Current Decay Research Articles

The Preharvest Application of Essential Oils (Carvacrol, Eugenol, and Thymol) Reduces Fungal Decay in Lemons

Lemon postharvest losses are mainly due to the presence of fungal diseases. Current postharvest decay strategies rely on synthetic chemical fungicides; however, consumers are demanding that fruit is free of any chemical residue. The use of new natural alternatives, including essential oils, is emerging due to their potential antimicrobial activity. Therefore, the aim of this work is the elucidation of the effect of carvacrol, eugenol, and thymol, individually and in combination, applied in preharvest. Three different concentrations (100, 500, and 1000 µL/mL) of carvacrol, eugenol, and thymol were individually applied and in combination in ‘Fino’ and ‘Verna’ lemon cultivars. The fungal incidence (mainly Penicillium digitatum and P. italicum) was evaluated weekly for 35 days. Moreover, the main different quality parameters (weight loss, firmness, colour, total soluble solids, titratable acidity, and total phenolic content) of lemons were evaluated at harvest and after 35 days of cold storage. The results showed that carvacrol at the lowest concentration (100 µL/L) provided the lowest fungal incidence with a non-negative effect on the lemon quality parameters during storage, while the highest concentrations and the combination of essential oils resulted in the opposite effect. Therefore, carvacrol applied at 100 µL/L in preharvest could be an eco-friendly alternative to the current fungicides to control lemon decay, while maintaining their optimal quality.

Nature of the abnormally high photocurrent relaxation time in the a-Ga2O3-based Schottky diodes

Ga2O3 is an ultra-wideband material with excellent optical characteristics. It is a promising material for power applications and optoelectronics because of its high electrical breakdown voltage and radiation hardness. It is optically transparent for visible light and UVA but UVC-sensitive. One of the main disadvantages of this material is the anomalous slow photoeffect: photoconductivity rise and decay characteristic times can be more than hundreds of seconds long. This "slow" photoconductivity effect severely limits the utilisation of the Ga2O3-based devices. The aim of this work is the investigation of the nature of this effect. The results of the photoinduced current rise and decay under 530 nm and 259 nm LED are measured in the HVPE-grown α-Ga2O3-based Schottky diode. Upon UV-illumination the photocurrent rise consists of three parallel processes: fast signal growth, slow growth and very slow decay with characteristic times near 70 ms, 40 s and 300 s respectively. Subsequent 530 nm LED illumination resulted in photoinduced current rise consisting of two mechanisms with characterisatic times 130 ms and 40 s on which a very slow decrease of the photocurrent amplitude with characteristic time of 1500 s was superimposed. 530 nm illumination stimulates this process. Protoinduced current relaxation analysis shows the presence of the deep levels with energies (EC - 0.17 eV). It is suggested that extremely slow relaxations can be associated with potential fluctuations near the Schottky barrier.

Impact of nuclear matrix element calculations for current and future neutrinoless double beta decay searches

Nuclear matrix elements (NME) are a crucial input for the interpretation of neutrinoless double beta decay data. We consider a representative set of recent NME calculations from different methods and investigate the impact on the present bound on the effective Majorana mass mββ by performing a combined analysis of the available data as well as on the sensitivity reach of future projects. A crucial role is played by the recently discovered short-range contribution to the NME, induced by light Majorana neutrino masses. Depending on the NME model and the relative sign of the long- and short-range contributions, the current 3σ bound can change between mββ< 40 meV and 600 meV. The sign-uncertainty may either boost the sensitivity of next-generation experiments beyond the region for mββ predicted for inverted mass ordering or prevent even advanced setups to reach this region. Furthermore, we study the possibility to distinguish between different NME calculations by assuming a positive signal and by combining measurements from different isotopes. Such a discrimination will be impossible if the relative sign of the long- and short-range contribution remains unknown, but can become feasible if mββ ≳ 40 meV and if the relative sign is known to be positive. Sensitivities will be dominated by the advanced 76Ge and 136Xe setups assumed here, but NME model-discrimination improves if data from a third isotope is added, e.g., from 130Te or 100Mo.

Similarity of Heterogeneous Kinetics to Delay of Double-Layer Capacitance Using Chronoamperometry

Chronoamperometric curves for the oxidation of a ferrocenyl derivative via a potential step, calculated using the Cottrell equation, showed less diffusion-controlled currents on a platinum wire electrode. This lower deviation cannot be explained via Butler–Volmer heterogeneous kinetics, but was ascribed to the negatively capacitive current associated with a redox reaction. The deviation in fully oxidized electrical potential corresponds to the non-zero concentration at the electrode surface, which cannot be predicted using the Nernst equation. This equation expresses the relationship between the electrical potential and activity at the electrode surface rather than the concentration. The diffusion equation determines the relationship between the current and surface concentration rather than activity. Negative capacitance or a non-zero concentration may arise from structure formation on the electrode owing to dipole–dipole interactions, which are similar to the generation of double-layer capacitance, including frequency dispersion. Following this concept, we derive expressions for a lowered diffusion-controlled current and time-dependent surface concentration. The negatively capacitive current shows the time dependence of t−0.9, which is similar to the decay of double-layer capacitive currents. The surface concentration decays with t−0.4-dependence.

Pregnenolone sulfate analogues differentially modulate GABAA receptor closed/desensitised states.

GABAA receptors are regulated by numerous classes of allosteric modulators. However, regulation of receptor macroscopic desensitisation remains largely unexplored and may offer new therapeutic opportunities. Here, we report the emerging potential for modulating desensitisation with analogues of the endogenous inhibitory neurosteroid, pregnenolone sulfate. New pregnenolone sulfate analogues were synthesised incorporating various heterocyclic substitutions located at the C-21 position on ring D. The pharmacological profiles of these compounds were assessed using electrophysiology and recombinant GABAA receptors together with mutagenesis, molecular dynamics simulations, structural modelling and kinetic simulations. All seven analogues retained a negative allosteric modulatory capability whilst exhibiting diverse potencies. Interestingly, we observed differential effects on GABA current decay by compounds incorporating either a six- (compound 5) or five-membered heterocyclic ring (compound 6) on C-21, which was independent of their potencies as inhibitors. We propose that differences in molecular charges, and the targeted binding of analogues to specific states of the GABAA receptor, are the most likely cause of the distinctive functional profiles. Our findings reveal that heterocyclic addition to inhibitory neurosteroids not only affected their potency and macroscopic efficacy but also affected innate receptor mechanisms that underlie desensitisation. Acute modulation of macroscopic desensitisation will determine the degree and duration of GABA inhibition, which are vital for the integration of neural circuit activity. Discovery of this form of modulation could present an opportunity for next-generation GABAA receptor drug design and development.

Long-Range Conductivity in Proteins Mediated by Aromatic Residues.

Single-molecule measurements show that many proteins, lacking any redox cofactors, nonetheless exhibit electrical conductance on the order of a nanosiemen over 10 nm distances, implying that electrons can transit an entire protein in less than a nanosecond when subject to a potential difference of less than 1 V. This is puzzling because, for fast transport (i.e., a free energy barrier of zero), the hopping rate is determined by the reorganization energy of approximately 0.8 eV, and this sets the time scale of a single hop to at least 1 μs. Furthermore, the Fermi energies of typical metal electrodes are far removed from the energies required for sequential oxidation and reduction of the aromatic residues of the protein, which should further reduce the hopping current. Here, we combine all-atom molecular dynamics (MD) simulations of non-redox-active proteins (consensus tetratricopeptide repeats) with an electron transfer theory to demonstrate a molecular mechanism that can account for the unexpectedly fast electron transport. According to our MD simulations, the reorganization energy produced by the energy shift on charging (the Stokes shift) is close to the conventional value of 0.8 eV. However, the non-ergodic sampling of molecular configurations by the protein results in reaction-reorganization energies, extracted directly from the distribution of the electrostatic energy fluctuations, that are only ∼0.2 eV, which is small enough to enable long-range conductivity, without invoking quantum coherent transport. Using the MD values of the reorganization energies, we calculate a current decay with distance that is in agreement with experiment.

Miniaturized HTS linear flux pump with a charging capability of 120 A

Owing to the presence of joint resistance and flux creep, high-temperature superconducting (HTS) coils without a power supply inevitably suffer from current decay. A flux pump is a voltage supply that requires connections with smaller footprints and a lower heat load than traditional current leads. In this study, we explain the principle of the upper limit for the output current of the traveling wave flux pumps. Based on this principle, a miniaturized linear flux pump device was developed. With narrow and misaligned iron teeth, elaborate 3D geometry of the iron pieces, and optimized driving current waveform, the miniaturized flux pump can support more than 120 A output current with only a 10 mm wide HTS tape and a compact size of 4.6 × 4.6 × 3.4 cm. Our experimental results show that the critical current of the HTS tape has a significant effect on the flux pump output. An HTS tape with a larger critical current supports a higher maximum transport current, whereas an HTS tape with a smaller critical current requires less applied current for positive output. Finally, excitation tests on HTS coils were performed. Charge/active discharge and field supplement experiments were done on a maglev HTS racetrack coil of 0.4 H, where charging/field supplement capability of the miniaturized flux pump were demonstrated up to 46.8 A (close to the critical current of the coil). It has also been proved that the flux pump can work together with an external power supply with persistent current switch. The miniaturized flux pump can also independently charge an HTS coil of 60 μH to 91.6 A, which is the critical current of the coil at a low voltage criterion.

Photo-stability of the Titan Yellow dye sensitized and Ethylenediaminetetraacetate photoreduced photogalvanic system

Photogalvanic cells are solar power and storage devices. Extensive study on the photo-stability and durability aspect of these cells has not attracted the attention of the researchers. With this aim, the present work reports the electrical output and stability study of the Titan Yellow sensitized photo-galvanic cells. The observed electrical output is 823 mV potential, 2800 μA current, and 511.10 μW power. The observed potential decay rate over 52.18 h is very low (i.e., 1.59 mV/h only) during illumination. This observation shows quite good photo-stability of the cell with respect to the open-circuit potential. The observed current decay rate over 52.18 h is very high (i.e., 15.67 μA/h) during illumination. This observation shows less photo-stability of the cell with respect to the short-circuit current. From initial charging to 1st re-charging to 2nd re-charging of the same cell, the power output decreases under experimental conditions. Overall, the power decay is observed with time in both dark and illuminated conditions. The trend of fall of power is suggestive of the inverse relation between half change time and initial power, and the power decay is of non-zero and non-first order decay. The dye decay and temperature rise in the electrolyte is observed. The power decay may be attributed to the photo-induced degradation of the dye electro-active species and high temperature induced aggregation (precipitation) of the Titan Yellow dye molecules. Despite this power decay, the Titan Yellow dye based photogalvanic cells are capable of producing solar power for sufficiently long hours.

Lattice-controllable in-situ synthesis of Co-Ni-mixed sulfide/polypyrrole nanostructures on carbon paper for hydrogen evolution reaction in alkaline media

Developing high-performance and low-cost electrocatalysts for the hydrogen evolution reaction (HER) favorably promotes large-scale hydrogen production from water. Here, we design a nanocomposite of Co9S8-Ni9S8 nanodiscs (CNS) in-situ grown from polypyrrole hollow nanospheres (PHS) on carbon paper (CP) via unipolar pulse electrodeposition (UPED) technique as HER catalyst in alkaline media. The lattice structure along with the interlacing nanodiscs-like morphology of the Co9S8-Ni9S8 mischcrystal is controllable by UPED method. The optimal CNS/PHS/CP electrode obtained with pulse potential of − 0.80 V exhibits favorable catalytic activity with low overpotential (186 mV at 10 mA cm−2), superior stability performance (for 100 h with no current density decay), and high electrochemically active surface area up to 1925 cm2, which should be attributed to the interlacing Co9S8-Ni9S8 mischcrystal with rich active sites, the ingenious combination with conductive polymer, and the integrated electron-proton conductive network. This work will provide a new sight to design low-cost bimetallic sulfide-based electrocatalysts for high-performance HER in water splitting.

Extracellular histone proteins activate P2XR7 channel current.

Extracellular histone proteins are elevated in circulation after injury or activation of the innate immune response. In resistance-size arteries, extracellular histone proteins increased endothelial cell (EC) Ca2+ influx and propidium iodide (PI) labeling, but paradoxically decreased vasodilation. These observations could be explained by the activation of an EC resident non-selective cation channel. We tested the hypothesis that the ionotropic purinergic receptor 7 (P2XR7), a non-selective cation channel associated with cationic dye uptake, is activated by histone proteins. We expressed mouse P2XR7 (C57BL/6J variant 451L) in heterologous cells and measured inward cation current using two-electrode voltage clamp (TEVC). Cells expressing mouse P2XR7 had robust ATP- and histone-evoked inward cation currents. ATP- and histone-evoked currents reversed approximately at the same potential. Current decay with agonist removal was slower for histone-evoked than ATP- or BzATP-evoked currents. As with ATP-evoked P2XR7 currents, histone-evoked currents were inhibited by non-selective P2XR7 antagonists (Suramin, PPADS, and TNP-ATP). Selective P2XR7 antagonists, AZ10606120, A438079, GW791343, and AZ11645373, inhibited ATP-evoked P2XR7 currents but did not inhibit histone-evoked P2XR7 currents. As previously reported with ATP-evoked currents, histone-evoked P2XR7 currents were also increased in conditions of low extracellular Ca2+. These data demonstrate that P2XR7 is necessary and sufficient for histone-evoked inward cation currents in a heterologous expression system. These results provide insight into a new allosteric mechanism of P2XR7 activation by histone proteins.

Footprints of New Physics in the angular distribution of [formula omitted] decays

We investigate the angular decay distribution of the four-fold Bc→Ds⁎(→Dsγ)μ+μ−, and Bc→Ds⁎(→Dsπ)μ+μ− decays that proceed through b→sμ+μ− quark level transition. We use the model independent effective Hamiltonian with vector and axial vector new physics operators to formulate the angular observables and study the implications of different latest new physics scenarios, taken from the global fits to all the b→s data, on these observables. We also give Standard Model and new physics predictions of several observables such as differential branching ratios, forward backward asymmetry, longitudinal polarization fraction of Ds⁎, and the unpolarized and polarized lepton flavor universality violating ratios. Future measurements of the predicted angular observables, both at current and future high energy colliders, will add to the useful complementary data required to clarify the structure of new physics in b→sℓℓ neutral current decays.

Rare decay t→cγγ via scalar leptoquark doublets

A calculation of the one-loop contribution to the rare three-body flavor changing neutral current top quark decay $t\to c\gamma\gamma$ is presented in the framework of models with one or more scalar leptoquark $SU(2)$ doublets with hypercharge $7/6$. Analytical expressions for the invariant amplitude of the generic decay $f_i\to f_j\gamma\gamma$, with $f_{i,j}$ a lepton or quark, are presented in terms of Passarino-Veltman integral coefficients, from which the amplitudes for the processes $t\to c\gamma\gamma$ and $\ell_i\to \ell_j\gamma\gamma$ follow easily. An analysis of the current constraints on the parameter space is presented in the scenario with only one scalar LQ doublet and bounds on the LQ couplings are obtained from the muon $g-2$ anomaly, the lepton flavor violating (LFV) decay $\tau\to \mu\gamma$ and extra constraints meant to avoid tension between theory predictions and experimental data. For a LQ with a mass in the range of $1$--$1.5$ TeVs, the estimate ${\rm Br}(t\to c\gamma\gamma)\sim 10^{-11}$--$10^{-12}$ is obtained for the largest allowed values of the LQ coupling constants, which means that this decay would be below the reach of future experimental measurements. We also consider an scenario with three scalar doublets, which was recently proposed to explain the lepton flavor universality violation anomalies in $B$ decays as well as the muon $g-2$ anomaly. Although this scenario allows large LQ couplings to the tau lepton and the $c$ and $t$ quarks, the branching ratio of the $t\to c\gamma\gamma$ decay is also of the order of $10^{-11}$--$10^{-12}$ for LQ masses of 1.7 TeV.

Extracellular histone proteins are novel activators of P2XR7 channel current

Extracellular histone proteins have been identified as important damage associated molecules that contribute to vascular dysfunction. Histones are elevated in circulation after traumatic injury and activation of the innate immune response. In prior work, we demonstrated that extracellular histone proteins induced endothelial cell (EC) Ca 2+ influx, increased EC propidium iodide labeling, and decreased vasodilatory responses. These paradoxical observations could be explained by activation of a non-selective cation channel. The ionotropic purinergic receptor 7 (P2XR7) stands out as a candidate as it has been shown to form a high-conductance, poorly selective, cation channel capable of conducting large cationic dyes. Herein, we test the hypothesis that P2XR7 channels are activated by histone proteins. We expressed mouse P2XR7 (C57BL/6J variant 451L) in heterologous cells ( Xenopus oocytes) and measured inward cation current using two-electrode voltage clamp (TEVC). Cells expressing mouse P2XR7 had robust ATP- and histone-evoked inward cation currents. ATP- and histone-evoked currents reversed approximately at the same potential. Current decay with agonist removal was much slower for histone-evoked than ATP- or BzATP-evoked currents. As with ATP-evoked P2XR7 currents, histone-evoked currents were inhibited by non-selective P2XR7 antagonists (Suramin, PPADS, and TNP-ATP). GW791343, a selective P2XR7 antagonist with a known binding site distinct from the ATP binding site, inhibited ATP-evoked currents but did not inhibit histone-evoked currents. As with ATP-evoked currents, histone-evoked P2XR7 currents were also increased in conditions of low extracellular Ca 2+ . These data demonstrate that P2XR7 is necessary and sufficient for histone-evoked inward cation currents. These results suggest a new allosteric mechanism of P2XR7 activation by histone proteins that may guide the development of more effective P2XR7 pharmacology and therapeutic strategies for a wide array of pathologies that involve P2XR7 function. DMC is supported by NIH R00HL133451 and R01HL155180 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Fe‐Induced Electronic Transfer and Structural Evolution of Lotus Pod‐Like CoNiFePx@P,N‐C Heterostructure for Sustainable Oxygen Evolution

Transition metal phosphides with metallic properties are a promising candidate for electrocatalytic water oxidation, and developing highly active and stable metal phosphide‐based oxygen evolution reaction catalysts is still challenging. Herein, we present a facile ion exchange and phosphating processes to transform intestine‐like CoNiPx@P,N‐C into lotus pod‐like CoNiFePx@P,N‐C heterostructure in which numerous P,N‐codoped carbon‐coated CoNiFePx nanoparticles tightly anchors on the 2D carbon matrix. Meanwhile, the as‐prepared CoNiFePx@P,N‐C enables a core‐shell structure, high specific surface area, and hierarchical pore structure, which present abundant heterointerfaces and fully exposed active sites. Notably, the incorporation of Fe can also induce electron transfer in CoNiPx@P,N‐C, thereby promoting the oxygen evolution reaction. Consequently, CoNiFePx@P,N‐C delivers a low overpotential of 278 mV (vs RHE) at a current density of 10 mA cm−1 and inherits excellent long‐term stability with no observable current density decay after 30 h of chronoamperometry test. This work not only highlights heteroatom induction to tune the electronic structure but also provides a facile approach for developing advanced and stable oxygen evolution reaction electrocatalysts with abundant heterointerfaces.

Flower-Like Amorphous MoO3- x Stabilized Ru Single Atoms for Efficient Overall Water/Seawater Splitting.

Benefitting from the maximum atom utilization efficiency, special size quantum effects and tailored active sites, single-atom catalysts (SACs) have been promising candidates for bifunctional catalysts toward water splitting. Besides, due to the unique structure and properties, some amorphous materials have been found to possess better performance than their crystalline counterparts in electrocatalytic water splitting. Herein, by combining the advantages of ruthenium (Ru) single atoms and amorphous substrates, amorphous molybdenum-based oxide stabilized single-atomic-site Ru (Ru SAs-MoO3- x /NF) catalysts are conceived as a self-supported electrode. By virtue of the large surface area, enhanced intrinsic activity and fast reaction kinetics, the as-prepared Ru SAs-MoO3- x /NF electrode effectively drives both oxygen evolution reaction (209mV @ 10mA cm-2 ) and hydrogen evolution reaction (36mV @ 10mA cm-2 ) in alkaline media. Impressively, the assembled electrolyzer merely requires an ultralow cell voltage of 1.487V to deliver the current density of 10mA cm-2 . Furthermore, such an electrode also exhibits a great application potential in alkaline seawater electrolysis, achieving a current density of 100mA cm-2 at a low cell voltage of 1.759V. In addition, Ru SAs-MoO3- x /NF only has very small current density decay in the long-term constant current water splitting test.

Electrochemically activated platinum nanoparticles trapped by carbon nanotubes for methanol oxidation reaction

In this work, we describe the in situ creation of Pt nanoparticles (NPs) through electrochemical activation by potential cycling method on the poly crystalline Pt electrode surface without the use of any binders or reducing agents. Further it has been shown that the Pt NPs formed by electrochemical activation could be entrapped by carbon nanotubes drop casted on the poly crystalline Pt electrode surface. The drop casted CNTs entrap the Pt NPs and make them dissolution resistant so that the Pt NPs would not leach from the surface. Thus prepared electrocatalyst displayed high electroactive surface area and better electrocatalytic activity towards methanol oxidation reaction in acid medium. CNTs supported Pt NPs on the poly crystalline Pt surface were microscopically characterized by FESEM, TEM, HRTEM, and physically characterized by XRD to confirm the presence of Pt NPs. The electrochemical activation, entrapment of Pt NPs on CNTs, measurement of electro active surface area, methanol oxidation and catalytic stability were examined by electrochemical studies. The morphology of the material was well maintained which could be ascribed to the effect of CNTs. Surface decorated CNTs by nanostructured Pt on poly crystalline Pt acting as the catalyst does not show any obvious current decay during the testing period. The catalyst exhibited a very good performance with a lower onset potential for methanol oxidation and the mass activity is found to be 25 A g−1 of Pt. The electrochemically active surface area is found to be high and is calculated to be 28.47m2g−1.

Interpretation of transient electromagnetic data using zero-level curves

Geophysical data has long been used to gain insight into the geologic structure and composition of the subsurface. The geometrical characteristics of geophysical data, such as the locations of the minimum, maximum, and zero-crossings, gives insight into the subsurface based on the physics of the measured geophysical field. These characteristics provide a preliminary understanding of subsurface properties without performing expensive 3D inversions. When examining the zero-level curve (or zero-crossings) of magnetic data collected at the surface, one finds that the zero-level curve corresponds to a conic section with properties related to the location and orientation of a subsurface magnetic dipole. The zero-level curve can be inverted using a least-squares fitting to find a corresponding magnetic dipole location and direction in the subsurface. This understanding is extended in our work to time-domain electromagnetics, where current is induced and flows inside a confined conductor. The induced current creates a magnetic dipole in the subsurface conductor that can be characterized by the zero-level curve. As the current decays, the magnetic dipole in the conductor changes. At times directly after the transmitter is turned off, the direction of current flow depends primarily on the geometry of the transmitter and conductor. As time advances, the current flow tends towards the long-axis of the conductor, and the magnetic dipole aligns perpendicularly to that long axes. Inverting the zero-level curve of the electromagnetic data at every time channel of interest enables the tracking of the magnetic dipole through time, giving insight to the orientation and location of the conductor. We examine the method of interpreting zero-level curves using synthetic examples. We also apply it to field data measured over a compact volcanogenic massive sulfide deposit at the Lalor Mine site in Canada, and demonstrate that the geometrical information obtained is consistent with the results from previous studies in the area.

Heterostructure of NiFe@NiCr-LDH for Active and Durable Oxygen Evolution Reactions in Alkaline Media.

Developing cost-effective, efficient, and durable catalysts for oxygen evolution reactions (OER) is the key for promoting large-scale H2 production through electrochemical water splitting. Herein, we report a facile method for fabricating an NiFe@NiCr-LDH catalyst toward alkaline OER. The electronic microscopy technique revealed that it has a well-defined heterostructure at the interface between the NiFe and NiCr phases. In 1.0 M KOH, the as-prepared NiFe@NiCr-LDH catalyst shows excellent catalytic performance, evidenced by an overpotential of 266 mV at the current density of 10 mA cm-2 and a small Tafel slope of 63 mV dec-1; both are comparable with the RuO2 benchmark catalyst. It also exhibits robust durability in long-term operation, manifested by a 10% current decay in 20 h, which is superior to that of the RuO2 catalyst. Such excellent performance is attributed to the interfacial electron transfer that occurs at the interfaces of the heterostructure, and the Fe(III) species facilitate the formation of Ni(III) species as active sites in NiFe@NiCr-LDH. This study offers a feasible strategy for preparing a transition metal-based LDH catalyst for OER toward H2 production and other electrochemical energy technologies.

Nitrogen-doped carbon dot/activated carbon nanotube-supported copper nanoparticles as an efficient electrocatalyst for the oxygen reduction reaction

Recent decades have witnessed remarkable progress in fuel cell technology for efficient energy conversion devices in stationary, automotive, and mobile systems. However, the choice of the electrode material in the fuel cell technologies is still limited to platinum and the other platinum group metals, necessitating further research for alternatives. Herein, activated carbon nanotubes (ACNTs) treated at a high temperature (500 °C) were used as a support to induce binding with N-doped carbon dots (NCDs). Cu(II) in the copper nanoparticles spontaneously reduced to Cu(0) using the NCDs as a reducing agent; thus, a Cu/NCD/ACNT hybrid catalyst was synthesized. The oxygen reduction reaction (ORR) activity of the Cu/NCD/ACNT catalyst (Eonset = 0.921 V) was higher than those of Cu/ACNT (Eonset = 0.821 V) and NCD/ACNT (Eonset = 0.869 V) catalysts. The Cu/NCD/ACNT catalyst also exhibited excellent tolerance to methanol, in relation to Pt/C, during a methanol fuel cell tolerance test. Moreover, the current decays after 10 h in the ORR durability test were 21% and 10% for the Pt/C and Cu/NCD/ACNT catalysts, respectively, demonstrating the greater durability of the non-metal catalyst. Thus, the Cu/NCD/ACNT catalyst, formed by the synergistic action of ACNT, N doping, and spontaneous reduction of Cu(II), is a promising alternative to commercial Pt/C catalysts.

Global Observations of the Short‐Term Disturbances in the Geomagnetic Field and Induced Currents During the Supersubstorms Events of Solar Cycle 24

AbstractFour supersubstorms of the solar cycle 24 are analyzed to investigate the global variations in the H‐component and geomagnetically induced currents (GICs). The response to the storm sudden commencement (SSC) of the 2012 and 2017 events is observed differently over different latitude bands. Initially, the latitude band of 0°–45° shows a step‐like preliminary positive impulse (PPI), 45°–65° shows a Gaussian‐kind of PPI and 65°–90° shows a preliminary reverse impulse, followed by a main impulse all over. The H‐component variations during the supersubstorm periods show a strong north‐south asymmetry over the high latitudes which is attributed to the seasonal dependence of the growth and decay of ionospheric currents respectively in the summer and winter hemispheres. The co‐latitude band of ∼55°–65° shows a complete reversal of phase (i.e., global positive peak) of the H‐component compared to the maximum depression observed from the close‐by latitude bands and peak depressions in the SYM‐H, SML, and AE indices. The low latitude variations exhibit a dominant local time‐dependent control of the perturbation electric fields over the short and long terms during the geomagnetic events. The D‐component variations reflect complex ionospheric contributions during the SSC and the main phase with more asymmetries and variability. The GIC threat represented by the dB/dt peaks during the supersubstorms shows the highest magnitude (∼900 nT/min) in the latitude band of 60°–75° with a secondary peak over the dip equatorial regions. Further, some scattered and prominent peaks over the mid and high latitudes outside the supersubstorm periods are also observed.