The Principle of Introducing Halogen Ions Into β-FeOOH: Controlling Electronic Structure and Electrochemical Performance

Abstract

Coordination tuning electronic structure of host materials is a quite effective strategy for activating and improving the intrinsic properties. Herein, halogen anion (X−)-incorporated β-FeOOH (β-FeOOH(X), X = F−, Cl−, and Br−) was investigated with a spontaneous adsorption process, which realized a great improvement of supercapacitor performances by adjusting the coordination geometry. Experiments coupled with theoretical calculations demonstrated that the change of Fe–O bond length and structural distortion of β-FeOOH, which is rooted in halogen ions embedment, led to the relatively narrow band gap. Because of the strong electronegativity of X−, the Fe element in β-FeOOH(X)s presented the unexpected high valence state (3 + δ), which is facilitating to adsorb SO32− species. Consequently, the designed β-FeOOH(X)s exhibited the good electric conductivity and enhanced the contact between electrode and electrolyte. When used as a negative electrode, the β-FeOOH(F) showed the excellent specific capacity of 391.9 F g−1 at 1 A g−1 current density, almost tenfold improvement compared with initial β-FeOOH, with the superior rate capacity and cyclic stability. This combinational design principle of electronic structure and electrochemical performances provides a promising way to develop advanced electrode materials for supercapacitor.

Cu9S5/Fe2O3 Nanospheres as Advanced Negative Electrode Materials for High Performance Battery-like Hybrid Capacitors

“…This result confirms the special electronic interaction, because the uneven charge distribution was appeared at the interface region of the Cu 9 S 5 /Fe 2 O 3 composite. As we all know, the charge distribution can affect the electric conductibility and wettability of the materials in the electrolyte and then influence the electrochemical performance . As for the XPS spectrum of S 2p (Figure c), the peaks at 161.2 and 162.4 eV are attributed to S 2p 3/2 and S 2p 1/2 of S 2– , respectively.…”

“Two Birds with One Stone”: F Doping Ni–Co Hydroxide as High-Performance Cathode Material for Aqueous Zn Batteries

“…It can be easily concluded from the calculation result that both NCH and FNCH exhibit a clear band gap, corresponding to the semiconductor characteristic ( Figure 5 a–d). Owing to the hybridization of the 2p orbit of F − , the denser electrons are collected in a valence band after the introduction of fluorine, which is beneficial for narrowing band gap and improving electrical conductivity in FNCH [ 38 ]. As expected, FNCH shows a lower band gap of 2.18 eV than NCH (3.01 eV), suggesting improved electrical conductivity of FNCH after F doping.…”

Design and Fabrication of Hierarchical NiCoP–MOF Heterostructure with Enhanced Pseudocapacitive Properties

“…The maximum energy density of 50.3 Wh kg −1 is delivered at a power density of 1011.2 W kg −1 , which is superior to some other HSCs in literatures, including CoNi–MOF//AC, [ 24 ] NiCoP nanoplates//graphene, [ 37 ] Co 0.1 Ni 0.9 P/CNF/CC||AC/CC, [ 44 ] NiCoP/NiCo‐OH30//PC, [ 54 ] ZnNiCoPNF//AC, [ 60 ] NC@SS//Fe 2 O 3 @SS, [ 61 ] P(Ni,Co)Se 2 //ZC, [ 62 ] NiCo 2 S 4 /GA//AC, [ 63 ] ZnNiPS//AC, [ 64 ] NiCoPCoP//PNGF, [ 65 ] and β‐FeOOH//NiCo hydroxides/Cu(OH) 2 /CF. [ 66 ] This device also displays a power density as high as 10 550.3 W kg −1 at 29.7 Wh kg −1 within 11 s, showing a high‐power nature. In addition, our device demonstrates excellent durability up to 10 000 charge/discharge cycles (≈100% capacity retention at 2 A g −1 ) with a nearly 100% Coulombic efficiency (Figure 6e).…”