Surface Power Density Research Articles

Effects of neoclassical tearing modes and toroidal field ripple on lost alpha power in the SPARC tokamak

Using the SPIRAL Monte Carlo, full particle-orbit simulation code, we investigate the effects of neoclassical tearing modes (NTMs) and toroidal field (TF) ripple on alpha power losses during steady-state operation of the SPARC primary reference discharge. Model perturbations for TF ripple and the and NTMs with exaggerated widths selected based on an H-mode plasma approaching thermal quench are added to a simulated SPARC magnetic equilibrium through which marker particles are tracked. The 3/2 and 2/1 NTMs are located at and respectively, well positioned to increase alpha particle transport into and within an outer lossy region of the plasma beyond where over 95% of lost alpha particles are born. Total alpha power losses are shown to increase modestly from 1.73% lost at a minimum to 2.34% lost at a maximum, and alpha particle surface power densities form localized hotspots on the first-wall near the low-field side midplane due to NTMs and TF ripple. We establish a conservative upper limit for first-wall alpha surface power densities on a toroidally symmetric wall for typical, flattop operation and motivate the consideration of NTMs in the design of three dimensional limiter surfaces for SPARC.

Determination of the Power Balance for Thin Ag–SnO₂ Electrodes Submitted to an Electric Arc Based on IR Thermography

The objective of the work presented here is to estimate the characteristics of the power balance, i.e., the power and the surface power density that the electric arc brings to silver–tin oxide (Ag–SnO2) electrodes. This work is first based on an experimental study carried out using an IR camera with which we measured the temperature in a zone close to the area impacted by the arc, but not flashed by it. In a second step, the temperature distributions obtained are compared with the results of a numerical model of the electrode heating. The model input parameters are the power <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P$ </tex-math></inline-formula> and the surface power density <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> . Solving this inverse problem thus makes it possible to estimate the values of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$P$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> leading to measured and calculated heating (temperature distribution) that are as similar as possible. Such a method has been applied for Ag–SnO2 cathodes and anodes and for various intensities of the arc current in a range of 80–200 A.

Assessment of Cytochrome c and Chlorophyll a as Natural Redox Mediators for Enzymatic Biofuel Cells Powered by Glucose

The development of new high-power biofuel cells has been limited in the past by slow or indirect charge transfer. In this study, enzymatic biofuel cell (EBFC) systems were explored with different materials used to evaluate their applicability as redox mediators. Redox mediators of different natures have been selected for this research. Cytochrome c, Chlorophyll a, and supernatant of ultrasonically disrupted algae Chlorella vulgaris cells were examined as potential redox mediators. The effect of heparin on the EBFC was also evaluated under the same analytical conditions. The measurements of open circuit potential (OCP) and the evaluation of the current response in two modes of measurement were performed (i) during potential cycling in cyclic voltammetry measurements or (ii) at the constant potential value in chronoamperometry, and were applied for the evaluation of EBFC. Cytochrome c, Chlorophyll a, and the supernatant of ultrasonically disrupted algae Chlorella vulgaris cells-based redox mediators were efficient in the glucose oxidase (GOx) based EBFC. Electron transfer from GOx to the electrode was facilitated through the redox mediators adsorbed on the electrode. Electrodes modified with Chlorophyll a- and Cytochrome c-based redox mediators were suitable for the development of glucose biosensors. This was demonstrated by increasing the glucose concentration within 0 mM–100 mM in the system, the current density increased, and the system reached equilibrium rather faster regarding the electrochemical reaction. The power density is an important feature in revealing the action of biofuel cells. The highest power values were generated by the systems based on the application of redox-mediated Chlorophyll a and the supernatant of ultrasonically disrupted Chlorella vulgaris cells. The surface power density was about 2.5–4.0 µW/cm2. Control of a study was performed with a polished graphite electrode and the maximum surface power density was 0.02471 µW/cm2.

Achieving High Power Density and Durability of Sliding Mode Triboelectric Nanogenerator by Double Charge Supplement Strategy

AbstractTriboelectric nanogenerators (TENGs), a promising energy harvesting technology for distributed power sources, faces inevitable issues regarding long‐term wear and durability. However, current low‐wear TENGs are impaired by lower performances due to low charge density. Here, both issues are addressed using a double charge supplement TENG (DCS‐TENG). Adding two low friction charge brushes allows the DCS‐TENG to achieve a high surface charge density (76.5 µC m−2) and power density (697.5 mW m−2 Hz–1), setting a new record among previously reported low‐wear TENGs. Moreover, the device exhibits unprecedented durability with an attenuation of only 5% after continuous operation for 110 h (3 960 000 cycles). Using a customized energy management module, a 3 × 7 hygrothermograph array, a high‐power vehicle's radar and accelerometer modules are stably powered, demonstrating the DCS‐TENG's strong electrical load capacity. This strategy provides a facile and effective path to conjointly boost power output and durability of TENGs, taking them to the next level for practical applications.

Hemicellulosa-derived Arenga pinnata bunches as free-standing carbon nanofiber membranes for electrode material supercapacitors

Carbon nanofibers derived from lignocellulosic materials have become the most prevalent free-standing electrode material for supercapacitors due to their renewable and sustainable nature. This study used Arenga pinnata bunches (APB) as raw material for hemicellulose compounds to produce carbon electrodes through carbonization processes at 650 °C, 700 °C, 750 °C, and 800 °C, in the presence of flowing N2 gas. The variations in carbonization temperature resulted in carbon electrodes with surface morphology having a nanofiber structure with micro-meso pore distribution. According to the results, the carbonization temperature of 700 °C (APB-700) is the optimum temperature for producing electrode surface morphology with a combination of nanofiber, micro-and mesopore distributions, as well as specific surface area, specific capacitance, energy density, and power density of 1231.896 m2 g−1, 201.6 F g−1, 28.0 Wh kg−1, and 109.5 W kg−1, respectively, for the two electrode systems. This shows the combination of nanofibers and the distribution of micro-and mesopores produced with variations in carbonization temperature has the capacity to improve the performance of supercapacitor cells. Therefore, carbon nanofibers derived from Arenga pinnata bunches have the potential to be used as free-standing electrode materials for supercapacitors without employing doping, binder, electrospinning, and heteroatom template methods.

Pyroelectric Nanogenerator Based on an SbSI-TiO2 Nanocomposite.

For the first time, a composite of ferroelectric antimony sulfoiodide (SbSI) nanowires and non-ferroelectric titanium dioxide (TiO2) nanoparticles was applied as a pyroelectric nanogenerator. SbSI nanowires were fabricated under ultrasonic treatment. Sonochemical synthesis was performed in the presence of TiO2 nanoparticles. The mean lateral dimension da = 68(2) nm and the length La = 2.52(7) µm of the SbSI nanowires were determined. TiO2 nanoparticles served as binders in the synthesized nanocomposite, which allowed for the preparation of dense films via the simple drop-casting method. The SbSI–TiO2 nanocomposite film was sandwiched between gold and indium tin oxide (ITO) electrodes. The Curie temperature of TC = 294(2) K was evaluated and confirmed to be consistent with the data reported in the literature for ferroelectric SbSI. The SbSI–TiO2 device was subjected to periodic thermal fluctuations. The measured pyroelectric signals were highly correlated with the temperature change waveforms. The magnitude of the pyroelectric current was found to be a linear function of the temperature change rate. The high value of the pyroelectric coefficient p = 264(7) nC/(cm2·K) was determined for the SbSI–TiO2 nanocomposite. When the rate of temperature change was equal dT/dt = 62.5 mK/s, the maximum and average surface power densities of the SbSI–TiO2 nanogenerator reached 8.39(2) and 2.57(2) µW/m2, respectively.

Energy deposition and melt deformation on the ITER first wall due to disruptions and vertical displacement events

An analysis workflow has been developed to assess energy deposition and material damage for ITER vertical displacement events (VDEs) and major disruptions (MD). This paper describes the use of this workflow to assess the melt damage to be expected during unmitigated current quench (CQ) phases of VDEs and MDs at different points in the ITER research plan. The plasma scenarios are modeled using the DINA code with variations in plasma current I p, disruption direction (upwards or downwards), Be impurity density n Be, and diffusion coefficient χ. Magnetic field line tracing using SMITER calculates time-dependent, 3D maps of surface power density q ⊥ on the Be-armored first wall panels (FWPs) throughout the CQ. MEMOS-U determines the temperature response, macroscopic melt motion, and final surface topology of each FWP. Effects of Be vapor shielding are included. Scenarios at the baseline combination of I p and toroidal field (15 MA/5.3 T) show the most extreme melt damage, with the assumed n Be having a strong impact on the disruption duration, peak q ⊥ and total energy deposition to the first wall. The worst-cases are upward 15 MA VDEs and MDs at lower values of n Be, with q ⊥,max = 307 MW m−2 and maximum erosion losses of ∼2 mm after timespans of ∼400–500 ms. All scenarios at 5 MA avoided melt damage, and only one 7.5 MA scenario yields a notable erosion depth of 0.25 mm. These results imply that disruptions during 5 MA, and some 7.5 MA, operating scenarios will be acceptable during the pre-fusion power operation phases of ITER. Preliminary analysis shows that localized melt damage for the worst-case disruption should have a limited impact on subsequent stationary power handling capability.

Layer-by-Layer Polydimethylsiloxane Modification Using a Two-Nozzle Spray Process for High Durability of the Cathode Catalyst in Proton-Exchange Membrane Fuel Cells.

The catalyst layer's high durability is essential in commercializing polymer electrolyte membrane fuel cells (PEMFCs), particularly for vehicle applications, because their frequent on/off operation can induce carbon corrosion, which affects surface properties and morphological characteristics of the carbon and results in aggregation and detachment of Pt nanoparticles on the carbon surface. Herein, to address the carbon corrosion problem while delivering a high-performance PEMFC, polydimethylsiloxane (PDMS) with high gas permeability, chemical stability, and hydrophobicity was employed to protect the catalyst layer from carbon corrosion and improve the mass transport. Because the catalyst slurry using alcohol-based solvents showed low compatibility with nonpolar solvents of the PDMS solution, a parallel two-nozzle system with separated solution reservoirs was developed by modifying a conventional three-dimensional printing machine. To determine the optimal PDMS amount in the cathode catalyst layer, PDMS solution concentration was varied by quantitatively controlling the PDMS amount coated on the electrode layer. Finally, the PEMFC with the PDMS-modified cathode of 0.1 mgPDMS cm-2 loading showed enhanced durability due to increased electrochemical surface and maximum power density by 37.2 and 21.7%, respectively, after the accelerated stress test. Furthermore, an improvement in the initial performance from enhanced water management was observed compared to those of PEMFCs with a conventional electrode.

Chitin and chitosan based biopolymer derived electrode materials for supercapacitor applications: A critical review

Supercapacitors have received a great attention owing to their exceptional characteristics like outstanding cycle life, high power and eco-friendly nature. In recent years, chitin/chitosan derived porous carbon electrode materials for energy storage applications have gained a substantial consideration due to their broad accessibility, high porosity, less weight, natural biodegradability, renewability, and eco-friendly. More importantly, chitin/chitosan biopolymers have a linear long chain-like moiety attached to functionalize the surface groups with -β-D glucosidic linkage which can be exploited as templates for constructing electrode materials with tunable and well-definite geometrics. The main focus was on porous carbon derived from heteroatoms doped chitin/chitosan biopolymers along with their composites in supercapacitor applications. In addition, the overall behaviors in supercapacitor application have been discussed in terms of specific capacitance, specific surface area, voltage window, energy density, and power density. Furthermore, the present review addresses the up-to-date development accomplished in chitin/chitosan materials for supercapacitor electrodes. Eventually, the recent challenges and forthcoming perspectives of the chitin/chitosan biopolymer derived porous carbon electrode materials with respect to the supercapacitor’s performance were thoroughly tinted along with future energy storage devices, such as fuel cell, solar cells and lithium ion battery.

Flexible electroactive PVDF/ZnO nanocomposite with high output power and current density

AbstractIn the present study, a lightweight and flexible polyvinylidene fluoride (PVDF)/zinc oxide (ZnO) nanocomposite was prepared using a low‐temperature phase‐inversion process. The synergetic effect of low‐temperature, phase‐inversion, and the integration of ZnO nanoparticles primes on enhancing the electroactive polar β‐phase in the nanocomposite. The transformation of the electroactive phase and its quantification were carried out using Fourier‐transform infrared spectroscopy and wide‐angle X‐ray diffraction. The PVDF/ZnO piezoelectric polymer nanocomposite was utilized for energy harvesting application that showed a better electromechanical response of ca. 69 V (peak to peak) at ~1.6 N, 250 μW/cm2 surface power density and 0.25 mA/cm2 surface current density. The fabricated piezoelectric polymer nanocomposite is a possible candidate for superior energy scavenging applications for capturing human kinematics.

Low-Cost Radiant Heater for Rapid Response, High-Temperature Heating

High-temperature processing has an irreplaceable role in many research and industrial applications. Despite remarkable development spanning over a century, the pursuit of even higher thermal flux density and more rapid thermal transients has not slowed down. As part of the ongoing energy evolution, many industrial applications are transitioning from direct combustion of fossil fuels as primary energy sources to increasing electrification, capable of adapting to renewable power grids. Thus, there is an emerging need for electrical heaters that can replace burners and supply the heat demand, especially at the highest temperatures. In this study, we report on a radiant heater design that can achieve cyclic heating/cooling rates of up to 400 K min–1 and a temperature range in excess of 1,800 K, comparable to those of commercial infrared gold image furnaces, at high surface and volumetric power densities. The heater consists of a modular unit of incandescent tungsten filament and is enclosed in an evacuated ceramic envelope, chemically inert, tolerant of thermal shock, and impervious to gasses. The material and manufacture cost of such heaters, which is estimated at ∼$0.05/W, is less than 0.03% of that for infrared gold image furnaces, which is at &amp;gt;$2/W. Tests of more than 10,000 demanding cycles (high temperature and high heating/cooling rate) over 350 h of total operational time and in different temperature ranges confirm the robust performance of radiant heater prototypes. The design is widely applicable to high-temperature reactor and furnace designs. In thermochemistry research and practice, these radiant heaters could offer multiple benefits compared to solar simulators, lasers, infrared gold furnaces, ceramic heaters, or direct concentration of solar input.

Experimental and numerical analysis of anti-icing a GLARE laminate

Abstract This study aimed at developing a numerical model to estimate the power consumption of a GLAss fiber REinforced aluminum-based electro-thermal ice protection system for anti-icing. The GLAss fiber REinforced aluminum laminate was embedded with recurred S-shaped copper meshes thermally energized by a surface power density. The model determined the influence of a forced convective heat loss and copper-mesh dimension on anti-icing. As a test case, the numerical model addressed the anti-icing performance of a GLAss fiber REinforced aluminum 5A-3/2 laminate at a sub-freezing ambient temperature of 267.95 K. The model demanded a surface power density of 13.03 kW/m2 in order to keep the temperature of the outer aluminum-skin at 285.44 K, which was clearly beyond the water freezing point. The numerically predicted power consumption for anti-icing was in excellent agreement with that from the experiment. The experiment was conducted in a miniature icing wind tunnel by incorporating the comparable icing condition of the numerical analysis. In the experiment, an infrared thermography camera determined the spatio-temporal temperature history of the outer aluminum skin in contact with the free-stream. The infrared thermography camera measurements of surface temperature collapsed in close proximity to that from the numerical analysis. The outcomes of this study will consolidate the confidence of aircraft manufacturers on the proposed anti-icing system.

Deicing of a GLAss fiber REinforced aluminum laminate – Part 2: Influence of substrate curvature

This two part study investigated the deicing performance of a GLAss fiber REinforced aluminum laminate and the influence of its surface curvature on the ice-to-water phase change. Part-1 of this study described the numerical model and the experiments conducted to validate the numerical model. In companion, Part-2 focused on interrogating the influence of substrate curvature on the phase transition based on a numerical model, in which an ice-to-water phase change method in a Lagrangian numerical framework predicted the deicing of a rectangular flat- and a curved GLAss fiber REinforced aluminum 5A-3/2 laminate embedded with a recurring S-shaped copper-mesh. As seen, deicing of the rectangular flat GLAss fiber REinforced aluminum 5A-3/2 model demanded a surface power density of 14.62 kW/m2 at an ambient temperature of 267.15 K. The numerically predicted deicing time, surface power density and deicing temperature of the rectangular flat GLAss fiber REinforced aluminum model were in excellent agreement with that of the rectangular flat GLAss fiber REinforced aluminum specimen of the experiment. Using the identical surface power density and power pulse duration, the curved GLAss fiber REinforced aluminum model required a deicing time 9 s shorter than that needed by the rectangular flat GLAss fiber REinforced aluminum model. After the melting of the entire ice-aluminum interface, temperature of the curved GLAss fiber REinforced aluminum model exhibited a steep increase and surpassed the temperature of the rectangular flat counterpart. A higher temperature of GLAss fiber REinforced aluminum is appreciated for efficient deicing, if the cyclic change of temperature does not induce thermal fatigue.

Thermal, Photometric and Radiometric Properties of Multi-Color LEDs Situated on the Common PCB

This paper presents the results of experimental investigations illustrating the influence of the spectra of the light emitted by power LEDs on their thermal, photometric and radiometric parameters. The investigations were performed for six diodes emitting white or monochromatic light of different spectra. Each of these diodes was produced by the same manufacturer, mounted in the same package and the tested devices were soldered to the common PCB. In the paper, the manner and set-ups making possible measurements of self and transfer transient thermal impedances, illuminance and the surface power density of the light emitted by the tested devices are described. Selected results of measurements are shown and discussed. These results prove that the spectra of the emitted light influence self-transient thermal impedances of the considered devices and transfer transient thermal impedances between some pairs of these devices. Additionally, it is proved that thermal couplings between the tested diodes strongly influence their junction temperature and the surface power density of the emitted radiation.

Fast-ion physics in SPARC

Potential loss of energetic ions including alphas and radio-frequency tail ions due to classical orbit effects and magnetohydrodynamic instabilities (MHD) are central physics issues in the design and experimental physics programme of the SPARC tokamak. The expected loss of fusion alpha power due to ripple-induced transport is computed for the SPARC tokamak design by the ASCOT and SPIRAL orbit-simulation codes, to assess the expected surface heating of plasma-facing components. We find good agreement between the ASCOT and SPIRAL simulation results not only in integrated quantities (fraction of alpha power loss) but also in the spatial, temporal and pitch-angle dependence of the losses. If the toroidal field (TF) coils are well-aligned, the SPARC edge ripple is small (0.15–0.30 %), the computed ripple-induced alpha power loss is small ( ${\sim } 0.25\,\%$ ) and the corresponding peak surface power density is acceptable ( $244\ \textrm{kW}\ \textrm {m}^{-2}$ ). However, the ripple and ripple-induced losses increase strongly if the TF coils are assumed to suffer increasing magnitudes of misalignment. Surface heat loads may become problematic if the TF coil misalignment approaches the centimetre level. Ripple-induced losses of the energetic ion tail driven by ion cyclotron range of frequency (ICRF) heating are not expected to generate significant wall or limiter heating in the nominal SPARC plasma scenario. Because the expected classical fast-ion losses are small, SPARC will be able to observe and study fast-ion redistribution due to MHD including sawteeth and Alfvén eigenmodes (AEs). SPARC's parameter space for AE physics even at moderate $Q$ is shown to reasonably overlap that of the demonstration power plant ARC (Sorbom et al., Fusion Engng Des., vol. 100, 2015, p. 378), and thus measurements of AE mode amplitude, spectrum and associated fast-ion transport in SPARC would provide relevant guidance about AE behaviour expected in ARC.

Deicing of a GLAss fiber REinforced aluminum laminate – Part 1: Experiments and numerical simulation

Deicing is a mandatory procedureto ensure the required aerodynamic lift of aircraft. Countless experimental and numerical investigations have been conducted to determine the deicing efficiency of various ice protection systems. The literature review, however, yielded no single study that has been dedicated to investigate the deicing performance of a GLAss fiber REinforced aluminum (GLARE)-based electro-thermal ice protection system. Of notes, the upper fuselage of the front- and the rear section of Airbus A380 comprises circa 469 m2 of GLARE. This study, therefore, proposed a phase change model based on thermo-dynamics to determine the power consumption and the de-icing performance of a GLARE laminate embedded with recurring S-shaped copper heater elements. The model addressed the influence of copper mesh length and orthotropic properties of GLARE on deicing.As a test case, the power budget for deicing a GLARE 5A-3/2 laminate was predicted numerically. The numerical analysis demonstrated that a surface power density of 14.62 kW/m2 sufficed to deice a GLARE 5A-3/2 laminate covered with a 0.8 mm thick ice layer at an ambient temperature of 267.15 K. To corroborate the numerical predictions, deicing experiments had been conducted in a miniature icing wind tunnel by incorporating icing conditions comparable to that of the numerical analysis. It was found that the predicted surface power density was in excellent agreement with that determined in the deicing experiment. In the experiment, an infrared camera measured the temperature gradient of the GLARE specimen, which was also in close proximity to that of the GLARE model in the numerical analysis.

A comparative study of energy harvesting performance of polymer‐piezoceramic composites fabricated with different piezoceramic constituents

Polymer-piezoceramic composites harness the flexibility of polymer and piezoelectric properties of ceramics to offer flexible piezoelectric materials for use in energy harvesting applications. Although, there is a general temptation to use piezoceramics which exhibits high piezoelectric coefficient (d33) in the fabrication of such composites, there are limitations posed by the processing conditions of the composite which eventually determines their overall performance. In the present work we have explored this aspect in detail. We fabricated composites with polyvinylidene fluoride (PVDF) as the polymer and three different piezoceramic powders namely BaTiO3 (BT), Ba(Ti0.97Sn0.03)O3 (BTS) and Sm-doped Pb (Mg1/3Nb2/3)O3-PbTiO3(Sm-PMN-PT). Our focus here is to understand the role of grain size of the ceramic powders in determining the dielectric, piezoelectric, and energy harvesting performance of the composites. To broaden the perspective, the results are compared with another analogous composite 0.59PbTiO3-0.41Bi(Zr0.5Ni0.5)O3 (PT-BNZ)-PVDF reported before. We found that, although, the dense ceramic specimen of Sm-PMN-PT exhibits exceptionally large d33, the composite with PT-BNZ exhibited the best piezoelectric and energy harvesting performance. BT, BTS and Sm-PMN-PT composites showed maximum surface power density of 6.24, 12.81 and 23.18 μW/cm2, respectively, and volume power density of 416.18, 854.1 and 1104 μW/cm3, respectively. Whereas surface power density and volume power density of PT-BNZ was 101.80 μW/cm2 and 5088.80 μW/cm3 respectively. We have also attempted to establish a correspondence between the piezoelectric response, energy harvesting performance and the poling induced domain reorientation/structural changes in the ceramic grains of the composites.

Nanogenerator for dynamic stimuli detection and mechanical energy harvesting based on compressed SbSeI nanowires

In this paper, a novel fabrication technology for generating antimony selenoiodide (SbSeI) nanowire pellets is presented, and their application as piezoelectric nanogenerators is discussed. The prepared samples can be used to convert mechanical energy into electrical energy via the piezoelectric effect. The SbSeI nanowires are fabricated sonochemically and then compressed under high pressure (120 MPa). The morphological and electrical properties of the samples have been investigated using various techniques, including scanning electron microscopy, high-resolution transmission electron microscopy, and other electrical and piezoelectric measurements. The relationship between frequency of impact and the piezoelectric signal has been measured to calculate the output voltage and power produced by the nanogenerator. The maximum open circuit voltage of 384.7 (11) mV, corresponding to a maximum surface power density of 14.1 (21) nW⋅cm-2 and volume power density of 0.380 (83) μW⋅cm-3 has been achieved for periodic striking excitation with force of 17.8 N and resonant frequency of 70 Hz. The presented SbSeI nanogenerator has been found as promising for mechanical energy harvesting applications. Furthermore, it can also be employed as a self-powered sensor for the detection of dynamic pressure changes and vibrations with frequencies up to 200 Hz.

Enhanced Performance of Microbial Fuel Cells with Anodes from Ethylenediamine and Phenylenediamine Modified Graphite Felt

A microbial fuel cell (MFC) is a promising renewable energy option, which enables the effective and sustainable harvesting of electrical power due to bacterial activity and, at the same time, can also treat wastewater and utilise organic wastes or renewable biomass. However, the practical implementation of MFCs is limited and, therefore, it is important to improve their performance before they can be scaled up. The surface modification of anode material is one way to improve MFC performance by enhancing bacterial cell adhesion, cell viability and extracellular electron transfer. The modification of graphite felt (GF), used as an anode in MFCs, by electrochemical oxidation followed by the treatment with ethylenediamine or p-phenylenediamine in one-step short duration reactions with the aim of introducing amino groups on the surface of GF led to the enhancement of the overall performance characteristics of MFCs. The MFC with the anode from GF modified with p-phenylenediamine provided approx. 32% higher voltage than the control MFC with a bare GF anode, when electric circuits of the investigated MFCs were loaded with resistors of 659 Ω. Its surface power density was higher by approx. 1.75 times than that of the control. Decreasing temperature down to 0 °C resulted in just an approx. 30% reduction in voltage generated by the MFC with the anode from GF modified with p-phenylenediamine.

A novel MEMS triboelectric energy harvester and sensor with a high vibrational operating frequency and wide bandwidth fabricated using UV-LIGA technique

A novel triboelectric energy harvesting (TEH) and sensing system scaled down to microelectromechanical systems (MEMS) size is presented. The design is structurally optimized for harvesting the highest average power and power density while ensuring the structural robustness. Unlike traditional triboelectric energy harvesters, this design results in a high operating frequency with a wide bandwidth. Adoption of MEMS fabrication techniques including the use of spin-coated Teflon AF rather than a Teflon sheet, adaptation of UV-LIGA (Ultra-Violet Lithographie, Galvanoformung, Abformung) with modifications and implementation of a thick polyimide sacrificial layer make the fabrication process unique. If excited by ±9.33 g external vibration with a frequency of 1.15 kHz, the TEH can generate 0.179 μW average power and 0.597 μW peak power at an optimum resistive load of 256 kΩ. The peak surface power density, volumetric power density and acceleration-normalized volumetric power density reach 3.98 μWcm−2, 2.64 mWcm-3 and 30.3 μWcm-3/g2, respectively. While the surface power density of the presented TEH is moderate, the volumetric power density and acceleration-normalized volumetric power density are quite competitive among the state-of-the-art designs. The TEH also demonstrates a wide operating frequency bandwidth of 920 Hz. If operated as an accelerometer, the device shows a linear sensitivity of 43 mV/g. Although the simulation predicts the optimum operating frequency and load resistance of the system to be at 800 Hz and 10 MΩ, respectively, the experimental results demonstrate these values to be at 1150 Hz and 256 KΩ. A few fabrication anomalies, most notably the notching in the Teflon layer and bowing of the proof-mass, are responsible for this deviation. In addition, a distortion is observed in the simulated output voltage profile which is not present in the experimental output voltage profile due to the presence of the parasitic capacitance in the experimental circuit. The aforementioned triboelectric energy harvester can have specific applications in the sensor and actuator systems in the aircraft industry as well as in the automobile industry, micro-robotic systems, prosthetic systems, and sensor nodes in the internet of things (IoT) due to its operating frequency and bandwidth range.