Ternary Hybrids of Amorphous Nickel Hydroxide–Carbon Nanotube‐Conducting Polymer for Supercapacitors with High Energy Density, Excellent Rate Capability, and Long Cycle Life

Abstract

take place on the surface or near-surface region of pseudocapacitive materials is particularly paramount to the development of supercapacitors with both high energy density, high rate capability, and long cycle life.Ni(OH) 2 /NiO(OH) couple is the main redox system used in the positive electrodes of alkaline rechargeable batteries, because of its good reversibility and cyclic behavior. [ 5,6 ] Ni(OH) 2 has also attracted great interest as pseudocapacitive materials for supercapacitors due to its high theoretical specifi c pseudocapacitance of 2082 F g −1 (in a potential window of 0.5 V), environmental friendliness, and low cost. [ 7 ] In particular, Ni(OH) 2 in amorphous phase is expected to have better electrochemical effi ciency due to more grain boundaries and ion diffusion channels in the disordered structure compared to the crystalline phase. [ 7,8 ] The key issues of applying Ni(OH) 2 in practical supercapacitors lie in its low electrical conductivity and short cycle life. The electrical conductivity of Ni(OH) 2 is very low at around 10 −15 Ω −1 m −1 . [ 9 ] Thus, the redox reactions can only take place on its surface, and most of Ni(OH) 2 is inaccessible to electrolyte ions and remains as dead volume in supercapacitors. [ 10,11 ] Several approaches have been explored to address the issues caused by the low electrical conductivity of Ni(OH) 2 , including synthesis of porous structures, nanoparticles, thin fi lms, and nanosheets to expose more Ni(OH) 2 surfaces to electrolyte ions, [ 12,13 ] forming Ni(OH) 2 and carbon materials or conducting polymers hybrids to have imbedded conductive networks, [14][15][16][17][18] introducing other metal ions into Ni(OH) 2 to enhance its conductivity. [ 17,19,20 ] Even though these nanoscale engineering approaches can improve the electrical conductivity of Ni(OH) 2 , the constructed nanoscale structures often degrade and Ni ions dissolve into electrolytes after repeated charge/discharge cycles, which can result in short cycle life of supercapacitors. [ 5,13,14,[20][21][22] In this study, with the aim of constructing supercapacitors with both high energy density, good rate capability, and long cycle life, we have designed and synthesized a novel ternary hybrid electrode material comprising of multiwalled carbon nanotubes (MWCNTs), amorphous(amor)-Ni(OH) 2 and poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as high performance pseudocapacitive materials. Other than the commonly used crystalline Ni(OH) 2 , a thin layer of disordered amor-Ni(OH) 2 was deposited on conductive acidtreated MWCNTs by using a "coordinating etching and precipitating" method, which enabled effi cient redox reactions to take place mostly on the surface of Ni(OH) 2 . To prevent the dissolution of Ni ions into electrolytes and preserve the nanoscale structures amor-Ni(OH) 2 upon long charge/discharge cycles, a conductive polymer layer was further wrapped around the MWCNT/amor-Ni(OH) 2 . Such a unique hybrid architecture design results in Ni(OH) 2 pseudocapacitive materials with ult...

Recent progress on nanostructured conducting polymers and composites: synthesis, application and future aspects

“…The developed stretchable wireshaped supercapacitors exhibited a high volumetric capacitance of 0.2 F cm −3 at a strain of 400%. Jiang et al [210] synthesized the coaxial ternary hybrid material with MWCNTs as a core, and thin layer (<5 nm) of amorphous Ni(OH) 2 and PEDOT:PSS as a shell. The high pseudocapacitance and excellent rate capability were achieved due to the amorphous Ni(OH) 2 that increases the probability of redox reactions to occur on or near the REVIEW .…”

Recent progress in carbon-based nanoarchitectures for advanced supercapacitors

“…Wallace et al [99] prepared highly flexible hybrid CNT/MnO 2 nanocomposite fibers via a wet-spinning process followed by electrodeposition of An alternative strategy, the incorporation of various metal oxide/hydroxides/sulfide to improve the electrical performance of CNTs, has attracted wide public concern because the CNTs not only can be employed as the conductive backbone to support metallic particles for increasing conductivity, but also can allow the electrolyte ions to easily diffuse through the electrode materials [100]. Moreover, multitudinous redox reactions mainly occurring on the surface or surrounding surface of the metal oxide/ hydroxides/sulfide could enhance the energy density of SCs [101]. Yamauchi et al [102] (Fig.…”

Recent Advances in Nanostructured Conducting Polymers: from Synthesis to Practical Applications

“…The coupling of PEDOT:PSS with nickel hydroxide Ni(OH) 2 and multi-walled carbon nanotubes (MWCNTs) has also been examined [161]. In this ternary architecture design, various synergistic effects were observed in their application as the electrode material for supercapacitors.…”