One pot synthesis of nickel foam supported self-assembly of NiWO₄ and CoWO₄ nanostructures that act as high performance electrochemical capacitor electrodes

Abstract

In this work, we report a facile one-step hydrothermal approach to synthesize NiWO 4 and CoWO 4 nanostructures on nickel foam as the binder-free electrodes for use as supercapacitors. The as-synthesized materials showed excellent electrochemical performance, with a high specific capacitance of 797.8 F g -1 and 764.4 F g -1 at a current density of 1 A g -1 after 3000 cycles, increasing the current density by 20 times, the rate capabilities still maintaining 55.6% and 50.6% of the original value for NiWO 4 /Ni foam and CoWO 4 /Ni foam, respectively. Moreover, both of these materials exhibited outstanding cycling stability, the 6000 th cycle at 50 mV s -1 demonstrated 2.06 and 2.81 times, better capacitance than the initial cycles for NiWO 4 /Ni foam and CoWO 4 /Ni foam, respectively. To our knowledge, this capacitance performance is better than any previously reported for these materials and is a consequence of the highly evolved surface area/microstructure of the materials formed by this technique. IntroductionIn order to satisfy the increasing demands for energy, many energy storage devices have been explored and intensively developed. Much attention has been paid to supercapacitors, also known as the electrochemical capacitors (ECs) in recent years due to their outstanding and unique abilities such as fast charge-discharge rate, high power density and long-cycle lifespan. 1 Based on their different charge storage mechanisms, supercapacitors can be classified into two groups: electrical double layer capacitors (EDLCs) and pseudocapacitors (PCs). EDLCs, carbon-based nanomaterials for example, store electrical energy via reversible ion-absorption at the interface of electrode and electrolyte. Compared with EDLCs, PCs exhibit higher specific capacitance and energy density, which are attributed to the fast reversible redox reactions between the different valence states of the transition metal oxide used as the electrode. Much effort has been focused on transition metal oxide (TMO) for PCs 7 . However, the poor electrical conductivity and the rapid decline of the capacitance for most binary metal oxides are the big hurdles to their practical applications. Ternary transition metal oxides with two different metal cations are promising electrode candidates for energy-storage applications. The combination of two different metal cations could enhance the conductivity greatly or provide a wide range of oxidation states in comparison with their individual binary oxide counter parts thus potentially enabling improvements in electrochemical properties. Accordingly, various ternary transition metal oxides with controlled morphologies have been synthesized and achieved better electrochemical performance, such as NiCo 2 O 4 , 8,9 CoMoO 4 , 10 NiMoO 4 , 11 and CoMn 2 O 4 . 12 Currently, the design and synthesis of novel ternary transition metal oxides nanomaterials with superior electrochemical properties is still a key area of research. Another method to enhance the conductivity could be exchanging O by S.13,14 Compared with meta...

Enhanced electron transfer mediated detection of hydrogen peroxide using a silver nanoparticle–reduced graphene oxide–polyaniline fabricated electrochemical sensor

“…This concluded that the reaction at the AgNPs-rGO-PANI-GCE was the surface controlled process. 41,42 3.2.3 Electrochemical impedance spectroscopy of AgNPsrGO-GCE and AgNPs-rGO-PANI-GCE. The EIS technique has been used for measuring the resistance of the modied electrode as a function of frequency because of variation in the interfacial properties.…”

Composite Metal Oxide‐Carbon Nanotube Electrocatalysts for the Oxygen Evolution and Oxygen Reduction Reactions

“…[30] It was also proposed that the iron centres act as catalytically active sites, leading to improved catalyst performance. [6] However, while materials such as CoWO 4 have received significant interest as electroactive compounds, [35,36,37] their application as OER and ORR catalysts has thus far been hindered by their low electronic and ionic conductivity. [34] Recent computational studies suggested that the electrocatalytic activity of 3d metal oxides can be further modulated by introducing high-valent heavy metals such as W, resulting in near-optimal adsorption energies for intermediates.…”

“…[16,30,31] These ground-breaking studies have led to a range of interesting mixed-metal OER catalysts such as CoFeO x , [32] Ni 1-x Fe x O y nanoparticles [33] and Co 1-x Fe x (OOH) oxy-hydroxides. [6,36] Thus, to immobilize these materials on high surface area conductive substrates such as carbon nanotubes (CNTs) can significantly enhance their electroactivity. [6] However, while materials such as CoWO 4 have received significant interest as electroactive compounds, [35,36,37] their application as OER and ORR catalysts has thus far been hindered by their low electronic and ionic conductivity.…”

Hydrothermal Synthesis of Hybrid Rod‐Like Hollow CoWO4/Co1−xS for High‐Performance Supercapacitors

“…used a simple wet‐chemical and hydrothermal methods to synthesis CoWO 4 nanoparticles, the results showed specific capacitances of 403 F ⋅ g −1 and 264 F ⋅ g −1 (0.5 A ⋅ g −1 ) for the synthetic amorphous and crystalline CoWO 4 , respectively. He et al . prepared NiWO 4 and CoWO 4 nanostructures via one‐step hydrothermal approach, demonstrated high specific capacitance of 797.8 F ⋅ g −1 and 764.4 F ⋅ g −1 (1 A ⋅ g −1 ).…”