Hybrid composite polyaniline-nickel hydroxide electrode materials for supercapacitor applications

Silver Decorated and Graphene Wrapped Polypyrrole@Ni(OH)2 Quaternary Nanocomposite for High Performance Energy Storage Devices

In this work, silver (Ag) anchored over graphene (GN) wrapped polypyrrole (PPy)@ nickel hydroxide (Ni(OH)₂) nanocomposites were synthesized through a combination of oxidative polymerization and hydrothermal processes. The synthesized Ag/GN@PPy-Ni(OH)₂ nanocomposites were characterized for their morphological characteristics by field emission scanning electron microscopy (FESEM), while the structural investigations were done by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The FESEM studies showed Ni(OH)₂ flakes and silver particles attached over the surface of PPy globules, along with the presence of GN sheets and spherical silver particles. The structural analysis also showed the presence of constituents, i.e., Ag, Ni(OH)₂, PPy, GN, and their interaction, therefore vouching that the synthesis protocol is efficacious. The electrochemical (EC) investigations were done in potassium hydroxide (1 M KOH) using a three electrode setup. The quaternary Ag/GN@PPy-Ni(OH)₂ nanocomposite electrode showed the highest specific capacity of 237.25 C g^-1. The highest electrochemical performance of the quaternary nanocomposite is associated with the synergistic/additional effect of PPy, Ni(OH)₂, GN, and Ag. The assembled supercapattery with Ag/GN@PPy-Ni(OH)₂ as a positive and activated carbon (AC) as a negative electrode displayed eminent energy density of 43.26 Wh kg^-1 with the associated power density of 750.00 W kg^-1 at a current density of 1.0 A g^-1. The cyclic stability of the supercapattery (Ag/GN@PPy-Ni(OH)₂//AC), comprising a battery-type electrode, displayed a high cyclic stability of 108.37% after 5500 cycles.

Nanostructured Carbon-Nitrogen-Sulfur-Nickel Networks Derived From Polyaniline as Bifunctional Catalysts for Water Splitting

The development of reliable production routes for sustainable hydrogen (H₂), which is an essential feedstock for industrial processes and energy carrier for fuel cells, is needed. It appears to be an unavoidable alternative to significantly reduce the dependence on conventional energy sources based on fossil fuels without increasing the atmospheric CO₂ levels. Among the different power-to-X scenarios to access high purity H₂, the electrochemical approach based on electrolysis looks to be a promising sustainable solution at both the small and large industrial scales. However, the practical realization of this important opportunity faces several challenges, including the efficient design of cost-effective catalytic materials to be used as a cathode with improved intrinsic and durable activity. In this contribution, we report the design and development of efficient nanostructured catalysts for the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in aqueous media, whereby noble metal-free elements are embedded in a matrix of a conducting polymer, polyaniline (PANI). To increase the electrical conductivity and further the electrocatalytic ability toward HER of the chemically polymerized PANI in the presence of nickel (II) salt (nitrate), the PANI-based materials have first been stabilized at a mild temperature of 250-350°C in air and then carbonized at 800-1,000°C under nitrogen gas to convert the chemical species into nitrogen, sulfur, nickel, and carbon nanostructured networks (CNNs). Different physicochemical (TGA-DSC, Raman spectroscopy, XRD, SEM, EDX, ICP, CHNS, BET, and XPS) and electrochemical (voltammetry and electrochemical impedance spectrometry) methods have been integrated to characterize the as-synthesized CNNs materials and interrogate the relationship of material-to-performance. It has been found that those synthesis conditions allow for the substantial increase of the electrocatalytic performance toward HER and OER in alkaline media in terms of the onset potential and charge transfer resistance and overpotential at the specific activity of 10 milliamps per square centimeter, thus ranking the present materials among the most efficient noble metal-free catalysts and making them possible candidates for integration in practical low-energy consumption alkaline electrolyzers.