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

ZIF-67 MOF-Derived Mn3O4 @ N-Doped C as a Supercapacitor Electrode in Different Alkaline Media

Transition-metal oxide has been identified as an auspicious material for supercapacitors due to its exceptional capacity. The inadequate electrochemical characteristics, such as prolonged cycle stability, can be ascribed to factors, such as low electrical conductivity, sluggish reaction kinetics, and a deficiency of active sites. The transition-metal oxides derived from the MOF materials offer a larger surface area with enriched active sites and a faster reaction rate along with good electrical conductivity. The manganese (Mn)-based metal-organic framework (MOF)-derived materials were produced using the pyrolysis method. Zeolitic imidazolate frameworks (ZIF-67) were fabricated in water at ambient temperature with the aid of triethylamine. Multiple techniques were used to examine the characteristics of the fabricated electrode materials. The influence of the electrolyte on the electrochemical activity of the Mn3O4@N-doped C electrode materials was determined in KOH, NaOH, and LiOH. For manufacturing of "Mn3O4@N-doped C", ZIF-67 was used as a precursor. The capacitive performance of the Mn3O4@N-doped C electrode increased as a result of nitrogen-doped carbon; after 5000th cycles, the electrode retained an excellent rate capability and a high specific capacitance (Cs) of 980 F g-1 at 1 A g-1 under 2.0 KOH electrolyte in a three electrode system. The carbonized manganese oxide displays also had a high Cs of 686 F g-1 in two electrode systems in 2.0 M KOH. Materials made from MOFs show promise as capacitive materials for applications in energy conversion storage owing to their straightforward synthesis and strong electrochemical performance.

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.

Ultrahigh Energy Density and Long-Life Cyclic Stability of Surface-Treated Aluminum-Ion Supercapacitors

In this study, aluminum-graphene supercapacitors (denoted as aluminum-ion supercapacitors; ASCs), consisting of a battery-type aluminum anode, a capacitor-type graphene cathode, and ionic liquid 1-ethyl-3-methylimidazolium chloride (EMImCl) and aluminum chloride (AlCl₃) electrolyte, were prepared. This study primarily aimed to investigate the enhanced electrochemical performance of ASCs arising from changes in the surface oxide layer and morphology via electrochemical surface treatments, including electropolishing and electrodeposition of aluminum anodes. The ASC devices based on an electrodeposited anode at a current density of 3 A g^-1 exhibited a high specific capacity of 211 F g^-1 compared to that of the electropolished anode (∼186 F g^-1); these were 20 and 5.7%, respectively, higher than that of the pristine aluminum anode. In particular, the electrodeposited ASC delivered an energy density of 151 W h kg^-1 at a power density of 3,390 W kg^-1. Furthermore, a maximum power density of 11,104 W kg^-1 was achieved at an energy density of 124.3 W h kg^-1. These values are among the best as compared to those of previously reported aluminum-based supercapacitors, suggesting the potential feasibility of these ASCs with outstanding energy and power densities for next-generation energy storage devices.