Electrochemical impedance spectroscopy: from breakthroughs to functional utility in supercapacitors and batteries - a comprehensive assessment.

Electrochemical impedance spectroscopy (EIS) is a powerful technique that can be used to investigate the properties of materials, interfaces, and their redox reactions. It is applied to describe electrochemical systems and support the development of important technologies, offering a much more detailed investigation of properties than other conventional electrochemical techniques. EIS employs a modulated frequency to understand frequency-dependent electrochemical processes, thereby clarifying both fast and slow processes. As a dynamic and robust tool, a thorough understanding of this technique allows the precise use of the information it provides. In this review, we cover the history of the technique's development, its fundamental theory, and necessary conditions for proper use, in addition to providing guidelines on how to use EIS for data collection and the acquisition of relevant information provided by the technique. We also discuss complications related to the necessary conditions, equivalent circuits used for describing systems, commonly used plots, the configuration of electrochemical cells and the possibilities for the use and application of EIS techniques to characterize supercapacitors and batteries. This paper provides meaningful information and discussion related to EIS and ways to better utilize it for investigating the properties of materials.

Enhanced enzymatic electrochemical detection of an organophosphate Pesticide: Achieving Wide linearity and femtomolar detection via gold nanoparticles growth within polypyrrole films.

The indiscriminate use of pesticides in agriculture demands the development of devices capable of monitoring contaminations in food supplies, in the environment and biological fluids. Simplicity, easy handling, high sensitivities, and low limits-of-detection (LOD) and quantification are some of the required properties for these devices. In this work, we evaluated the effect of incorporating gold nanoparticles into indigo carmine-doped polypyrrole during the electropolymerization of films for use as an acetylcholinesterase (AChE) enzyme-based biosensor. As proof of concept, the pesticide methyl parathion was tested towards the inhibition of AChE. The enzyme was immobilized simply by drop-casting a solution, eliminating the need for any prior surface modification. The biosensors were characterized with cyclic voltammetry, scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy. The assays for the detection of methyl parathion with films containing polypyrrole, indigo carmine and AChE (PPy-IC-AChE) presented a sensitivity of 5.7 µA cm-2 g-1 mL and a LOD of 12 nmol L-1 (3.0 ng L-1) with a linear range from 1.3 x 10-7 mol L-1 to 1.0 x 10-5 mol L-1. The introduction of gold nanoparticles (AuNP) into the film (PPy-IC-AuNP-AChE) led to remarkable improvements on the overall performance, such as a lower redox potential for the enzymatic reaction, a 145 % increase in sensitivity (14 µA cm-2 g-1 mL), a wider detection dynamic range (from 1.3x10-7 to 1.0x10-3 mol L-1), and a very low LOD of 24 fmol L-1 (64 ag mL-1). These findings underscore the potential of using AuNPs to improve the enzymatic performance of biosensor devices.

Gel Biopolymer Electrolytes Based on Saline Water and Seaweed to Support the Large-Scale Production of Sustainable Supercapacitors.

Climate change and the demand for clean energy have challenged scientists worldwide to produce/store more energy to reduce carbon emissions. This work proposes a conductive gel biopolymer electrolyte to support the sustainable development of high-power aqueous supercapacitors. The gel uses saline water and seaweed as sustainable resources. Herein, a biopolymer agar-agar, extracted from red algae, is modified to increase gel viscosity up to 17-fold. This occurs due to alkaline treatment and an increase in the concentration of the agar-agar biopolymer, resulting in a strengthened gel with cohesive superfibres. The thermal degradation and agar modification mechanisms are explored. The electrolyte is applied to manufacture sustainable and flexible supercapacitors with satisfactory energy density (0.764 Wh kg-1 ) and power density (230 W kg-1 ). As an electrolyte, the aqueous gel promotes a long device cycle life (3500 cycles) for 1 A g-1 , showing good transport properties and low cost of acquisition and enabling the supercapacitor to be manufactured outside a glove box. These features decrease the cost of production and favor scale-up. To this end, this work provides eco-friendly electrolytes for the next generation of flexible energy storage devices.

Peering into the Formation of Template-Free Hierarchical Flowerlike Nanostructures of SrTiO3.

The development of efficient advanced functional materials is highly dependent on properties such as morphology, crystallinity, and surface functionality. In this work, hierarchical flowerlike nanostructures of SrTiO3 have been synthesized by a simple template-free solvothermal method involving poly(vinylpyrrolidone) (PVP). Molecular dynamics simulations supported by structural characterization have shown that PVP preferentially adsorbs on {110} facets, thereby promoting the {100} facet growth. This interaction results in the formation of hierarchical flowerlike nanostructures with assembled nanosheets. The petal morphology is strongly dependent on the presence of PVP, and the piling up of nanosheets, leading to nanocubes, is observed when PVP is removed at high temperatures. This work contributes to a better understanding of how to control the morphological properties of SrTiO3, which is fundamental to the synthesis of perovskite-type materials with tailored properties.