Electric Flux Approach for Surface Charges on Current Carrying Conductor

Lee Yeon Ho 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.1

When a straight conductor of fnite length is connected to a battery, the positive and negative charges on the upper and lower plates of the conductor induce an electric feld and a current in the conductor. In the conventional method, it is assumed that the internal electric feld is uniform as steady current fows in the conductor. However, the electric feld is induced by electric charges but not by currents. A steady current can fow in a wire when guided by charge accumulated on the surface of the conductor. Although the existence of surface charge has been confrmed in several studies, an analytical approach to determine the surface charge distribution was successful only when the conductor was considered infnitely long. Numerical methods were used to compute the electric fux incident on the conductor surface and to determine the surface charge that balances the incoming electric fux. However, the relationship between the incoming electric fux and the surface charge has not been established in a closed form. In this study, the conduction current is considered to be the relaxation of the electrode and surface charges and is treated as the sum of the electric fuxes entering and leaving the conductor surface. The relationship between the incoming electric fux and surface charge is obtained in a closed form by applying the continuity equation and boundary conditions for the electric feld at the interface between two dissimilar materials. This relationship is applicable to any interface, including conductor-conductor and lossy dielectric-dielectric interfaces. A two-dimensional model of a current-carrying wire is developed using slab conductors to numerically compute the surface charge densities, electric felds, and equipotential surfaces inside and outside the conductor. Our results show that the charge peaks at the corners of the conductor and at the point where two dissimilar conductors meet.

탄산 에틸렌계 용액 중에서 생성되는 흑연 음극 표면피막의 형상 및 저항에 미치는 충방전 속도의 영향

정순기,김보겸 한국수소및신에너지학회 2013 한국수소 및 신에너지학회논문집 Vol.24 No.2

The behavior of surface film formation was greatly dependent on the speed of potential cycling. In LiClO4 / EC + DEC, cyclic voltammetry results showed that the peaks originated from surface film formation on graphite electrode at the high charge-discharge rate was shifted to the lower potentials as the charge-discharge rate decrease. This indicates that surface films with different morphology and thickness were formed by different charge-discharge rate. Transmission electron microscopy (TEM) results indicated that the properties such as thickness and morphology of the surface film were greatly affected by the charge-discharge rate. Electrochemical impedance spectroscopy (EIS) showed that the resistance of surface film was affected by the speed of potential cycling. In addition, the charge transfer resistance was also dependent on the charge-discharge rate indicating that the charge transfer reaction was affected by the nature of surface film. TEM and EIS results suggested that the chemical property as well as the physical property of the surface film was affected by the charge-discharge rate.

Effects of Charge Density on Water Splitting at Cation-Exchange Membrane Surface in the Over-Limiting Current Region

Kang, Moon-Sung,Choi, Yong-Jin,Moon, Seong-Hyeon 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.1

To determine the correlation between surface properties and concentration polarization (CP) behaviors, cation exchange membranes with varying fixed charge densities were prepared by using several electrochemical analyses such as chronopotentiometry, zeta potential, and current-voltage measurements. Results showed that CP behavior depended mainly on surface charge density. With higher surface charge density, stronger electroconvection was observed, suggesting that an increase in the surface charge density increased the concentration of the counter ions at the membrane surface. As such, the electric field around the membrane surface was strengthened at a current over the limiting current density. Water splitting was also proportional to the surface charge density. This results was consistent with the classical electric field-enhanced water splitting theory, indicating that water splitting increased due to increases in the electric field and prepolarization of water molecules at the membrane-solution interface of the cation-exchange membrane.

Effects of Charge Density on Water Splitting at Cation-Exchange Membrane Surface in the Over-Limiting Current Region

문승현,강문성,최용진 한국화학공학회 2004 Korean Journal of Chemical Engineering Vol.21 No.1

To determine the corelation betwen surface properties and concentration polarization (CP) behaviors,cation exchange membranes with varying fixed charge densities were prepared and characterized by using severalelectrochemical analyses such as chronopotentiometry, zeta potential, and current-voltage measurements. Resultsshowed that CP behavior depended mainly on surface charge density. With higher surface charge density, strongerelectroconvection was observed, suggesting that an increase in the surface charge density increased the concentrationof the counter ions at the membrane surface. As such, the electric field around the membrane surface was strengthenedat a curent over the limiting curent density. Water spliting was also proportional to the surface charge density. Thisresult was consistent with the classical electric field-enhanced water spliting theory, indicating that water splitingincreased due to increases in the electric field and prepolarization of water molecules at the membrane-solution interfaceof the cation-exchange membrane.

Electron blocking layer-based interfacial design for highly-enhanced triboelectric nanogenerators

Park, Hyun-Woo,Huynh, Nghia Dinh,Kim, Wook,Lee, Choongyeop,Nam, Youngsuk,Lee, Sangmin,Chung, Kwun-Bum,Choi, Dukhyun Elsevier 2018 Nano energy Vol.50 No.-

<P><B>Abstract</B></P> <P>The key to enhance the output power from triboelectric nanogenerators (TENGs) is to control the surface charge density of tribo-materials. In this study, we introduce an electron blocking layer (EBL) between a negative tribo-material and an electrode to dramatically enhance the output power of TENGs. For the first time, we suggest that the tribo-potential can be significantly reduced by the presence of interfacial electrons; electrostatically induced positive charges at the interface beneath a negative tribo-material can be screened out by the electrons, thereby decreasing the surface charge density. By employing an EBL between a negative tribo-material and an electrode, we can maintain a high surface charge density at the surface of the negative tribo-material. Furthermore, an EBL with high permittivity can enhance the polarization of the tribo-material, resulting in an improved surface charge density. As a proof of concept, polydimethylsiloxane (PDMS) and aluminum (Al) are used as a negative tribo-material and an electrode, respectively. A TiO<SUB>x</SUB> EBL is then deposited in between these materials by radio frequency (RF) sputtering. Due to the coupling effects of the electron blocking and enhanced polarization, the output peak power from the TENG with a TiO<SUB>x</SUB> EBL reaches approximately 2.5 mW at 3 Hz and 5 N, which is 25 times larger than that of a TENG without an EBL. To understand the improved behavior of the TENG with a TiO<SUB>x</SUB> EBL, we investigate the correlations between the output behavior of the TENG and the physical properties of the surface/interface of TiO<SUB>x</SUB> and PDMS (e.g., the surface potential, dielectric properties, and electronic structures). We expect that our results can provide a novel design way to significantly improve the output performance of TENGs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We first report the critical effects of an electron blocking layer (EBL) to significantly enhance TENG performance. </LI> <LI> A high surface charge density of tribo-material by electron blocking property of an EBL. </LI> <LI> An EBL with high permittivity can enhance the polarization of the tribo-material. </LI> <LI> An improved surface charge density and contributing to the enhanced performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Surface charge characterization of nanofiltration membranes by potentiometric titrations and electrophoresis: Functionality vs. zeta potential

Rho, Hojung,Chon, Kangmin,Cho, Jaeweon Elsevier Scientific Pub. Co 2018 Desalination Vol. No.

<P><B>Abstract</B></P> <P>The surface charge properties (i.e., functionality and zeta (ζ) potential) of two nanofiltration (NF) membranes were characterized by potentiometric titrations and electrophoresis to predict the electrostatic transport at the membrane surfaces affecting their salt rejection and fouling propensities. The ζ potential was not suitable for evaluating the rejection of Na<SUP>+</SUP> (NE20 membrane=21–25%; NE70 membrane=65–70%) and Cl<SUP>−</SUP> ions (NE20 membrane=19–22%; NE70 membrane=60–63%), and the fouling propensities of organic materials in the NF membranes due to its inherent measurement inaccuracies (∆ ζ potential=−1.8×(∆ amount of desorbed organic foulants)+45.9, R<SUP>2</SUP> =0.07). The functionality accurately predicted both the rejection of NaCl and the fouling propensities of the organic materials, as the charge densities of the membranes determined by the functionality measurements (only TFC membranes are applicable) truly reflected the acid dissociation constants of the carboxylic and amine functional groups and the points of zero charge values. These results indicate that potentiometric titrations may provide valuable insights into the electrostatic transport at the membrane surface influencing the salt rejection and fouling mechanisms of the NF membranes.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Potentiometric titration gives new insights into intrinsic surface charge properties of NF membranes. </LI> <LI> The pH value of the lowest salt rejection corresponds to not the IEP but the PZC. </LI> <LI> ζ potential could not predict the ionization degree of amine functional groups. </LI> <LI> Functionality truly reflects the electrostatic transport of organic materials at membrane surfaces. </LI> </UL> </P>

Equilibrium Crystal Shape of BaZrO3 and Space Charge Formation in the (011) Surface by Using Ab-Initio Thermodynamics

김지수,김영철 한국물리학회 2017 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.70 No.1

We investigated the equilibrium crystal shape of BaZrO3 and the space charge formation in an O-terminated (011) surface by using ab-initio thermodynamics. Twenty-two low-indexed (001), (011), and (111) surfaces were calculated to analyze their surface Gibbs-free energy under the stable condition of BaZrO3. Based on the Gibbs-Wulff theorem, the equilibrium crystal shape of BaZrO3 changed from cubic to decaoctahedral with decreasing Ba chemical potential. The dominant facets of BaZrO3 were {001} and {011}, which were well consistent with experimental observations. The space charge formation in the (011) surface was evaluated using the space-charge model. We found that the (011) surface was even more resistive than the (001) surface.

Facile and controllable surface-functionalization of TiO₂ nanotubes array for highly-efficient photoelectrochemical water-oxidation

Kim, Jin Un,Han, Hyun Soo,Park, Joonsuk,Park, Woosung,Baek, Ji Hyun,Lee, Jae Myeong,Jung, Hyun Suk,Cho, In Sun Academic Press 2018 Journal of catalysis Vol.365 No.-

<P><B>Abstract</B></P> <P>We report facile and effective surface-functionalization of TiO<SUB>2</SUB> nanotubes array (NTs) via a TiCl<SUB>3</SUB>-mediated solution treatment and its effects on the charge transport and transfer properties for photoelectrochemical (PEC) water-oxidation. TiO<SUB>2</SUB> NTs with ∼5 μm length were prepared by hydrothermal-etching a TiO<SUB>2</SUB> nanorods array. Subsequently, TiO<SUB>2</SUB> NTs were treated with an aqueous TiCl<SUB>3</SUB> solution at 80 °C to generate surface oxygen vacancies and to deposit a TiO<SUB>2</SUB> nano-branch layer on the side-walls of TiO<SUB>2</SUB> NTs, and these modifications were confirmed by X-ray photoelectron spectroscopy and transmission electron microscopy. Through electrochemical impedance spectroscopy analysis, we found that the TiCl<SUB>3</SUB>-mediated surface-functionalization of TiO<SUB>2</SUB> NTs significantly improves the charge carrier transport and transfer properties, owing to the increase in the charge carrier density (due to the generation of surface oxygen vacancies) and surface roughness (due to the formation of nano-branches), respectively. The TiCl<SUB>3</SUB> treatment considerably improves the incident photon-to-current conversion efficiency (IPCE) and photocurrent density of TiO<SUB>2</SUB> NTs (especially at low-bias potentials) during the PEC water-oxidation, and the treated material demonstrates a maximum IPCE of ∼93% and a photocurrent density of ∼2.25 mA/cm<SUP>2</SUP> at 1.23 V versus the reversible hydrogen electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Development of facile and effective surface-functionalization via TiCl<SUB>3</SUB> solution treatment. </LI> <LI> Dual functionality; generation of oxygen vacancies and deposition of nano-branches. </LI> <LI> Simultaneous improvement of charge transport and transfer efficiencies in TiO<SUB>2</SUB> nanotubes. </LI> <LI> Significantly improved PEC water-oxidation performance; 2.25 mA cm<SUP>−2</SUP> at 1.23 V<SUB>RHE.</SUB> </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Controlling Cell Alignment On the Charged Surface Pattern without Topological Height Difference

김동갑,김민수,정영도 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

Controlling morphological property of surface including various micro-patterns can modulate cells' adhesion, proliferation, and alignment. However, the variation of depth between patterns impedes the cell-cell communication, threatening cells’ homeostasis. Here, we report a new approach for surface modification able to provide both spatial cell alignment and environment for intercellular communications using charged nanoparticles. We fabricated that the periodic patterns of a surface with different charges using photolithography and nanoparticle with charged ligands. The cells on the patterned surface aligned the lines of the pattern without geometrical variations. The surface fabricated by our approach can provide more enhanced environments to communicate via gap junctions than groove patterned surfaces. This strategy using the difference of charge density paves a new way to control the cell behavior on surfaces, providing a clue to regulate spatially physiologic processes.

Strategy for enhancing the solar-driven water splitting performance of TiO₂ nanorod arrays with thin Zn(O,S) passivated layer by atomic layer deposition

Shin, S.W.,Suryawanshi, M.P.,Hong, H.K.,Yun, G.,Lim, D.,Heo, J.,Kang, S.H.,Kim, J.H. Pergamon Press 2016 ELECTROCHIMICA ACTA Vol.219 No.-

An array of one dimensional (1D) TiO<SUB>2</SUB> nanorods (TONRs) has been regarded as an attractive candidate for electrochemical energy conversion and as storage device due to its large surface area, effiective light scattering, and undisturbed charge transport pathway. However, the high defect/trap densities on surface of the nanostructured morphology and architecture may generally hinder the performance enhancement by providing electron-hole recombination sites. Hence, the surface passivation of nanoarchitectures based photoelectrodes has recently received much attention as an effective strategy to enhance the charge-separation and charge-transfer processes in photoelectrochemical (PEC) water splitting devices. In particular, a coating layer with narrowing band gap materials can promote enhanced light harvesting in the UV-vis region as well as surface passivation, directly supplying a driving force for charge separation and charge transfer due to band alignment. In this paper, the surface of TONRs were passivated by 10 and 30nm thick Zn(O,S) layers with a relatively narrow band gap using an atomic layer deposition technique to modulate the thickness exactly. The 10nm Zn(O,S)/TONR array exhibits a significantly enhanced photocurrent density (J<SUB>sc</SUB>) of 5.94mA/cm<SUP>2</SUP> at 1.23eV vs NHE and an incident photon-to-electron conversion efficiency (IPCE) of 49% at 374nm compared with that of TONR arrays (J<SUB>sc</SUB> of 1.99mA/cm<SUP>2</SUP> at 1.23eV vs NHE and an IPCE of 20% at 380nm). However, the PEC performance is worse in the 30nm Zn(O,S)/TONR arrays, showing a J<SUB>sc</SUB> of 3.09mA/cm<SUP>2</SUP> at 1.23eV vs NHE and an IPCE of 29% at 374nm. To clearly demonstrate these PEC behaviors, the TONR and Zn(O,S)/TONR arrays were characterized by electrochemical impedance spectroscopy (EIS), open circuit voltage decay (OCV) measurement, and X-ray photoelectron spectroscopy (XPS). The above mentioned characterizations indicate that the enhanced PEC performance of the 10nm Zn(O,S)/TONR array resulted from the (i) increased light harvesting in the UV-vis region, (ii) lower charge transfer resistance and (iii) high value of valence band offset (VBO, -1.44eV) and conduction band offset (CBO, -1.2eV) than those of the TONR. However, the deterioration of J<SUB>sc</SUB> in the 30nm Zn(O,S)/TONR array is attributed to the negative value of VBO (-0.13eV) and positive value of CBO (+0.27eV), as well as the higher charge transfer resistance to the electrolyte than that of the TONR arrays, despite of the improved light absorption in the visible region. The photocurrent densities of 10nm Zn(O,S)/TONR and 30nm Zn(O,S)/TONR photocathodes decay to 4.718mA/cm<SUP>2</SUP> (5.90mA/cm<SUP>2</SUP> at 0min) and 2.212mA/cm<SUP>2</SUP> (3.03mA/cm<SUP>2</SUP> at 0min) after 90min, respectively, they retain of about~80% and 70% of its original values. These experimental results and discussions not only provide the physical insights into the surface passivation effect and band alignment but also can open a promising route to design the thin passivation layer having the narrowing band gap energy (1.0eV~2.5eV) on the 1D TiO<SUB>2</SUB> nanostructure for further enhanced performance and realization of a TiO<SUB>2</SUB> based PEC system.