Mesoporous Gold and Palladium Nanoleaves from Liquid–Liquid Interface: Enhanced Catalytic Activity of the Palladium Analogue toward Hydrazine-Assisted Room-Temperature 4‑Nitrophenol Reduction

The importance of an interfacial reaction to obtain mesoporous leafy nanostructures of gold and palladium has been reported. A new synthetic strategy involving 1,4-dihydropyridine ester (DHPE) as a potential reducing agent performs exceptionally well for the desired morphologies of both the noble metals at room temperature. The DHPE in turn transforms into its oxidized aromatic form. The as-synthesized gold leaves exhibit high surface-enhanced Raman scattering activity with rhodamine 6G (R6G) due to their hyperbranched structure. It is worthwhile that as-synthesized porous architectures of palladium support the room-temperature hydrogenation of 4-nitrophenol (4-NP) by hydrazine hydrate (N₂H₄·H₂O), reported for the first time. Furthermore, MPL exhibits exceptionally good catalytic activity toward electrooxidation of formic acid. Therefore, an aromaticity driven synthetic technique achieves a rationale to design leafy nanostructures of noble metals from the liquid–liquid interface for multifaceted applications

Suitable Morphology Makes CoSn(OH)₆ Nanostructure a Superior Electrochemical Pseudocapacitor

Morphology of a material with different facet, edge, kink, etc., generally influences the rate of a catalytic reaction., Herein, we account for the importance of altered morphology of a nanomaterial for a supercapacitor device and employed CoSn­(OH)₆ as an electrode material. Suitable fabrication of a stable aqueous asymmetric supercapacitor (AAS) using metal hydroxide as positive electrode can be beneficial if the high energy density is derived without sacrificing the power density. Here we have synthesized an uncommon hierarchical mesoporous nanostructured (HNS) CoSn­(OH)₆ to fabricate a pseudocapacitor. In this endeavor, NH₃ is found to be a well-suited hydrolyzing agent for the synthesis. Serendipitously, HNS was transformed into favored cubic nanostructure (CNS) in NaOH solution. In solution, NaOH acts as a structure directing as well as an etching agent. Both the samples (HNS & CNS) were used as pseudocapacitor electrodes in KOH electrolyte independently, which is reported for the first time. The HNS exhibits very high specific capacitance value (2545 F/g at 2.5 A/g specific current) with better cyclic durability over CNS sample (851 F/g at 2.5 A/g specific current). To examine the real cell application, we used HNS sample as the positive electrode material with the activated carbon (AC) as the negative electrode material for the development of an aqueous asymmetric supercapacitor (AAS). The as-fabricated AAS exhibited very high specific capacitance value of 713 F/g at a specific current of 1.5 A/g and retained 92% specific capacitance value even after 10 000 charge–discharge cycles. A maximum energy density of 63.5 Wh kg^–1 and a maximum power density of 5277 W kg^–1 were ascertained from the as-fabricated AAS, HNS CoSn­(OH)₆//AC

Advance Aqueous Asymmetric Supercapacitor Based on Large 2D NiCo₂O₄ Nanostructures and the rGO@Fe₃O₄ Composite

NiCo₂O₄ nanostructure is a widely studied pseudocapacitor material because of its high specific capacitance value. Most of the time, the thickness of the nanostructure inhibits the electrode material from whole-body participation and causes sluggish charge transportation. These phenomena directly interfere with the electrochemical performance of the electrode, such as specific capacitance value, stability, energy density, and so forth. Here, two different thin two-dimensional morphologies (nanosheet and nanoplate) of the NiCo₂O₄ nanocomposite with a large lateral size are reported using ammonia as a hydrolyzing agent. The large size and flat surface of the as-synthesized materials offer enormous active sites during the electrochemical reaction, and the thin wall makes the ion penetration and transportation very effective and facile. Therefore, the NiCo₂O₄ nanosheet and nanoplate structures exhibited high specific capacitance values of 1540 and 1333 F/g, respectively, with excellent rate and good cycling stability. Here also, two different advance aqueous asymmetric supercapacitors have been reported utilizing two NiCo₂O₄ nanostructure materials as positive electrodes and the rGO@Fe₃O₄ composite as a negative electrode, which exhibited excellent rate and high specific energy without sacrificing the specific power. We also studied the electrochemical activity of the rGO@Fe₃O₄ composite at different compositions

Superb Dye Adsorption and Dye-Sensitized Change in Cu₂O–Ag Crystal Faces in the Dark

Hybrid Cu₂O–Ag is attractive because of its many applications in the fields of photocatalysis, surface-enhanced Raman scattering (SERS), and optical features. In this article, we have presented a newer application of Cu₂O–Ag. Cu₂O–Ag has been found to exhibit excellent anionic dye adsorption properties together with organic transformation for effective water remediation. Cu₂O–Ag was prepared through a facile but controlled galvanic reaction between cuprous oxide (Cu₂O) and silver nitrate (AgNO₃), rendering stability and porosity. The experimental results of adsorption showed that Cu₂O–Ag bears an exceptionally high adsorption capacity toward methyl orange (501.23 mg g^–1), which is higher than most reported results. The adsorption of MO on Cu₂O–Ag happens because of the definite chemical interaction between Cu­(I) and the SO₃^– functionality of MO. A kinetic study revealed that the MO adsorption on Cu₂O–Ag primarily followed the pseudo-second-order kinetic model. The kinetic model followed the Langmuir adsorption isotherm. A very significant feature that emerged during MO adsorption by Cu₂O–Ag is the transformation of the 3-D morphology of Cu₂O–Ag into 2-D nanosheets under ambient and dark conditions. This morphology change corroborates that the adsorption occurred through chemical interaction, i.e., the chemisorption process. This feature, a morphology change in the dark, presumably happened through the participation of the highly interactive exposed high-index facet of spherical Cu₂O–Ag nanoparticles. This unique recrystallization of Cu₂O–Ag due to the chemisorption of MO is reported for the first time. Cu₂O–Ag was also found to have a high adsorption capacity (976.30 mg g^–1) even for Congo red (an anionic azo dye), which is also higher than the reported adsorption capacities of various materials. In another water remediation aspect, Cu₂O–Ag has also been applied to the transformation of organic toxic pollutant, 4-nitrophenol (4-NP), into its nontoxic and medicinally important amino derivative through catalytic reduction. The catalysis of 4-NP reduction by Cu₂O–Ag in the presence of sodium borohydride (NaBH₄) exhibited a high rate constant value (<i>k</i> = 0.38 min^–1). Thus, two novel properties, adsorption and catalytic reduction on organic pollutants, of Cu₂O–Ag have been ascertained for water remediation

A Gel-Based Approach To Design Hierarchical CuS Decorated Reduced Graphene Oxide Nanosheets for Enhanced Peroxidase-like Activity Leading to Colorimetric Detection of Dopamine

Supramolecular colorless copper­(I)–thiourea hydrogel (Cu-TU gel) has been made a mechanically strong functional hybrid material in the graphene oxide (GO) framework. Mild heat treatment (85 °C) of the hybrid material fetches black product containing hierarchical copper sulfide decorated reduced graphene oxide nanosheets (CuS-rGO) through an obvious in-house redox transformation reaction between Cu­(I) and GO without any additive. The as-synthesized CuS-rGO nanocomposite exhibits impressive peroxidase-like activity where oxidation of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue product is observed in solution phase with H₂O₂. Systematic control experiments suggest that strong covalent interaction between CuS and rGO synergistically enhances the catalytic activity of CuS-rGO in comparison to its individual counterparts. Furthermore, an important biomolecule, dopamine, has been found to selectively inhibit, in succession, the oxidizing action of H₂O₂ for TMB oxidation reaction. Thus, dopamine-dependent successive inhibition reaction creates a one-pot reporter platform to sense dopamine down to the 0.48 μM concentration level by UV–vis spectrophotometry

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities

Enhanced Catalytic Activity of Ag/Rh Bimetallic Nanomaterial: Evidence of an Ensemble Effect

A synergistic electronic interaction between the constituent metals in a bi/multimetallic system fine-tunes its catalytic property to be enhanced compared to those of the individual metal analogues. Such a proposition toward enhancing the catalytic activity of precious Rh metal by otherwise inactive Ag is done here in a cost-effective dilution method. The generated heterostructure of Ag/Rh independently drives two industrially important model reactions: 4-nitrophenol (4-NP) reduction and hydrogen peroxide (HP) decomposition. An impressive catalytic activity parameter for 4-NP reduction (256.67 s^–1 g^–1) with hydrazine and HP decomposition (39 × 10^–3 min^–1 g^–1) at room temperature ensures the importance of the “ensemble effect”. Spectroscopic evidence also certifies the dilution range to justify improved catalytic activities relating to the ensemble effect. Moreover, our theoretical study rationalizes the experimental observation where the enhanced charge transfer or occurrence of charge separation within the bimetallic system is responsible for the chemical reactivity of these bimetallic systems. Finally, the thermodynamics of formation of bimetallic nanoparticles finds support from the experimentally observed results and electronic interactions between Ag and Rh for improved catalytic activity that complies with spectral information

Redox-Driven Route for Widening Voltage Window in Asymmetric Supercapacitor

Although aqueous asymmetric supercapacitors are promising technologies because of their high-energy density and enhanced safety, their voltage window is still limited by the narrow stability window of water. Redox reactions at suitable electrodes near the water splitting potential can increase the working potential. Here, we demonstrate a kinetic approach for expanding the voltage window of aqueous asymmetric supercapacitors using <i>in situ</i> activated Mn₃O₄ and VO₂ electrodes. The underlying mechanism indicates a specific potential of ∼1 V <i>vs</i> Ag/AgCl for the oxidation of Mn⁴⁺-to-Mn⁷⁺ at the positive electrode and ∼ –0.8 V <i>vs</i> Ag/AgCl for the reduction of V³⁺-to-V²⁺ at the negative electrode, which limits oxygen and hydrogen evolution reactions, respectively. The as-fabricated aqueous asymmetric supercapacitor exhibited a working voltage of 2.2 V with a high-energy density of 42.7 Wh/kg and a power density of ∼1.1 kW/kg. This mechanism improves the voltage window and energy and power densities