Monodispersed PtPdNi Trimetallic Nanoparticles-Integrated Reduced Graphene Oxide Hybrid Platform for Direct Alcohol Fuel Cell

The direct alcohol fuel cell has recently emerged as an important energy conversion device. In the present article, superior alcohol (ethanol, ethylene glycol, and glycerol) electrooxidation performance using trimetallic platinum–palladium–nickel (PtPdNi) alloy nanoparticles of diameters from 2–4 nm supported on a reduced graphene oxide (rGO) electrocatalyst is demonstrated. A simple and single-step solvothermal technique is adopted to fabricate the alloy/rGO hybrid electrocatalysts by simultaneous reduction of metal ions and graphene oxide. The detailed electrochemical investigation revealed that the performance of the trimetallic/rGO hybrid toward electrooxidation of different alcohols is higher than that of bimetallic alloy/rGO hybrids and the state-of-the-art Pt/C catalyst. The incorporation of Ni into the PtPd alloy is found to change the surface of the electronic structure PtPd alloy leading to higher electrochemical surface areas and improved kinetics. In addition, the hydrophilic nature of Ni not only facilitates alcohol electrooxidation but also electrooxidation of residual carbon impurities formed on the catalyst surface, thus reducing catalyst poisoning, demonstrating its role in the development of anode catalysts for the alcohol fuel cells

Stimulating the Visible-Light Catalytic Activity of Bi₂MoO₆ Nanoplates by Embedding Carbon Dots for the Efficient Oxidation, Cascade Reaction, and Photoelectrochemical O₂ Evolution

The present work demonstrates the facile synthesis and applications of carbon dots (CD)-embedded Bi₂MoO₆ nanoplates photocatalyst in the oxidative coupling of amines and oxidation of toluene and ethylbenzene. The synthetic protocol is applied to afford good yields of benzimidazole/benzothiazole via the cascade reaction between benzylamine and <i>o</i>-aminothiophenol/<i>o</i>-phenylenediamine. These photocatalytic reactions are performed under very mild conditions using the household light-emitting diode bulb as a light source and O₂ (1 atm). The CD-embedded, 2.4 wt % CD/Bi₂MoO₆ exhibits the best photocatalytic activity. Impressive visible-light absorbance coefficient, quantum confinement, photoluminescence up-conversion, and stable photoelectrochemical properties of CD are contemplating the excellent photocatalytic activity of CD/Bi₂MoO₆ than the pristine Bi₂MoO₆. Generation and influence of various reactive species in these catalytic reactions are investigated by radical scavenging, fluorescence spectroscopy, and cyclic voltammetric (CV) analysis. Both qualitative and quantitative estimation of the in situ generated H₂O₂ in the photocatalytic oxidative coupling of amines was ascertained using CV and redox titration, respectively. Further, the influence of substitution in the benzylamine and involvement of the carbocations are confirmed using Hammett plot. The developed catalysts are also used as photoanode for O₂ evolution from water oxidation in a photoelectrochemical (PEC) cell. Several PEC techniques evaluate the PEC activity of the photoanodes. The reactivity order for various substituted benzylamine and the involvement of reactive oxygen species (O₂·^–) in the oxidation reaction was obtained and confirmed from the band edge potentials of the best photocatalyst using Mott–Schottky analysis. Efficient catalytic recyclability and photostability are additional important features of the present investigation. This study provides a feasible alternative to the development of non-noble metal (CD)-based nanocomposite photocatalysts that can manifest important photocatalytic and photoelectrocatalytic applications in chemical synthesis and solar fuel production

Shape-Dependent Photocatalytic Activity of Hydrothermally Synthesized Cadmium Sulfide Nanostructures

The effective surface area of the nanostructured materials is known to play a prime role in catalysis. Here we demonstrate that the shape of the nanostructured materials plays an equally important role in their catalytic activity. Hierarchical CdS microstructures with different morphologies such as microspheres assembled of nanoplates, nanorods, nanoparticles, and nanobelts are synthesized using a simple hydrothermal method by tuning the volume ratio of solvents, i.e., water or ethylenediamine (en). With an optimum solvent ratio of 3:1 water:en, the roles of other synthesis parameters such as precursor’s ratio, temperature, and precursor combinations are also explored and reported here. Four selected CdS microstructures are used as photocatalysts for the degradation of methylene blue and photoelectrochemical water splitting for hydrogen generation. In spite of smaller effective surface area of CdS nanoneedles/nanorods than that of CdS nanowires network, the former exhibits higher catalytic activity under visible light irradiation which is ascribed to the reduced charge recombination as confirmed from the photoluminescence study

An Efficient, Visible Light Driven, Selective Oxidation of Aromatic Alcohols and Amines with O₂ Using BiVO₄/g‑C₃N₄ Nanocomposite: A Systematic and Comprehensive Study toward the Development of a Photocatalytic Process

In this study, BiVO₄ was prepared by a hydrothermal synthesis route in the presence of sodium dodecyl sulfate using aqueous NH₃ as precipitant. g-C₃N₄ was prepared by a combustion method using melamine. In order to develop highly efficient photocatalyst, a heterojunction catalyst based on g-C₃N₄ and BiVO₄ was prepared. Different amounts of BiVO₄ and g-C₃N₄ were mixed and annealed to obtain heterojunction photocatalysts. FeVO₄ and LaVO₄ were also prepared for the comparative catalytic investigation. Catalysts were characterized by a series of complementary combinations of powder X-ray diffraction, thermogravimetric analysis, elemental analysis, N₂ adsorption–desorption, scanning electron microscopy, transmission electron microscopy, temperature-programmed desorption of NH₃ and CO₂, diffuse reflectance ultraviolet visible spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, and photoelectrochemical studies. Catalysts were investigated in the visible light driven oxidation of benzyl alcohol, benzyl amine, and aniline with O₂. In order to propose the electrons, holes, and radicals mediated reaction pathways, reactions were performed in the presence of an electron/hole/radical scavenger. Further, in order to confirm various products formed during the photocatalytic oxidation of benzyl alcohol, benzyl amine, and aniline, several model reactions were carried out. Based on the results obtained, the reaction mechanism and structure–activity relationship were established

Hybrid Dot–Disk Au-CuInS₂ Nanostructures as Active Photocathode for Efficient Evolution of Hydrogen from Water

The synthesis of hybrid 0D-2D dot–disk Au-CIS heterostructures is enabled through nucleating wurtzite ternary I–III–VI CuInS₂ (CIS) semiconductor nanostructures on cubic Au particles via thiol-activated interface reactions. Chemistry of formation of these unique hybrid metal–semiconductor nanostructures is established by correlating successive X-ray diffraction patterns and microscopic images. Furthermore, these nanostructures are explored as an efficient photocathode material for photoelectrochemical (PEC) production of hydrogen from water. Although CIS nanostructures are extensively used as PEC active materials for solar-to-hydrogen conversion, the coupled structures with Au for their exciton–plasmon coupling is observed in producing a higher photocurrent with efficient evolution of hydrogen. In the comparison of materials properties, it is observed that the cathodic photocurrent, onset potential, and the half-cell solar-to-hydrogen efficiency (HC-STH) are recorded to be superior to all CIS-based photocathodes reported up to the current time. These results suggest that designing proper heterostructured functional materials can enhance the hydrogen production in the PEC cell and would be helpful for the ongoing technological needs for a greener way of generating and storing hydrogen energy

Graphene Oxide-Impregnated PVA–STA Composite Polymer Electrolyte Membrane Separator for Power Generation in a Single-Chambered Microbial Fuel Cell

The present study deals with the development and application of a proton-exchange polymer membrane separator consisting of graphene oxide (GO), poly­(vinyl alcohol) (PVA), and silicotungstic acid (STA) in a single-chambered microbial fuel cell (sMFC). GO and the prepared membranes were characterized by FT-IR spectroscopy, XRD, SEM, TEM, and AC impedance analysis. Higher power was achieved with a 0.5 wt % GO-incorporated PVA–STA–GO membrane compared to a Nafion 117 membrane. The effects of oxygen crossover and membrane-cathode-assembly (MCA) area were evaluated in terms of current density and Coulombic efficiency. The electrochemical behavior of the membrane in an MFC was improved by adding different amounts of GO to the membrane to reduce biofouling and also to enhance proton conductivity. A maximum power density of 1.9 W/m³ was obtained when acetate wastewater was treated in an sMFC equipped with a PVA–STA–GO-based MCA. Therefore, PVA–STA–GO could be utilized as an efficient and inexpensive separator for sMFCs

Bifunctional Manganese Ferrite/Polyaniline Hybrid as Electrode Material for Enhanced Energy Recovery in Microbial Fuel Cell

Microbial fuel cells (MFCs) are emerging as a sustainable technology for waste to energy conversion where electrode materials play a vital role on its performance. Platinum (Pt) is the most common material used as cathode catalyst in the MFCs. However, the high cost and low earth abundance associated with Pt prompt the researcher to explore inexpensive catalysts. The present study demonstrates a noble metal-free MFC using a manganese ferrite (MnFe₂O₄)/polyaniline (PANI)-based electrode material. The MnFe₂O₄ nanoparticles (NPs) and MnFe₂O₄ NPs/PANI hybrid composite not only exhibited superior oxygen reduction reaction (ORR) activity for the air cathode but also enhanced anode half-cell potential upon modifying carbon cloth anode in the single-chambered MFC. This is attributed to the improved extracellular electron transfer of exoelectrogens due to Fe³⁺ in MnFe₂O₄ and its capacitive nature. The present work demonstrates for the first time the dual property of MnFe₂O₄ NPs/PANI, i.e., as cathode catalyst and an anode modifier, thereby promising cost-effective MFCs for practical applications

Double-Metal-Ion-Exchanged Mesoporous Zeolite as an Efficient Electrocatalyst for Alkaline Water Oxidation: Synergy between Ni–Cu and Their Contents in Catalytic Activity Enhancement

The kinetics of total water splitting is mostly hampered by the sluggish oxygen evolution reaction (OER) at the anode of the electrolyzer. Herein, we focus on the design of a cost-effective porous OER catalyst for efficient water to fuel conversion. A simple metal-ion-exchange protocol is adapted to implant electroactive metal centers in the mesoporous architecture of Zeolite Socony Mobil-5 (ZSM-5). OER-active Ni is incorporated as catalytic sites in the mesoporous ZSM-5. Further, simultaneous incorporation of both Ni²⁺ and Cu²⁺ into the mesoporous ZSM-5 (Meso-Z) matrix significantly boost the OER catalytic activity. The optimization of Ni and Cu contents (1.04 wt % Ni and 0.44 wt % Cu) in the catalyst is found to be essential to achieve high catalytic activity. The Cu content influences the onset potential, and the Ni content determines the catalytic current during OER. Among developed catalysts, Ni₂Cu₁-Meso-Z offers the best performance even better than the state-of-art OER catalyst IrO₂. Ni₂Cu₁-Meso-Z delivers a current density of 10 mA/cm² at an overpotential of 407 mV and exhibits a low Tafel slope of 55 mV/dec, a high electrochemical active surface area of 6.26, and a roughness factor of 89.42. Moreover, Ni₂Cu₁-Meso-Z retains 92% of its initial current density after 1000 potential cycles of a test run. The best performing Ni₂Cu₁-Meso-Z offers a faradic efficiency of 92%, whereas the state-of-the-art IrO₂ efficiency was decreased by 22% under the similar experimental condition. Further, Ni₂Cu₁-Meso-Z-modified anode exhibits better performance in its single cell than IrO₂, in which Pt is used as cathode. The excellent OER catalytic activity of double-metal-ion-exchanged Meso-Z is attributed to the large surface area of mesoporous ZSM-5, hydrophilicity, fast diffusion of water molecules through the favorable interaction with Si–OH groups, and optimum binding and dissociation of different oxygeneous OER intermediates on the catalyst surface. Excellent current density and sustainable performance suggest that the double-metal-ion-exchanged mesoporous zeolite can serve as a potential candidate to improve the overall water splitting in the electrolyzer

Chemically Filled and Au-Coupled BiSbS₃ Nanorod Heterostructures for Photoelectrocatalysis

The synergistic effects of foreign ion incorporation into a semiconductor host crystal lattice can produce new functional properties. This concept has been adopted in the design of various energy materials for light harvesting, charge transport, and energy storage applications. Going beyond the traditionally used group II–VI and III–V semiconductor nanostructures, herein, 1D materials involving Bi­(III) and Sb­(III) sulfides are reported. Upon Sb dilution into the Bi₂S₃ lattice, exciting new material properties, including induction of localized surface plasmon resonance (LSPR) and a drastic change to the 1D crystal growth pattern, were observed. The presence of the Sb­(III) precursor along with Bi­(III) led to nanotubes with controlled length as the ultimate product, and their transformation to nanorods via chemical filling emerged as a new fundamental mechanism of crystal growth. Due to its slow thermal decomposition rate, the Sb­(III) precursor dominantly filled these tubes, resulting in graded alloy Bi_1.09Sb_0.91S₃ (BAS) nanorods. Further, by coupling with Au via seeded nucleation, Au–Bi_1.09Sb_0.91S₃ (Au-BAS) 1D heteronanostructures were designed, in which Au remained at the center of the BAS nanorods. On the basis of these advantages, these nanostructures were employed for photoelectrocatalytic (PEC) water splitting, and significant enhancement was observed in the Au-coupled rods

A Metal-Free Covalent Organic Polymer for Electrocatalytic Hydrogen Evolution

Metal-free catalysis for electrocatalytic hydrogen evolution from water is very demanding for the production of sustainable and clean fuel. Herein, we report the synthesis of a porphyrin-based metal-free covalent organic polymer (TpPAM) through a simple condensation between triformyl phloroglucinol (Tp) and 5,10,15,20-tetra­(4-aminophenyl)-21<i>H</i>,23<i>H</i>-porphyrin (PAM). The as-prepared porous TpPAM exhibited superior activity for the hydrogen evolution reaction (HER) current density of 10 mA cm^–2 at a low overpotential of 250 mV and a small Tafel slope of 106 mV decade^–1, which are better than those of related metal-free electrocatalysts. The high HER activity of TpPAM was investigated in-depth via theoretical density functional theory (DFT) calculations. The theoretical findings were correlated with the experimental results, and these were in good agreement for high HER catalytic efficiency of the porous TpPAM polymer. The Faradaic efficiency of the TpPAM-based electrode was found to be 98%, which is very close to the ideal value of 100%, reflecting its potential for practical implementation. Moreover, the as-synthesized catalyst showed good stability by retaining 91% of the initial current density after 1000 cycles