Electrodeposition from molybdate aqueous solutions: a preliminary study

The electrochemistry of molybdenum (Mo) and its oxides is very important for several applications in electrocatalysis,batteries,sensors and in particular for CIGS-based solar cells,where metal Mo is used as back contact.Properties and the fabrication method of Mo films are of fundamental importance,because they could induce significant changes in solar cell performances.The most important issues in the electrochemical behaviour of Mo are the nature and stability of its surface oxides,which are strongly dependent on deposition bath pH.Ivanova et al. (2006) reported that it is possible to accomplish the cathodic reduction of molybdate ions to metallic Mo from electrolytes containing HF.The addition of this acid selectively prevents the polymerization of MoO42- anions,therefore its concentration plays a fundamental role.A hard drawback connected to deposition in acid media is the strong hydrogen evolution,since H+ reduction is the reaction thermodynamically favoured,therefore it is necessary to apply a very high current density for appreciably depositing Mo.In this work,we report some preliminary results dealing with the electrodeposition process from molybdate aqueous solutions to grow thin films on different substrates and nanowires inside the channels of polycarbonate membranes;electrolyte pH was varied in order to evidence its role on the nature of the deposits,which were characterized by EDS,SEM,RAMAN and XRD analyses

Random quasi-phase-matched second-harmonic generation in periodically poled lithium tantalate

We observe second harmonic generation via random quasi-phase-matching in a 2.0 micron periodically poled, 1-cm-long, z-cut lithium tantalate. Away from resonance, the harmonic output profiles exhibit a characteristic pattern stemming from a stochastic domain distribution and a quadratic growth with the fundamental excitation, as well as a broadband spectral response. The results are in good agreement with a simple model and numerical simulations in the undepleted regime, assuming an anisotropic spread of the random nonlinear component

Nanostructured electrochemical devices for sensing, energy conversion and storage

Nanostructured materials are attracting growing interest for improving performance of devices and systems of large technological interest. In this work, the principal results about the use of nanostructured materials in the field of electrochemical energy storage, electrochemical water splitting, and electrochemical sensing are presented. Nanostructures were fabricated with two different techniques. One of these was the electrodeposition of the desired material inside the channels of a porous support acting as template. The other one was based on displacement reaction induced by galvanic contact between metals with different electrochemical nobility. In the present work, a commercial polycarbonate membrane was used as template. In the field of the electrochemical energy storage, the attention was focused on lead-acid battery, and it has been found that nanostructured morphology enhances the active mass utilization up to about 80%, with consequent increase of specific energy and cycling rates to unattainable values for the commercial battery. Nanostructured Ni-IrO2 composite electrodes showed valuable catalytic activity for water oxidation. By comparison with other Ni-based electrocatalyst, this electrode appears as the most promising anode for electrochemical water splitting in alkaline cells. Also in the field of sensing, the nanostructured materials fabricated by displacement reaction showed performance of high interest. Some new results about the use of copper nanowires for H2O22 sensing will be showed, evidencing better performance in comparison with copper thin film. In this work, we will show that nanostructured electrodes are very promising candidate to form different electrochemical setups that operate more efficiently comparing to device with flat electrode materials

Nanostructured Ni-Fe-S Based Electrode for Hydrogen Production by Water Electrolysis

Green hydrogen is a real alternative to change the current energy system. Electrochemical water splitting is considered an attractive solution to convert and store the surplus of renewable energy sources. However, hydrogen production by water electrolysis is not economically sustainable due to the use of high noble metals as catalysts (generally platinum or palladium). In order to reduce costs, in this work we have synthesized a ternary alloy of nickel, iron and sulfur and used it as the cathode in an alkaline electrolyzer to produce hydrogen from water. Furthermore, to increase the features of the proposed alloy, this material was synthesized into the pore of a polycarbonate membrane to obtain a nanostructured electrode that exposes a very high surface area to the solution and consequently a large number of electrocatalytic active sites. The electrode fabrication was carried out by potential-controlled pulsed electrochemical deposition where the potential switch from -0.45 V to -1.3 V vs. SCE for 60 cycles. The electrode was characterized by SEM and EDS showing the nanostructured nature and the composition of the electrode. Then it was tested as the cathode in an alkaline electrolyzer (30% KOH) at room temperature. Preliminary results show that the addition of sulfur to the alloy permits to increase in the electrode features compared to the binary alloy of nickel and iron

Diversity and ethics in trauma and acute care surgery teams: results from an international survey

Background Investigating the context of trauma and acute care surgery, the article aims at understanding the factors that can enhance some ethical aspects, namely the importance of patient consent, the perceptiveness of the ethical role of the trauma leader, and the perceived importance of ethics as an educational subject. Methods The article employs an international questionnaire promoted by the World Society of Emergency Surgery. Results Through the analysis of 402 fully filled questionnaires by surgeons from 72 different countries, the three main ethical topics are investigated through the lens of gender, membership of an academic or non-academic institution, an official trauma team, and a diverse group. In general terms, results highlight greater attention paid by surgeons belonging to academic institutions, official trauma teams, and diverse groups. Conclusions Our results underline that some organizational factors (e.g., the fact that the team belongs to a university context or is more diverse) might lead to the development of a higher sensibility on ethical matters. Embracing cultural diversity forces trauma teams to deal with different mindsets. Organizations should, therefore, consider those elements in defining their organizational procedures. Level of evidence Trauma and acute care teams work under tremendous pressure and complex circumstances, with their members needing to make ethical decisions quickly. The international survey allowed to shed light on how team assembly decisions might represent an opportunity to coordinate team member actions and increase performance

Plasma Electron Kinetics and Distribution Functions in Laser Fields

A concise review of the properties of electron distribution functions in a fully ionized plasma in the presence of a high-frequency laser field is presented. In detail is discussed the physical origin of most of the reported results in the case of strong fields. The presence of a laser field, through the inverse bremsstrahlung absorption, alters dynamically the roles of and the interplay between electron-ion and electron-electron collisions shaping the distribution function. Special attention is paid to the role of e-e collisions in the process of laser-plasma interaction

Template electrodeposition and characterization of nanostructured Pb as a negative electrode for lead-acid battery

Despite Lead Acid Battery (LAB) is the oldest electrochemical energy storage system, diffusion in the emerging sectors of technological interest is inhibited by its drawbacks. The principal ones are low energy density and negative plate sulphating on high rate discharging. In this work, it is shown the possibility of overcoming such drawbacks by using nanostructured lead as a negative electrode. Lead nanowires (NWs) were fabricated by electrochemical deposition in template, which is an easy, cheap, and easily scalable process. Their morphology and crystal structure have been characterized by electron microscopy and X-ray diffraction, respectively. An electrochemical cell simulating LAB has been assembled with PbO2 as a counter electrode and an AGM separator, both from commercial battery. Cycling tests were conducted at 10C-rate, setting the cut-off voltage on discharging at 1.2 V. For comparison, also cycling tests at 1C-rate have been carried out, in otherwise identical conditions. At both C-rates, performances in terms of cycling efficiency and lifetime were found a lot better than those of current LABs. The high porosity formed under cycling at 10C-rate provides a reliable explanation of the results

Ultrafast lead-acid battery with nanostructured Pb and PbO2 electrodes

Lead-acid batteries (LABs) are still extensively used in the field of energy storage, owing to a well-known and reliable technology. LABs can deliver high power and store energy for a very long time. In addition, they are reliable and easy to produce. The raw materials for their manufacture are practically unlimited, and about 95% of the materials can be recovered and reused. However, the lower specific energy storage (about 30-40 Wh kg-1), in comparison with other storage systems, limits their use in the most emerging and challenging applications, like electrical mobility, due to the high atomic weight of lead [1]. One of the principal limitations in the use of LABs in electric vehicles (EV) is related to the inadequacy of the negative plates in accepting high charge/discharge currents. Besides, LABs operate in EVs at high rate partial state-of-charge, which leads to rapid sulphation of the negative plates. Many approaches were proposed in order to overcome these problems and make LABs suitable for emerging applications. A possible approach is based on electrodes with nanostructured active materials, which are progressively emerging as an alternative to the conventional plates because their high aspect ratio and consequent high superficial area allow to fabricate LABs with high specific energy and power density. We have developed template electrodeposition as an easy and direct technique for fabrication of nanostructured electrodes, with very large active area, consisting of PbO2 and Pb [2-3]. Both active materials (Pb and PbO2) were electrodeposited using a nonporous template to obtain the regular arrays of nanowires shown in Figure 1, well attached to a compact film of the same material, acting as a current collector and mechanical support of the nanostructures. Nanostructured PbO2 and Pb electrodes were assembled and tested using aqueous 5 M H2SO4 solution in a zero gap configuration, and was discharged up to 90% of the gravimetric capacity to a cut-off voltage of 1.2 V. In comparison to commercial LABs, which usually deliver about 30 mAh/g for only 15-20 cycles at 1C rate, our batteries are able to charge and discharge at very high rate without fading up to 1500 cycles with a cycling efficiency of about 90%. Besides, nanostructured electrodes show better performances without time-consuming curing and formation process. These performances are attributable to their large surface area (about 70 times higher than the geometrical one), leading to a new LAB with high specific energy and power density. Another interesting finding is the ability of our batteries to be cycled up to 30C [4]