High Current Region Research Articles

Toward Ideal Low-Frequency Noise in Monolayer CVD MoS2 FETs: Influence of van der Waals Junctions and Sulfur Vacancy Management.

The pursuit of sub-1-nm field-effect transistor (FET) channels within 3D semiconducting crystals faces challenges due to diminished gate electrostatics and increased charge carrier scattering. 2D semiconductors, exemplified by transition metal dichalcogenides, provide a promising alternative. However, the non-idealities, such as excess low-frequency noise (LFN) in 2D FETs, present substantial hurdles to their realization and commercialization. In this study, ideal LFN characteristics in monolayer MoS2 FETs are attained by engineering the metal-2D semiconductor contact and the subgap density of states (DOS). By probing non-ideal contact resistance effects using CuS and Au electrodes, it is uncovered that excess contact noise in the high drain current (ID) region can be substantially reduced by forming a van der Waals junction with CuS electrodes. Furthermore, thermal annealing effectively mitigates sulfur vacancy-induced subgap density of states (DOS), diminishing excess noise in the low ID region. Through meticulous optimization of metal-2D semiconductor contacts and subgap DOS, alignment of 1/f noise with the pure carrier number fluctuation model is achieved, ultimately achieving the sought-after ideal LFN behavior in monolayer MoS2 FETs. This study underscores the necessity of refining excess noise, heralding improved performance and reliability of 2D electronic devices.

Inorganic Composition Modulation of Solid Electrolyte Interphase for Fast Charging Lithium Metal Batteries.

The solid electrolyte interphase (SEI) with lithium fluoride (LiF) is critical to the performance of lithium metal batteries (LMBs) due to its high stability and mechanical properties. However, the low Li ion conductivity of LiF impedes the rapid diffusion of Li ions in the SEI, which leads to localized Li ion oversaturation dendritic deposition and hinders the practical applications of LMBs at high-current regions (>3 C). To address this issue, a fluorophosphated SEI rich with fast ion-diffusing inorganic grain boundaries (LiF/Li3P) is introduced. By utilizing a sol electrolyte that contains highly dispersed porous LiF nanoparticles modified with phosphorus-containing functional groups, a fluorophosphated SEI is constructed and the presence of electrochemically active Li within these fast ion-diffusing grain boundaries (GBs-Li) that are non-nucleated is demonstrated, ensuring the stability of the Li || NCM811 cell for over 1000 cycles at fast-charging rates of 5 C (11mA cm-2). Additionally, a practical, long cycling, and intrinsically safe LMB pouch cell with high energy density (400Wh kg-1) is fabricated. The work reveals how SEI components and structure design can enable fast-charging LMBs.

Capturing accurate kelp canopy extent: integrating tides, currents, and species-level morphology in kelp remote sensing

Surface-canopy forming kelps (Macrocystis pyrifera and Nereocystis luetkeana) can be monitored along the Northeast Pacific coast using remote sensing. These kelp canopies can be submerged by tides and currents, making it difficult to accurately determine their extent with remote sensing techniques. Further, both species have morphologically distinct canopies, each made up of structures with differing buoyancies, and it is not well understood whether the differing buoyancies between these species’ canopies affects their detectability with remote sensing technologies. Here, we collected in situ above-water spectral signatures for the surface-canopies of Nereocystis and Macrocystis, providing the first direct hyperspectral comparison between the structures that make up the canopies of these species. Additionally, we compare the strength of their red-edge and near-infrared band signals, as well as the normalized difference red-edge (NDRE) and normalized difference vegetation index (NDVI) values. At the bed level, we compare detection of kelp canopy extent using both NDRE and NDVI classified unoccupied aerial vehicle imagery. We also characterized how changing tides and currents submerge the canopies of both species, providing insights that will allow remote sensors to more accurately determine the extent of kelp canopy in remote sensing imagery. Observations of canopy structures paired with in situ hyperspectral data and simulated multispectral data showed that more buoyant kelp structures had higher reflectance in the near-infrared wavelengths, but even slightly submerged canopy structures had a higher reflectance in the red-edge rather than the near-infrared. The higher red-edge signal was also evident at the bed level in the UAV imagery, resulting in 18.0% more canopy classified with NDRE than with NDVI. The area of detected canopy extent decreased by an average of 22.5% per meter of tidal increase at low current speeds (<10 cm/s), regardless of the species present. However, at higher current speeds (up to 19 cm/s), Nereocystis canopy decreased at nearly twice the average rate of kelp beds in low-current conditions. Apart from the strong differences in high-current regions, a robust linear relationship exists between kelp canopy extent and tidal height, which can aid in understanding the errors associated with remote sensing imagery collected at different tidal heights.

Research of Proton Exchange Membrane Fuel Cell Modeling on Concentration Polarization under Variable-Temperature Operating Conditions

In this study, a concentration overvoltage model that focuses on describing variable-temperature operating condition properties for PEMFCs is established. Sensitivity analysis and a quantification study of oxygen transport resistance are carried out based on the oxygen transport resistance model and measurement data. By analyzing the influence of temperature on cathode oxygen transport resistance, the key structural parameters of the cathode oxygen transport resistance models are estimated, and the parameter modification method of fuel cell limiting current density under variable temperatures is proposed. Based on the polarization curve test experiments under variable-temperature conditions, it is demonstrated that the newly developed concentration overvoltage model reduces the relative error of simulation for a low Pt loading fuel cell in the high current region by 2.97% and 10.06% at 60 °C and 80 °C, respectively. The newly established concentration overvoltage model of a PEMFC solves the problem that the parameter of limiting current density is set without considering the influence of fuel cell temperature fluctuation, which leads to the poor simulation accuracy of the concentration overvoltage model in the high current region.

Comprehensive Molecular Dynamics Study of Oxygen Diffusion in Carbon Mesopores: Insights for Designing Fuel-Cell Catalyst Supports.

Mesoporous carbon is often used as a support for platinum catalysts in polymer electrolyte fuel-cell catalyst layers. Mesopores in the carbon support improve the performance of fuel cells by inhibiting the adsorption of ionomer onto the catalyst particles. However, the mesopores may impair mass transport. Hence, understanding molecular behaviors in the pores is essential to optimizing the mesopore structures. Specifically, it is crucial to understand the oxygen transport in the high-current region. In this study, the diffusion coefficients of oxygen molecules in carbon mesopores were calculated for various pore lengths, pore diameters, filling rates, and water contents in the ionomer via molecular dynamics simulations. The results show that oxygen diffusion slows by 2 orders of magnitude because of pore occlusion, and it slows down by an additional 1 or 2 orders of magnitude if ionomers are present in the pores. The occlusion can be theoretically predicted by considering the surface free energy. This theory provides some insight into mesoporous carbon designs; for instance, the theory suggests that narrow pores should be shortened to prevent occlusion. Slow diffusion in the presence of ionomers was attributed to the localization of oxygen at the dense ionomer-carbon interface. Thus, to improve oxygen transport properties, carbon surfaces and ionomer structures may be designed in such a manner as to prevent densification at the interface.

Linear resistance limiting the current of intergranular barriers in varistor ceramics

Method for measuring the linear resistivity ρlin, which affects the volt-ampere characteristic (VAC) nonlinearity of varistor materials in a high current region is proposed. For ZnO based varistor ceramics the dependence of ρlin on amplitude density Jmax of current pulse is studied in the range 5 A cm-2 – 4600 A cm-2. At Jmax < 200 A cm-2 a sharp decrease of ρlin with increasing Jmax takes place. This behavior indicates a non-uniform distribution of high current over the cross section of ceramics sample. At Jmax > 1000 A cm-2 ρlin does not depend on Jmax and has a value of 0.49 – 0.50 Ohm cm corresponding to the volume resistivity ρg of ZnO grains. The decrease in nonlinearity of VAC at high currents is due to the formation of conductive paths of electric current between the electrodes of a sample. Along such paths, all intergranular double Schottky barriers are in a reversible electrical breakdown mode, probably due to impact ionization. The current in these paths is limited by small linear volume resistance of the grains. A spread of grain sizes is the reason for existence of current paths with different numbers of contacts between grains and therefore with different breakdown voltages. At voltage increases, the sequential formation of parallel-connected conductive paths occurs. This explains the inhomogeneous distribution of high current over the cross section of a sample at Jmax < 200 A cm-2. At Jmax > 1000 A cm-2 almost all current paths in a sample are switched on and the value of ρlin limiting the barriers current is close to the volume resistivity ρg of grains.

Melting Characteristics of C-Type Filler Metal in GTAW

A C-type filler metal was developed to overcome the low deposition rate (DR) of gas tungsten arc welding (GTAW). The present study investigated the maximum DR for a novel C-type filler metal and compared it to conventional circular welding wires during GTAW using an Alloy 625 filler metal. For comparison with conventional circular welding wires, a ø1.2-mm (0.047-in.) welding wire, which is most widely used in practice, and a ø2.4-mm (0.094-in.) welding wire, which has almost the same sectional area as the novel C-type filler metal, were used in this research. An industrial robot was utilized to produce bead-on-plate welds in the flat position. The results revealed that at the same 200-A welding current, the DR of the C-type filler metal was higher than the conventional circular welding wires by 1.17 to 1.4 times according to the sectional area of the circular welding wires. At a high welding current of 500 A, it was impossible for the ø1.2-mm welding wire to deposit quality welds, and the acceptable range of the DR for the ø2.4-mm welding wire was narrow (i.e., 7–8 kg/h [15.4–17.6 lb/h]). However, the acceptable range of the DR for the C-type filler metal was as broad as 5.04–12.1 kg/h (11.1–26.6 lb/h) under the high welding current of 500 A. The maximum DR of the C-type filler metal was 1.51 times that of the ø2.4-mm welding wire. The mechanism of obtaining a high DR using the C-type filler metal was analyzed from the viewpoint of the continuous bridging transfer at the melting edge of the C-type filler metal. The ability of the C-type filler metal to achieve high DRs at high-current regions was superior to the conventional ø1.2- and ø2.4-mm welding wires.

Noise-induced dynamics and photon statistics in bimodal quantum-dot micropillar lasers

Emission characteristics of quantum-dot micropillar lasers (QDMLs) are located at the intersection of nanophotonics and nonlinear dynamics, which provides an ideal platform for studying the optical interface between classical and quantum systems. In this work, a noise-induced bimodal QDML with orthogonal dual-mode outputs is modeled, and nonlinear dynamics, stochastic mode jumping and quantum statistics with the variation of stochastic noise intensity are investigated. Noise-induced effects lead to the emergence of two intensity bifurcation points for the strong and the weak mode, and the maximum output power of the strong mode becomes larger as the noise intensity increases. The anti-correlation of the two modes reaches the maximum at the second intensity bifurcation point. The dual-mode stochastic jumping frequency and effective bandwidth can exceed 100 GHz and 30 GHz under the noise-induced effect. Moreover, the noise-induced photon correlations of both modes simultaneously exhibit super-thermal bunching effects () in the low injection current region. The -value of the strong mode can reach over 6 in the high injection current region. Photon bunching () of both modes is observed over a wide range of noise intensities and injection currents. In the presence of the noise-induced effect, the photon number distribution of the strong or the weak mode is a mixture of Bose–Einstein and Poisson distributions. As the noise intensity increases, the photon number distribution of the strong mode is dominated by the Bose–Einstein distribution, and the proportion of the Poisson distribution is increased in the high injection current region, while that of the weak mode is reduced. Our results contribute to the development preparation of super-bunching quantum integrated light sources for improving the spatiotemporal resolution of quantum sensing measurements and enhancing the security of optical communication.

4H-SiC Schottky barrier diodes as radiation detectors: A role of Schottky contact area

Large-area SiC Schottky barrier diodes can significantly improve the sensitivity in radiation detection due to the increased interacting SiC volume. In this work, we tested a large SiC detector with an area of 1 × 1 cm2. Extensive electrical characterization was performed at temperatures ranging from 150 K to 390 K, demonstrating the impact of barrier inhomogeneities on the electrical performance of the diode. Forward current-voltage (I-V) measurements of the diodes revealed two distinct regions caused by Schottky barrier inhomogeneity present throughout the entire temperature range. The barrier heights in the low- and high-current forward voltage regions were extracted from Richardson plots corrected for the Gaussian distribution of barrier heights, yielding values of 1.52 eV and 1.79 eV, respectively. Deep-level transient spectroscopy (DLTS) revealed only one deep-level defect, Z1/2, with an activation energy for electron emission of 0.67 eV, which was assigned to the known carbon vacancy. The DLTS study showed no correlation between electrically active defects and barrier inhomogeneity. An excellent energy resolution of 3.2 % was measured using a large area 241Am radiation source, consistent with values for small area SiC detectors that exhibited no barrier height inhomogeneities. The impact of temperature on the alpha particle radiation response was determined within a temperature range of 200 K to 390 K.

Current Effect on the Performances of All-Solid-State Lithium-Ion Batteries—Peukert’s Law

The results from measuring the capacity of thin-film solid-state lithium-ion batteries (SSLIBs) Ti|Si@O@Al|LiPON|LiCoO2|Ti, Ti|Si@O@Al|LiPON|LixV2O5|Ti, and Ti|LiPON|LiCoO2|Ti at different charge currents are reported. It is shown that the dependence of the capacity on the current density Q(j) follows Peukert’s law, which is characterized by a low value of Peukert’s exponents in the region of low currents and a high value of the exponents in the region of high currents. Peukert’s exponent for the anode-free cell remains constant through the entire range of current density variation. A model for SSLIB capacity based on the balance of ion (diffusion and drift) and electron currents is proposed. The model predicts a Q(j) dependence well approximating the experimental results and fitting Peukert’s law. The model allows a qualitative interpretation of the change in the Peukert exponent with increasing current density, based on the effect of the charge current saturation.

SOFTWARE FOR MEASURING THE NONLINEARITY COEFFICIENT OF VOLT-AMPERE CHARACTERISTIC FROM RASTER IMAGE OF OSCILLOGRAM

The web application that allows by scanning a raster image of the pulsed signals analog os-cillogram registered in the region of high electric currents to measure the nonlinearity coef-ficient of volt-ampere characteristic and its dependence on voltage and current is described.

Study of Temperature Rise Characteristics and Voltammetry Characteristics of ZnO Varistor under 10/350μs Pulse Current

To study the effect of 10/350μs pulse current on the electrical performance of ZnO varistor, a high-current impulse experimental study was conducted in this paper. Firstly, the varistor was subjected to different amplitude impulse discharge experiments, and the temperature change of the varistor after the impulse was recorded. Then, the temperature of the varistor at the moment of 1 second after the pulse impulse was suffered by the Asymptotic function, and the Levenberg-Marquardt optimization algorithm was calculated to compare the temperature rise of the varistor under different current amplitudes. Finally, the upward shift of voltammetry characteristics in the high-current region after the impulse was explained according to the double Schottky barrier model and the linear chain aging theory. The results show that the higher the pulse current amplitude is, the higher the temperature rise of the varistor is at the 1s moment. The highest voltammetry characteristic upshift is caused by the 6.4kA pulse current. The temperature rise and the voltammetry characteristic drift in the high-current region are positively correlated. The results of the study can provide a reference for manufacturers to produce ZnO varistors for direct lightning protection of buildings.

Improving Durability of Fuel Cells with Platinum-rich Alloy Cathode Catalysts

Pt3Co-alloy based nanoparticle catalysts are very active for oxygen reduction reaction (ORR) thereby enabling high performance of proton exchange membrane fuel cells (PEMFC) for automotive propulsion. However, these catalyst materials degrade due to a combination of electrochemical surface area (ECSA) loss and dissolution of cobalt-alloying element from the nanoparticles. Dissolution of cobalt has a two-fold impact on the durability of fuel cells—i) a loss in the low-current density kinetic region due to a decrease in specific activity and ii) a loss in the high-current density transport region due to Co2+ contamination of the ionomer phase. Cobalt dissolution-contamination needs to be mitigated as it limits fuel cell performance and lifetime for heavy-duty automotive applications. In this article, we study the use of PtCo-alloy catalysts with Pt-rich compositions using catalyst-specific accelerated stress test measurement in membrane electrode assemblies to decrease the amount of dissolved Co and mitigate its subsequent contamination effects. We demonstrate Pt5Co and Pt7Co compositions to enable significant improvements in durability (∼50 mV and ∼100 mV with respect to Pt3Co after 30,000 voltage cycles) with a minor but acceptable compromise in the initial specific activity of the catalyst.

Low-frequency noise characteristics of indium–gallium–zinc oxide ferroelectric thin-film transistors with metal–ferroelectric–metal–insulator–semiconductor structure

We investigate the low-frequency noise characteristics of indium–gallium–zinc oxide ferroelectric thin-film transistors (FeTFTs) with a metal–ferroelectric–metal–insulator–semiconductor (MFMIS) structure. MFMIS FeTFTs are fabricated with different metal-to-FE area ratios (AM/AF's). It is revealed that the noise generation mechanism differs depending on the operation region [low and high drain current (ID) regions] and AM/AF. Excess noise in the low ID region is observed in the MFMIS FeTFTs with AM/AF's of 4 and 6 due to carrier mobility fluctuations. In the high ID region, the carrier number fluctuation generates the 1/f noise of the devices regardless of the AM/AF.

Comparative study on short-circuit and surge current capabilities of 1.2 kV SiC SBD-embedded MOSFETs

This paper presents a comparative study on the short-circuit and surge current withstanding capabilities and the static and turn-on switching characteristics of commercial 1.2 kV SiC Schottky barrier diode (SBD)-embedded metal–oxide–semiconductor field-effect transistors (MOSFETs). The results confirmed that MOSFETs with a larger SBD area ratio had higher leakage current through the SBD during short-circuit transients due to a higher electric field and lattice temperatures as high as roughly 1120 K at the SBD, which resulted in reduced short-circuit withstanding capabilities. It was also found that MOSFETs with a smaller SBD area ratio had reduced surge-current capabilities in embedded SBDs. We conclude that is not due to the small SBD area ratio but to a weak bipolar operation of the Junction Barrier and Schottky rectifiers even in high current regions.

Assessing the influence of peak current distributions of first return strokes on the lightning performance of transmission lines: Instrumented tower distributions versus standard distributions

• The effect of peak current distributions on backflashover is shown. • Instrumented tower and standard distributions are adopted. • IEEE and CIGRE distributions overestimate backflashover for high voltage level TLs. • MCS distribution leads to largest BFOR probability for low insulation level TL. • A new formulation to reproduce high current region of MCS distribution is proposed. The influence of peak current distributions of first return strokes of instrumented towers and international standards on the calculated lightning performance of 138 kV and 500 kV transmission lines is evaluated. This performance, expressed by the backflashover probability, is determined by computational simulations using the Hybrid Electromagnetic model (HEM) and the Disruptive Effect method (DE). The performance is calculated considering the cumulative peak-current distributions obtained from direct measurements at the instrumented towers of Morro do Cachimbo (MCS) and Monte San Salvatore (MSS) stations and those provided by IEEE and CIGRE standards. According to the results, using the standard distributions yields larger backflashover probabilities of transmission lines of higher insulation level, in relation to those calculated using instrumented-tower distributions. Considering transmission lines of lower insulation level, the performances calculated using standard distributions are close to those obtained using MSS distribution, but yields lower backflashover probabilities in relation to those obtained using MCS distribution. The latter leads to backflashover probabilities about 40% and 47% larger than those obtained by using IEEE and CIGRE distributions, respectively, in the tower-footing impedance range of 20 Ω – 40 Ω.

Synthetic perylenequinone as anchoring center of sulfur and catalyst for polysulfides conversion

Lithium-sulfur batteries (LSBs) with high theoretical specific capacities are one of the most promising energy storage systems for the next generation. However, the issues of shuttle effect and poor cycle stability seriously hold off their commercialization. In this work, the organic molecule of perylenequinone (6,12-dihydroxyperylene-1,7-dione, DPD) was anchored on the surface of carbon material through π-π interaction and the prepared composite was applied as the cathode of LSBs. The combination of theory and experiment proved that the π-π interaction between DPD and carbon materials can overcome the solvation effect of DPD in organic electrolytes, which provided a prerequisite for the stable existence of DPD in the long-cycle process of LSBs. The further density functional theory (DFT) calculations indicated that both carbonyl and hydroxyl groups in DPD can form Li-O bonds with Li to covalently fix polysulfides, and the interacting mechanism was revealed by in-situ infrared spectroscopy. The prepared S@DPD/C electrode exhibited an initial discharge specific capacity of 625.3 mAh g−1 at 1C current density. A good cycling stability was observed at high current region with a capacity decay rate of 0.069% per cycle for 500 cycles.

A Stable Rechargeable Aqueous Zn-Air Battery Enabled by Heterogeneous MoS2 Cathode Catalysts.

Aqueous rechargeable zinc (Zn)-air batteries have recently attracted extensive research interest due to their low cost, environmental benignity, safety, and high energy density. However, the sluggish kinetics of oxygen (O2) evolution reaction (OER) and the oxygen reduction reaction (ORR) of cathode catalysts in the batteries result in the high over-potential that impedes the practical application of Zn-air batteries. Here, we report a stable rechargeable aqueous Zn-air battery by use of a heterogeneous two-dimensional molybdenum sulfide (2D MoS2) cathode catalyst that consists of a heterogeneous interface and defects-embedded active edge sites. Compared to commercial Pt/C-RuO2, the low cost MoS2 cathode catalyst shows decent oxygen evolution and acceptable oxygen reduction catalytic activity. The assembled aqueous Zn-air battery using hybrid MoS2 catalysts demonstrates a specific capacity of 330 mAh g-1 and a durability of 500 cycles (~180 h) at 0.5 mA cm-2. In particular, the hybrid MoS2 catalysts outperform commercial Pt/C in the practically meaningful high-current region (>5 mA cm-2). This work paves the way for research on improving the performance of aqueous Zn-air batteries by constructing their own heterogeneous surfaces or interfaces instead of constructing bifunctional catalysts by compounding other materials.

Channel Diameter Effect of Porous Carbon Microparticles on PEMFC Performance for Highly Active Ultra-Low Pt Catalysts

Proton exchange membrane fuel cells (PEMFCs) have received much attention as environmentally benign automotive power sources. PEMFCs can offer a large amount of electricity required for autonomous vehicles that battery-powered systems may not be able to provide. However, because PEMFC electrodes are based on expensive and scarce Pt catalysts, Pt minimization is necessary to expand the PEMFC market. To reduce Pt usage, various attempts have been made to increase the intrinsic activity of Pt catalysts, particularly at the cathode where the oxygen reduction reaction (ORR) occurs. Despite decades of progress, high ORR activity was typically reported in half-cell setups and frequently failed to show corresponding performance in single-cell. Catalysts with low Pt content perform poorly in the high-current density region because the thick catalyst layer limits mass transport.[1] In addition, low Pt loading catalysts typically suffer more in long-term operation.[2] As a result, it is critical to develop PEMFC catalysts with low Pt content that can facilitate mass transport while also exhibiting high durability.Herein, we report highly active and durable PtFe@C catalysts with ultra-low amounts of Pt (1 wt%) on channeled mesoporous carbon (CMC) particles. These CMC particles are designed to have continuous channels with open porosity and a large surface area, facilitating the mass transport behavior and maximizing cell performance. Block-copolymer particles (BCPs) with different molecular weights were used to fabricate CMC particles with pore diameters ranging from 13 to 63 nm. Two steps of pre-crosslinking and hyper-crosslinking were conducted prior to the carbonization step to preserve the porous internal structure of the BCP-based carbon support during high-temperature treatment. After depositing Pt onto the support by facile incipient wetness impregnation method followed by reduction, thin layers of carbon shell were observed to encapsulate the PtFe alloy nanoparticles.The channel diameter effect on the mass transport was studied in both half-cell and single-cell. Interestingly, from the cell performance obtained with varying channel diameters and different oxygen concentrations, we concluded that both reactant (proton and oxygen) supply and product (water) removal were greatly enhanced with larger channel size. With the largest channel diameter of 63 nm, initial mass activity in the single-cell was obtained to be 3.5 A mgPt -1, which is the highest value reported to date to the best of our knowledge. Cell performance under H2-air flow, which is the industrially relevant condition, surpassed the commercial 20 wt% Pt/C with only 1/20 of the Pt loading. The origin of enhanced cell performance upon enlarging the channel diameter was investigated by separating kinetic, ohmic (electronic and ionic charge transport), and mass transport overpotentials. Both the proton and oxygen transport resistance were confirmed to be reduced with larger channel size. Moreover, carbon shell protected Fe from getting leached out in an acidic environment, resulting in preserved catalyst structure and high durability. The outstanding performance of 51 kW/gPt in H2/air condition after 30,000 cycles of accelerated degradation tests (ADTs) was observed. This work will open a new paradigm to develop PEMFC catalysts with much higher activity and durability while simultaneously minimizing Pt use.

Sensitivity analysis of operating parameters on a 65 kW proton exchange membrane fuel cell stack performances

It is widely acknowledged that the operating parameters of fuel cell stack have significant influences on the output performances. However, there is still a lack of relevant research on the parameter sensitivity test for high-power vehicular stacks. In the study, the orthogonal test method is adopted for a 65 kW fuel cell stack. Effects of operating temperature, relative humidity, stoichiometric ratio, and inlet pressure are quantitatively investigated. It is found that the stack voltage increases significantly when the operating temperature rises from 60 °C to 70 °C while no remarkable performance differences are observed when the temperature further rises from 75 °C to 80 °C. With the increase of reactant relative humidity, the change of voltage change ratio is more obvious in the low current density regions. It is also inferred that the stack performance enhancement caused by better hydration level will be less effective once the inlet relative humidity reaches a certain degree. Increasing the inlet reactant pressure promotes the mass transfer capacity. Besides, the performance is improved more significantly in the high current density regions, which may be attributed to the improvement of concentration polarization. When the stoichiometric ratio increases, the stack output voltage does not increase significantly at lower current regions, but there exists significant performance optimization at higher current regions. The paper contributes to the deeper understanding of transport phenomena as well as better performance enhancement suggestions for vehicular fuel cell stacks.