Enhancement of the Ni-Co hydroxide response as Energy Storage Material by Electrochemically Reduced Graphene Oxide

Schottky Interface Enabled Electrospun Rhodium Oxide Doped Gold for Both pH Sensing and Glucose Measurements in Neutral Buffer and Human Serum

This study has focused on adjusting sensing environment from basic to neutral pH and improve sensing performance by doping electrodeposited gold (Au) with metal oxide for nonenzymatic glucose measurements in forming a Schottky interface for superior glucose sensing with detailed analysis for the sensing mechanism. The prepared sensor also holds the ability to measure pH with the identical electrospun metal oxide-electrodeposited Au, which composed a dual sensor (glucose and pH sensor) through applying chronoamperometry and open circuit potential methods. The rhodium oxide nanocoral structure was fabricated with an electrospinning precursor solution, followed by a calcination process, and it was mixed with electrodeposited nanocoral gold to form the Schottky interface by constructing a p-n type heterogeneous junction for improved sensitivity in glucose detection. The prepared materials were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS), etc. The prepared materials were used for both pH responsive testing and amperometric glucose measurements. The rhodium oxide nanocoral doped gold demonstrated a sensitivity of 3.52 μA mM-1 cm-2 and limit of detection of 20 μM with linear range up to 3 mM glucose concentration compared to solely electrodeposited gold for a sensitivity of 0.46 μA mM-1 cm-2 and a limit of detection of 450 μM. The Mott-Schottky method was used for the analysis of an electron transfer process from noble metal to metal oxide to electrolyte in demonstrating the improved sensitivity at neutral pH for glucose measurements due to the Schottky barrier adjustment mechanism at an applied flat band potential of 0.3 V. This work opens a new venue in illustrating the metal oxide/metal materials in the glucose neutral response mechanism. In the end, human serum samples were tested against current commercial glucose meter to certify the accuracy of the proposed sensor.

Removal of Sb(III) by 3D-reduced graphene oxide/sodium alginate double-network composites from an aqueous batch and fixed-bed system

We created 3D-reduced graphene oxide/sodium alginate double network (GAD) beads to address the problem of local water pollution by antimony. GAD is a novel material with the high specific surface area of graphene and biosecurity of sodium alginate. Due to the introduction of graphene, the thermal stability and specific surface area of GAD are enhanced, as shown from the FTIR, TGA, BET, Raman, and XRD characterizations. The influence of different environmental variables-such as the pH, dosage, temperature, contact time, and sodium chloride concentration on the Sb(III) sorption with GAD-was investigated. The adsorption results fit well with both the pseudo-second order (R² > 0.99) and Freundlich (R² > 0.99) isotherm models. The temperature rise has a negative influence on the adsorption. The Langmuir adsorption capacity is 7.67 mg/g, which is higher than many adsorbents. The GAD results from the fixed-bed adsorption experiment were a good fit with the Thomas model (R² > 0.99). In addition, GAD appears to be a renewable and ideal adsorbent for the treatment of antimony pollution in aqueous systems.

Ionic liquids to monitor the nano-structuration and the surface functionalization of material electrodes: a proof of concept applied to cobalt oxyhydroxide

This paper reports on an innovative and efficient approach based on the use of ionic liquids to govern the nano-structuration of HCoO₂, in order to optimize the porosity and enhance the ionic diffusion through the electrode materials. In this work, we show that (1-pentyl-3-methyl-imidazolium bromide (PMIMBr) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF₄)) ionic liquids (ILs) used as templates during the synthesis orientate the nanoparticle aggregation which leads to increase of the porosity and the average pore size of the electrode material. It is also demonstrated that the ILs are strongly bonded to the HCoO₂ surface, leading to surface functionalized HCoO₂ materials, also called nanohybrids. This surface tailoring stabilizes the material upon cycling and shifts the oxidation potential linked to the Co(iii)/Co(iv) redox couple to lower voltage in an alkaline 5 M KOH electrolyte. The surface and porosity optimizations facilitate the ionic diffusion through the material, improve the electron transfer ability within the electrode and lead to greatly enhanced specific capacity in both alkaline 5 M-KOH and neutral 0.5 M-K₂SO₄ aqueous electrolytes (66.7 mA h g^-1 and 47.5 mA h g^-1 respectively for HCoO₂-PMIMBr and HCoO₂-EMIMBF₄ compared to 18.1 mA h g^-1 for bare HCoO₂ in 5 M-KOH at 1 A g^-1).

Porous nanorods of nickel-cobalt double hydroxide prepared by electrochemical co-deposition for high-performance supercapacitors

Nickel-cobalt double hydroxides (Ni-Co DHs) combined with cost-effectively commercial expanded graphite (EG) was prepared via a facile in-situ electrodeposition in mixed solvents of N,N-dimethylformamide and water. By simply adjust molar ratios of Ni²⁺/Co²⁺, a Ni-Co DHs/EG electrode in which Ni-Co DHs showing a porous-nanorod microstructure was fabricated. Thanks to synergistic effects between Ni(OH)₂ and Co(OH)₂ as well as the unique morphology of porous nanorods, an optimal Ni-Co DHs/EG electrode with a total mass loading of 4.0 mg cm^-2 can deliver a specific capacitance of 1246 F g^-1 at 1 A g^-1, a rate capability of 91.8% as the discharging current density increasing from 1 to 10 A g^-1, and a capacitance retention of 80.1% after 1000 cycles charged/discharged at 10 A g^-1. Thus we can draw a conclusion that the Ni-Co DHs/EG electrode possesses a satisfactory specific capacitance, extremely superior rate performance, and good cycle stability, therefore it can be very competitive for practical applications in supercapacitors.

Life cycle assessment of emerging Ni–Co hydroxide charge storage electrodes: impact of graphene oxide and synthesis route

An addition of reduced graphene oxide to nickel–cobalt hydroxide electrodes results in net reduction of cumulative energy demand due to improved electrochemical properties.

Tailoring morphology of cobalt-nickel layered double hydroxide via different surfactants for high-performance supercapacitor

Tailoring the morphology of cobalt-nickel layered double hydroxide (LDH) electrode material was successfully achieved via the process of cathodic electrodeposition by adding different surfactants (hexamethylenetetramine, dodecyltrimethylammonium bromide (DTAB) or cetyltrimethylammonium bromide). The as-prepared Co0.75Ni0.25(OH)2 samples with surfactants exhibited wrinkle-like, cauliflower-like or net-like structures that corresponded to better electrochemical performances than the untreated one. In particular, a specific capacitance of 1209.1 F g-1 was found for the cauliflower-like Co0.75Ni0.25(OH)2 electrode material using DTAB as the surfactant at a current density of 1 A g-1, whose structure boosted ion diffusion to present a good rate ability of 64% with a 50-fold increase in current density from 1 A g-1 to 50 A g-1. Accordingly, the asymmetric supercapacitor assembled by current LDH electrode and activated carbon electrode showed an energy density as high as 21.3 Wh kg-1 at a power density of 3625 W kg-1. The relationship between surfactant and electrochemical performance of the LDH electrode materials has been discussed.

3D structured polypyrrole/reduced graphene oxide (PPy/rGO)-based electrode ionic soft actuators with improved actuation performance

We report a facile approach to fabricate 3D polypyrrole/reduced graphene oxide (PPy/rGO)-based electrodes for Nafion-based ionic soft actuators.