Stability-Enhanced α-Ni(OH)₂ Pillared by Metaborate Anions for Pseudocapacitors

Abstract

α-Ni­(OH)2 is an ideal candidate material for a supercapacitor except for its low conductivity and poor stability. In this work, BO2 –-intercalated α-Ni x Co(1–x)(OH)2 is synthesized by a hydrothermal method at a low cost. The Co dopant can decrease the charge-transfer resistance and enhance the cyclic stability. The special unsaturated electronic state of BO2 – enhances the bonding with metal ions and attracts water molecules. Thus, the BO2 – ions support the hydroxide layers as pillars and create efficient paths for proton transportation, optimizing the utilization of α-Ni­(OH)2. The three-dimensional (3D) flowerlike morphology supplies an enormous number of active sites, and r-GO is added to improve the conductivity. As a result, the modified α-Ni­(OH)2 exhibits the specific capacitance of 2179, 1592, and 1423 F·g–1 at 1, 20, and 40 A·g–1, respectively, showing improved rate performance. Matching with the commercial activated carbon (AC) as an anode, the asymmetric capacitor delivers an energy density of 40.66 W·h·kg–1 when its power density is 187.06 W·kg–1. Meanwhile, it retains 81.5% capacitance of the initial cycle at 5 A·g–1 after 3000 cycles. With conductivity enhanced and structure stabilized, the modified α-Ni­(OH)2 confronts broader fields of application.

Zeolitic-imidazolate framework derived Ni–Co layered double hydroxide hollow microspheres with enhanced pseudocapacitive properties for hybrid supercapacitors

“…It is reported that the existence of Co 3+ improves the conductivity of Ni-Co hydroxides. 10 Thus, the strong correlation between Co contents and conductivity could be attributed to the higher concentration of Co 3+ in the Co abundant Ni-Co-LDH-Cs, which has been confirmed by XPS results.…”

“…3c), where the corresponding characteristic peaks located at 1324, 1420 and 1577 cm À1 typically are assigned to varied n(-COO-) modes and that at 1074 cm À1 is assigned to the n(C-O) modes. Based on the structure and previous reports, 10,25 it is reasonable to assume that citrate acts as charge balancing anions and pillars in the interlayer to stabilize the a-phase layer structure with a wide interlayer spacing, which is critically important for improving the capacity retention of Ni-Co-LDH-Cs during the charge-discharge process. The survey XPS spectra (Fig.…”

“…6 Unfortunately, a-Co(OH) 2 or a-Ni(OH) 2 is unstable in an alkaline environment because it will lose the intercalated anions or crystal water in the interlayers and transfer to the compacted b-phase. 9,10 Tremendous efforts have been dedicated to addressing the issue in stabilizing the structure of a-Co(OH) 2 or a-Ni(OH) 2 . The promising approaches mainly include partly substituting with other transition metal cations (Ni, Co, Mn, Al, Fe, etc.…”

“…6 Unfortunately, α-Co(OH) 2 or α-Ni(OH) 2 is unstable in an alkaline environment because it will lose the intercalated anions or crystal water in the interlayers and transfer to the compacted β-phase. 9,10…”

Template-Free Preparation of α-Ni(OH)2 Nanosphere as High-Performance Electrode Material for Advanced Supercapacitor

“…In recent years, transition-metal hydroxide, especially Ni(OH) 2 , has attracted intensive concerns as a result of its low cost, remarkable energy density and theoretical specific capacitance [14][15][16]. Even so, the shortcomings of inferior electric conductivity and poor rate capability are becoming serious obstacles to the widespread application of supercapacitors [17][18][19][20][21].…”