Paraotwayite-type α-Ni(OH)₂ Nanowires: Structural, Optical, and Electrochemical Properties

Abstract

Paraotwayite-type nickel hydroxide [Ni(OH) 2 ] nanowires with typical diameters of 20−30 nm and lengths up to several micrometers were prepared via a simple hydrothermal synthesis. The as-prepared nanowires had a mean composition of Ni(OH) 1.64 (SO 4 ) 0.18 •0.3H 2 O and crystallized in a layered monoclinic structure (unit cell parameters: a = 0.78867(1) nm, b = 0.29661(3) nm, c = 1.35164(2) nm, and β = 91.1°), which is isostructural to α-Ni(OH) 2 and has sulfate anions and water molecules sandwiched in the two-dimensional Ni(OH) 2 principle layers. The as-prepared Paraotwayite-type α-Ni(OH) 2 nanowires showed an indirect-allowed electron transition with a band gap energy E g of about 3.8 eV, whereas the corresponding NiO nanowires obtained from a topotactic transformation of Paraotwayite-type α-Ni(OH) 2 nanowire precursors exhibited a direct-allowed electron transition with a similar band gap energy of E g ∼ 3.8 eV. Both Paraotwayite-type α-Ni(OH) 2 nanowires and NiO nanowires performed similar electrochemical redox reactions in aqueous alkaline solutions, whereas the OH − ion insertion/ extraction reactions were found to be greatly enhanced in Paraotwayite-type α-Ni(OH) 2 nanowires due to their intrinsic layered structure. The as-prepared Paraotwayite-type α-Ni(OH) 2 nanowires exhibited an anodic electrochromism related to the redox couple of Ni 2+ → Ni 3+ , which corresponds to the coloration from light green to dark brown. Paraotwayite-type α-Ni(OH) 2 nanowires are an interesting material system for photoelectrochemical devices and energy-storage applications.

Controlled Synthesis of a Hexagonal‐Shaped NiO Nanocatalyst with Highly Reactive Facets {1 1 0} and Its Catalytic Activity

“…The sample exhibits major peaks at 2q values of 11.63, 23.77, 33.66, 41.18, and 59.608, which correspond to (0 0 1), (0 0 2), (11 0), (1 0 3), and (3 0 0) crystal planes, respectively (JCPDS PDF number 00-022-0444). [52] All peaks are well indexed to a pure hexagonal structure of a-Ni(OH) 2 with an P-31m space group and lattice parameters a = 0.534 and c = 0.750 nm. The wideangle XRD profiles of both calcined hexagonal-shaped NiO nanocrystals display sharp peaks (Figure 2 B), indicating high crystallinity of the obtained powder.…”

Ni@NiO core/shell dendrites for ultra-long cycle life electrochemical energy storage

“…S7 †). A distinctive pair of redox peaks between À0.2 and 0.65 V is due to the insertion/extraction of OH À ions (NiO + OH À À e À # NiOOH), 41 illustrating the typical faradaic behaviour of the DNE. Fig.…”

Remarkable electrochemical lithium storage behaviour of two-dimensional ultrathin α-Ni(OH)2 nanosheets

“…There are great reports about their applications as electrode active material in rechargeable alkaline batteries and supercapacitors. [25][26][27] Recently, β-Ni(OH) 2 nanosheets, Ni(OH) 2 nanosheet arrays on nickel foam, and Ni(OH) 2 /graphene composite are proposed as novel lithium storage materials. [28][29][30] These published papers reported good electrochemical results and offered an overture of application of Ni(OH) 2 materials in lithium ion batteries.…”