Hierarchical MnO₂/NiS–MnS with Rich Electro-Microstructural Physiognomies for Highly Efficient All-Solid-State Hybrid Supercapacitors

Abstract

To revolutionize the charge storage efficiency of electrode materials for their utilizations in high Ragone efficient electrochemical energy storage devices, herein, a slow-precipitation-induced material growth approach has been innovated to design a hetero oxide–sulfide [MnO2/NiS–MnS (MnO2/Ni–Mn–S)] material with smaller crystallite size, ultrathin assembled-sheet-like microstructure, and perceptible phase physiognomies (α-MnO2, MnS, and α-NiS). The electroredox assessment of MnO2/Ni–Mn–S illustrates high pseudocapacitive energy storage efficiency, significant redox reversibility, lowly constrained bulk accessibility of the OH– ions at higher rate electrochemical reaction conditions, dominance of semi-infinite diffusion-controlled electrochemical processes, and extremely low charge-transfer resistance (∼1.45 Ω), total series resistance (∼0.51 Ω) and diffusion (Warburg) resistance. A fabricated 1.8 V MnO2/Ni–Mn–S||nitrogen-doped reduced graphene oxide (N-rGO) all-solid-state hybrid supercapacitor (ASSHSC) device with N-rGO as the negative electrode material delivers high area and mass specific capacitance/capacity, ∼100% Columbic efficiency at high-rate operating conditions, and very low charge-transfer and Warburg resistance. The MnO2/Ni–Mn–S||N-rGO ASSHSC device also delivers excellent Ragone efficiency (E D = 31.5 W h kg–1 at P D = 937.5 W kg–1 and E D = 15.5 W h kg–1 at P D = 2767.5 W kg–1) and ∼97.6% retention of charge storage after 11,000 uninterrupted charge–discharge cycles. The significantly improved supercapacitive charge storage efficacy of MnO2/Ni–Mn–S is ascribed to the cohesive redox activity of Ni2+, Ni3+, Mn2+, and Mn3+ and nonstoichiometric Ni2±δ, Ni3±δ, Mn2±δ, and Mn3±δ ions, rich ion-disseminating bulk, S2– vacancy-induced electronic conductivity, and suitable electro-microstructural physiognomies for the electrochemical processes.

Hierarchical CoMoS4 flakes with rich physico-electrochemical physiognomies for electrocatalytic oxygen evolution reaction

“…The FT-Raman spectrum shows vibrational phonon modes at 352, 368, 508, and 665 cm À1 corresponding to the Co-S, Mo-S, S-S, and Mo-S vibrations in CoMoS 4 , respectively. 38 Further, the FT-Raman peaks are found to be fairly broad, which suggests the lower crystallinity of CoMoS 4 , arising due to translational symmetry loss in the crystal lattice. 40,42 This translational symmetry loss arises because of the presence of sulfur atom vacancies in the crystal lattice of the CoMoS 4 .…”

“…Moreover, the surface oxide phases are very typical in transition metal sulfide materials. 34,38 Using the diffraction peak corresponding to the (221) lattice plane, the average crystallite size was estimated (using the Scherrer equation) to be B23 nm, which shows the nanocrystallinity of CoMoS 4 . 39 As CoMoS 4 is only partially oxidized at its surface due to unavoidable air exposure, the oxidation process may not drastically disturb the overall crystallinity of the material.…”

Archetypical 2D sheet-like Cu2MoS4 for all-solid-state symmetric pseudocapacitors with ultra-steady performance efficiency

“…4B, and the C s values at various scan rates were estimated graphically by integrating the area under the corresponding C s vs. V plots. The conversion of i (A g −1 ) to C s was performed using eqn (2), where m (g), i (A) and DV (V) in eqn (2) refer to the mass of the active electrode material, the current response and the working voltage window, respectively. 22,41…”

“…Actually, under low current density conditions, the OH − ions have sufficient time to access the bulk matrix of the material, whereas under high current density conditions, the OH − ions only have time to access the outer surface of the material, which results in a reduced number of redox reactions, leading to lower charge storage efficiency. 2,3,5 Fundamentally, the supercapacitive charge storage by Cu 2 MoS 4 is governed by (i) a diffusion (semi-innite)-controlled process, which occurs in battery-type materials and (ii) surface-controlled double layer-forming process, which occurs in capacitor-type materials. 57 Thus, to assess the nature and the dominance of electrochemical processes, eqn ( 5) and ( 6) were thoroughly examined.…”

“…In this context, supercapacitors with high performance efficiency are signicant given that they offer outstanding Ragone efficiency and ultra-steady chargedischarge efficiency for numerous cycles. [1][2][3][4] Among the various supercapacitors, pseudocapacitors, in which charge storage occurs through effective redox reactions on the electrode materials, are very fascinating, given that these devices deliver supplemented charge storage and show electrochemical durability for extended cycles. 5,6 The kinetically faster electrochemical reactions and facilitated charge transfer play major roles in the excellent energy storage efficiency of pseudocapacitors.…”