48 research outputs found
Data_Sheet_1_Toward Low-Cost and Sustainable Supercapacitor Electrode Processing: Simultaneous Carbon Grafting and Coating of Mixed-Valence Metal Oxides by Fast Annealing.pdf
No full textThere is a rapid market growth for supercapacitors and batteries based on new materials and production strategies that minimize their cost, end-of-life environmental impact, and waste management. Herein, mixed-valence iron oxide (FeOx) and manganese oxide (Mn3O4) and FeOx-carbon black (FeOx-CB) electrodes with excellent pseudocapacitive behavior in 1 M Na2SO4 are produced by a one-step thermal annealing. Due to the in situ grafted carbon black, the FeOx-CB shows a high pseudocapacitance of 408 mF cm−2 (or 128 F g−1), and Mn3O4 after activation shows high pseudocapacitance of 480 mF cm−2 (192 F g−1). The asymmetric supercapacitor based on FeOx-CB and activated-Mn3O4 shows a capacitance of 260 mF cm−2 at 100 mHz and a cycling stability of 97.4% over 800 cycles. Furthermore, due to its facile redox reactions, the supercapacitor can be voltammetrically cycled up to a high rate of 2,000 mV s−1 without a significant distortion of the voltammograms. Overall, our data indicate the feasibility of developing high-performance supercapacitors based on mixed-valence iron and manganese oxide electrodes in a single step.</p
Simple preparation of carbon-bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts
No full textThe lack of efficient cost-effective electrocatalysts for reversible oxidation of water is by far the most notorious obstacle in the development of fuel cells and electrolyzers. Here, oxygen bifunctional electrocatalysts based on C-CoFe and C-NiFe oxide nanospinels are developed by simple autocombustion between ethylene glycol/acetate and the metal nitrates. The effects of electronic modulation and the mass (or surface area) effect were examined based on the cyclic voltammograms of the unary and binary metal oxides in alkaline solution, and their high oxygen evolution and reduction activities were attributed to the synergic intermetallic interactions. The C-CoFe oxide, in particular, shows an oxygen evolution overpotential of 350 mV (without iR correction) at 10 mA cm−2 with excellent stability over 10 hours and a Tafel slope of 49 mV per decade. Furthermore, it exhibits the highest oxygen reduction activity among the synthesized electrocatalysts due the particular synergy between Co and Fe centers
Mind the Solid Side: Electrochemical Thermodynamics, Kinetics, and Hysteresis in Energy Materials
No full textBulk electrochemical phase transformations (EPTs) govern the operation of many modern electrochemical systems, from batteries to electrocatalysts. These EPTs involve a coupled interplay of ion transport from a liquid into an electrode film, electron transfer, and phase transformations in the film. Yet, despite their importance, a unified thermodynamic and kinetic understanding of EPTs remains lacking. Grounded in the theory of phase transitions and mixtures, this mini‐review introduces, for the first time, a general thermodynamic framework that classifies EPTs into three main categories: regular solutions, Fickian diffusion, and spinodal decomposition. It highlights how galvanostatic charge–discharge and cyclic voltammetry modeling can elucidate reaction mechanisms using prototypical examples from electrochemical ion insertion systems such as Ni(OH)2, MnO2, and LiFePO4. The concepts presented here provide a unifying foundation for interpreting solid‐to‐solid EPTs across mesoscopic and macroscopic scales and inspire new strategies for diagnosing and designing high‐performance energy materials
Electrochemical solid phase formation and dissolution; a non-equilibrium thermodynamic view
No full textHerein, solid-state electrochemical reactions are collectively viewed and studied as the formation and dissolution of a solid phase under non-equilibrium. We first consider an ideal reaction pathway where a solid phase grows and shrinks along the same reaction path. Next, the realistic situation is studied based on the voltammetry of solids to reveal how a solid phase is formed and dissolved in contact with either a liquid or another solid phase. Finally, the reaction asymmetry between phase formation and dissolution, hysteresis, and the memory effect are studied and discussed in detail
A Thermodynamic Model for the Insertion Electrochemistry of Battery Cathodes
No full textThe transition to Ni‐based battery cathodes enhances the energy density and reduces the cost of batteries. However, this comes at the expense of losing energy efficiency which could be a consequence of charge–discharge hysteresis. Here, a thermodynamic model is developed to understand the extent and origin of charge–discharge hysteresis in battery cathodes based on their cyclic voltammograms (CVs). This was possible by defining a Gibbs energy function that weights random ion insertion/expulsion, i. e., a solid solution pathway, against selective ion insertion/expulsion, i. e., a phase separation route. The model was verified experimentally by the CVs of CoOOH and Ni(OH)2 as solid‐solution and phase‐separating cathodes, respectively. Finally, a microscopic view reveals that phase separation and hysteresis are a consequence of large ionic radii difference of the reduced and oxidized central metal atoms
Methods—On the Reliability of the Electrochemical Data Recorded on Nickel Foam in Alkaline Solution: The Illusive Surface Oxide Layer
No full textInternational audienceThe extensive application of nickel foam (Ni foam) as current collector in supercapacitors has raised caveats on the contribution of the redox-active Ni foam to the measured capacities. However, due to the overlooked qualitative features (i.e., shapes) of the cyclic voltammograms (CVs), the redox reaction of the Ni foam oxide layer (NiFOL) has been frequently confused with the true electrochemical signature of the coated materials in alkaline solution. Herein, experimental CVs, scanning electron microscopy images, and estimations reveal that due to the high porosity of the Ni foam and its surface reactivity in alkaline solution (1–6 M KOH), the redox peak couple of the NiFOL can potentially be confused with or lead to misinterpretation of the true electrochemical features of the coatings. A classification of previous papers on a group of metal oxides investigated as battery-type or pseudocapacitive electrodes in the positive potential window is also presented to reveal the confusion between NiFOL and the coating when operated in alkaline solution
Toward Low-Cost and Sustainable Supercapacitor Electrode Processing: Simultaneous Carbon Grafting and Coating of Mixed-Valence Metal Oxides by Fast Annealing
No full textThere is a rapid market growth for supercapacitors and batteries based on new materials and production strategies that minimize their cost, end-of-life environmental impact, and waste management. Herein, mixed-valence iron oxide (FeOx) and manganese oxide (Mn3O4) and FeOx-carbon black (FeOx-CB) electrodes with excellent pseudocapacitive behavior in 1 M Na2SO4 are produced by a one-step thermal annealing. Due to the in situ grafted carbon black, the FeOx-CB shows a high pseudocapacitance of 408 mF cm−2 (or 128 F g−1), and Mn3O4 after activation shows high pseudocapacitance of 480 mF cm−2 (192 F g−1). The asymmetric supercapacitor based on FeOx-CB and activated-Mn3O4 shows a capacitance of 260 mF cm−2 at 100 mHz and a cycling stability of 97.4% over 800 cycles. Furthermore, due to its facile redox reactions, the supercapacitor can be voltammetrically cycled up to a high rate of 2,000 mV s−1 without a significant distortion of the voltammograms. Overall, our data indicate the feasibility of developing high-performance supercapacitors based on mixed-valence iron and manganese oxide electrodes in a single step
Fielding Peter Carey: economy, archive, celebrity
No full text© 2018 Dr. Keyvan AllahyariThis thesis accounts for a method of reading Carey’s fiction as works of national literature in the minor register (colonial, peripheral, small) which refract a sense of the possibility of circulation in transnational literary markets. The publication of Carey’s debut work, The Fat Man in History, by the University of Queensland Press in 1974 coincided with the termination of The Traditional Markets Agreement, which resulted in assisting American publishers to roam more freely in the Australian literary market. Drawing on Pierre Bourdieu’s concepts of the literary field, capital, and habitus, my thesis starts by examining the publication of The Fat Man as a microevent to better understand the macroevent of Carey’s position-taking in the transnational marketplace. The mid-1970s shifted Carey’s position in the field and established a trajectory through which he accumulated significant cultural and economic capital in the following decades. This method interrogates Carey’s rising visibility in relation to the construction of a new status for the postcolonial authors and the possibilities of the global publishing industry since the 1960s throughout to the present moment, including the politics of literary prizes and literary festivals, the rise of literary agents, the commodification of literary archives, and the merging of conglomerate publishing houses.
Carey’s fiction exhibits the anxieties of an Australian author ensnared in neoliberal systems of literary production and distribution, a free market economy biased against national territories (such as Australia) on the periphery of a world republic of letters. Drawing on the sociological paradigm of Pierre Bourdieu, this thesis asks how, and to what extent, can we think of Carey’s fiction and his writerly persona as cultural objects circulating within the global literary marketplace? How does his fiction refract the global forces that produce and distribute his books and celebrity? And what is the relationship between Carey’s stories and the literary marketplace, between the making of his books and the reading of them? Thus, my study offers a lateral examination of two interrelated aspects of Carey’s fiction. On the one hand, it captures a continuum of Australian and transnational practices of literary distinction and advancement that governed the critical and financial success of Carey’s fiction; on the other, it produces insights into the structural homologies between the literary spaces that Carey inhabits and those of his Australian characters confined to minor systems of cultural production and consumption
Determining the Gibbs Energy Contributions of Ion and Electron Transfer for Proton Insertion in ϵ‐MnO2
No full textElectrochemically active ϵ‐MnO2 and ɣ‐MnO2 as tunnel‐type host‐guest structures have been extensively studied by crystallography and electrochemical techniques for application in battery cathode materials. However, the Gibbs energies of the underlying ion and electron transfer processes across the electrode interfaces have not yet been determined. Here we report for the first time these data for ϵ‐MnO2. This was possible by measuring the mid‐peak potentials in cyclic voltammetry and the open‐circuit potentials under electrochemically reversible conditions
