Hierarchical Bimetallic Hydroxides Built by Porous Nanowire‐Lapped Bundles with Ultrahigh Areal Capacity for Stable Hybrid Solid‐State Supercapacitors

Abstract

Exploring advanced electrode materials with superb energy/power densities and long lifetime as well as low cost is the recent focus of hybrid solid‐state supercapacitor (HSSC). This study reports a novel hierarchical bimetallic hydroxide (Ni1Co1‐OH) built by nanowire‐lapped bonfire‐like bundles through a facile and scalable method, and provides thorough insights into possible formation mechanism and structural merits of the interesting hierarchical architecture. Benefiting from multistep redox reactions, high accessible surface area and fast kinetics contributed by the unique structure, Ni1Co1‐OH using 2 m KOH electrolyte can achieve highly improved gravimetric capacity/capacitance of 876.8 C g−1/1753.6 F g−1 at active mass loading of 3 mg cm−2 at 1 A g−1, and especially deliver a record‐high areal capacity of 7.6 C cm−2 at 1 A g−1 under a commercial loading of 15 mg cm−2. 1.5 V Ni1Co1‐OH based HSSC with the poly(vinyl alcohol)/KOH gel electrolyte verifies the intriguing performance including high energy/power densities of 27.9 Wh kg−1/13812.9 W kg−1, a long life over 10 000 cycles, and a low self‐discharge rate with a voltage decline of 20% after 24 h. The findings identify the scalable production of high‐performance bimetal compounds, which will boost the development of highly demanding HSSC devices.

Unveiling the Occurrence of Co(III) in NiCo Layered Electroactive Hydroxides: The Role of Distorted Environments

“…[20,24,27,28] It is important to point out, that the Co(III):Co(III) ratio can have an effect on the active sites in the redox reaction, while the increment of this ratio leads to as ignificant enhancement of the specific capacitance. [29] Moreover,d ensity functional theory (DFT) calculations suggest,t hat the presence of certain trivalent cations can affect the electrochemical behavior through ab and gap modification. [30] Hence, the occurrence of Co(III) in these materials must be understood in order to thoroughly rationalize the design andp hysical properties of these compounds.…”

Interconnected network‐like single crystalline bimetallic carbonate hydroxide nanowires for high performance hybrid supercapacitors

“… 32 Similarly, the deconvoluted Co 2p 3/2 (781.07 eV) and Co 2p 1/2 (797.68 eV) spectra represent four Co species corresponding to the Co(II) (783.06/799.34 eV) and Co(III) (780.85/796.84 eV) species with two satellites peaks (286.54/803.45 eV) (Figure 4C). 32 The multiple valance states of the Ni and Co species for the NiCoCH nanowires provide abundant redox‐active sites for the high capacitance 33,34 . The high‐resolution O 1s spectrum (531.37 eV) indicates two oxygen species, which are fitted as O1 (531.27 eV) and O2 (532.23 eV) (Figure 4D).…”

“…Besides, the atomic ratio of Ni and Co elements of NiCoCH nanowires is close to 1:1, which is consistent with the stoichiometry of orthorhombic Figure 4B). 32 Figure 4C). 32 The multiple valance states of the Ni and Co species for the NiCoCH nanowires provide abundant redox-active sites for the high capacitance.…”

“…32 Figure 4C). 32 The multiple valance states of the Ni and Co species for the NiCoCH nanowires provide abundant redox-active sites for the high capacitance. 33,34 The high-resolution O 1s spectrum (531.37 eV) indicates two oxygen species, which are fitted as O1 (531.27 eV) and O2 (532.23 eV) ( Figure 4D).…”

“…Such a high SSA and porosity can provide rapid electrolytic ion transport pathways and alleviate volume expansion during an ion insertion/ desertion process. 31,32 The XPS spectrum was recorded to investigate the surface valence states and chemical compositions of NiCoCH nanowires. The full XPS survey spectrum of NiCoCH identifies four distinct elements of Ni, Co, O, and C ( Figure 4A).…”