Toward Low-Cost and Sustainable Supercapacitor Electrode Processing: Simultaneous Carbon Grafting and Coating of Mixed-Valence Metal Oxides by Fast Annealing

There 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

A Thermodynamic Model for the Insertion Electrochemistry of Battery Cathodes

The 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

International 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

There 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 1M 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 408mF cm 122 (or 128 F g 121), and Mn3O4 after activation shows high pseudocapacitance of 480 mF cm 122 (192 F g 121). The asymmetric supercapacitor based on FeOx-CB and activated-Mn3O4 shows a capacitance of 260 mF cm 122 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 2,000mV s 121 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

Electrochemically 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

Simple preparation of carbon-bimetal oxide nanospinels for high-performance bifunctional oxygen electrocatalysts

The 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 122 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