Co-doped Ni hydroxide and oxide nanosheet networks: laser-assisted synthesis, effective doping, and ultrahigh pseudocapacitor performance

Abstract

Morphology control and impurity doping are two widely applied strategies to improve the electrochemical performance of nanomaterials. Herein, we report an environmentally friendly approach to obtain Co-doped Ni(OH) 2 nanosheet networks using a laser-induced cobalt colloid as a doping precursor followed by an aging treatment in a hybrid medium of nickel ions. The shape and specific surface area of the doped Ni(OH) 2 can be successfully adjusted by changing the concentration of sodium thiosulfate. Furthermore, a Co-doped Ni(OH) 2 nanosheet network was further converted into Co-doped NiO with its pristine morphology retained via facile thermal decomposition in air. The structure and electrochemical performance of the as-prepared samples are investigated with scanning and transmission electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, Fourier transform infrared spectroscopy, the nitrogen adsorption-desorption isotherm technique, and electrochemical measurements. The Codoped Ni(OH) 2 electrode shows an ultrahigh specific capacitance of 1421 F g À1 at a current density of 6 A g À1 , and a good retention level of 76% after 1000 cycles, in sharp contrast with only a 47% retention level of the pure Ni(OH) 2 electrode at the same current density. In addition, the Co-doped NiO electrode exhibits a capacitance of 720 F g À1 at 6 A g À1 and 92% retention after 1000 cycles, which is also superior to the corresponding values of relevant pure NiO electrodes. The Co 2+ partially substitutes for Ni 2+ in the metal hydroxide and oxide, resulting in an increase of free holes in the valence band, and, therefore, enhancement of the p-type conductivity of Ni(OH) 2 and NiO. Moreover, such novel mesoporous nanosheet network structures are also able to enlarge the electrode-electrolyte contact area and shorten the path length for ion transport. The synergetic effect of these two results is responsible for the observed ultrahigh pseudocapacitor performance.

Multi‐Anion Intercalated Layered Double Hydroxide Nanosheet‐Assembled Hollow Nanoprisms with Improved Pseudocapacitive and Electrocatalytic Properties

“…[25,[27][28][29] The band at 1614 cm À1 could be ascribed to the bending mode of OÀHvibration. [27,41,43] The intercalation of CO 3 2À ion is known for its strong affinity to cationic host LDH layers, which was revealed by the symmetric and asymmetricv ibration of C=Oa t1 502 cm À1 and 1390 cm À1 ,r espectively. [27,41,43] The intercalation of CO 3 2À ion is known for its strong affinity to cationic host LDH layers, which was revealed by the symmetric and asymmetricv ibration of C=Oa t1 502 cm À1 and 1390 cm À1 ,r espectively.…”

“…[29,36,37] The bandsat645 and 471 cm À1 was related to CoÀOa nd NiÀOs tretching vibrations, respectively,f urther verifying the formation of NiCo-LDH. [27,41,43] The intercalation of CO 3 2À ion is known for its strong affinity to cationic host LDH layers, which was revealed by the symmetric and asymmetricv ibration of C=Oa t1 502 cm À1 and 1390 cm À1 ,r espectively. [27,28,41] For the HNP and NF sample, the band at 1306 cm À1 could be ascribed to the N-O vibration, suggesting the intercalation of NO 3 À ions that originated from the reactant nickel nitrate, [29,36,37] and the band at 1055cm À1 is associated with typicala lcoholic CÀOs tretching mode of solvent etha- nol.…”

“…[27,41,43] The intercalation of CO 3 2À ion is known for its strong affinity to cationic host LDH layers, which was revealed by the symmetric and asymmetricv ibration of C=Oa t1 502 cm À1 and 1390 cm À1 ,r espectively. [27,28,41] For the HNP and NF sample, the band at 1306 cm À1 could be ascribed to the N-O vibration, suggesting the intercalation of NO 3 À ions that originated from the reactant nickel nitrate, [29,36,37] and the band at 1055cm À1 is associated with typicala lcoholic CÀOs tretching mode of solvent etha- nol. [27,40,42] For the HNP sample, the band at 1560 cm À1 and 1380 cm À1 (overlapped with the vibration band of C=Oi n CO 3 2À )w as caused by the asymmetrica nd symmetric stretching vibrations of COO À , [27,40,43] and the bands at 2855 cm À1 and 2925 cm À1 waso wing to the CÀHv ibration, respectively, [27,40,42] implyingt he intercalation of CH 3 COO À ions.…”

Nonsiliceous Mesoporous Materials: Design and Applications in Energy Conversion and Storage

“…The synergetic effects of hybrid elements enable high pseudocapacitor performance. In a codoped Ni(OH) 2 nanosheet network, Co 2+ partially replaces Ni 2+ in the metal hydroxide and oxide, resulting in an increase in the number of free holes in the valence band and a consequent increase in the p‐type conductivity of Ni(OH) 2 and NiO . Carbon materials as supports for metal and metal oxide nanomaterials can further increase the specific surface area and electrical conductivity.…”

Laser‐Assisted Fabrication of Pseudohexagonal Phase Niobium Pentoxide Nanopillars for Lithium Ion Battery Anodes

“…The synthetic process can be illustratively shown in Scheme . Laser ablation in liquids (LAL) has been proven to be a powerful technique to generate ultrafine and well‐dispersed nanoparticles without using any stabilizers or surfactants, because of its non‐equilibrium thermodynamic process and quenching dynamic process . The relevant report indicated that, the less chemical reagents used, the more possibility to form metastable TT‐Nb 2 O 5 nanostructures under hydrothermal conditions .…”