Electron Current Density Research Articles

Electronic current densities and origin-independent property densities induced by optical fields.

The interaction of a molecule with optical fields is customarily interpreted by means of induced time-dependent electric polarizabilities, magnetizabilities and mixed electric-magnetic polarizabilities. In general, these properties can be rationalized by integrals of density functions formulated in terms of induced charge and current densities. In this perspective, we focus on what has been done so far at the theoretical level, and on what can be expected to be unveiled from the topological study of suitable density functions, endowed with the fundamental requirement of origin invariance. Densities characterized by such a property can be integrated all over the configuration space to obtain electric dipole polarizability and optical rotatory power. Corresponding maps visualize domains mainly involved in the molecular response. The diagonal components of origin-independent density tensor functions that, on integration, yield corresponding electric dipole polarizability tensor of benzene, naphthalene, phenanthrene and ovalene, have been computed, confirming the ubiquitous presence of counter-polarization regions in the proximity of the atomic nuclei. They are associated with toroidal electron currents, induced by time derivative of the electric field of impinging radiation. Electron (de)localization in these systems is readily observed and estimated. The optical rotation density of the carbonyl chromophore is studied in detail. Its essential feature is the separation in quadrants of alternating sign of density about the CO bond. The presence of an extrachromophoric perturbation determines asymmetry in the extension of the quadrant distribution, thus causing optical rotation.

TCAD Modeling of High-Field Electron Transport in Bulk Wurtzite GaN: The Full-Band SHE-BTE

Gallium Nitride (GaN) High-Electron Mobility Transistors (HEMTs) actually represent one of the best candidates for medium-high power and radio frequency applications. As they operate at large bias and electric fields, a comprehensive analysis of the high-field transport properties is fundamentals, as hot electrons are expected to play a relevant role for the device reliability. In this perspective, Technology Computer-Aided Design (TCAD) simulations can be a very useful tool for the understanding of the phenomena dominating hot-electron degradation mechanisms. The most-accurate modeling approaches are based on the direct solution of the Boltzmann equation, which is not actually available for the GaN material. In this work, the deterministic solution of the Boltzmann transport equation via the spherical-harmonics expansion (SHE-BTE), as incorporated in a commercial TCAD tool, has been extended to the analysis of GaN electrons. To this purpose, the details of the full-band structure has been derived from DFT calculations as in state-of-art literature works, and the electron density of states, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$g(E)$ </tex-math></inline-formula> , and group velocity <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$u_{g}(E)$ </tex-math></inline-formula> , have been calculated for the SHE-BTE for the first time. In addition to this, an accurate calibration of the total scattering rate accounting for nonpolar acoustic and optical carrier-phonon interaction, Coulomb scattering and impact ionization has been carried out against available Monte Carlo data and experiments. The proposed model is also shown to correctly predict the temperature dependence of the electron impact-ionization coefficient and current density up to breakdown.

The features of the InGaAs/InP detectors in plasma converter systems

The features of the plasma cell with the InGaAs/InP detector are explored. The detector is composed of InGaAs and InP wafers. Mean electron energies, migrative electron flux and current densities are evaluated by theoretical simulation analyses. The results helped to understand the uncertain plasma parameters and made the plasma structure more understandable, thereby, the complex plasma reactions can be solved via the COMSOL package. New plasma studies have focused on uniform discharges. However, the optimization of the plasma structure should be ascertained in order to explain the complex physical and chemical features in the complicated media having different discharge mechanisms. The non-thermal plasmas are famous especially for the microelectronic systems and surface processes such as etching and purification.

Probing Electronic Symmetry Reduction during Charge Migration via Time-Resolved X-Ray Diffraction.

The present work focuses on probing ultrafast charge migration after symmetry-breaking excitation using ultrashort laser pulses. LiCN is chosen as prototypical system because it can be oriented in the laboratory frame and it possesses optically-accessible charge transfer states at low energies. The charge migration is simulated within the hybrid time-dependent density functional theory/configuration interaction framework. Time-resolved electronic current densities and simulated time-resolved x-ray diffraction signals are used to unravel the mechanism of charge migration. Our simulations demonstrate that specific choices of laser polarization lead to a control over the symmetry of the induced charge migration. Moreover, time-resolved x-ray diffraction signals are shown to encode transient symmetry reduction at intermediate times.

Steady states stability features of the electron–positron plasma diode

Stationary states stability features of a planar geometry diode with electron and positron counter flows are studied. Such a diode may be considered as a model to elucidate the nature of the pulsar radio emission. The equation for the electric field perturbation amplitude is derived. The exact solution of this equation for the homogeneous stationary field is found. On the basis of the plasma dispersion relation, the stability threshold in terms of the electron current density is found above which the stationary solutions become unstable. This threshold turned out to be 2 times higher than the known Pierce threshold. It can be expected that the development of the detected instability will lead to the electric field oscillations that induce electromagnetic radiation.

Cathodoluminescence monitoring of quantum emitter activation in hexagonal boron nitride

The ability to locally activate or generate quantum emitters in two-dimensional materials is of major interest for the realization of integrated quantum photonic devices. In particular, hexagonal boron nitride (hBN) has recently been shown to allow a variety of techniques for obtaining quantum emitters at desired locations. Here, we use cathodoluminescence (CL) to monitor in situ the local activation of color centers by an electron beam in hBN. We observe that the CL signal saturates at a given surface dose, independently of the electron current density. Based on photoluminescence and photon correlations, we show that the number of photoactive color centers is proportional to the CL signal, and we estimate the maximum density of quantum emitters that can be generated by our technique. Our results provide insight about the activation mechanism and could help to optimize the controlled generation of single photon sources in hexagonal boron nitride.

Recent Developments in MaMFIS Technology for the Production of Highly Charged Ions

We present results for the production of highly charged ions in a rippled electron beam propagating in a multi-section drift tube with different electrostatic potentials in an axial magnetic focusing field. The inner-shell ionization of target atoms by electron impact occurs in local ion traps formed at the electron-beam crossovers. The utmost electron current density achieved is assessed at ~10 kA/cm2. The successive ionization of cathode materials and working substances such as xenon and bismuth was investigated as a function of the confinement time. The characteristic X-ray radiation from ions including Ir62+, Ce48+, Xe46+, and Bi60+ was detected. It is shown that it is possible to extract highly charged ions from local ion traps for a certain geometry of the drift tube structure and a certain distribution of the electric potentials.

Oriented CuWO4 Films for Improved Photoelectrochemical Water Splitting.

Hydrogen generation through photoelectrochemical (PEC) technology is one of the most appropriate ways for delivering sustainable fuel. Simultaneously, anisotropic properties will be exhibited by the materials with low crystal symmetry, allowing the tuning of the PEC properties by controlling the crystallographic orientation and exposed facets. Therefore, we synthesized copper tungstate films (CuWO4) with highly exposed (100) crystal facets by regulating anions in the precursor solution. According to experimental characterization and density functional theory calculations, the CuWO4 film with a high exposure ratio of the (100) crystal facet has promoted charge transport with trap-free mode and reduced recombination of electrons and holes. Meanwhile, the oxygen evolution reaction is promoted on the (100) facet because of the relatively low energy barrier. Compared to the CuWO4 with other mixed exposure facets, CuWO4 with a highly exposed (100) facet presents a twofold current density (0.38 mA/cm2) and one-fifteenth electron transit time (0.698 ms) and also has great stability (more than 6 h). These results provide an easy way to enhance the PEC performance by modulating the exposure facets of the film electrode.

Nuclear versus electronic ring currents in oriented torsional molecules induced by magnetic fields. II. Electronic currents of toluene

The theory of nuclear ring currents of torsional molecules induced by an external magnetic field along the torsion axis was developed in the preceding paper [D. Jia et al., preceding paper, Phys. Rev. A 106, 042801 (2022)]. Here we study the magnetically induced electronic current density (MIC) for toluene in the presence of an external magnetic field that is aligned with the torsion axis of the methyl group. Properties of the MIC are studied in detail at the density-functional theory (DFT) level using our gauge-including magnetically induced current method, the derivation of which is briefly outlined. The strength of the MIC is determined by numerical integration and compared to the estimated strength of the magnetically induced nuclear ring current reported in the preceding paper. Spatial contributions to the diatropic and paratropic MICs are discussed in detail, where the diatropic MIC flows in the classical direction and the paratropic MIC flows in the opposite direction. The MIC in the vicinity of the methyl group is mainly diatropic, whereas the phenyl group ring is dominated by a paratropic MIC of $\ensuremath{-}14.90\phantom{\rule{4pt}{0ex}}\mathrm{nA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$ localized to the carbon atoms. The strength of the MIC near the methyl group is $10.41\phantom{\rule{4pt}{0ex}}\mathrm{nA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$, which is of about the same size as the strength of the ring current of benzene when the magnetic field is perpendicular to the molecular ring. The strength of the magnetically induced nuclear ring current of the whole toluene molecule is $19.9\phantom{\rule{4pt}{0ex}}\mathrm{pA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$, which is two orders of magnitude smaller than the electronic one of $\ensuremath{-}1.93\phantom{\rule{4pt}{0ex}}\mathrm{nA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$ calculated for the eclipsed structure at the employed DFT level. This value is in perfect agreement with the current strength of $\ensuremath{-}1.93\phantom{\rule{4pt}{0ex}}\mathrm{nA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$ calculated at the coupled-cluster singles and doubles level with a perturbative treatment of the triple excitations. The current strength calculated at the second-order M\o{}ller-Plesset perturbation level is $1.20\phantom{\rule{4pt}{0ex}}\mathrm{nA}\phantom{\rule{0.16em}{0ex}}{\mathrm{T}}^{\ensuremath{-}1}$, which is of the same size with opposite sign.

Characteristics and Underlying Physics of Bipolar Corona Discharge of Floating Conductor

Bipolar corona discharge is the fundamental phenomenon that preoccurs in air breakdown for nongrounded objects facing a high-voltage source, which sets important bases for aircraft protection crossing thunderclouds and improvement of high-voltage switches with floating conductors, while this phenomenon has not been fully understood to date. This article proposes a bipolar corona plasma model (BCPM) based on the plasma hydrodynamic process and the chemical reactions of air discharge. The numerical analysis of the charged particle distribution matches the experimental result of the bipolar corona discharge appearance. Furthermore, the characteristics of bipolar corona discharge are described from the perspective of electric field and electron current density at the two opposite ends of the floating conductor. Results show that, at the positive end, the corona discharge has a long columnar shape in a faint light blue. While at the negative end, the corona presents a spherical shape in a stronger luminous light purple. There exists a density extremum at the position 0.03 cm away from the conductor ends in the distribution of electrons, where a low electron density zone with a concentration of 0.42 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{13}\,\,\text{m}^{-3}$ </tex-math></inline-formula> forms at the positive end, while electrons group to a high density of 2 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times \,\,10^{16}\,\,\text{m}^{-3}$ </tex-math></inline-formula> at the negative end. The geometric length of the high-density ions zone is enlarged by 2 times at the positive end compared to the negative end. The peak electric field at the negative end is about 1.5 times stronger than the electric field at the positive end, consistent with the space charge distribution at the positive and negative ends. The unbalance of the emission and entry of electron current results in a slightly positive polarity for the floating conductor. This study can be consulted for shedding light on the underlying physics of bipolar corona discharge of floating conductors.

Graphene-Based High Current Density Electron Emitters for THz-VEDs

One of the critical technologies for the development of a compact high-power terahertz (THz)-VEDs is the requirement of efficient cathodes with emission density in excess of 1000 A/cm2. In view of this, it is proposed to develop graphene-based field emitters with low electrical resistivity. Average ~100-nm ultrathin free-standing reduced graphene oxide (rGO) films (4 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times4$ </tex-math></inline-formula> mm) were developed using modified hummers method followed by hydrothermal technique and thermal reduction. The <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I-V$ </tex-math></inline-formula> characterization of the developed film was carried out in specially designed UHV chamber in closely spaced diode (CSD) mode. The maximum current density obtained from the rGO film was ~500 A/cm2 at 4 V/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> . Further improvement in the current density was achieved by doping tungsten ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> ) into rGO film using dc sputtering followed by thermal annealing. The average resistivity of the film was found to be very low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sim 15\,\,\times \,\,10^{-7}\,\,\Omega $ </tex-math></inline-formula> -m, due to the uniform doping of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> nanoparticles into the film. The emission characterization result showed that this <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -rGO film could deliver a maximum current density in excess of 1500 A/cm2 at 4 V/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> , which makes it a potential candidate for use in THz-VEDs applications.

Putrescine adsorption on pristine and Cu-decorated B12N12 nanocages: A density functional theory study

Putrescine (Put) adsorption on pure B12N12 and Cu-decorated (Cu– B12N12) nanocages was evaluated using density functional theory (DFT) calculations. Adsorption of copper on B12N12 results in two optimized geometries, named Cu@b66 and Cu@b64, with adsorption energies of approximately −2.01 and −2.07 eV, respectively. The results revealed that adsorption was a chemical process and adsorption energy decreased as follows: B12N12 > Cu@b64 > Cu@b66. DFT calculations indicated that the changes in gap energy (ΔEgap) of Cu@b66 (+16.28%) and Cu@b64 (+24.17%) were larger than that of B12N12 (−1.37%); so, Cu@b66 and Cu@b64 were more sensitive toward Put than pure B12N12. The changes in work function (ΔΦ) of the nanocages after interacting with Put increased as follows: B12N12 (23.33%) < Cu@b66 (34.21%) < Cu@b64 (41.97%), indicating that Put can be detected by the increase in electron current density of the nanocage–Put complexes. Quantum molecular dynamic reveal one interconversion from Cu@b66 to Cu@b64 with and without putrescine, implying that only Cu@b64 should be employed as potential conductometric and work function-type sensor for detecting of putrescine.

Characterization of Pseudospark Discharge-Based Multigap Plasma Cathode Electron Source for the Generation of Short Pulsed Energetic Electron Beam

Pseudospark (PS) discharge-based devices are known as excellent source for the generation of high current density and energetic self-focused electron beam in the hollow cathode (HC) phase. In this article, short pulsed ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\!\!\!&lt; 100$ </tex-math></inline-formula> ns) and high energetic (~20 keV) electron beam has been generated and propagated (up to ~60 mm) in the drift region without using any external guiding magnetic field from the four-gap configuration of PS discharge-based plasma cathode electron (PD-PCE) source. The particle-in-cell (PIC) simulation code OOPIC Pro has been employed, whose results have shown the strong dependence of beam propagation into the drift region on the penetration and distribution of potential lines. The combined experimental and simulation investigations have also been carried for the multigap (four-gap) with wide range of external storage capacitor (40 pF–18 nF) and operating voltages (5–35 kV). The circuit parameter controls the appearance of HC phase for the energetic (50%–70% applied voltage) electron beam and conductive phase for the high current (~10 A to ~0.5 kA) electron beam. The potential distribution has clearly indicated that the electron beam with higher applied voltages can propagate more focused in the drift region. The investigations have evidently shown the generation of low energy and high current to high energy and low current electron beams suitable to cover the potential applications in the field of extreme ultraviolet (EUV)/soft X-ray radiation generation, surface modification, and microwave-terahertz radiation generation.

High-temperature Knudsen thermionic converter with multicavity emitter

This article describes an experimental study of the electrical and kinetic parameters of a Knudsen-mode thermionic converter (TIC) equipped both with a multicavity and a smooth emitter that converts heat into electrical energy using a combination of cesium and barium vapors. In the study, we recorded and analyzed data on how the maximum electron current density and the specific power are affected by the values of cesium and barium vapors pressure, the width of the interelectrode gap, and such parameters of the emitters as temperature and surface geometry. By analyzing the influence of surface geometry, it was revealed that the values of the electron current density and the electric power are four times higher in a TIC with a multicavity emitter compared to a TIC with a smooth emitter. TIC efficiency was analyzed taking into account the effective emissivity of the multicavity emitter. It is shown that the efficiency of such a TIC exceeds that of a TIC with a smooth emitter despite a slight increase in heat transfer from the emitter to the collector due to radiation.

Fluid simulation on effect of background magnetic field on plasma characteristics in a Hall thruster

Herein, the effect of the background magnetic field on plasma characteristics in a Hall thruster is numerically investigated using DUT-HTFS [Li et al., AIP Adv. 12, 015117 (2022)], an integrated fluid simulation platform on Hall thruster plasmas. The research shows that the background magnetic field significantly influences the distribution of the plasma density, especially the radial profiles of the plasma density near the ionization region and the acceleration region. In addition, the positions of the peak values of the electron power absorptions mainly occur near the dielectric walls of the exhaust plane, and the electron power absorption mechanism is mainly dominated by the Ohmic heating. The peak values of the axial electron current density on the inner and outer dielectric walls are higher than that on the centerline. This phenomenon is closely related to the near wall conduction mechanism of the electrons. In addition, the background magnetic field significantly influences the shapes, positions, and magnitudes of the peak values of the plasma parameters, such as the plasma density, the electron current density, the axial electric field, the electric potential, and the ionization rate. These results will help us to provide a valuable reference and reduce the risk for the experimental test programs and the applications of Hall thrusters in the future.

Atomically dispersed Co anchored on N,S-riched carbon as efficient electrocatalysts for advanced Li-S batteries

Lithium-sulfur (Li-S) battery possess the advantage of high specific energy but suffer from unstable cyclic performance due to the sluggish liquid-solid conversion kinetics causing severe lithium polysulfides (LiPS) shuttling. Designing multifunctional electrocatalysts with improved activity and abundant active sites to regulate the dynamics for sulfur electrochemistry is still a significant challenge. Herein, we proposed a thiourea assisted pyrolysis combined with hard template method to synthesize cobalt single atoms co-coordinated by N and S atoms embedded hollow carbon spheres (Co-NS-HCS) as a novel sulfur host. The Co-NS-HCS mainly consists of well-dispersed Co-N 3 S-C center sites where Co is co-bonded by N and S atoms. Systematical characterizations revealed that the Co-NS-HCS exhibit improved SRR electrocatalytic properties with higher exchange current density and larger electron transfer number than that of Co-N-HCS. When equipped in sulfur cathodes, the S@Co-NS-HCS exhibits superior rate performance (925 mAh g −1 at 2 C), long cycle stability (69.1% of capacity retention after 500 cycles at 1 C). Moreover, the assembled Li-S pouch type cell also exhibits competitive cyclic performance that work stably for 100 cycles at 0.1 C with a high capacity retention of 84.7%. This work furnishes a feasible scheme for the rational design of single atoms catalysts with improved electrocatalytic activity for sulfur cathodes based on the coordination environment regulation strategy. Cobalt single atoms co-coordinated by N and S atoms embedded hollow carbon spheres is synthesized as a highly efficient sulfur electrocatalyst to boost both the sulfur reduction and Li 2 S oxidation for advanced Li-S batteries with improved cyclic performance. • Co single atoms coordinated by N/S are designed as efficient electrocatalysts. • The redox reaction kinetics of LiPS are boosted through S modulation. • The shuttle effect of LiPS is efficiently suppressed. • A high capacity retention of 84.7% is obtained in Li-S pouch cell.

Blending fiber-shaped long-range conductive additives for better battery performance: Mechanism study based on heterogeneous electrode model

Conductive additives in lithium-ion batteries are indispensable for constructing electronic conductive networks and enabling continuous electrochemical reactions. Fine carbon black powder, typically composed of small round particles with a diameter of tens of nanometers, is the most commonly used conductive additive. The experimental results in some literature indicate that blending fiber-shaped conductive additives can help boost battery performance. The heterogenous electrode model is employed in this study to explore the distribution of electronic current density within lithium-ions batteries, demonstrate the benefits of blending fiber-shaped long-range conductive additives, and shed light on its mechanism. Our findings show that the introduction of long-range conductive additives leads to reallocation of the electron flow: as the proportion/weight ratio of long-range conductive additives increases, the electronic current undertaken by all conductive additives increases, while that undertaken by the active particles decreases. Without changing the total wt.% of conductive additives in batteries, the ohmic resistance of the electrode and the whole cell can be significantly reduced due to more electrons passing through compositions with better conductivity. These results help researchers gain a better understanding on the correlation between conductive network geometry and electron transfer effectiveness.

Recent progress on the J-TEXT three-wave polarimeter-interferometer

The J-TEXT three-wave polarimeter-interferometer system (POLARIS), which measures time-space distribution of electron density and current density, has been optimized with both the optical system and the equilibrium reconstruction method. The phase resolution of a Faraday rotation angle has been improved from 0.1 to 0.06 degree in chords from –0.18 to 0.18 m (plasma minor radius), and the sawtooth oscillation behavior has been detected by Faraday rotation angle measurement. By combining the POLARIS measured data and the equilibrium and fitting code (EFIT), an upgraded equilibrium reconstruction method has been developed, which provides a more accurate temporal and spatial distribution of current density and electron density. By means of the optimized POLARIS and improved equilibrium reconstruction, variations of profiles with increasing density have been carried out, under both Ohmic and electron cyclotron resonance heating discharges.

Conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled plasmas

A numerical model is developed to study the conductivity effects during the transition from collisionless to collisional regimes in cylindrical inductively coupled argon plasmas at pressures of 0.1–20 Pa. The model consists of electron kinetics module, electromagnetics module, and global model module. It allows for self-consistent description of non-local electron kinetics and collisionless electron heating in terms of the conductivity of homogeneous hot plasma. Simulation results for non-local conductivity case are compared with predictions for the assumption of local conductivity case. Electron densities and effective electron temperatures under non-local and local conductivities show obvious differences at relatively low pressures. As increasing pressure, the results under the two cases of conductivities tend to converge, which indicates the transition from collisionless to collisional regimes. At relatively low pressures the local negative power absorption is predicted by non-local conductivity case but not captured by local conductivity case. The two-dimensional (2D) profiles of electron current density and electric field are coincident for local conductivity case in the pressure range of interest, but it roughly holds true for non-local conductivity case at very high pressure. In addition, an effective conductivity with consideration of non-collisional stochastic heating effect is introduced. The effective conductivity almost reproduces the electron density and effective electron temperature for the non-local conductivity case, but does not capture the non-local relation between electron current and electric field as well as the local negative power absorption that is observed for non-local conductivity case at low pressures.

Microbial Electrochemically Assisted Treatment Wetlands: Current Flow Density as a Performance Indicator in Real-Scale Systems in Mediterranean and Northern European Locations.

A METland is an innovative treatment wetland (TW) that relies on the stimulation of electroactive bacteria (EAB) to enhance the degradation of pollutants. The METland is designed in a short-circuit mode (in the absence of an external circuit) using an electroconductive bed capable of accepting electrons from the microbial metabolism of pollutants. Although METlands are proven to be highly efficient in removing organic pollutants, the study of in situ EAB activity in full-scale systems is a challenge due to the absence of a two-electrode configuration. For the first time, four independent full-scale METland systems were tested for the removal of organic pollutants and nutrients, establishing a correlation with the electroactive response generated by the presence of EAB. The removal efficiency of the systems was enhanced by plants and mixed oxic–anoxic conditions, with an average removal of 56 g of chemical oxygen demand (COD) mbed material–3 day–1 and 2 g of total nitrogen (TN) mbed material–3 day–1 for Ørby 2 (partially saturated system). The estimated electron current density (J) provides evidence of the presence of EAB and its relationship with the removal of organic matter. The tested METland systems reached the max. values of 188.14 mA m–2 (planted system; IMDEA 1), 223.84 mA m–2 (non-planted system; IMDEA 2), 125.96 mA m–2 (full saturated system; Ørby 1), and 123.01 mA m–2 (partially saturated system; Ørby 2). These electron flow values were remarkable for systems that were not designed for energy harvesting and unequivocally show how electrons circulate even in the absence of a two-electrode system. The relation between organic load rate (OLR) at the inlet and coulombic efficiency (CE; %) showed a decreasing trend, with values ranging from 8.8 to 53% (OLR from 2.0 to 16.4 g COD m–2 day–1) for IMDEA systems and from 0.8 to 2.5% (OLR from 41.9 to 45.6 g COD m–2 day–1) for Ørby systems. This pattern denotes that the treatment of complex mixtures such as real wastewater with high and variable OLR should not necessarily result in high CE values. METland technology was validated as an innovative and efficient solution for treating wastewater for decentralized locations.