Designing of nanoflakes anchored nanotubes-like MnCo2S4/halloysite composites for advanced battery like supercapacitor application

Current Trends and Promising Electrode Materials in Micro-Supercapacitor Printing

The development of scientific and technological foundations for the creation of high-performance energy storage devices is becoming increasingly important due to the rapid development of microelectronics, including flexible and wearable microelectronics. Supercapacitors are indispensable devices for the power supply of systems requiring high power, high charging-discharging rates, cyclic stability, and long service life and a wide range of operating temperatures (from -40 to 70 °C). The use of printing technologies gives an opportunity to move the production of such devices to a new level due to the possibility of the automated formation of micro-supercapacitors (including flexible, stretchable, wearable) with the required type of geometric implementation, to reduce time and labour costs for their creation, and to expand the prospects of their commercialization and widespread use. Within the framework of this review, we have focused on the consideration of the key commonly used supercapacitor electrode materials and highlighted examples of their successful printing in the process of assembling miniature energy storage devices.

Enhanced Electrochemical Performance of Metallic CoS-Based Supercapacitor by Cathodic Exfoliation

Two-dimensional nanomaterials hold great promise as electrode materials for the construction of excellent electrochemical energy storage and transformation apparatuses. In the study, metallic layered cobalt sulfide was, firstly, applied to the area of energy storage as a supercapacitor electrode. By a facile and scalable method for cathodic electrochemical exfoliation, metallic layered cobalt sulfide bulk can be exfoliated into high-quality and few-layered nanosheets with size distributions in the micrometer scale range and thickness in the order of several nanometers. With a two-dimensional thin sheet structure of metallic cobalt sulfide nanosheets, not only was a larger active surface area created, but also, the insertion/extraction of ions in the procedure of charge and discharge were enhanced. The exfoliated cobalt sulfide was applied as a supercapacitor electrode with obvious improvement compared with the original sample, and the specific capacitance increased from 307 F∙g^-1 to 450 F∙g^-1 at the current density of 1 A∙g^-1. The capacitance retention rate of exfoliated cobalt sulfide enlarged to 84.7% from the original 81.9% of unexfoliated samples while the current density multiplied by 5 times. Moreover, a button-type asymmetric supercapacitor assembled using exfoliated cobalt sulfide as the positive electrode exhibits a maximum specific energy of 9.4 Wh∙kg^-1 at the specific power of 1520 W∙kg^-1.

A Novel Synthesized 1D Nanobelt-like Cobalt Phosphate Electrode Material for Excellent Supercapacitor Applications

In the present report, we synthesized highly porous 1D nanobelt-like cobalt phosphate (Co₂P₂O₇) materials using a hydrothermal method for supercapacitor (SC) applications. The physicochemical and electrochemical properties of the synthesized 1D nanobelt-like Co₂P₂O₇ were investigated using X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, and scanning electron microscopy (SEM). The surface morphology results indicated that the deposition temperatures affected the growth of the 1D nanobelts. The SEM revealed a significant change in morphological results of Co₂P₂O₇ material prepared at 150 °C deposition temperature. The 1D Co₂P₂O₇ nanobelt-like nanostructures provided higher electrochemical properties, because the resulting empty space promotes faster ion transfer and improves cycling stability. Moreover, the electrochemical performance indicates that the 1D nanobelt-like Co₂P₂O₇ electrode deposited at 150 °C deposition temperature shows the maximum specific capacitance (Cs). The Co₂P₂O₇ electrode prepared at a deposition temperature 150 °C provided maximum Cs of 1766 F g^-1 at a lower scan rate of 5 mV s^-1 in a 1 M KOH electrolyte. In addition, an asymmetric hybrid Co₂P₂O₇//AC supercapacitor device exhibited the highest Cs of 266 F g^-1, with an excellent energy density of 83.16 Wh kg^-1, and a power density of 9.35 kW kg^-1. Additionally, cycling stability results indicate that the 1D nanobelt-like Co₂P₂O₇ material is a better option for the electrochemical energy storage application.

Transition metal oxy/hydroxides functionalized flexible halloysite nanotubes for hydrogen evolution reaction

The hierarchical halloysite nanotubes (HNT) have alumina containing positive Al-OH groups on its inner surface and silica-containing negative siloxane groups of Si-O-Si on its outer surface. The silicate laminate consists of silicon-oxygen at tetrahedral sites and aluminum-oxygen at octahedral sites. Since HNT has an abundant hydroxyl group on the surface with exceptional cation/anion exchange capacity, the surface-functionalized HNT could boost electrocatalytic activity. Hence, we have synthesized Ni, Co, and Cu metal oxy/hydroxides functionalized HNT by a facile hydrothermal method for HER. Among them, Co(OH)₂@HNT on flexible carbon cloth displays an ultra-low overpotential of 65 mV at 10 mA cm^-2 current density and Tafel slope of 181 mV dec^-1 and also exhibited a larger exchange current density of 3.98 mA cm^-2 in alkaline 1 M KOH electrolyte due to superior electrostatic affinity between OH^- and Co²⁺. The electrolyzers with anion exchange membrane consisting of RuO₂||Co(OH)₂@HNT show remarkable stability of over 50 h at 10 mA cm^-2 in alkaline electrolyte. The post stability sample retains the same surface oxidation state which confirms the robustness of the electrocatalyst. The reported results are far better than many of the transition metal oxides/chalcogenides electrocatalysts and hence it is expected that HNT could act as a potential alternative candidate to replace the benchmark platinum catalyst.

Cellulose Nanofiber Composite with Bimetallic Zeolite Imidazole Framework for Electrochemical Supercapacitors

Cellulose nanofiber (CNF) and hybrid zeolite imidazole framework (HZ) are an emerging biomaterial and a porous carbonous material, respectively. The composite of these two materials could have versatile physiochemical characteristics. A cellulose nanofiber and cobalt-containing zeolite framework-based composite was prepared using an in-situ and eco-friendly chemical method followed by pyrolysis. The composite was comprised of cobalt nanoparticles decorated on highly graphitized N-doped nanoporous carbons (NPC) wrapped with carbon nanotubes (CNTs) produced from the direct carbonization of HZ. By varying the ratio of CNF in the composite, we determined the optimal concentration and characterized the derived samples using sophisticated techniques. Scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) confirmed the functionalization of CNF in the metallic cobalt-covered N-doped NPC wrapped with CNTs. The CNF–HZNPC composite electrodes show superior electrochemical performance, which is suitable for supercapacitor applications; its specific capacitance is 146 F/g at 1 A/g. Furthermore, the composite electrodes retain a cycling stability of about 90% over 2000 charge–discharge cycles at 10 A/g. The superior electrochemical properties of the cellulose make it a promising candidate for developing electrodes for energy storage applications.

Electrochemically Synthesized Nanoflowers to Nanosphere-Like NiCuSe2 Thin Films for Efficient Supercapacitor Application

Developing efficient electrochemically active nanostructures from Earth-abundant elements has gained significant interest in recent years. Among different transition metals, nickel and copper are abundant electrocatalysts for energy-storage applications. Nickel–copper selenide (NiCuSe2) nanostructures were prepared on a stainless-steel mesh with a cost-effective, simple, and versatile electrodeposition method for supercapacitor applications. The change effect in the bath concentration of nickel and copper altered the structural and electrochemical properties of NiCuSe2 electrode. X-ray diffraction (XRD) patterns confirmed the pure phase of ternary NiCuSe2 thin films with a cubic crystal structure. The surface morphology of NiCuSe2 was tuned by nickel and copper from spherical porous nanoflowers, nanoplates, nanocubes, and nanosphere-like nanostructures deposited on the stainless-steel mesh. The electrochemical performance of the electrodeposited NiCuSe2 was investigated in alkaline 1 M KOH electrolyte. The synergetic effect of bimetallic nickel and copper with the selenide electrode showed superior specific capacity of about 42.46 mAh g−1 at 10 mV s−1 along with reasonable cycling stability.