PVP-stabilized PdAu nanowire networks prepared in different solvents endowed with high electrocatalytic activities for the oxidation of ethylene glycol and isopropanol

Recent advances in nanoflowers: compositional and structural diversification for potential applications

In recent years, nanoscience and nanotechnology have emerged as promising fields in materials science. Spectroscopic techniques like scanning tunneling microscopy and atomic force microscopy have revolutionized the characterization, manipulation, and size control of nanomaterials, enabling the creation of diverse materials such as fullerenes, graphene, nanotubes, nanofibers, nanorods, nanowires, nanoparticles, nanocones, and nanosheets. Among these nanomaterials, there has been considerable interest in flower-shaped hierarchical 3D nanostructures, known as nanoflowers. These structures offer advantages like a higher surface-to-volume ratio compared to spherical nanoparticles, cost-effectiveness, and environmentally friendly preparation methods. Researchers have explored various applications of 3D nanostructures with unique morphologies derived from different nanoflowers. The nanoflowers are classified as organic, inorganic and hybrid, and the hybrids are a combination thereof, and most research studies of the nanoflowers have been focused on biomedical applications. Intriguingly, among them, inorganic nanoflowers have been studied extensively in various areas, such as electro, photo, and chemical catalysis, sensors, supercapacitors, and batteries, owing to their high catalytic efficiency and optical characteristics, which arise from their composition, crystal structure, and local surface plasmon resonance (LSPR). Despite the significant interest in inorganic nanoflowers, comprehensive reviews on this topic have been scarce until now. This is the first review focusing on inorganic nanoflowers for applications in electro, photo, and chemical catalysts, sensors, supercapacitors, and batteries. Since the early 2000s, more than 350 papers have been published on this topic with many ongoing research projects. This review categorizes the reported inorganic nanoflowers into four groups based on their composition and structure: metal, metal oxide, alloy, and other nanoflowers, including silica, metal-metal oxide, core-shell, doped, coated, nitride, sulfide, phosphide, selenide, and telluride nanoflowers. The review thoroughly discusses the preparation methods, conditions for morphology and size control, mechanisms, characteristics, and potential applications of these nanoflowers, aiming to facilitate future research and promote highly effective and synergistic applications in various fields.

Effect of Anode Material on Electrochemical Oxidation of Low Molecular Weight Alcohols-A Review

The growing climate crisis inspires one of the greatest challenges of the 21st century-developing novel power sources. One of the concepts that offer clean, non-fossil electricity production is fuel cells, especially when the role of fuel is played by simple organic molecules, such as low molecular weight alcohols. The greatest drawback of this technology is the lack of electrocatalytic materials that would enhance reaction kinetics and good stability under process conditions. Currently, electrodes for direct alcohol fuel cells (DAFCs) are mainly based on platinum, which not only provides a poor reaction rate but also readily deactivates because of poisoning by reaction products. Because of these disadvantages, many researchers have focused on developing novel electrode materials with electrocatalytic properties towards the oxidation of simple alcohols, such as methanol, ethanol, ethylene glycol or propanol. This paper presents the development of electrode materials and addresses future challenges that still need to be overcome before direct alcohol fuel cells can be commercialized.

Morris M, G. Lyons M, Gun’ko YK. One Dimensional AuAg Nanostructures as Anodic Catalysts in the Ethylene Glycol Oxidation

Direct alcohol fuel cells are highly promising as efficient power sources for various mobile and portable applications. However, for the further advancement of fuel cell technology it is necessary to develop new, cost-effective Pt-free electrocatalysts that could provide efficient alcohol oxidation and also resist cross-over poisoning. Here, we report new electrocatalytic materials for ethylene glycol oxidation, which are based on AuAg linear nanostructures. We demonstrate a low temperature tunable synthesis that enables the preparation of one dimensional (1D) AuAg nanostructures ranging from nanowires to a new nano-necklace-like structure. Using a two-step method, we showed that, by aging the initial reaction mixture at various temperatures, we produced ultrathin AuAg nanowires with a diameter of 9.2 ± 2 and 3.8 ± 1.6 nm, respectively. These nanowires exhibited a high catalytic performance for the electro-oxidation of ethylene glycol with remarkable poisoning resistance. These results highlight the benefit of 1D metal alloy-based nanocatalysts for fuel cell applications and are expected to make an important contribution to the further development of fuel cell technology.

Synthesis, growth mechanisms, and applications of palladium-based nanowires and other one-dimensional nanostructures

Palladium-based nanostructures have attracted the attention of researchers due to their useful catalytic properties and unique ability to form hydrides, which finds application in hydrogen storage and hydrogen detection. Palladium-based nanowires have some inherent advantages over other Pd nanomaterials, combining high surface-to-volume ratio with good thermal and electron transport properties, and exposing high-index crystal facets that can have enhanced catalytic activity. Over the past two decades, both synthesis methods and applications of 1D palladium nanostructures have advanced greatly. In this review, we start by discussing different types of 1D palladium nanostructures before moving on to the different synthesis approaches that can produce them. Next, we discuss factors including kinetic vs. thermodynamic control of growth, oxidative etching, and surface passivation that affect palladium nanowire synthesis. We also review efforts to gain insight into growth mechanisms using different characterization tools. We discuss the effects of concentration of capping agents, reducing agents, metal halides, pH, and sacrificial oxidation on the growth of Pd-based nanowires in solution, from shape control, to yield, to aspect ratio. Various applications of palladium and palladium alloy nanowires are then discussed, including electrocatalysis, hydrogen storage, and sensing of hydrogen and other chemicals. We conclude with a summary and some perspectives on future research directions for this category of nanomaterials.

Ultrathin Rh nanosheets as a highly efficient bifunctional electrocatalyst for isopropanol-assisted overall water splitting

In this work, we synthesized ultrathin Rh nanosheets (Rh-NSs) with atomic thickness, which revealed excellent activity for the hydrogen evolution reaction (HER) and super activity and extraordinary selectivity for the isopropanol oxidation reaction (IOR) in alkaline medium. When using Rh-NSs as a bifunctional electrocatalyst for water electrolysis in the presence of isopropanol, a voltage of only 0.4 V was required for H2 production, accompanied by the production of valuable acetone at the anode.

3D-2D heterostructure of PdRu/NiZn oxyphosphides with improved durability for electrocatalytic methanol and ethanol oxidation

The rational design and engineering of bimetallic Pd-based nanocatalysts with both high activity and durability are of paramount significance for the practical applications of fuel cells. Herein, a new class of well-defined 2D NiZn oxyphosphide nanosheets (NiZnP NSs) have been successfully engineered to support unique 3D PdRu nanoflowers (PdRu NFs) via a facile strategy. Such nanohybrids with abundant surface active areas and modified electronic structure exhibit a great enhancement in electrocatalytic activity for the methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR), whose mass/specific activities are 1739.5 mA mg-1/4.5 mA cm-2 and 4719.8 mA mg-1/12.3 mA cm-2, which are 8.3/9.0 and 8.3/9.5 times higher than those of commercial Pd/C catalysts, respectively. More interestingly, with the remarkable promotional effect of NiZnP NSs, such 3D-2D PdRu/NiZn oxyphosphide nanohybrids can even retain 72.4% and 70.1% of initial catalytic activity toward MOR and EOR for 1000 potential cycles with negligible morphological or compositional variations. The successful construction of this new class of electrocatalysts opens up a new way for designing 3D-2D nanohybrids with high performance for electrochemical reactions and beyond.

Phosphorus-doped cobalt-iron oxyhydroxide with untrafine nanosheet structure enable efficient oxygen evolution electrocatalysis

Although explosive progresses have been achieved in the field of water splitting, the design and development of stable and inexpensive electrocatalysts for oxygen evolution remain a formidable challenge. Herein, the cost-efficient two dimensional (2D) phosphorus-doped CoFe oxyhydroxide nanosheets (denoted as CoFeP NSs) are successfully engineered and showing exceptional oxygen evolution reaction (OER) activity and chemical stability in 1 M KOH solution. This unique 2D nanosheet structure facilitates the mass transfer and electron transport, resulting in the remarkable OER activity that delivers a current density of 10 mA cm^-2 at a low overpotential of 305 mV with an ultra-small Tafel slope 49.6 mV/dec. More significantly, the doped P also plays a vital role in modulating the surface active sites, leading to the substantial enhancement of electrocatalytic performances. Our study provides a facile one-pot method for the successful fabrication of 2D P-doped CoFe NSs which display superior electrocatalytic performance, shedding great promise for environment and energy-related fields.

PdAg Bimetallic Nanoalloy-Decorated Graphene: A Nanohybrid with Unprecedented Electrocatalytic, Catalytic, and Sensing Activities

Recent reports about the promising and tunable electrocatalytic activity and stability of nanoalloys have stimulated an intense research activity toward the design and synthesis of homogeneously alloyed novel bimetallic nanoelectrocatalysts. We herein present a simple one-pot facile wet-chemical approach for the deposition of high-quality bimetallic palladium-silver (PdAg) homogeneous nanoalloy crystals on reduced graphene (Gr) oxide sheets. Morphological, structural, and chemical characterizations of the so-crafted nanohybrids establish a homogeneous distribution of 1:1 PdAg nanoalloy crystals supported over reduced graphene oxide (PdAg-Gr). The PdAg-Gr nanohybrids exhibit outstanding electrocatalytic, catalytic, and electroanalytical performances. The PdAg-Gr samples were found to exhibit exceptional durability when subjected to repeated potential cycles or long-term electrolysis. In the CVs recorded for fuel cell reactions, viz. methanol oxidation reaction and oxygen reduction reaction, and for detoxification of environmental pollutants, viz. electroreduction of methyl iodide and chloroacetonitrile over PdAg-Gr with potential sweep rate of 25 mVs^-1, the peak potentials were observed to be just -0.221, -0.297, (vs Ag/AgCl, 3 M KCl) -1.508, and -1.189 V (vs Fc⁺/Fc), respectively. The potential of PdAg-Gr nanohybrid for simultaneous and sensitive electrochemical sensing and estimation of hydroxybenzene isomers with very low detection limits (0.05 μM for hydroquinone, 0.06 μM for catechol, 6.7 nM for 4-aminophenol, and 13.7 nM for 2-aminophenol) is demonstrated. Additionally, PdAg-Gr was observed to offer excellent solution-phase catalytic performance in bringing about the reduction of notorious environmental pollutant 4-nitrophenol to pharmaceutically important 4-aminophenol with an apparent rate constant ( k_app) of 3.106 × 10^-2 s^-1 and a normalized rate constant ( k_nor) of 6.21 × 10² s^-1 g^-1. The presented synthetic scheme besides being high yielding, low cost, and easy to carry out results in the production of PdAg-Gr nanohybrids with stability and activity significantly better than most of the nanomaterials purposefully designed and testified so far by various groups.

Hierarchical branched platinum-copper tripods as highly active and stable catalysts

Designing and manipulating the structure of nanomaterials can efficiently tailor their catalytic properties, enabling the promotion of both their activity and stability. We herein report the shape-controlled synthesis of advanced Pt-Cu hierarchical tripod nanocrystals (HTNCs) by controlling the amount of KI and reaction time. The as-prepared nanocrystals (NCs) look like a typical tripod on the whole, consisting of similar branch structural units. In addition, the structure of the HTNCs could also be obtained with a narrow Pt/Cu feeding ratio. Owing to the unique HTNC structure and exposed high-index facets, as well as probable electronic effects between Cu and Pt, the as-obtained Pt-Cu HTNCs can exhibit greatly enhanced electrocatalytic activity toward ethylene glycol oxidation reaction (EGOR) and glycerol oxidation (GOR), which are 5.1 and 6.5 times higher in mass activity, as well as 5.6 and 7.3 times higher in specific activity relative to commercial Pt/C, showing that they are a class of promising electrocatalyst for fuel cells. This work presents huge opportunities for optimizing the electrocatalytic oxidation reaction by designing the structure of nanocatalysts.

Particle size effects of PtAg nanoparticles on the catalytic electrooxidation of liquid fuels

The electrocatalytic oxidation of ethylene glycol and glycerol in the presence of PtAg NPs catalyst showed a linear decrease with the increasing particle sizes, providing new clues and hypotheses on how quantum confinement phenomena affect the electrocatalytic performances.

Facile construction of fascinating trimetallic PdAuAg nanocages with exceptional ethylene glycol and glycerol oxidation activity

Highly open metallic nanocages represent a novel class of nanostructures for advanced catalytic applications in direct liquid fuels cells due to their specific capability of providing easy access to reactants in both internal and external active sites and also desirable electronic structures for the adsorption of molecules, which render superior catalytic performances. However, to date, the rational design of trimetallic nanocages with tunable compositions remains a challenge. Herein, we demonstrate a facile method combining seed mediated and galvanic replacement for the preparation of unique trimetallic Pd-Au-Ag nanocages catalysts with tunable compositions. A series of controlled experiments reveal that the reaction time plays a crucial role in affecting the morphology of the final product. Importantly, the newly-generated Pd-Au-Ag nanocages are high-performance electrocatalysts for the oxidation of both ethylene glycol and glycerol with mass activities of 7578.2 and 5676.1 mA mg^-1, respectively, which are far superior to that of commercial Pd/C. We firmly believe that the strategy and enhanced electrocatalysts developed in this study can be well applied to boost the commercial development of fuel cell technologies.