall, this study provides important insights into the fundamental questions regarding the impact of the rinsing process on display glass panel surfaces and what characterization techniques are sensitive to the chemistry change in the topmost layer, which will facilitate future research and development efforts. [ABSTRACT FROM AUTHOR]

We have performed density functional theory calculations to study the binding and charge transfer at interfaces between blue phosphorene and various metal substrates. The substrates considered are Al(111), Ag(111), Au(111), Pt(111), Zr(0001) and Sc(0001). The substrates suitable for use for synthesis and exfoliation of blue phosphorene, or instead for use as electrodes for either making contacts or charge doping blue phosphorene, are identified. We find that both the charge transfer and strength of binding correlate excellently with a simple descriptor D = Δ χ / Δ R , where Δ χ is the difference in Pauling electronegativities between the metal and phosphorus, and Δ R the corresponding difference in covalent radii. The predictions of the descriptor are validated by subsequent calculations on Pd(111), Cu(111) and Ir(111) substrates. This easily computed descriptor should help in the rapid identification of two-dimensional material + metal combinations suitable for specific applications. Unlabelled Image • We study interfaces between blue phosphorene and various metal substrates using density functional theory caalculations. • We formulate a descriptor = Δχ/Δℛ, where Δχ and Δℛ are the differences in electronegativities and atomic sizes respectively. • This descriptor can be used to predict both the charge transfer and the strength of binding at the interface. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ultraviolet irradiation in vacuum technique enhancing flashover voltage of SIR. • Illustrate the influence of UVIV on the chain structure of SIR. • Establish a relation between crosslinking of SIR and surface trap parameters. • Explain the effects of surface traps on surface charging and flashover. • Clarify the UVIV improved flashover mechanisms from microscopic to macroscopic. In surface science, surface flashover, which poses a severe danger to the safe operation of modern silicone rubber (SIR)-based electrical equipment, is a continuous discharge event that happens when an intense electric field is produced along the gas-solid interface. To improve the flashover performance, the ultraviolet irradiation in vacuum (UVIV) technique is proposed to modify the SIR surface and the DC flashover threshold increases approximately 14.8 % after 6 h UVIV treatment. Then, the influence mechanisms of UVIV are investigated from microscopic molecule modification to macroscopic flashover performance: The UVIV generates high-energy photons to break C H and Si C bonds in SIR chains, and atoms, group, side chains, and free radicals in chains recombine through the thermally dynamic, causing SIR chains to crosslink. The crosslink chain structure enhances the deep trap energy around the Si O Si bond and introduces large amounts of deep traps. The increment in surface deep trap energy and density captures electrons. It establishes a high electrostatic near the cathode barrier that impedes subsequent electron injection, causing surface charge density decreases far away from the cathode. The reduced surface charges restrict the collision ionization in gas, finally increasing the DC surface flashover voltage through UVIV treatment. [ABSTRACT FROM AUTHOR]

In bio-neural systems, ionic fluxes dominate the regulation of neuroplasticity. Inspired by such biological strategies, indium-zinc-oxide (IZO) transistors gated by nanogranular SiO 2 electrolyte films were proposed for synaptic behavior emulations. Due to the strong proton/electron coupling effect, the carrier density of IZO channel layer can be effectively tuned by a pH buffer solution on the SiO 2 electrolyte dielectrics. The pH-dependent synaptic responses, such as excitatory postsynaptic current (EPSC) and paired pulse facilitation (PPF), were discussed in detail based on the surface charging effect. Most importantly, an enhanced pH sensitivity in terms of the relative gain of EPSC amplitude between pH = 4 and pH = 10 was demonstrated by multi-spike trains. Such IZO-based synaptic transistors are promising for low-power neuromorphic sensing systems. Unlabelled Image • Indium-zinc-oxide synaptic transistors gated by SiO 2 electrolyte films were proposed for synaptic behavior emulations. • The pH-dependent synaptic responses were discussed in detail based on the surface charging effect. • The pH sensitivity in terms of relative amplitude gain between pH = 4 and pH = 10 can be enhanced by multi-spike trains. [ABSTRACT FROM AUTHOR]

In order to obtain efficient electrophoretic inks, Tridodecylamine (Dod 3 N), has been studied as charge control agent (CCA) in a non-polar paraffin solvent (Isopar G) for various inorganic pigments (TiO 2 and Fe 2 O 3 ). All hydrophobic mineral oxides, i.e. treated with octyltrimethoxysilane (C8) or dodecyltrimethoxysilane (C12), were found to be negatively charged in presence of Dod 3 N. The electrophoretic mobilities of inorganic pigments seemed to be strongly dependent of their isoelectric point (IEP) and also of the concentration of dod 3 N with an optimum range between 10 and 20 mM depending on the pigments. Finally, an electrophoretic ink constituted of hydrophobic mineral oxides in presence of Dod 3 N was tested in a device. Its efficiency as charge control agent to negatively charge hydrophobic particles was confirmed through good optical properties and fast response time (220 ms at 200 kV m −1 ). [ABSTRACT FROM AUTHOR]

[Display omitted] • DFT and DFTB models mimic surface plasmon effects of localize extra charge density. • DFT ground model is able to predict *CO 2 δ− formation over pristine Ag(1 1 1) surface. • A second CO 2 adsorption forms *2CO 2 δ− activated species, weakening the C O bonds. The CO 2 reduction reaction on Ag in the presence of surface plasmons are of strong interest in photocatalysis. Here, two Density Functional Theory (DFT) approaches are proposed to localize charges at the Ag surface to mimic surface plasmon excitation. These calculations predict charge localization at the outermost surface layer, a result confirmed via light excitation at the plasmon resonance modeled by Density Functional Tight Binding Hamiltonian (DFTB) theory. The CO 2 (gas) reduction initial steps are studied by DFT models showing that bonded species can be created on top of an Ag-atom in the presence of extra charges. A second CO 2 molecule can assist the first molecule, decreasing the charge carrier density requirement for CO 2 reduction bonded species. A Molecular Dynamics (MD) study shows a possible interaction among CO 2 molecule. These results show that a static DFT simulation can mimic charge localization resulting from surface plasmon effects, thus enabling studies on surface plasmon-enhanced chemical reactions, paving the way for future time-dependent (TD) studies. [ABSTRACT FROM AUTHOR]

The ability to retain localized charges at the surface or interface of dielectric materials is a universal property that applies to many different fields such as tribocharging, charge nanopatterning, nanoxerography, etc. Once the surface is charged, its stability and subsequent discharging rate will determine the potential applications of a given system. This decay rate is properly defined by the macroscopic equations which depend on dielectric constants and conductivities of the two media. Here, we derive the equations to model the decay of charge distributions localized at the surface/interface of materials and solve them avoiding additional approximations made so far. Addressing the problem in the Fourier space, we arrive to a compact generic equation which provides a useful tool to determine both the bulk and surface conductivities of a material. Furthermore, we show that Kelvin Probe Force Microscopy (KPFM) is a particularly suited method to exploit this tool. Monitoring the charge decay of previously injected charge patches on silicon dioxide (SiO 2), together with an appropriated data analysis, we verify the behavior predicted by our equations. This allows us to characterize the surface and bulk conductivities of SiO 2 layers as well as its dependence with the relative humidity. [Display omitted] • Surface charging of dielectric materials is a universal property. • The dependence of the surface charge decay rate with the system geometry is established. • Surface and bulk conductivities are obtained with Kelvin probe force microscopy. [ABSTRACT FROM AUTHOR]

The abnormal stability of bulk nanobubbles has attracted substantial attention from academia and industry since classical Epstein–Plesset theory predicts that gas bubbles cannot keep stable thermodynamic equilibrium spontaneously. The dual nature of ionic surfactants, acting simultaneously as charge carriers and attenuators of surface tension at the gas–liquid interface, enables them to play a unique role in bulk nanobubble stabilization. Herein the stability of bulk nanobubbles in anionic, cationic and nonionic surfactant solutions over a wide range of concentration is studied. Experimental results show that different kinds of surfactant molecules are involved in the nucleation and stabilization of bulk nanobubbles in different ways. We demonstrate that the accumulation of net charges carried by surfactant ions at the interface is predominantly responsible for stabilizing nanobubbles, instead of the reduction of surface tension. With theoretical calculations, we further quantify the coupling action of interfacial tension and surface charge on the stable equilibrium state of bulk nanobubbles. The result illustrates that the interfacial tension and the degree of gas saturation together determine the upper limit of the bubble size that can exist stably. Our study identifies a route to explore the intrinsic mechanism of bulk nanobubble's stability. [Display omitted] • Stability of bulk nanobubbles in ionic and nonionic surfactant solutions is studied. • Surfactant molecules are involved in the nucleation and stabilization of nanobubbles. • Accumulation of net charges is predominantly responsible for stabilizing nanobubbles. • Coupling action of interfacial tension and surface charge is revealed. • Interfacial tension and gas supersaturation together determine the upper bound size. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analysis of the pH-dependent contact angles, freezing temperatures and ice adhesion on aluminium samples is presented. It is not yet known whether externally applied electric fields or charged interfaces sufficiently affect the heterogeneous freezing and ice adhesion in order to provide technical solutions for refrigeration engineering, de-icing techniques and food preservation. It was found that surfaces charges that are generated on polished aluminium samples by changing the pH value of the adjacent KCl solution significantly reduce the advancing contact angle. The effect of surface charges on the freezing behaviour was determined by cooling an array of droplets of KCl solutions with pH values between 3 and 12 with a cooling rate of 1 K min−1. Ice adhesion was evaluated using an in-house developed pusher test at -10 °C in a climate chamber. Both icephobicity tests revealed that surface charges seem ineffective to significantly change the freezing behaviour and ice adhesion strength on polished aluminium samples. [Display omitted] • The advancing contact angles reach their maximum at the potential of zero charge. • Higher ion contents increase the achievable supercooling and decreases ice adhesion. • There is no significant effect of pH-generated surface charge on icephobicity. • Heterogeneous freezing follows a generalised extreme probability density function. • Naturally occurring charges are insufficient to provide icephobicity on Al samples. [ABSTRACT FROM AUTHOR]

[Display omitted] • The identification of different surface charge effects in a variety of epitaxial ferroelectric thin films. • A novel strategy to predict surface charging compensation in piezoelectric force microscopy imaging of ferroelectric materials. • Identified a predominant role of semiconducting properties of the ferroelectric material in the surface state and, concomitantly, in the piezoelectric force microscopy response. • Demonstration of application of the findings to predict and compensate extrinsic effects in non-ferroelectric materials. Piezoelectric force microscopy (PFM) has demonstrated to be a powerful tool to characterize ferroelectric materials. However, extrinsic effects, most notably, those resulting from surface charges, often mask or mirror genuine piezoelectric response, challenging PFM data understanding. The contribution of surface charges to PFM signal is commonly compensated by using appropriate external bias voltage, which is ad-hoc selected and sample dependent. Here, we determine the compensating voltage in thin films of different ferroelectric materials and we compare with the corresponding I-V characteristics recorded using suitable electrodes. It turns out that the sign and magnitude of the bias voltage required to compensate the surface charges are related to the asymmetry of the I-V characteristics. We propose that this relation results from the fact that the semiconducting properties of the material determine both the I-V dependence, and the sign of charged adsorbates. We show how to make use of this correlation to predict the required compensation voltage of a non-ferroelectric material and we show that spurious piezoelectric-like contributions are largely cancelled. The results provide guidelines to mitigate common extrinsic contributions in PFM imaging. [ABSTRACT FROM AUTHOR]

The effects of the presence of a native oxide film or surface contamination as well as variations in material density on the total electron yield (TEY) of Ru and B 4 C were assessed in the absence of any surface charging effect. The experimental results were analyzed using semi-empirical Monte Carlo simulations and demonstrated that a native oxide film increased the TEY, and that this effect varied with film thickness. These phenomena were explained based on the effect of the backscattered electrons (BSEs) at the interface between Ru and RuO 2 , as well as the lower potential barrier of RuO 2 . Deviations in the material density from the theoretical values were attributed to the film deposition procedure based on fitting simulated TEY curves to experimental results. In the case of B 4 C, the TEY was enhanced by the presence of a 0.8-nm-thick surface contamination film consisting of oxygenated hydrocarbons. The effect of the low potential barrier of the contamination film was found to be significant, as the density of the B 4 C was much lower than that of the Ru. Comparing the simulation parameters generated in the present work with Joy’s database, it was found that the model and the input parameters used in the simulations were sufficiently accurate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Investigation of N 2 physisorption at room temperature in porous thin films. • Identification of challenges for the correct analysis of gas phase core levels. • Simulation of surface-induced dipole as source of measurable energy shifts. • Analysis of N1s FWHM dependence with surface charge in porous thin films. Near ambient pressure XPS in nitrogen atmosphere was utilized to investigate gas-solid interactions within porous SiO 2 films ranging from 30 to 75 nm thickness. The films were differentiated in terms of porosity and roughness. The XPS N1s core levels of the N 2 gas in presence of the SiO 2 samples showed variations in width, binding energy and line shape. The width correlated with the surface charge induced in the dielectric films upon X-ray irradiation. The observed different binding energies observed for the N1s peak can only partly be associated with intrinsic work function differences between the samples, opening the possibility that the effect of physisorption at room temperature could be detected by a shift in the measured binding energy. However, the signals also show an increasing asymmetry with rising surface charge. This might be associated with the formation of vertical electrical gradients within the dielectric porous thin films, which complicates the assignment of binding energy positions to specific surface-related effects. With the support of Monte Carlo and first principles density functional theory calculations, the observed shifts were discussed in terms of the possible formation of transitory dipoles upon N 2 physisorption within the porous SiO 2 films. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiO 2 /CdIn 2 S 4 -annealed photoanode was successfully fabricated. • TiO 2 /CdIn 2 S 4 -annealed exhibited 6.21 mA/cm2 at 1.23 V vs. RHE in 0.5 M Na 2 SO 4. • Interfacial charge and surface defect regulation together to boost performance. As an n-type narrow band gap ternary sulfide semiconductor, CdIn 2 S 4 exhibits favourable photoelectrochemical (PEC) water splitting performance. However, severe photogenerated carrier recombination and slow surface dynamics at the interface of monomer CdIn 2 S 4 restrict its application. Herein, we addressed the problem by fabricating a TiO 2 /CdIn 2 S 4 -annealed photoanode by two-step anodization method, hydrothermal method and annealing treatment. As a result, the TiO 2 /CdIn 2 S 4 -annealed photoanode exhibited 6.21 mA/cm2 at 1.23 V vs. RHE, which was much higher than the pure CdIn 2 S 4 (0.05 mA/cm2) and TiO 2 (0.14 mA/cm2), and was 9 times higher than TiO 2 /CdIn 2 S 4 (0.68 mA/cm2). This excellent performance can be attributed to the synergistic effect of interfacial charge regulation (introducing TiO 2 NTs as electron transport layer) and surface defect regulation (introducing sulfur vacancies as OER active centers to facilitate hole transport). By this way, the photogenerated electrons and holes of CdIn 2 S 4 were simultaneously extracted in opposite directions. Experimental characterizations confirmed the introduction of TiO 2 and sulfur vacancies can enhance the separation and injection efficiency of carriers. This work provides a new idea for regulating interface charges and surface defects to improve the PEC activity of CdIn 2 S 4. [ABSTRACT FROM AUTHOR]

A simple mechanical grinding method was used to adsorb aniline organic molecules on the surface of TiO 2. The reduction capacity of the photocatalyst and the amount of surface charge increase simultaneously. [Display omitted] • At room temperature, simple mechanical grinding was used to successfully adsorb organic aniline molecules on the surface of TiO 2. • After aniline was adsorbed, the photoreduction capacity of TiO 2 and the amount of surface charge increased synchronously. • The preparation method is simple, without precious metal additives, and the raw materials are abundant and easy to obtain. • Improved photocatalytic hydrogen production performance of commercial P25 with the help of a simple molecular adsorption strategy. The work explains the mechanism of photocatalytic performance enhancement and contributes to a better understanding of the process of photolytic hydrogen precipitation from molecularly modified nanomaterials. A higher conduction band position and more photogenerated electrons are distinctly important for the high-efficiency photocatalytic hydrogen evolution performance. However, raising conduction band position will enlarge the band gap and reduce the production of photogenerated electrons. Herein, a super simple and efficient ammonia molecular adsorption strategy was proposed and designed to promote efficient hydrogen production by a simple ammonia molecules adsorption on commercial TiO 2 surface. The experimental and theoretical calculation results indicated that aniline can be successfully adsorbed on TiO 2 surface by a straightforward mechanical grinding method, and the photocatalytic hydrogen production performance of TiO 2 can be improved by more than 9 times after the adsorption of aniline. This is because the adsorbed aniline can provide electrons to the TiO 2 surface and lead to a charge redistribution and accumulation on the surface of TiO 2. Excessive electrons make the conduction band of TiO 2 bend upward, thus improving the photogenerated electron reduction ability and the photocatalytic performance of TiO 2. In addition, the adsorption of aniline enables TiO 2 to show light absorption in the visible region, generating more photogenerated electrons to participate in the photocatalytic water splitting reaction. In this work, the molecular adsorption strategy is not only simple to operate, but also can improve the photoreduction ability and surface charge quantity of materials. It provides a simple and efficient new method for photocatalyst modification in addition to the traditional modification methods such as doping compounds. [ABSTRACT FROM AUTHOR]

Just in time for an oil change : As verified by parallel chemical analyses showing the extent of oxidation, a single (tribo)electric signal reflecting the contact charging between an oil-dipped paper and a common polymer can predict the time for an oil change for engine oils. The method is a simple and cost-effective one - it can help protect the environment by preventing the premature or late change of oil in engines and prevents machine wear and economic losses. [Display omitted] • Triboelectric signal generated from two contacting polymers can be used to monitor the lubricant oil condition. • A parallel spectroscopic analysis of oil proves that the triboelectric signal follows the course of oil oxidation. • The concept overall is applicable (in comparison to complex chemical analysis) and general (uses common polymers in contact). Lubrication of machine parts is necessary to prevent friction and wear in machine operation. However, oxidation of lubricants upon operation changes their chemical and physical properties and causes lubrication performance to deteriorate. Besides, one liter of wasted/used lubricant oil can contaminate a million liters of water. Current methods for the timely detection of oil deterioration lack practicality. Here we show simple, a triboelectrification-based method for oil degradation monitoring, in which the oxidation can be monitored by the changes in the contact charging (and separation) signals of oil-dipped cellulose and a common polymer tapped to each other. The commercial and base oil samples are oxidized at 100–200 °C for up to 80 h, simultaneously monitored by ATR-FTIR and the triboelectric method. The results show that a 40–90% decrease in the triboelectric open-circuit potentials in the presence of oxidized oil can directly indicate the start of oil oxidation without other accompanying analyses. [ABSTRACT FROM AUTHOR]

[Display omitted] • NiS/rGO/Cd 0.3 Zn 0.7 S photocatalysts prepared by facile hydrothermal and photochemical methods. • NiS are uniformly distributed on C 0.3 Z 0.7 S nanorods. • The NiS/rGO/C 0.3 Z 0.7 S exhibits excellent photocatalytic H 2 evolution activity of 1058 μmol h−1. • A possible mechanism was proposed based on the synergistic effect of rGO and NiS. Effectively improving the separation efficiency of photoinduced carriers is of crucial importance for the design of photocatalysts with excellent hydrogen evolution activity. Herein, by combining CdZnS nanorods with rGO and further depositing NiS as cocatalysts, the separation and transfer of photoinduced carriers for CdZnS is significantly improved. Without using any noble metals as cocatalysts, the optimal NiS/0.5%rGO/C 0.3 Z 0.7 S exhibits an outstanding H 2 evolution activity of 1058 μmol h−1 under visible light illumination, which is evidently better than that of pure CdZnS nanorods and most CdZnS-based photocatalysts reported previously. Our study indicates that the introduction of rGO can effectively assist the transfer of photoinduced electrons and evenly distributed NiS on the surface, as the active center for H 2 evolution reaction, can easily capture photoinduced electrons to participate in photocatalytic process. Thus, the synergistic effect of rGO and NiS is considered to be the main cause for the improved photocatalytic performance. This work could offer a facile and low-cost strategy for the construction of composite photocatalysts with high-efficiency hydrogen generation activity. [ABSTRACT FROM AUTHOR]

Highlights: [•] A novel approach for the analysis of the secondary electron emission in connection with the surface density of trapped charges. [•] Experimental estimation of the effective cross section for electron–hole recombination and electron trapping in defects. [•] A simplified charge transport and trapping model which corroborates qualitatively the interpretation of the results. [ABSTRACT FROM AUTHOR]

The surface potential decay time is related to the number of collisions neutral gas particles with the polymer surface per unit area per time. [Display omitted] • We measured surface potential of an insulating sample using Kelvin probe system to investigate the neutral gas effect on charge compensation. • Gas cluster ion beam was used to accumulate charges and to minimize damage to the sample surface. • Neutral gas effect on surface charge of insulating sample depends on the type of injection gas. • Surface potential curves were fitted by exponential decay function to obtain decay time. Surface charging of an insulating sample has been a significant issue in surface analysis. In time-of-flight secondary ion mass spectrometry, the charge also accumulates on the surface of an insulating sample by the primary ion beam, such as an argon gas cluster ion beam. Such charging can lead to not only degraded mass resolution but also low image resolution, and thus it is necessary to compensate for surface charging of insulating sample. Therefore, several efficient methods have been proposed for charge compensation, such as using a low-energy electron flood gun, applying a bias voltage to the sample stage, and using a gas flooding system. Here, we measured the surface potential of a polymer film to investigate the gas effect on the charge compensation using a Kelvin probe. During the measurements, the chamber pressure was gradually increased by injecting gases, such as He, Ne, Ar, N 2 , and O 2. We found that the injection gas may reduce the surface charging of the sample, depending on the type of gas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Bi-MOF as a co-catalyst is introduced on BiVO 4 surface for PEC water oxidation. • Photocurrent density of the Bi-MOF/BiVO 4 is 2.06 times larger than bare BiVO 4. • Surface charge transfer efficiency of Bi-MOF/BiVO 4 is 1.56 times higher than that of bare BiVO 4. • The co-catalyst of Bi-MOF can efficiently separate photogenerated charges. • Operation stability is also enhanced after Bi-MOF decoration. Metal-organic frameworks (MOFs) are promising co-catalysts for increasingenhancing the performance of photoelectrochemical (PEC) water splitting. In this work, we successfully fabricated an efficient BiVO 4 photoanode for PEC water oxidation by decorating its surface with Bi-based MOF as a co-catalyst via an unconventional immersion process at an ambient temperature. Bi-MOF exhibits a large surface area and promotes bulk charge separation and surface charge transfer in the water oxidation reaction, resulting in an enhancement in the photocurrent density, which is approximately two times larger than that of the bare BiVO 4 photoanode. In addition, the operation stability of our Bi-MOF/BiVO 4 photoanode was dramatically improved, and more than 95% of its initial photocurrent density was retained even after 24 h, indicating that the improved charge transfer by the Bi-MOF layer prohibits the dissolution of the BiVO 4 layer into the solution during the water oxidation reaction. [ABSTRACT FROM AUTHOR]

Prior to the flashover across an insulator in vacuum, the insulator surface is usually charged. It is of great importance to investigate the charging phenomena for better understanding the flashover characteristics. It is considered that there are two kinds of mechanisms closely related to the surface charging of insulator i.e., the secondary electron emission occurred over an insulator, and while employing a perfect electrode contact ahead of electron emission into vacuum, the charge injection and accumulation occurred inside the surface layer of an insulator. Based on the rigorous analysis of the kinetic processes of both primary and secondary electrons, the related surface charges were theoretically deduced. Involving the detrapping of charges trapped and the recombination of charges injected, the charging process due to charge injection and accumulation was analyzed. Some formulas were given to express the density of surface charges. [Copyright &y& Elsevier]