Open-circuit Output Research Articles

Neodymium Doped Zinc Oxide Based Advanced Flexible Piezoelectric Energy Harvester and Self-powered Biomotion Sensor

Flexible piezoelectric devices have garnered a lot of attention for their potential as energy harvesters and transducers. In this work, Neodymium (Nd) doped Zinc Oxide (ZnO) based flexible piezoelectric energy harvester and sensory device has been developed. Nd-doped ZnO has been synthesized using wet chemical co-precipitation and incorporated in Polyvinylidene Difluoride (PVDF) polymer matrix along with Multiwalled Carbon Nanotubes (MWCNT) to produce flexible piezoelectric films. The piezoelectric output of the device is tested at variable tapping frequency (60 to 240 BPM) and pressure (10 to 40 psi). The device has also been tested with conventional electronics like bridge rectifiers, capacitors, resistors, LEDs to show its potential as an energy harvester. Compared to other modified ZnO-PVDF based unpoled piezoelectric energy harvesters, this device has shown the most open-circuit output voltage of 75.8 V and short circuit current of 28.8 µA. It has shown an optimum power density of 12.55 μwcm-2 at 1 MΩ load impedance. Energy harvesting capacity has been further tested by placing the device between the shoe soles during running and jogging. This study endorses the potential of Nd-ZnO/PVDF/MWCNT based piezoelectric energy harvester as the most efficient Piezoelectric Nanogenerator (PENG) which shows superior power generation along with self-powered sensory applications.

Weavable, Reconfigurable Triboelectric Ferrofluid Fiber for Early Warning.

As communication technologies have become omnipresent, the prevalence of electromagnetic field (EMF) exposures poses possible health risks, particularly to vulnerable groups such as pregnant women. In response, we introduce a triboelectric ferrofluid fiber (TFF) that moves in response to EMF, thereby generating charge in a way that is self-powered. The TFF is flexible, stretchable (470%), and can be woven into fabrics. The TFF utilizes a soft-contact (ferrofluid-silicon rubber fiber) triboelectric core layer to enhance its sensitivity to EMF, enabling it to detect even minor electromagnetic fluctuations, such as those from cell phone typing. By integrating hydrogel electrodes that offer conductivity and minimal electromagnetic interference shielding, the TFF's sensitivity to magnetic fields is further amplified. Moreover, its open-circuit voltage output is increased by 50% compared to the conventional electrodes. Building on this technology, we designed a smart fabric for environmental early warning and potential real-time pulse monitoring, specifically tailored for the safety and healthcare needs of vulnerable groups. Finally, we developed a sensing and communication apparel (SCA) by integrating TFF into the apparel and exploring its capabilities in a wireless transmission of warning signals and long-distance NFC functionality.

Underwater blade-free triboelectric nanogenerator for harvesting current energy in low-speed current

Ocean current energy bears the characteristics of wide distribution and high energy density. Harvesting current energy as the in-situ power for distributed ocean sensors will greatly enhance the sustainability of ocean sensing. In many parts of the ocean, the current speed is not desirable (low or unstable) for conventional current energy harvesting devices. Here, an underwater blade-free triboelectric nanogenerator (UBF-TENG) is developed to effectively utilize the low-speed currents through the flow-induced vibration (FIV). The power generation unit is fully enclosed inside the shell, effectively reducing the direct impact and underwater corrosion. The study demonstrates that within the established experimental parameters space, the optimized UBF-TENG can facilitate a start-up speed as low as 0.14 m/s. The UBF-TENG has achieved a maximum open-circuit voltage output of 250 V and a maximum short-circuit current output of 2.2μA at 0.76 m/s. The charging capacity of the UBF-TENG is tested with various capacitors, demonstrating the application potential of the UBF-TENG as an in-situ power supply underwater.

Lithium-based water-absorbent hydrogel with a high solar cell cooling flux

The lifetime and photovoltaic conversion efficiency of the solar cell will decline as the temperature rises. Herein, a versatile hydrogel allowing atmospheric water harvesting and evaporative cooling is introduced to passively reduce the working temperature of the solar cell. As a flexible substrate, the lithium-rich and highly absorbent polyacrylamide hydrogel is employed to satisfy these specifications. Preferentially, the water-saturated hydrogel, which is bonded to the backside of the solar cell, collects the waste heat produced by the cell and dissipates it into the atmosphere by water evaporation. Importantly, the hydrogel naturally gathers atmospheric vapor at night or on overcast days to revive its cooling ability. This configuration endows the PV cell with a cooling flux of up to 529 W m−2 and thus reduces the working temperature of a polycrystalline silicon cell by 26 °C at 1 sun (=1 kW m−2) illumination. More importantly, the hydrogel arrangement supports 6.2 % and 17 % improvements in average open-circuit and maximum power output (or photovoltaic efficiency), respectively. This is devoid of limits on access to liquid water resources, making it a potential option for efficient and sustainable solar cell power generation.

Design of metamaterial thermoelectric generators for efficient energy harvesting

Thermoelectric generators (TEGs) are widely recognized as clean energy solutions that can convert low-grade waste heat into electricity through a temperature gradient. Despite their significant potential, challenges such as low conversion efficiency and high costs have limited their practical applications. In this paper, we present an innovative metamaterial design concept for TEGs with significantly improved efficiency. A Finite Element Model is validated using Bi0.5Sb1.5Te3 bulk samples fabricated via the drop-cast method. This model can predict open-circuit voltage and output power as a function of an arbitrary metamaterial design using the commercial software ANSYS®. Four different metastructure designs, including 2D Triangular Honeycomb, Re-entrant, body-centered cubic (BCC), and triply periodic minimal surface (TPMS) structures, are systematically investigated. Through experiments and numerical analysis, the effects of annealing temperature, porosity, and unit cell numbers (UCNs) on the performance of TE legs are explored. It is found that 2D Triangular Honeycomb and BCC structures outperform other configurations due to their capacity to maintain a higher thermal gradient. Optimizing their porosity and UCNs can further enhance the output power. Compared to the traditional designs with bulk TE legs, implementing a 2D metastructure design with 30 % porosity and UCNs of 4 × 4 × 4 can lead to approximately a 100 % increase in power output.

On the role of sliding friction effect in nonlinear tri-hybrid vibration-based energy harvesting

This work aims to develop an experimental investigation into the effectiveness of the sliding-mode approach for hybrid vibration-based energy harvesting. A proposed sliding-mode triboelectric-electromagnetic-piezoelectric energy harvesting model involves a cantilever beam with a tip mass exposed to magnetic and frictional forces. The experimental findings indicate that the system can achieve its peak inter-well oscillation output within a low-frequency range of 4Hz–6Hz. Friction has a lesser impact on the open-circuit voltage output at an excitation acceleration of 1.5g compared with 1g. The distribution of tri-stability changes with the presence of friction. This model provides a deeper understanding of the influence of the dry friction coefficient (0.2–0.5) on the interactive behaviors of different generator units.

Wave-inspired piezoelectric bistable energy harvester considering stress distribution: Design, simulation and experimental investigation

The rapid development of IoT technology has spurred the need for self-driven and low-power sensors. Numerous research studies focused on exploring the efficiency of energy harvesting as a means of powering miniaturized sensors, but the issue of the fatigue life of these energy harvesters has been largely overlooked. Inspired by wave motion, this study proposes a novel bistable piezoelectric energy harvester. The host structure of the harvester is made of a 301 stainless steel sheet preformed to a W-shaped beam, with PVDF piezoelectric films on its upper and lower surfaces. The results show that the proposed wave-inspired beam can significantly improve stress distribution, and the peak stress is 27.5 % lower than that of the arch beam. Experimental results show that the peak open-circuit output voltage can reach 11.8 V, when the pre-deformation height of the wave-inspired beam is 5 mm, the mass of the proof mass is 20 g and the frequency range is 13.6 Hz-18.9 Hz. When the excitation frequency is 13 Hz, the maximum root-mean-square voltage of the PVDF piezoelectric film and output power can reach 4.64 V and 16.25μW (single piece), respectively.

Tuning ZnO-based piezoelectric nanogenerator efficiency through n-ZnO/p-NiO bulk interfacing

ZnO based piezoelectric nanogenerators (PENG) hold immense potential for harvesting ambient vibrational mechanical energy into electrical energy, offering sustainable solutions in the field of self-powered sensors, wearable electronics, human–machine interactions etc. In this study, we have developed flexible ZnO-based PENGs by incorporating ZnO microparticles into PDMS matrix, with ZnO concentration ranging from 5 to 25 wt%. Among these, the PENG containing 15 wt% ZnO exhibited the best performance with an open-circuit output voltage/short-circuit current of ~ 42.4 V/2.4 µA. To further enhance the output performance of PENG, p-type NiO was interfaced with ZnO in a bulk hetero-junction geometry. The concentration of NiO was varied from 5 to 20 wt% with respect to ZnO and incorporated into the PDMS matrix to fabricate the PENGs. The PENG containing 10 wt% NiO exhibits the best performance with an open-circuit output voltage/short-circuit current of ~ 65 V/4.1 µA under loading conditions of 30 N and 4 Hz. The PENG exhibiting the best performance demonstrates a maximum instantaneous output power density ~ 37.9 µW/cm2 across a load resistance of 20 MΩ under loading conditions of 30 N and 4 Hz, with a power density per unit force and Hertz of about ~ 0.32 µW/cm2·N·Hz. The enhanced output performance of the PENG is attributed to the reduction in free electron concentration, which suppresses the internal screening effect of the piezopotential. To assess the practical utility of the optimized PENG, we tested the powering capability by charging various commercial capacitors and used the stored energy to illuminate 10 LEDs and to power a stopwatch displays. This work not only presents a straightforward, cost-effective, and scalable technique for enhancing the output performance of ZnO-based PENGs but also sheds light on its underlying mechanism.

Performance evaluation of flexible thermoelectric generator with Bi2Te3 thin-film

In the information society, carrying devices such as smartphones and tablets is crucial, and ensuring their power supply is essential. Furthermore, from the perspective of energy security, being able to secure their power supply from low-quality energy sources could reduce dependence on fossil fuels. In this study, we fabricated a flexible thermoelectric generator capable of harvesting energy from a low-temperature difference between a low-temperature heat source and room or outdoor temperature and evaluated its performance. The device was fabricated by depositing an n-type Bismuth telluride (Bi2Te3) film onto a polyimide film substrate using radio frequency (RF) magnetron sputtering. A 3D printer was used to fabricate flexible fins for attaching and bonding the films. Owing to their adaptability, these flexible models can be installed on heat sources of different shapes. The experimental conditions for this study were as follows: the temperature in the test chamber was maintained at 25 ± 1 °C and that of the heat source ranged from 35 to 75 °C; further, thermoelectric elements in numbers varying from 1 to 6 were installed. The maximum open-circuit output voltage |E| and power generation (Pmax) were determined to be 11.4 mV and 69 nW, respectively. The fins with the Bi2Te3 thin film maintained a temperature of approximately 25 to 30 °C at the tip of the fin, even when exposed to the highest temperature (75 °C) of the heat source during the experiment. As a result, the thermoelectric device developed in this study has demonstrated the potential to power sensors operating in the tens of nW range.

Enhancing piezoelectric properties of PVDF-HFP composite nanofibers with cellulose nanocrystals

With the increasing interest in flexible self-powering energy devices, piezoelectric polymers such as poly(vinylidene fluoride) (PVDF), PVDF-trifluoroethylene (PVDF-TrFE and poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) have garnered substantial research attention. Among these, PVDF-HFP has demonstrated immense research potential in harvesting mechanical energy and converting it to electric energy. It is also particularly attractive due to its low cost compared to some other PVDF co-polymers. In this study, PVDF-HFP nanofibers were produced by electrospinning with cellulose nanocrystal (CNC) employed as a filler to improve their piezoelectric performance. Smooth and bead-free fibers were obtained with up to 1 wt% of CNC in the solution. The inclusion of CNC increased the uniformity of fiber diameter and improved thermal stability. Higher CNC concentration (2–3 wt%) engendered agglomeration and adversely impacted the conversion of non-polar phase to electroactive phase for PVDF-HFP molecules. At the optimal CNC concentration of 1 wt%, the voltage and current sensitivities for 1 cm2 samples were obtained as 0.146±0.048 mV/mN and 0.009±0.003 nA/mN, respectively. The open-circuit voltage output of 2.69±1.11 V was achieved under an average impact force of 40 N, and this increased with increased magnitude and frequency of the applied force. The mechanical properties of composite nanofibers maximized at 0.5 wt% CNC with tensile strength of 37.85±4.35 MPa, elastic modulus of 124.96±42.17 MPa, and strain at failure of 82.32±14.84 %. The improved piezoelectric and mechanical properties of the CNC-aided electrospun PVDF-HFP fibers will open new pathways for flexible energy harvesting systems.

Design and development of a horizontal contact separated (HCS) test setup for measuring the performance of triboelectric nanogenerator for sustainable energy harvesting applications.

Triboelectric nanogenerators (TENGs) can play a pivotal role in harnessing non-utilized reciprocating motion and convert it into electrical energy that can later be stored in a battery or capacitor to power various Internet of Things-based smart electronic and wearable devices. Herein, we designed a cost-effective instrumental test bed focused on investigating the output performance of a horizontal contact separation mode triboelectric nanogenerator by varying the input parameters, such as applied force, motor speed, triboplate separation, and frequency of instrumental setup. The test bed mainly consists of three major parts: (i) application of force, (ii) tapping of TENG sample, and (iii) output parameters measurement. The output performance in terms of open circuit output voltage (VOC), short circuit current (ISC), and power density of polydimethylsiloxane-based TENG was monitored and optimized by varying the input parameters. A low-cost current measuring circuitry using an operational amplifier integrated circuit has been proposed with 92% accuracy. The maximum value of VOC and ISC was observed to be 254V and 31.8 µA at a motor speed of 600rpm, the distance between both the plates was 6mm, the input applied force of 40 N, and the striking frequency of 3Hz. The maximum power density of 2.1 W/m2 was obtained at an input impedance of 8 kΩ. The durability of the test bed as well as the TENG sample was also measured for 25h. The degree of uncertainty was measured for VOC, ISC, and applied force and calculated to be 1.62%, 7.45%, and 6.27%, respectively.

Application of PZT Nanofiber Flexible MEMS Technology in Human Resource Employment Pressure Management

The advancement of society has led to increasing pressure on employment in human resources. Effectively managing and alleviating this pressure has emerged as an urgent problem to be addressed. This study presents a novel pressure sensor utilizing microelectromechanical systems technology, with the aim of offering a fresh solution for managing employment pressure in the human resource sector. Firstly, this study presents the preparation and characterization of lead zirconate titanate nanofibers, followed by the development of a flexible pressure sensor using microelectromechanical systems technology specifically designed for these fibers. Finally, this study evaluates the performance of the developed pressure sensor. The results revealed that the open circuit output voltage of the sensor peaked at a pressure frequency of 110 Hz, indicating the highest level of response. In addition, it was observed that the open circuit output voltage of the fabricated sensor exhibited fluctuations within the voltage range of –3.8 V to 5.0 V, confirming its ability to precisely respond to variations in external pressure at any given moment. The features of this developed pressure gauge render it an ideal tool for real-time monitoring and evaluation of pressure, thereby possessing wideranging application prospects.

Waste heat recovery from the biomass engine for effective power generation using a new array-based system

Thermoelectric generator (TEG)-thermosyphon-based heat recovery system (HRS) for harvesting the heat from the high temperature sources is a well-known technology for power generation. However, various thermal resistances (a total of nine) are involved in the thermosyphon-based HRS between the heat sources and TEGs which generate irreversibility that ultimately reduces its performance. In this work, a new design of HRS i.e. TEG-array-based is proposed for effective power generation even at low temperatures of sustainable heat source by minimizing the thermal resistances. This TEG-array-based HRS is driven by a salt gradient thermal storage device (SGTSD) which is used for efficiently recovering and storing of sustainable waste heat generated from a biomass(renewable energy)-based engine-generator. The proposed system is experimentally studied to analyse the temperature variations in SGTSD, characteristics of sustainable waste heat temperature, and performance features of TEGs in terms of obtained electrical parameters, output power and conversion efficiency. The experimental results showed that the maximum open circuit voltage, output power and conversion efficiency of TEG are obtained as 81.62V, 7.438W and 4.63\\% respectively. With this proposed system, seven thermal resistances (out of total nine) are totally eliminated while the others two are lowered that leads to effectively transfer the energy from sustainable heat source to TEGs via minor equivalent thermal resistance of 0.01198oC/W. The proposed system is found to be capable of charging a 12 V, 80 Ah heavy-duty battery for real life applications.

Unveiling the role of vanadium doping in modulating morphological and electrical properties of piezoelectric Na0.46K0.46Li0.08NbO3 ceramics for energy harvesting

We report the enhancement of ferro/piezo-electric properties of lead-free alkali based perovskite Na0.46K0.46Li0.08NbO3 (NKLN) by vanadium doping (NKLNV) for high performing piezoelectric devices. Lead-free NKLN and NKLNV ceramics are synthesized via solid state reaction route as a substitute to the lead-based ceramic for the applications in sensors, transducers, and other electronic devices. The structural phase of synthesized ceramics is found to be pure perovskite as observed from powder X-ray diffraction. In dielectric studies, Curie temperature is found to be around 450 °C for both the samples. SEM images revealed the formation of homogeneous microstructure with well-defined grains. Dense polycrystalline ceramics having grain size of about 5 μm are obtained as a result of sintering at optimised temperature of 1050 °C. The micrographs showed that the grain size begins to evolve with reduced porosity in vanadium doped NKLN. Vicker's microhardness indentation test is performed for different loads at dwell time of 30 s, in which it was observed that the V-doping has enhanced the hardness. In ferroelectric studies, NKLNV shows higher value of remnant polarization as compared to NKLN as observed in P-E hysteresis loop. Fine microstructure and larger grain size felicitated the movement and reorientation of dipoles which resulted in enhanced piezoelectric coefficient for vanadium substituted NKLN ceramics. Flexible energy harvesters were fabricated by making a composite with PDMS, and then coating a thick film over ITO/PET sheet. NKLNV-based flexible device showed an improvement in open-circuit output voltage of 13.8 V under gentle finger tapping. NKLNV ceramics are a viable lead-free alternative for dielectric, piezoelectric, and ferroelectric applications.

Structural optimization of laminated leaf-like piezoelectric wind energy harvesters based on topological method

In this paper, a series of leaf-like piezoelectric elements are proposed by using laminated structure of polypropylene (PP) and Polyvinylidene fluoride (PVDF) film to collect wind energy through vortex induced vibration. Topology optimization based on solid isotropic material with penalization method is employed in seeking optimal configurations of the elements. The PP and PVDF layer were set as optimization variables respectively to obtain topological layouts that would be equivalent to maximizes the overall strain energy as the objective function. Four simple shapes of piezoelectric elements with different topological configurations are manufactured and tested in wind tunnel to estimate the energy harvesting capabilities. The experimental results show that the reinforcement optimized long trapezoid model has the highest open-circuit output voltage of 4.01 V and output power of 6.125 μW at the wind speed of 12 m/s. For the optimization of piezoelectric materials, the short trapezoid model can reach the open circuit output voltage of 2.061 V and output power of 1.158 μW. It indicated that the topology optimization can indeed improve the energy harvesting efficiency of the piezoelectric element. However, this method is not universal at present, which means that the external shape of the model will influence the performance of the relevant optimization results.

Structural Performance and Evaluation of PDMS-Based Planar Membrane for Electromagnetic Vibration Energy Harvester (EM-VEH)

This paper discusses the performances of Polydimethylsiloxane (PDMS) membranes with the electromagnetic coils and magnetic arrangement as the supporting structure to generate electricity by capturing the energy from vibrating ambient source. The membrane attached to the permanent magnet moved according to the structure of the electromagnetic system. The study first designed the PDMS planar membrane to allow the vibration energy capturer to induce the coils efficiently. Membrane vibration from a loudspeaker with an operating frequency of 32 Hz was used as the vibration source. The generated energy stored in a storage circuit using a 220 µF/25 Volt capacitor, while a 1.5 Volt LED was used as a tested load in the system. The results showed that the moving membrane attached with a 10 mm diameter magnet revealed an open circuit output voltage of 500 mV on the EM coil. An experiment within a 20-minute flashing LED load test produced an output voltage of 2.2 Volts. This study would benefit the development of vibration energy harvester used to supply a low electrical power for microdevices in an isolated area.

Experimental study of the influences of surface roughness and thermal interface material on the performance of a thermoelectric generator

Reducing surface roughness and using thermal interface materials (TIMs) at the interfaces between a thermoelectric generator (TEG), heat source, and heat sink are effective strategies for decreasing the thermal contact resistance (TCR) and enhancing the TEG performance. To evaluate the influences of parameters such as the surface roughness, the thermal conductivity of TIM and loading pressure, we conducted experiments to measure the open-circuit voltage and output power of the TEG under various installation conditions. We also analysed the changes in TCR and temperature difference across the TEG module. The experimental findings were validated with numerical simulations using COMSOL Multiphysics under specific conditions. Our results revealed that reducing surface roughness and using TIM could substantially reduce the TCR, increase the temperature difference across the TEG, and increase the output power from the TEG. In our experiments, we used a temperature controller, cartridge heaters and thermocouples to regulate and record the temperatures of the heat source and heat sink. When maintaining a temperature difference of 53 K between the heat source and heat sink, and loading pressure set at 0.2 MPa, without using TIM, as the surface roughness decreased from 2.2 μm to 0.37 μm and to 0.03 μm, leading to a reduction in the TCR from 0.22 K W−1 to 0.17 K W−1 and to 0.13 K/W. Simultaneously, the open-circuit voltage increased from 1.32 V to 1.65 V and to 1.86 V, and the maximum output power increased from 0.26 W to 0.44 W and to 0.58 W. Additionally, when the surface roughness was 0.37 μm, after using TIM with thermal conductivity of 1 W/m-K, 2 W m−1-K−1, and 5 W m−1-K−1, the open-circuit voltage reached 1.44 V, 1.74 V and 1.94 V, respectively, and the maximum power reached 0.31 W, 0.51 W and 0.65 W, respectively.

Interfacial energy barrier tuning in MnO2/MoS2/Carbon fabric integrated with low resistance textrode for highly efficient wearable thermoelectric generator

Wearable thermoelectric (TE), enabling direct conversion of human body heat into electricity have become the most promising alternative for conventional batteries on the Internet of Things based wearable electronic devices. The prime challenge in fabricating a high-performance wearable thermoelectric material is to combine the non-toxicity with high mechanical flexibility, excellent electrical conductivity and high Seebeck coefficient. This paper proposes a facile approach to fabricate a textile-based wearable thermoelectric generator (WTEG) with outstanding TE properties and exceptional flexibility. Herein, molybdenum disulphide (MoS2) nanosheets were grown on conductive carbon fabric (CF) via in-situ binder-free hydrothermal technique and manganese dioxide (MnO2) nanorods were decorated on it via dip coating, to form a 1D/2D interface. We investigated the in-plane TE properties of MnO2/MoS2/CF and achieved a superior power factor of 548.7 nW/mK2 which is 49.5 % higher than that of the pristine MoS2/CF. Such behaviour can be explained by the selective transmission of high energy carriers at the optimized MnO2/MoS2 interface. Moreover, this study is the first to employ a textile-based contact electrode in fabrication of WTEG that resulted in ultra-low internal resistance of the fabricated device (30–300 Ω). The lack of rigid contact electrodes leaves more flexibility, which benefits in enhanced wearability of the device. Owing to minimal internal resistance (29.4 Ω), the WTEG comprising of 1 -n/p pair could produce an open circuit voltage, as high as 0.2 mV under the thermal gradient of 15–20 K. Additionally, we demonstrated that increasing the number of modules from 1 pair to 4 pairs systematically improved the device performance. The open circuit voltage and output power generated for WTEG comprising of 4 -n/p pairs is measured to be 1.2 mV and 1 nW, respectively. This work provides a feasible design solution for a low resistance, rigid-free WTEGs with high performance which can significantly support the growth of research in wearable thermoelectrics.

The Microbial Communities of Anaerobic Respiration and Fermentation Degrading Chitin Exist in the Anaerobic Sludge of Microbial Fuel Cell Anodes

Chitin is one of the most abundant polymers in nature, with chitinous biomass often discarded as food waste and marine debris. To explore an effective way to degrade chitin, in this work, anaerobic sludge was inoculated at the anode of a two-chamber microbial fuel cell (MFC), and chitin was degraded via anaerobic respiration and fermentation. The results showed that the anaerobic sludge could degrade chitin under both the anaerobic respiration and fermentation modes, with similar degradation rates (7.10 ± 0.96 and 6.96 ± 0.23 C-mg/L·d−1). The open-circuit voltage and output current density could roughly reflect the degradation of chitin in the MFC. The maximum current density generated through the anaerobic sludge degradation of chitin via anaerobic respiration was 160 mA/m2, and the maximum power density was 26.29 mW/m2. The microbial sequencing results revealed substantially different microbial community profiles, with electroactive bacteria (EAB) flora and fermentative bacteria (Longilinea) as the main microbial groups that degraded chitin via anaerobic respiration and fermentation, respectively. Therefore, anaerobic sludge may be a good choice for the treatment of refractory biomass due to its abundant electroactive and fermentative flora.

Temperature dependent behavior of a kA-class superconducting flux pump with a continuous cylindrical stator

A high temperature superconducting (HTS) dynamo is a type of device known as a “flux pump” that can inject DC into a closed superconducting circuit. Here, we report experimental results from a variable-temperature dynamo-type HTS flux pump operated within a cryo-cooled chamber. This device employs a “continuous stator” topology, whereby an HTS “coated conductor” is wrapped to form a cylinder around a mechanical rotor such that applied flux from the rotor magnet must always penetrate the stator. This leads to a high current device that can inject >1 kA into a series-connected HTS coil at 53 K. The open-circuit DC output voltage (Voc) from this HTS dynamo has been studied at stator temperatures between 35 and 95 K and attained a maxima at a temperature ∼5 K lower than the stator Tc. At lower temperatures, Voc decreases and falls to zero below ∼40 K. This non-intuitive effect is found to be due to flux-screening by critical currents flowing with the HTS stator, which increase with decreasing temperature. These shielding currents prevent flux from penetrating the HTS stator and, hence, reduce the magnitude of locally induced emf (and thus DC output) within the HTS film. A key implication of these results is that all magnetically driven HTS flux pumps should be operated at temperatures well above their flux-screening point, and this consideration must be taken into account for future designs of multi-kA class HTS flux pumps.