10 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
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
The evolution of roman frontier defence systems and fortifications the lower danube provinces in the first and second centuries AD
No full textThe defence of the Roman Empire from barbarian attacks depended on two distinct but interrelated features: the actual fortifications on the borders of the imperial provinces and the troops that garrisoned them. The main aim of this dissertation is to provide a collective analysis of Roman defence systems on the Lower Danube region, i.e. the provinces of Pannonia Inferior, Moesia Superior, Moesia Inferior and Dacia. The period of study spans from the early first century to the middle of the second century AD, a period which corresponds to the gradual emergence and final consolidation of the Roman frontier defence systems in the area. On the basis of the physical evidence that has survived from the frontier fortifications of the Lower Danube area, this study attempts to present a reconstruction of the strategic and tactical situation on the frontier and to provide some fresh observations on the motives behind the creation, purpose and function of Roman frontiers during the early Principate. After a brief introduction on some of the views that have been put forward on the subject, the main part of the thesis is divided into four separate chapters, one for each of the provinces studied. These chapters study the fortifications themselves in order to establish their date and garrison so as to offer an evaluation of the characteristic features of the defensive system of each frontier sector. The last chapter brings together the above information in order to produce some conclusions on the defence systems in the area, especially in relation to the rationale behind their creation and subsequent development
