Evaluating the lead affinity of graphite additives in lead-acid batteries by electrochemical deposition

The improvement of lead-acid batteries with respect to charge acceptance and cycle life in partial state of charge operations due to carbon additives in negative electrodes is state of the art. However, there is still a lack of knowledge about the mechanisms which generate these enhancements. Especially the influence of the physicochemical connection between the carbon additives and the surrounding lead skeleton has not been investigated in much detail yet, but seems to play an important role. Therefore, we developed a new method for characterizing the degree of interaction between lead and carbon additives with focus on graphite materials. By potentiostatic deposition of lead on graphite electrodes, we observe a correlation between the deposition overpotential and the number density of nucleation sites. Chronoamperometry is used to calculate the number density of nucleation sites on graphite electrodes which is in accordance with microscopic observations. We found that expanded graphite exhibits a significantly higher number of nucleation sites than synthetic graphite. Finally, a correlation between this number density of nucleation sites and the integration of the graphite particles in real lead electrodes is observed. Thus, the technique can be used to predict the integration of different graphite particles into the negative active material

Technologien für die Zukunft - Anorganische Rohstoffbasis im Wandel

It will not be long until the peak oil problem will spread onto a number of metals. Profitable sources of many inorganic raw materials have already been exhausted. In primary raw materials, the ore content of metals is beginning to be very low, so that the exploitation is increasingly time- and energy consuming. By way of application examples, it will be demonstrated that many raw materials have a tremendous influence on our day-to-day life even though their actual content in a final product may appear to be negligible. The recovery of precious raw materials and their recycling back into the substance cycle will remain one of the main head topics on society's agenda for decades to come. Development of novel recovery processes is in full swing as will be shown by the examples chosen for this article

Manganese Oxide Coated Carbon Materials as Hybrid Catalysts for the Application in Primary Aqueous Metal-Air Batteries

One of the major challenges of metal-air batteries is the impeded oxygen reduction reaction (ORR) during discharge occurring at the gas diffusion electrode (GDE) of the battery. Due to the impeded ORR, high overpotentials emerge and result in a loss of energy efficiency. In order to improve the latter, suitable catalysts have to be employed. Transition metal oxides like manganese oxides (e.g., MnO2, Mn2O3, Mn3O4, Mn5O8, MnOOH) [1,2] are known as good and inexpensive materials for the ORR in alkaline media. A drawback of manganese oxide catalysts is the poor electrical conductivity. Hence, the approach presented in this work aims to enhance the catalytic activity of Mn3O4 and γ–MnO2 by the incorporation of conductive carbon material into the pure manganese oxide. The resulting hybrid catalysts are prepared either by impregnation of Super C 65, Vulcan XC 72, and Kuraray YP 50F via a sol-gel technique employing a MnO2 precursor sol or by direct precipitation of Mn3O4 or γ–MnO2 particles in the presence of the carbon materials mentioned above. Investigations by rotating disc electrode (RDE) show a noticeably higher catalytic activity of the hybrid catalysts than for the pure materials. For verification of the results measured by RDE, screen printed GDEs are prepared and tested in Zn-air full cells

Amorphous silica in ultra-high performance concrete: First hour of hydration

Amorphous silica in the sub-micrometer size range is widely used to accelerate cement hydration. Investigations including properties of silica which differ from the specific surface area are rare. In this study, the reactivity of varying types of silica was evaluated based on their specific surface area, surface silanol group density, content of silanol groups and solubility in an alkaline suspension. Pyrogenic silica, silica fume and silica synthesized by hydrolysis and condensation of alkoxy silanes, so-called Stoeber particles, were employed. Influences of the silica within the first hour were further examined in pastes with water/cement ratios of 0.23 using in-situ X-ray diffraction, cryo scanning electron microscopy and pore solution analysis. It was shown that Stoeber particles change the composition of the pore solution. Na+, K+, Ca2+ and silicate ions seem to react to oligomers. The extent of this reaction might be highest for Stoeber particles due to their high reactivity

Microencapsulation of alkaline salt hydrate melts for phase change applications by surface thiol-michael addition polymerization

The microencapsulation of alkaline salt hydrates suitable as inorganic phase change materials (PCMs) via surface Michael-type addition polymerization of thiols and acrylates is reported. The encapsulation performance depending on the resins' acrylate-to-thiol ratio and monomer functionality is investigated, and the best encapsulation performance is found for resin compositions with considerable acrylate excess ratios. The step-growth nature of the reaction can be substantiated via comparative bulk polymerizations. A multistage encapsulation mechanism is proposed in order to explain the different dependencies on the acrylate to thiol ratio observed in PCM encapsulations in comparison to bulk polymerizations

Environmental assessment of electrically controlled variable light transmittance devices

A comprehensive benchmark analysis has been performed on five electrically controlled state-of-theart transmittance modulation devices including their production routes, from 'cradle-to-gate'. The benchmarks have been modeled employing the GaBi life cycle assessment software tool, which successfully yielded the most important environmental problem areas for the product life cycles of electrochromic and electrotropic light-modulating devices. In terms of the energy demand of processing, all-solid-state technology was found to be less favorable than wet-chemical electrodeposition processes; however, the effect is interestingly overcompensated for by the resource depletion resulting from higher layer thicknesses in the latter case. As opposed to the mineral-glass based benchmarks, a plastic-film based system was particularly favorable, implying that the substrate is a factor with a strong environmental impact in transmittance modulation devices. Eventually, very high impacts were found for tin-doped indium oxide (ITO) and iridium oxide, i.e. a common transparent conductor and anodic electrochromic material, respectively. The results obtained support important current trends such as in-line manufacturing of electrochromic devices, the quest for ITO replacement materials, and, in general, the replacement of energy- and resource-intensive processes (sputter deposition of heavy metal oxides) by less demanding methods

Towards core-shell bifunctional catalyst particles for aqueous metal-air batteries: NiFe-layered double hydroxide nanoparticle coatings on γ-MnO2 microparticles

Herein, we investigated the synthesis of a bifunctional catalyst particle system for aqueous metal-air batteries. To target a system which possesses both, oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) capabilities, γ-MnO2 microparticles were combined with NiFe layered double hydroxides (LDH) to a core-shell system. NiFe-LDH can be optimized in its constituency to yield a very low onset potential (at 10 mA cm−2) for the oxygen evolution reaction of only 569 mV vs. Hg/HgO. We investigated different coating processes (in-situ precipitation coating and sonochemical assisted coating) in order to create a bifunctional system of LDH shell@γ-MnO2 core. It was found that the overall catalytic functionality of the bifunctional system strongly depends on the coating process, as this ultimately determines the surface nature and thus the behavior in ORR and OER reactions, respectively, of this core-shell system