Exchange Currents Research Articles

Enhanced Alkaline Hydrogen Oxidation Reaction by Modifying Pt Nanoparticle Surface with Another Metal

Anion exchange membrane fuel cells (AEMFCs) can reduce the cost of fuel cell systems because they allow the use of non-precious metals in catalysts due to their less corrosive internal environments, which gives them an advantage over conventional proton exchange membrane fuel cells (PEMFCs) with highly corrosive environments. Taking this advantage, non-precious-metal catalysts have been developed in particular for cathode, i.e., for the oxygen reduction reaction (ORR). However, the cell performance of AEMFCs is still inferior to that of PEMFCs. One of the reasons is sluggish hydrogen oxidation reaction (HOR) on anode, as represented by the fact that the HOR rate on Pt catalysts in alkaline conditions is two orders of magnitude slower than that in acidic conditions. It would be reasonable to consider that development of catalysts for the HOR enhances the AEMFC performance. In fact, the previous studies have demonstrated that alloying and size-control of metal nanoparticle catalysts improve the HOR activity and the cell performance. Recently, the cell performance has been getting closer to that of PEMFCs by the improvement of HOR catalysts with the help of the state-of-the-art anion exchange membranes having high ion conductivity. However, a lot of precious metals are needed on AEMFC anode to obtain such high cell performance. Therefore, the HOR catalysts in alkaline conditions have to be further developed for widespread use of AMFCs as an alternative of PEMFCs. Previous studies on the alkaline HOR have suggested two mechanisms accounting for enhancement of the HOR activity: hydrogen-binding-energy (HBE) mechanism and bifunctional mechanism. The HBE mechanism can account for the variation of HOR activity with pH of electrolyte as well as with metal species. The bifunctional mechanism has been recently suggested as another mechanism contributing to the improved HOR kinetics. In the bifunctional mechanism, catalyst surface not only adsorbs hydrogen but also supplies reactive oxygen species to the adsorbed hydrogen. These mechanisms have driven us to modify catalyst surface systematically, because tuning of surface property is expected to change the HBE and/or the reactive oxygen species, and consequently improve the HOR activity based on the bifunctional mechanism. In this paper, we show enhanced or lowered HOR activity of Pt/C by surface modification of Pt nanoparticles with various metals on the group 4-11 of the 4th and 5th period in the periodic table except for Tc, i.e., Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Rh, Pd, Ag (fifteen metals). Commercially available Pt/C (TEK10E50E, Pt 46.7wt%) is modified with the fifteen metals using a conventional impregnation method to load 7.7at% of the metals on Pt/C. The catalysts are denoted as M/Pt/C. The electrochemically active surface area (ECSA) is determined from the electric charge due to HUPD in 0.1 M NaOH aq. saturated with N2. The HOR activity is determined from linear sweep voltammograms obtained using a rotating disk electrode method in 0.1 M NaOH aq saturated with H2 at 25°C. The exchange current (i0) is determined using the approximate Butler-Volmer equation. The mass activity (MA) is determined by dividing i0 by the total amount of Pt and added metals. Interestingly, most M/Pt/C samples presents higher MA values than Pt/C, although the modifying metals are less active than Pt when used individually for the HOR. Thus, modifying Pt/C enhance the HOR on Pt/C. Modification with Co was most effective for enhancing the MA of the metals in the third period, with a MA twice that of Pt/C; Ru in the fourth period exhibited a MA 2.5 times higher than that of Pt/C. It is noteworthy that the MAs of various M/Pt/C samples including Mo, Ru, and Pd/Pt/C are significantly higher than a state-of-the-art Pt-Ru alloyed nanoparticle catalyst (TEC61E54 supplied by Tanaka Kikinzoku Kogyo). The specific activity (SA) of M/Pt/C for the HOR is determined by dividing i0 by the ECSA. The SA varies with a volcano shape on both elemental periods with a peak at Co on the 4th period and at Ru on the 5th period, where the SA value is enhanced two times compared to Pt/C. The mechanism of the enhanced HOR activity is investigated in terms of the hydrogen binding energy (HBE) on catalysts. However, the variation of HOR activity exceeds the effect of HBE, suggesting contribution of bifunctional mechanism. The bifunctional mechanism is supported by volcano-shaped dependence of the SA on the following descriptors for reactivity of surface oxygen species: the standard oxidation potential and the standard formation enthalpy of the modifying metals.

Experimental Validation of a Simplified Electrochemical-Thermal Model for a NCM532 Large Format Battery Cell

Battery management systems (BMS) for advanced portable electronics (e.g. cellphones, computers), medical devices (e.g. cardiac pacemakers), and transportation (e.g. electric vehicles) are essential to ensure reliable and safe operation of Li-ion battery (LIB) packs. Specific to EV applications, the U.S. Advanced Battery Consortium (USABC) has established several targets for deployed battery stacks, including: 1) thermal stability from -30 to +52 oC; 2) 15 year life; and 3) 300 mile driving range per charge.1 To achieve the long driving range, it is important to increase the energy density of operating cells, but this often comes with the risk of reduced safety and potentially shorter life. The safety of high energy density Li-ion batteries is of major concern, due to its propensity to undergo catastrophic cell failure and release of energy through thermal runaway. Therefore, the BMS plays a pivotal role in improving performance, protecting battery packs from over-charge/discharge, thermal management, state of charge (SOC) estimation, drift correction, etc. by leveraging mathematical models to conduct state-predictions and assessment.2 Onboard BMS modules must conduct fast, accurate, and continuous parameter estimation to assess the state-of-health/charge/power of the battery. Physics-based models developed by Newman’s group in the 1990’s leverage PDEs to describe the transport of charge carriers (e.g. e-, ions, holes) and reactants across different interfaces.3,4 Newman’s pseudo-2D (P2D) models are able to capture the complex dynamics of LIBs under a variety of environments and operating conditions (e.g. high current, varying temperature). At low to moderate currents, where the current distribution and concentration gradients are negligible, the P2D model can be simplified to a single particle model (SPM). Both P2D and SPM models require many parameters (P2D ≃40 and SPM ≃22), which can be obtained with experiments and/or data fitting to describe electrodes, separator, and electrolyte properties. The extraction of the needed modeling parameters from experiments is traditionally difficult. Additionally, the computational load can be significant, requiring fine meshes to predict the concentration and voltage gradients.5 Therefore, it would be advantageous to develop other modeling strategies that have a considerably reduced computational load. Lower dimension or nondimensional models typically evaluate LIBs in terms of equivalent circuits (e.g. resistors, capacitors, inductors); however, the components of the equivalent circuit models cannot be directly associated to a specific phenomenon in a LIB – making them mostly empirical in nature and unable to fully describe the system over a wide range of operating conditions. This study investigates a simplified numerical electrochemical-thermal battery model that requires only four unknown parameters (diffusion time constant, charge exchange current, ohmic overpotential, entropic heat coefficient), which require fitting and/or experimental validation. This presentation will detail the experimental determination of the critical modeling parameters and report an extremely high accuracy in predicting the voltage and temperature profiles of a commercial 50Ah Li ion battery. References Lu, J., Li, L., Park, J.B., Sun, Y.K.,Wu, F., Amine, K. Aprotic and Aqueous Li–O2 Batteries. Chem. Rev. 114, 5611–5640 (2014).Zhang, R. Xia, B., Li, B., Cao, L., Lai, Y. Zheng, W., Wang, H., Wang, W. State of the Art of Lithium-Ion Battery SOC Estimation for Electrical Vehicles. Energies 11, 1820 (2018).Fuller, T. F. & Newman, J. Relaxation Phenomena in Lithium-ion-Insertion Cells. 141, (1994).Doyle, M. & Newman, J. Comparison of Modeling Predictions with Experimental Data from Plastic Lithium Ion Cells. J. Electrochem. Soc. 143, 1890–1903 (1996).Ekström, H., Fridholm, B. & Lindbergh, G. Comparison of lumped diffusion models for voltage prediction of a lithium-ion battery cell during dynamic loads. J. Power Sources 402, 296–300 (2018).

Measurement of the single-spin asymmetry [formula omitted] in quasi-elastic 3He↑(e,e′n) scattering at 0.4 < Q2 < 1.0 GeV/c2

Due to the lack of free neutron targets, studies of the structure of the neutron are typically made by scattering electrons from either 2H or 3He targets. In order to extract useful neutron information from a 3He target, one must understand how the neutron in a 3He system differs from a free neutron by taking into account nuclear effects such as final state interactions and meson exchange currents. The target single spin asymmetry Ay0 is an ideal probe of such effects, as any deviation from zero indicates effects beyond plane wave impulse approximation. New measurements of the target single spin asymmetry Ay0 at Q2 of 0.46 and 0.96 (GeV/c)2 were made at Jefferson Lab using the quasi-elastic He↑3(e,e′n) reaction. Our measured asymmetry decreases rapidly, from >20% at Q2=0.46 (GeV/c)2 to nearly zero at Q2=0.96 (GeV/c)2, demonstrating the fall-off of the reaction mechanism effects as Q2 increases. We also observed a small ϵ-dependent increase in Ay0 compared to previous measurements, particularly at moderate Q2. This indicates that upcoming high Q2 measurements from the Jefferson Lab 12 GeV program can cleanly probe neutron structure from polarized 3He using plane wave impulse approximation.

Electropolymerised-hemin-catalysed reduction and analysis of tartrazine and sunset yellow

Colourants are widely added in various foods; nevertheless, recent research has revealed that the azo-colourants in foods pose a potential risk to human health. In the present study, the electropolymerised hemin electrode was demonstrated to efficiently catalyse the reduction of azo-colourants. Taking advantage of the ability of cyclic protoporphyrin to exhibit π−π stacking interactions with azo compounds and the capability of the central ferric ion to electrostatically attract the negatively charged sulfonate group, sulphonated azo compounds were readily adsorbed by hemin molecules, facilitating the redox reaction of azo compounds. In response to 2 μM tartrazine (TT), the hemin-functionalised electrode exhibited a well-defined wave in square wave voltammograms (SWVs), and the wave current was approximately 5-fold greater than the signal yielded with the bare electrode. The parameters of hemin electropolymerisation yielding the maximum sensitivity were investigated, leading to a limit of detection of 360 nM (n = 3). Furthermore, simultaneous analysis of TT and sunset yellow (SY) in a mixture was demonstrated to be feasible, with well-separated (ΔE = 160 mV) voltammetric peaks obtained that corresponded to TT and SY. The electrode was also successfully tested with a drink-mimicking sample, indicating the negligible effects of oxygen and ions on analytical performance. To gain insight into the advanced catalytic property, catalytic kinetics were analysed, which revealed that the number of electrons transferred was 1.63 (for TT) and 1.67 (for SY). The reaction order of TT and SY was 2.7 and 1.8, respectively. The Tafel slope of TT and SY, derived from the polarisation curves, was 172 and 86 mV dec−1, respectively, and an approximately 33% increase in the exchange current was obtained compared with when the unmodified electrode was employed. The catalytic performance supports that electropolymerised hemin is a superior catalyst with promise for practical application in the detection of azo-colourants.

Testing of quasi-elastic neutrino charged-current and two-body meson exchange current models with the MiniBooNE neutrino data and analysis of these processes at energies available at the NOvA experiment

The charged-current quasi-elastic (CCQE) scattering of muon neutrinos on a carbon target is analyzed using the relativistic distorted-wave impulse approximation (RDWIA) taking into account the contribution of the two-particle and two-hole meson exchange current ($2p-2h$ MEC) to the weak response functions. A fit the RDWIA+MEC model to the MiniBooNE neutrino data is performed and the best fit value of nucleon axial mass $M_A=1.2 \pm 0.06$ GeV is obtained. We also extract the values of the axial form factor $F_A(Q^2)$ as a function of the squared momentum transfer $Q^2$ from the measured $d\sigma/dQ^2$ cross section. The flux-integrated CCQE-like differential cross sections for neutrino scattering at energies of the NOvA experiment are estimated within the RDWIA+MEC approach.

Synergistic effect of ascorbic acid on the synthesis of mesoporous rGO-MoS2(100) nanocomposites and promotion of hydrogen evolution reaction

Abstract We report a new method for the preparation of MoS2 (100)-reduced graphene oxide (rGO) nanocomposites for enhancement of HER. Ascorbic acid synergistically is applied to reduce graphene oxide and controls the sulfur content of MoS2 resulted in texturing of MoS2 (100) by up taking sulfur and proposing Mo(VI) oxidation state. Variety of characterization were performed to support this hypothesis including XRD, FESEM, TEM, EDX elemental mapping, XPS, Raman, FT-IR and UV–Vis spectroscopies, TGA and BET-BJH analyses. By incorporating ascorbic acid in the synthesis process, the atomic ratio of S Mo is 0.02 for rGO-Mo(VI)S2 hybrid structure with quenched (002) Bragg diffraction peak. rGO-MoS2 shows a net 0.08 mA cm−2 polarized photocurrent in light off-on measurement. A Tafel slope of 44 mV.dec−1, an exchange current of 0.62 mA cm−2, over potential of 156 mV 10 mA cm−2 and onset potential of 25 mV was obtained. This report opens a new pass way in simple and cheap preparation of controlled defective MoS2-rGO structures with new crystal growth (100) of MoS2 for enhanced Hydrogen Evolution Reaction using ascorbic acid. Mechanisms for the role of ascorbic acid on the formation of such defective structure as well as the process of enhancement of HER have been suggested.

Enhanced Depolarization Drive in Failing Rabbit Ventricular Myocytes: Calcium-Dependent and β-Adrenergic Effects on Late Sodium, L-Type Calcium, and Sodium-Calcium Exchange Currents.

Heart failure (HF) is characterized by electrophysiological remodeling resulting in increased risk of cardiac arrhythmias. Previous reports suggest that elevated inward ionic currents in HF promote action potential (AP) prolongation, increased short-term variability of AP repolarization, and delayed afterdepolarizations. However, the underlying changes in late Na+ current (INaL), L-type Ca2+ current, and NCX (Na+/Ca2+ exchanger) current are often measured in nonphysiological conditions (square-pulse voltage clamp, slow pacing rates, exogenous Ca2+ buffers). We measured the major inward currents and their Ca2+- and β-adrenergic dependence under physiological AP clamp in rabbit ventricular myocytes in chronic pressure/volume overload-induced HF (versus age-matched control). AP duration and short-term variability of AP repolarization were increased in HF, and importantly, inhibition of INaL decreased both parameters to the control level. INaL was slightly increased in HF versus control even when intracellular Ca2+ was strongly buffered. But under physiological AP clamp with normal Ca2+ cycling, INaL was markedly upregulated in HF versus control (dependent largely on CaMKII [Ca2+/calmodulin-dependent protein kinase II] activity). β-Adrenergic stimulation (often elevated in HF) further enhanced INaL. L-type Ca2+ current was decreased in HF when Ca2+ was buffered, but CaMKII-mediated Ca2+-dependent facilitation upregulated physiological L-type Ca2+ current to the control level. Furthermore, L-type Ca2+ current response to β-adrenergic stimulation was significantly attenuated in HF. Inward NCX current was upregulated at phase 3 of AP in HF when assessed by combining experimental data and computational modeling. Our results suggest that CaMKII-dependent upregulation of INaL in HF significantly contributes to AP prolongation and increased short-term variability of AP repolarization, which may lead to increased arrhythmia propensity, and is further exacerbated by adrenergic stress.

A novel and enigmatic two-holed shell aperture in a new species of suspension-feeding worm-snail (Vermetidae)

Shell aperture modifications are well known in terrestrial and aquatic gastropods, with apertural lip thickening and tooth development common in species with terminal (determinate) shell growth. In contrast, secondary shell openings are rare in snails and are largely limited to slit shells, keyhole limpets, and abalone of the Vetigastropoda. When such features occur in other groups, they are noteworthy and raise interesting questions concerning the functional/adaptive significance of these shell modifications. Here we report on one such modification in a newly described species of vermetid snail. Members of the worm-snail family Vermetidae are sessile, suspension-feeding caenogastropods found in warm temperate to tropical marine environments worldwide. As juveniles, vermetids permanently cement their shells to hard substrata and subsequently produce irregularly coiled polychaete-like shell tubes with indeterminate growth and typically a simple circular shell aperture. In one previously studied group (genusCupolaconcha), the aperture can be covered by a shell dome with a central slit that retains its widest opening in the center of the aperture. Vermetid specimens collected in the barrier reefs of Belize and the Florida Keys show an extreme aperture modification previously unknown in Gastropoda, in which the shell opening is covered by an apertural dome that leaves two equal-sized circular holes, each corresponding to the inflow and outflow water exchange currents of the animal’s mantle cavity. The function of this perforated apertural dome is unknown, and it is in some ways antithetical to the suspension feeding habit of these snails. Further field and laboratory-based studies will be needed to clarify the functional significance and trade-offs of this unique morphology. The new taxon, which is not closely related to the previously described dome-building cladeCupolaconcha, is described and named asVermetus biperforatusBieler, Collins, Golding &amp; Rawlings n. sp.

DEPENDENCE ACTIVATION ENERGY OF THE ELECTROREDUCTION OF PALLADIUM(II) BIS-HYDROXYETHYLIMINODIACETATE COMPLEXES ON THE OVERPOTENTIAL

The kinetic (exchange currents, apparent elect-ron transfer coefficients) and energetic (activation energies of diffusion and electron-transfer reaction) parameters of electroreduction of palladium (II) bis-hydroxyethyliminodiacetate complexes from an ele-ctrolyte containing an excess of free ligand have been determined. A method is proposed for calculating the actual activation energy of the electrode process that is controlled by mixed kinetics, based on the dif-fusion activation energy, transition reaction and the ratio of surface and volume concentrations of potenti-al-determining ions in the solution under study or the ratio of the limiting diffusion current jd and dischar-ge current jk of palladium (II) hydroxyethyliminodi-&#x0D; &#x0D; acetate complexes. The actual activation energy Af of the electrode process, which is controlled by mixed kinetics, is calculated based on the diffusion activati-on energy, transition reaction and the ratio of the li-miting diffusion current jd and discharge current jk of palladium (II) bis-hydroxyethyliminodiacetate com-plexes. The contribution of the activation energy of the transition stage (slow discharge) and the diffusion activation energy of bis -hydroxyethyliminodiacetate palladium (II) complexes to the actual activation ener-gy of the electrode process limited by mixed kine-tics is determined. The dependence of actual activation energy on electrode process overpotential has been stu-died. The actual activation energy Af of the electro-de process varies from the value of the activation ener-gy of the transition reaction At (63.4 kJ×mol–1) to the value of the diffusion activation energy Ad (22.5 kJ ×mol–1). The activation energy calculated according to Tyomkin can be considered as the actual activation energy Af of the discharge stage at a given polarizati-on DE only with a purely kinetic control of the pro-cess rate. The activation energy experimentally deter-mined by the temperature-kinetic method according to the Arrhenius equation and calculated by the pro-posed method is the actual activation energy Af of the electrode process, controlled by mixed kinetics. There is a coincidence of the experimentally determi-ned by the Gorbachev method and the actual Af acti-vation energy of electrode process controlled by mi-xed kinetics calculated by the proposed method. A good agreement between the calculated and experi-mentally determined values of the actual activation energy of the electrode process is observed.

Electrochemical Kinetics of SEI Growth on Carbon Black: Part II. Modeling

Mathematical models of capacity fade can reduce the time and cost of lithium-ion battery development and deployment, and growth of the solid-electrolyte interphase (SEI) is a major source of capacity fade. Experiments in Part I reveal nonlinear voltage dependence and strong charge-discharge asymmetry in SEI growth on carbon black negative electrodes, which is not captured by previous models. Here, we present a theoretical model for the electrochemical kinetics of SEI growth coupled to lithium intercalation, which accurately predicts experimental results with few adjustable parameters. The key hypothesis is that the initial SEI is a mixed ion-electron conductor, and its electronic conductivity varies approximately with the square of the local lithium concentration, consistent with hopping conduction of electrons along percolating networks. By including a lithium-ion concentration dependence for the electronic conductivity in the SEI, the bulk SEI thus modulates the overpotential and exchange current of the electrolyte reduction reaction. As a result, SEI growth is promoted during lithiation but suppressed during delithiation. This new insight establishes the fundamental electrochemistry of SEI growth kinetics. Our model improves upon existing models by introducing the effects of electrochemical SEI growth and its dependence on potential, current magnitude, and current direction in predicting capacity fade.

Neutrino–oxygen CC0π scattering in the SuSAv2-MEC model

We present the predictions of the joint SuperScaling Approach version 2—Meson Exchange Currents model for the double differential charged-current muonic neutrino (antineutrino) cross section on water for the T2K neutrino (antineutrino) beam. We validate our model by comparing with the available inclusive electron scattering data on oxygen and compare our predictions with the recent T2K νμ-16O data (Abe et al (T2K Collaboration) 2018 Phys. Rev. D 97 012001), finding good agreement at all kinematics. We show that the results are very similar to those obtained for νμ-12C scattering, except at low energies, and we comment on the origin of this difference. A factorized spectral function model of 16O is also included for purposes of comparison.

Computational Screening of Electrocatalytic Materials for Hydrogen Evolution: Platinum Monolayer on Transitional Metals

Searching for none or less Pt-containing electrocatalytic materials for hydrogen evolution is a promising way to reduce the cost of hydrogen production. Thus, a computational screening of electrocatalytic materials for hydrogen evolution reaction (HER), Pt monolayer on transitional metals (Pt/TM), are carried out by DFT in this work. According to several prerequisites, including difficulty of synthesis, stability in electrochemical environment, HER activity, and economical cost, several stable, high activity, and low cost surfaces for HER are chosen. In detail, the Pt/TM(001)[TM = Fe, Mo, V, W or Nb], Pt/TM(111)[TM = Ag, Pd or Au], and Pt/Re(0001) moieties are found to have a predicted high activity comparable to pure Pt. In particular, the five Pt/TM(001) surfaces are economical and seldom reported. Even more, Pt/TM(001)[W, Nb, V, Fe] may be even much better than pure Pt, for both the suitable hydrogen adsorption ability and larger exchange current. Further DFT analysis indicates the HER activity on Pt/TM is related with the d-band center of the Pt layer, which could be tuned by the transition metal in substrate. Our results are expected to contribute to the understanding of the HER on Pt/TM and give theoretical evidence for corresponding experiments.

Fe3O4@MoS2/RGO as an effective nano-electrocatalyst toward electrochemical hydrogen evolution reaction and methanol oxidation in two settings for fuel cell application

A three-component nano-electrocatalyst, magnetite coated molybdenum disulfide hybridized with reduced graphene oxide (Fe3O4@MoS2/RGO), is synthesized by a two-step hydrothermal method. This catalyst is applied as an effective substitution for the platinum catalyst in methanol oxidation and hydrogen evolution reactions. Cyclic voltammetry, chronoamperometry, and linear sweep voltammetry are used to evaluate the performance of the electrocatalyst in acidic and basic media. The results of methanol oxidation reaction on the hybridized nano-electrocatalyst showed good electrocatalytic properties with considerable diffusion currents. This fact is confirmed by the Tafel plots and the calculated kinetic parameters of electron transfer. Fe3O4@MoS2/RGO showed an anodic transfer coefficient and exchange current of 0.464 and 4.80 × 10−8, respectively that are higher than Fe3O4/RGO. The presence of the porous MoS2 in catalyst has a key effect on supplying electroactive sites for electron transfer. Also, the high actual surface area obtained for the hybridized nano-electrocatalyst (A = 0.0295 cm2). The maximum power density of 35.03 mW cm−2 obtained for a single cell containing the prepared hybridized catalyst as the anode which shows a competitive feature of the synthetic catalyst compared to other reports. Furthermore, the synthetic catalyst shows the low-value overpotential of 108 mV and Tafel slope of 48 mV dec−1 during the hydrogen evolution process in acidic media. This is attributed to the synergistic effect between Fe3O4 and MoS2 and also increase the electron transfer rate due to adding conductive RGO to the catalyst. The results show that the synthetic nanocatalyst can have promising applications for hydrogen evolution and methanol oxidation reactions.

Dual Activation of Phosphodiesterases 3 and 4 Regulates Basal Spontaneous Beating Rate of Cardiac Pacemaker Cells: Role of Compartmentalization?

Spontaneous firing of sinoatrial (SA) node cells (SANCs) is regulated by cyclic adenosine monophosphate (cAMP)-mediated, protein kinase A (PKA)-dependent (cAMP/PKA) local subsarcolemmal Ca2+ releases (LCRs) from ryanodine receptors (RyR). The LCRs occur during diastolic depolarization (DD) and activate an inward Na+/Ca2+ exchange current that accelerates the DD rate prompting the next action potential (AP). Basal phosphodiesterases (PDEs) activation degrades cAMP, reduces basal cAMP/PKA-dependent phosphorylation, and suppresses normal spontaneous firing of SANCs. The cAMP-degrading PDE1, PDE3, and PDE4 represent major PDE activities in rabbit SANC, and PDE inhibition by 3-isobutyl-1-methylxanthine (IBMX) increases spontaneous firing of SANC by ∼50%. Though inhibition of single PDE1–PDE4 only moderately increases spontaneous SANC firing, dual PDE3 + PDE4 inhibition produces a synergistic effect hastening the spontaneous SANC beating rate by ∼50%. Here, we describe the expression and distribution of different PDE subtypes within rabbit SANCs, several specific targets (L-type Ca2+ channels and phospholamban) regulated by basal concurrent PDE3 + PDE4 activation, and critical importance of RyR Ca2+ releases for PDE-dependent regulation of spontaneous SANC firing. Colocalization of PDE3 and PDE4 beneath sarcolemma or in striated patterns inside SANCs strongly suggests that PDE-dependent regulation of cAMP/PKA signaling might be executed at the local level; this idea, however, requires further verification.

Electrodeposition of Copper on Mild Steel: Peculiarities of the Process

The process of electrodeposition of copper coatings on a mild steel substrate was analyzed. The reasons for poor adhesion of the coatings from acid and alkaline cyanideless electrolytes were determined. It was shown that the problem of the direct copper coatings’ electrochemical plating on a steel substrate from cyanideless electrolytes results from the presence of the adjoint process of contact exchange in a copper ions–iron system. Good adhesion coatings can be developed only on termination of the contact exchange at the initial stage until the steel substrate under the sediment pores is not subjected to significant etching. In acid electrolytes, the adhesion is poor because of a large value of the contact exchange current. In alkaline cyanideless electrolytes iron is passivated, and adhesion of the coating is insufficient because of the presence of a separating passive film at the substrate–coating interface. In neutral electrolytes, it is possible to obtain a coating with a good adhesion to the substrate, but the results are not stable due to a low buffer capacity of the solution. During the deposition of a copper coating from acid electrolytes using a prenickel-plating, a thin nickel sublayer has pores through which the process of the contact exchange occurs. It is shown that, in order to develop coatings with a good adhesion, the minimum thickness of the nickel sublayer must be 3–5 μm.

Unique Ca2+-Cycling Protein Abundance and Regulation Sustains Local Ca2+ Releases and Spontaneous Firing of Rabbit Sinoatrial Node Cells

Spontaneous beating of the heart pacemaker, the sinoatrial node, is generated by sinoatrial node cells (SANC) and caused by gradual change of the membrane potential called diastolic depolarization (DD). Submembrane local Ca2+ releases (LCR) from sarcoplasmic reticulum (SR) occur during late DD and activate an inward Na+/Ca2+ exchange current, which accelerates the DD rate leading to earlier occurrence of an action potential. A comparison of intrinsic SR Ca2+ cycling revealed that, at similar physiological Ca2+ concentrations, LCRs are large and rhythmic in permeabilized SANC, but small and random in permeabilized ventricular myocytes (VM). Permeabilized SANC spontaneously released more Ca2+ from SR than VM, despite comparable SR Ca2+ content in both cell types. In this review we discuss specific patterns of expression and distribution of SR Ca2+ cycling proteins (SR Ca2+ ATPase (SERCA2), phospholamban (PLB) and ryanodine receptors (RyR)) in SANC and ventricular myocytes. We link ability of SANC to generate larger and rhythmic LCRs with increased abundance of SERCA2, reduced abundance of the SERCA inhibitor PLB. In addition, an increase in intracellular [Ca2+] increases phosphorylation of both PLB and RyR exclusively in SANC. The differences in SR Ca2+ cycling protein expression between SANC and VM provide insights into diverse regulation of intrinsic SR Ca2+ cycling that drives automaticity of SANC.

Study of Cleaning Products Effect on Corrosion By Means of RGB Video-Electrochemical Techniques

A digital endoscope camera with a USB connection was used to capture full-colored digital videos during spontaneous and electrochemical forced corrosions of technological metals digital videos at suitable regular intervals using a free software. The set of images, which included the complete interval time of the experiences, were automatically read and converted into intensity arrays by Mathcad® v14 software. After selecting the area under study, cropped images were decomposed into red, green and blue components as intensity subarrays using the Image Processing Functions included in the software. Values of arrays were classified between 0 and 255 intensity levels. Electrochemical experiments were performed with a PAR 273A potentiostat/galvanostat. The electrochemical cell was a 2×2 cm high-transmittance glass cell (Hellma, OG quality). Digital endoscope camera (EPA-503278) with USB connection was used to capture 640×480 color digital videos up to 30 framessecond. Digital images obtained from video were jpg RGB 8 bits per channel. The electrochemical cell was illuminated in a home-made white box with a T5 6400K fluorescent tri-phosphor lamp (color rendering index 80). An electrode of reference Hg/HgSO4/ K2SO4 (saturated) was used [1],The results of this work shown as an example are the effect of some types of commercial industrial cleaning products that differ in the contents of aggressive substances such as peroxides, hypochlorite or chloride ion on three types of metallic materials widely used in industrial factory: aluminum, steels stainless steel and brass. The reference electrode Hg / HgSO4 / K2SO4 (saturated) was used. For comparative purposes, the quantification of the potential for zero intensity prior to the anodic dissolution provides an approximate value of the corrosion potential. The height of the anodic dissolution peak gives an approximate value of the apparent corrosion rate. Both measures in potentiodynamic regime involve a rapid evaluation of the corrosion kinetics of the metal in the test media. The intensity changes in red (R), green (G) and blue (B) give a quantitative idea of changes in surface composition or within the dissolution. When convenient, the experiment can focus on the potential range of the anodic oxidation signal, at a maximum rate of 1 millivolt per second, and then calculate the exchange current (corrosion), the equilibrium potential (corrosion potential) and the slope of Tafel by a classical way. Color histograms of RGB intensity subarrays showed the statistical distribution of Intensities-Red, green and blue component analysis from RGB digital image video opens up a new direction to evaluate and quantify the electrochemical corrosion of large electrode areas and to improve the inhibitors of corrosion and surface treatments fields. RGB digital image video is a very versatile and low cost optical technique for investigating the electrochromic and corrosion processes. This mixed electrochemical-optical methodology can be especially indicated for the characterization of large surface samples, even dark substrates [2]. [1] J. Agrisuelas, J. J. García-Jareño, F. Vicente Spatiotemporal colorimetry to reveal electrochemical kinetics of poly(o-toluidine) films along ITO surface. Electrochim. Acta, 269 (2018) 350-358[2] J. Agrisuelas, J.J. García-Jareño, E. Perianes, F. Vicente, Use of RGB digital video analysis to study electrochemical processes involving color changes, Electrochem. Commun. 78 (2017) 38–42. This work was supported by Betelgeux -IVACE IMDITA2016/155 and MINECO-FEDER CTQ2015-71794-R

Thermodynamic Limit of Solar to Fuel Conversion for Generalized Photovoltaic–Electrochemical Systems

Daily and seasonal variability of the solar irradiation poses a major hurdle to the widespread adoption of photovoltaic (PV) systems. An integrated photovoltaic–electrochemical (EC)-storage system offers a solution, but the thermodynamic efficiency $({\eta _{{\rm{sys}}}})$ of the “ideal” integrated system and the optimum configuration needed to realize the limit is known only for a few simple cases. Moreover, these limits are often derived through complex numerical simulations. In this paper, we show that a simple, conceptually transparent and physically intuitive analytical formula can precisely describe the ${\eta _{{\rm{sys}}}}$ of a “generalized” PV-EC integrated system. An M -cell PV module of N -junction bifacial tandem cells is illuminated under S-suns and mounted over ground of albedo $R$ . There are $K$ -EC cells in series, each defined by their reaction potential, exchange current, and Tafel slope. We derive the optimum thermodynamic limit ${\eta _{{\rm{sys}}}}({N,M,K,R,S})$ for all possible combinations of a PV-EC design. For a setup with optimal- $({M,K})$ and large $N$ , under 1-sun illumination and albedo = 0, the ultimate limit is ${\eta _{{\rm{sys}}}}\sim 52$ %. A comparison of our results with experimental results published by various groups worldwide suggests opportunities for further progress toward the corresponding thermodynamic limit.

Corrosion Rates of Stainless Steels in Renewable Biofuel Sources of Refined Rapeseed Oil, Waste Cooking Oil and Animal Waste Lard

The 1.4541 and the 1.4571 stainless steels and a carbon steel were subjected to immersion corrosion tests in stagnant and stirred biomass fuel sources such as rapeseed oil, waste cooking oil and animal waste lard as well as their emulsions with 5 and 50 wt.% aqueous citric acid solutions at a temperature of 80°C so as to model storage, handling and purification conditions. Passivation of carbon steel was facilitated by flow of the less acidic rapeseed and waste cooking oils and increased flux of oxygen. Carbon steel was sensitive for the higher concentration of proton donor species, acidity of the waste lard. Higher mass loss rates correlated with increased corrosion currents measured in citric acid solution by electrochemical methods. Flow of the biomasses and increased acid concentration of the emulsions were beneficial for the passivation of stainless steels. Although corrosion related mass loss, dissolution rate of the passive layers increased by flow and high acidity of the fluids, both the formation and compactness of passive layers are facilitated by the biomasses with higher concentration of oxygen donating species like water, alcohol and acids. Surface transformation of the passivating steels was reflected by decreasing electrochemical pseudo-capacity of the interfaces and increasing resistance of the passive layers derived from the results of Tafel and Stern methods as well as impedance results. Anti-correlation between mass loss results obtained by immersion in the biomasses and electrochemical data measured in dilute aqueous citric acid solution is explained by the varied compactness, resistance of the passive layers and exchange currents of the steel electrodes due to the orders of magnitude different activities of the hydrogen ion in the biomass mixtures and citric acid solution.

Basal Spontaneous Firing of Rabbit Sinoatrial Node Cells Is Regulated by Dual Activation of PDEs (Phosphodiesterases) 3 and 4.

Spontaneous firing of sinoatrial node cells (SANCs) is regulated by cAMP-mediated, PKA (protein kinase A)-dependent (cAMP/PKA) local subsarcolemmal Ca2+ releases (LCRs) from RyRs (ryanodine receptors). LCRs occur during diastolic depolarization and activate an inward Na+/Ca2+ exchange current that accelerates diastolic depolarization rate prompting the next action potential. PDEs (phosphodiesterases) regulate cAMP-mediated signaling; PDE3/PDE4 represent major PDE activities in SANC, but how they modulate LCRs and basal spontaneous SANC firing remains unknown. Real-time polymerase chain reaction, Western blot, immunostaining, cellular perforated patch clamping, and confocal microscopy were used to elucidate mechanisms of PDE-dependent regulation of cardiac pacemaking. PDE3A, PDE4B, and PDE4D were the major PDE subtypes expressed in rabbit SANC, and PDE3A was colocalized with α-actinin, PDE4D, SERCA (sarcoplasmic reticulum Ca2+ ATP-ase), and PLB (phospholamban) in Z-lines. Inhibition of PDE3 (cilostamide) or PDE4 (rolipram) alone increased spontaneous SANC firing by ≈20% (P<0.05) and ≈5% (P>0.05), respectively, but concurrent PDE3+PDE4 inhibition increased spontaneous firing by ≈45% (P<0.01), indicating synergistic effect. Inhibition of PDE3 or PDE4 alone increased L-type Ca2+ current (ICa,L) by ≈60% (P<0.01) or ≈5% (P>0.05), respectively, and PLB phosphorylation by ≈20% (P>0.05) each, but dual PDE3+PDE4 inhibition increased ICa,L by ≈100% (P<0.01) and PLB phosphorylation by ≈110% (P<0.05). Dual PDE3+PDE4 inhibition increased the LCR number and size (P<0.01) and reduced the SR (sarcoplasmic reticulum) Ca2+ refilling time (P<0.01) and the LCR period (time from action potential-induced Ca2+ transient to subsequent LCR; P<0.01), leading to decrease in spontaneous SANC cycle length (P<0.01). When RyRs were disabled by ryanodine and LCRs ceased, dual PDE3+PDE4 inhibition failed to increase spontaneous SANC firing. Basal cardiac pacemaker function is regulated by concurrent PDE3+PDE4 activation which operates in a synergistic manner via decrease in cAMP/PKA phosphorylation, suppression of LCR parameters, and prolongation of the LCR period and spontaneous SANC cycle length.