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Reduction of dissolved oxygen at a copper rotating disc electrode
No full textUndergraduates from chemical engineering, applied chemistry, and environmental science courses, together with first-year postgraduate research students in electrochemical technology, are provided with an experiment that demonstrates the reduction of dissolved oxygen in aerated seawater at 25°C. Oxygen reduction is examined using linear sweep voltammetry (i.e., the recording of steady-state current vs. electrode potential curves at a constant potential sweep rate). The use of forced convection to a smooth, rotating disc electrode (RDE) of 3.8 mm diameter (area = 0.113 cm2) in laminar flow provides control of the rate of mass transport of dissolved oxygen toward the cathode surface. The use of rotation speeds in the range of 200-9500 revolutions per minutes (angular velocity of 20-1000 rad s-1) allows a linear (Levich) plot of limiting current vs. the square root of rotation speed to be made. From the slope of this plot, the diffusion coefficient of oxygen can be calculated as (1.5 ± 0.2) x 10-5 cm2 s-1 at 25°C
Development of the all-vanadium redox flow battery for energy storage: a review of technological, financial and policy aspects
Get PDFThe commercial development and current economic incentives associated with energy storage using redox flow batteries (RFBs) are summarised. The analysis is focused on the all-vanadium system, which is the most studied and widely commercialised RFB. The recent expiry of key patents relating to the electrochemistry of this battery has contributed to significant levels of commercialisation in, for example, Austria, China and Thailand, as well as pilot-scale developments in many countries. The potential benefits of increasing battery-based energy storage for electricity grid load levelling and MW-scale wind/solar photovoltaic-based power generation are now being realised at an increasing level. Commercial systems are being applied to distributed systems utilising kW-scale renewable energy flows. Factors limiting the uptake of all-vanadium (and other) redox flow batteries include a comparatively high overall internal costs of 0.10?kW?1?h?1. There is also a low-level utility scale acceptance of energy storage solutions and a general lack of battery-specific policy-led incentives, even though the environmental impact of RFBs coupled to renewable energy sources is favourable, especially in comparison to natural gas- and diesel-fuelled spinning reserves. Together with the technological and policy aspects associated with flow batteries, recent attempts to model redox flow batteries are considered. The issues that have been addressed using modelling together with the current and future requirements of modelling are outlined
A novel flow battery—A lead-acid battery based on an electrolyte with soluble lead(II) V. Studies of the lead negative electrode
No full textThe structure of lead deposits (approximately 1 mm thick) formed in conditions likely to be met at the negative electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. The quality of the lead deposit could be improved by appropriate additives and the preferred additive was shown to be the hexadecyltrimethylammonium cation, C16H33(CH3)3N+, at a concentration of 5 mM. In the presence of this additive, thick layers with acceptable uniformity could be formed over a range of current densities (20–80 mA cm?2) and solution compositions. While electrolyte compositions with lead(II) concentrations in the range 0.1–1.5 M and methanesulfonic acid concentrations in the range 0–2.4 M have been investigated, the best quality deposits are formed at lower concentrations of both species. Surprisingly, the acid concentration was more important than the lead(II) concentration; hence a possible initial electrolyte composition is 1.2 M Pb(II) + 5 mM C16H33(CH3)3N+ without added acid
A novel flow battery — a lead-acid battery based on an electrolyte with soluble lead(II): part VI. Studies of the lead dioxide positive electrode
No full textThe structure of thick lead dioxide deposits (approximately 1 mm) formed in conditions likely to be met at the positive electrode during the charge/discharge cycling of a soluble lead-acid flow battery is examined. Compact and well adherent layers are possible with current densities >100 mA cm?2 in electrolytes containing 0.1–1.5 M lead(II) and methanesulfonic acid concentrations in the range 0–2.4 M; the solutions also contained 5 mM hexadecyltrimethylammonium cation, C16H33(CH3)3N+. From the viewpoint of the layer properties, the limitation is stress within the deposit leading to cracking and lifting away from the substrate; the stress appears highest at high acid concentration and high current density. There are, however, other factors limiting the maximum current density for lead dioxide deposition, namely oxygen evolution and the overpotential associated with the deposition of lead dioxide. A strategy for operating the soluble lead-acid flow battery is proposed
The rotating cylinder electrode for studies of corrosion engineering and protection of metals—an illustrated review
No full textThe uniform flow generated at moderate rotation speeds, controlled mass transport rate and uniform current distribution make the RCE attractive for turbulent flow studies of corrosion and protection. Controlled flow and mass transport are characterised by peripheral velocity and mass transport coefficient. Important aspects in corrosion include metal dissolution, oxygen reduction, stability of surface oxide films and porosity of protective coatings. Computational studies allow fluid flow, current distribution and mass transport to be simulated; multiphase electrolytes and nanofluids have been experimentally studied over the last decade. Diverse uses of the RCE include cathodic protection, corrosion inhibitors and protective coatings
Pumped Hydroelectricity and Utility-Scale Batteries for Reserve Electricity Generation in New Zealand
No full textNon-pumped hydroelectricity-based energy storage in New Zealand has only limited potential to expand to meet projected growth in electricity demand. Seasonal variations of hydro inflows have also led to several 'dry-year' events over the last decade and dedicated fast-start 'peaker' capacity may also be required to support wind power as it approaches a 20% generation share. In this research, the New Zealand electricity industry has been surveyed in regard to the feasibility of reducing CO2-e emissions through the introduction of pumped hydroelectricity and utility-scale batteries by 2025. A desk-based review of the economic costs of these technologies has also been performed and their drivers and barriers critically assessed.
Most respondents to the survey projected that peak power demand will continue to increase and this will result in new-build centralised (~150 MW) thermal reserve power sources. In New Zealand, the costs of pumped hydro and batteries are seen to be prohibitive to their introduction, even though they are almost universally assumed to be technically capable of providing renewables support and peak power adequacy. The perception of the poor economic viability of pumped hydro may, in part, be due to the relatively high capital cost estimate associated with the Manorburn-Onslow proposal (~NZ$3 billion). This research has shown, however, that smaller, 'more-internationally-representative' pumped hydro schemes, if available in NZ with low associated environmental impact, are cost-competitive with thermal peakers, especially diesel peakers. Conversely, utility-scale batteries have very high storage costs per kWh and are most likely to be used only for very high value applications where there is a strong technical advantage, such as the six-second fast instantaneous reserve
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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