Hierarchical Mn₃O₄/NiSe₂–MnSe₂: A Versatile Electrode Material for High-Performance All-Solid-State Hybrid Pseudocapacitors with Supreme Working Durability

Abstract

As highly efficient electrochemical energy storage devices are in indispensable demand for numerous modern-day technologies, herein sluggish precipitation followed by an anion exchange procedure has been developed to synthesize an oxide-selenide mixed phase (Mn3O4/NiSe2–MnSe2) novel electrode material with high surface area and porosity for high-performance all-solid-state hybrid pseudocapacitors (ASSHPC). Mn3O4/NiSe2–MnSe2 shows a rich Tyndall effect (in H2O) and possesses randomly arranged low-dimensional crystallites of nearly similar size and uniform shape. The electrochemical analyses of Mn3O4/NiSe2–MnSe2 corroborate good electrochemical reversibility during charge transfer, superior pseudocapacitive charge-storage efficiency, and very low charge transfer and series resistance, ion-diffusion resistance, and relaxation time, which endorse the quick pseudocapacitive response of the material. The Mn3O4/NiSe2–MnSe2||N-rGO ASSHPC device demonstrates excellent charge-storage physiognomies suggestive of rich electrochemical and electromicrostructural compatibility between the electrode materials in the fabricated assembly. The Mn3O4/NiSe2–MnSe2||N-rGO ASSHPC device delivers high mass and area specific capacitance/capacity, very low charge-transfer resistance (∼0.74 Ω), total series resistance (∼0.76 Ω), diffusion resistance, and a relaxation time constant, which endorse the quick pseudocapacitive response of the device. The device delivers higher energy and power density (∼34 W h kg–1 at ∼2994 W kg–1), rate efficiency (∼17 W h kg–1 at ∼11,995 W kg–1), and cyclic performance (∼97.2% specific capacity/capacitance retention after 9500 continuous GCD cycles). The superior Ragone and cyclic efficiencies of the ASSHPC device are ascribed to the multiple redox-active Ni and Mn ions which lead to the supplemented number of redox reactions; “electroactive-ion buffering pool”-like physiognomics of Mn3O4/NiSe2–MnSe2, which facilitate the electrolyte ion dissemination to the electroactive sites even at high rate redox condition; and ideal electro-microstructural compatibility between the electrode materials, which leads to assisted charge transfer and absolute ion dissemination during the charge-storage process.

Hierarchical and Nanocrystallite-Assembled Ultraporous NiO/MnCo2O4 for All Solid-State Hybrid Supercapacitors with Robust Energy Efficiency and Extended Operational Durability

“…The chemical reactions that occur during the formation of NiO/MnCo 2 O 4 are depicted in the reaction set R1. ,,, During the precipitation reactions, NH 4 F acts as the surface-trapping and pH-controlling reagent. In the hydrothermal heating condition, NH 4 F decomposition leads to a decrease in the pH of the medium of reaction, which essentially regulates the kinetics of crystal growth and controls the surface physiognomies of the material. , .25ex2ex C 4 H 4 Na 2 O 6 → 160 ° normalC C 4 H 4 O 6 2 − + 2 Na + Ni 2 + + 2 Co 2 + + Mn 2 + + 4 C 4 H 4 O 6 2 − + n normalH 2 normalO → 160 ° normalC / 24 normalh MnCo 2 false( C 4 H 4 O 6 false) 3 · n normalH 2 normalO + Ni ( normalC 4 normalH 4 normalO 6 ) · n normalH 2 normalO ...…”

“…Various strategies are adopted in order to enhance the energy efficiency of supercapacitors; one such strategy involves the design of electrode materials with facilitated electroactive ions throughout the materials’ matrices, which increases the number of electrochemical reactions. The other approach involves the strategic elemental and chemical design of electrode materials such that more number of electroactive sites can be integrated in them . Such approaches facilitate more number of electrochemical reactions for enhanced charge storage, offer lowly impeded ion diffusion and electrode microstructure with ion-buffering pool alike physiognomies, which shorten the diffusion path-length of the ions in charge storage even during high rate reaction conditions.…”

“…Further, good electrochemical and electromicrostructural compatibility between the active materials of hybrid supercapacitors improves the charge storage performance and working efficiency of the devices . Among various electrode materials for pseudocapacitors, first-row transition-metal oxides, particularly those based on Ni, Mn, and Co, are preferred due to their superior conductivity and pseudocapacitive physiognomics during charge storage . These oxides possess redox-active multiple transition-metal ions, tunable surface functionality, and bulk microstructural architecture, which offer multiple electrochemical advantages. , These factors of the electrode materials collectively minimize polarization and improve the redox reversibility of the electrochemical reactions during the working of the supercapacitors .…”

“…In this regard, various oxides, i.e., NiO, Co 3 O 4 , MnO 2 , Mn 3 O 4 , etc. have been studied as electrode materials for pseudocapacitive charge storage. − However, the subpar electronic conductivity and limited nonstoichiometric metal ions in the single metal oxides severely limit the charge-transfer efficiency and redox reactivity during the charge storage process. ,, Hence, to develop supercapacitors with high energy efficiency and working durability, binary metal oxides possessing multiple nonstoichiometric redox-active oxidation states of metals, excellent electrical conductivity, and large electroactive surface area have often been used as electrode materials . In this regard, spinel and antispinel oxides involving Ni, Mn, Co, and so forth are extensively used. − However, in these materials, the metal ions are majorly in +2 and +3 oxidation states, which typically allow two redox oscillations during the charge storage process.…”

Hierarchically Uniform 2D Porous Sheet-like NiO/NiCo2O4: A High-Performance Positrode Material for All-Solid-State Hybrid Pseudocapacitors with Superior Ragone and Cyclic Efficiencies

“…Further, cyclic stability of the supercapacitors is an existing challenge, which occurs due to (i) the microstructural degradation of the electrode materials arising due to the repeated insertion/deinsertion of the electroactive ions in the materials’ matrices during the charging/discharging for multiple cycles, (ii) possible electrochemical degradation of electrolytes during each charging/discharging cycle, and (iii) poor electrochemical reversibility of the electrode materials during charging/discharging of the devices . Among various supercapacitor devices, pseudocapacitors possess the advantage of higher energy delivery efficiency due to the faster redox kinetics and the presence of multiredox active species in the electrode materials. − Therefore, to fabricate superior performance (superior Ragone and cyclic efficiency) pseudocapacitors, redox-active electrode materials offering more number redox reactions and high electrochemical reversibility are preferred. In this context, transition metal oxide materials with variable oxidation states and multiredox species have been extensively employed as electrode material in pseudocapacitors. , Among various such materials, oxides of Ni and Co in particular are significant owing to their tunable microstructure, significant electromicrostructural physiognomies, good electronic conductivity, and excellent chemical stability in basic electrolyte media .…”