High-Quality Metal Oxide Core/Shell Nanowire Arrays on Conductive Substrates for Electrochemical Energy Storage

Abstract

The high performance of a pseudocapacitor electrode relies largely on a scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. We present a powerful two-step solution-based method for the fabrication of transition metal oxide core/shell nanostructure arrays on various conductive substrates. Demonstrated examples include Co(3)O(4) or ZnO nanowire core and NiO nanoflake shells with a hierarchical and porous morphology. The "oriented attachment" and "self-assembly" crystal growth mechanisms are proposed to explain the formation of the NiO nanoflake shell. Supercapacitor electrodes based on the Co(3)O(4)/NiO nanowire arrays on 3D macroporous nickel foam are thoroughly characterized. The electrodes exhibit a high specific capacitance of 853 F/g at 2 A/g after 6000 cycles and an excellent cycling stability, owing to the unique porous core/shell nanowire array architecture, and a rational combination of two electrochemically active materials. Our growth approach offers a new technique for the design and synthesis of transition metal oxide or hydroxide hierarchical nanoarrays that are promising for electrochemical energy storage, catalysis, and gas sensing applications.

Nanoporous Metal Papers for Scalable Hierarchical Electrode

“…In those instances where the value was higher than that of carbon, the areal capacitance (3.7–4.4 F cm −2 ) measured at a discharge current density of 0.04–1 A g −1 (1.04–26 mA cm −2 ) was roughly three times greater than that of conventional and oxy‐hydroxide nanoporous Ni (0.7–1.7 F cm −2 ) 13, 20, 21. It even proved to be higher than, or similar to, previously reported values for free‐standing pseudocapacitive electrodes such as Co 3 O 4 /MnO 2 nanowires/nanosheets (0.4–0.71 F cm −2 ),27 Co 3 O 4 /NiO core‐shell nanostructure arrays (1.3–2.56 F cm −2 ),28 MnO 2 –NiO nanoflakes (0.22–0.4 F cm −2 ),29 NiCo 2 O 4 nanoneedle/Ni forms (0.59–3.12 F cm −2 ),30 and 3D ordered nanoporous NiMoO 4 (2.18–4.25 F cm −2 ) 31. Moreover, the volume of the electrode minus its pore volume that was estimated from its BET surface area suggests a value of 4.4 F cm −2 corresponds to ≈887 F cm −3 .…”

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

“…1e), a distinct ring is observed, corresponding to the (111) plane of Ni nanocrystals. 33,34 The shell of dendrites is, however, amorphous. This core-shell structure is also veried by the fast Fourier transformation (FFT) patterns, as shown in Fig.…”

Transition metal oxides/hydroxides nanoarrays for aqueous electrochemical energy storage systems

“…>4 F cm −2 ), the inevitable substrate contribution (~0.2 F cm −2 ) can be neglected [23]. In a word, Ni foam is a good current collector in alkaline or neutral electrodes as long as we subtract the possible capacitive contribution to get corrected specific capacitances of the active material [24]. As an alternative option of Ni foam, Cu foam has been used widely because of its high resistance to acidity and negligible capacitive contribution [25,26].…”

“…In general, high mass-loading on conventional electrodes usually leads to an increase of "dead volume" in electrode materials which is not accessible to the electrolyte in the SC, and thus results in low utilization efficiencies of the materials. In this regard, hierarchical design of complex core-shell nanoarrays with porous structures is considered as an effective approach to simultaneously achieve high mass-loading and high utilization of the electrode material, because they not only provide large active surface area and short diffusion path lengths to electrons and ions, but also show a potential synergistic effect of each component, leading to high capacitance, low internal resistance, remarkable rate capability, and excellent stability [5,24,[82][83][84][85][86].…”