Anion De/Intercalation in Nickel Hydroxychloride Microspheres: A Mechanistic Study of Structural Impact on Energy Storage Performance of Multianion-Containing Layered Materials

Abstract

Electrochemical cation de/intercalation has long been investigated for energy-relevant applications, while anion de/intercalation is comparatively highly challenging, although promising for promoting the performance of materials. Herein, layered nickel hydroxychloride was selected as a model multianion-containing inorganic functional material to study. Hierarchical flower-like microspheres self-assembled from nanosheets were synthesized via a solvothermal method. The as-prepared nickel hydroxychloride was built up from neutral layers of [Ni(OH) 3/3 Cl 3/3 ] octahedra, showing an expanded interlayer spacing of 0.57 nm. With this unique microstructure, Cl − deintercalation and OH − intercalation were accomplished through an effective nonelectrochemical process. The nickel hydroxychloride Ni(OH) 0.99 Cl 1.01 with a maximum Cl − ion content was found to possess the largest interlayer spacing, which when first employed as electrode materials for supercapacitor, delivered an ultrahigh specific capacitance of 3831 F/g at a current density of 1 A/g. For the latter case, Ni(OH) 2.18 (H 3 O) 0.18 with a maximum OH − content showed a specific capacitance of 1489 F/g at 1 A/g. Expanded interlayer spacing associated with the anion de/intercalation is the key that enhances ion diffusion kinetics between layers. The methodology of anion de/intercalation reported in this work would provide hints of exploring novel multianion-containing materials with anion de/intercalation necessary for high-performance energy applications.

Crystal Growth of Bimetallic Oxides CuMnO2 with Tailored Valence States for Optimum Electrochemical Energy Storage

“…Peaks a and b can be indexed to the Mn–O hybridization according to previous reports . CuMnO 2 obtained at 140 °C showed peak a at 528.6 eV, exhibiting an obvious shift toward higher energy at 529 eV when the crystal growth temperature exceeded 180 °C, which is originated from the rising valence state of Mn cations (Mn 2+ → Mn 3+ ), as reported previously. , On the basis of the crystal field theory, Mn 2+ has the electronic configuration of 3d 5 (t 2g 3 e g 2 ) and that of Mn 3+ is 3d 4 (t 2g 3 e g 1 ). So the electron will preferentially occupy the t 2g orbital of Mn 2+ with low energy (528.6 eV), while it will preferentially occupy the e g orbital of Mn 3+ with high energy (529 eV).…”

“…A comparison of cyclic voltammetry (CV) curves (Figure a) of CuMnO 2 crystals was tested in a voltage range of 0–0.5 V at a scan rate of 50 mV/s. CV curves at different scan rates, i.e., 5, 10, 20, 50, and 100 mV/s of every electrode (Figure S3) showed typical redox peaks, implying ideal pseudocapacitive behaviors that involves reversible faradaic redox reactions of M-O/M-O–OH (M represents Cu and Mn) with the OH – ions in alkaline electrolyte. , Especially for the CuMnO 2 crystal obtained at 160 °C, the interval of redox peak positions significantly increased with the increasing scan rates, implying a dominant diffusion-controlled process during pseudocapacitive reaction, as reported elsewhere. , The diffusion-controlled process is only limited by the ion diffusion rate, so that controllable oriented growth of one-dimensional CuMnO 2 crystals can effectively liberate the surface limitation of the bulk material. A histogram (Figure b) that exhibited the graphing key indicators was given based on the comparative CV curves.…”

“…26 CuMnO 2 obtained at 140 °C showed peak a at 528.6 eV, exhibiting an obvious shift toward higher energy at 529 eV when the crystal growth temperature exceeded 180 °C, which is originated from the rising valence state of Mn cations (Mn 2+ → Mn 3+ ), as reported previously. 26,27 On the basis of the crystal field theory, Mn 2+ has the electronic configuration of 3d 5 (t 2g 3 e g 2…”

“…40,41 Especially for the CuMnO 2 crystal obtained at 160 °C, the interval of redox peak positions significantly increased with the increasing scan rates, implying a dominant diffusion-controlled process during pseudocapacitive reaction, as reported elsewhere. 27,41 The diffusion-controlled process is only limited by the ion diffusion rate, so that controllable oriented growth of one-dimensional CuMnO 2 crystals can effectively liberate the surface limitation of the bulk material. A histogram (Figure 8b) that exhibited the graphing key indicators was given based on the comparative CV curves.…”

Nickel hydroxide/sulfide hybrids: halide ion controlled synthesis, structural characteristics, and electrochemical performance

“…24–26 It is found that anions can intercalate into the gallery of transition metal hydroxides to form intercalation compounds, increasing the interlayer spacing of products and affecting their electrochemical performance. 27–29 In particular, the intercalation compound (Ni(OH)–Cl) is found to enable it to further evolve into Ni(OH)Cl. 30 However, the effects of these anions on the microstructure, subsequent structural evolution, and structural characteristics of transition metal materials are still not clear.…”