Development of a highly active electrocatalyst via ultrafine Pd nanoparticles dispersed on pristine graphene

Supercritical Fluid-Assisted Fabrication of Pd Nanoparticles/Graphene Using a Choline Chloride-Oxalic Acid Deep Eutectic Solvent for Enhancing the Electrochemical Oxidation of Glycerol

A green method for synthesizing Pd nanoparticles/graphene composites from a choline chloride-oxalic acid deep eutectic solvent (DES) without a reducing agent or a surfactant is reported. Deep eutectic solvents are usually composed of halide salts and hydrogen-bond donors, and many are biocompatible and biodegradable. The merits of deep eutectic solvents include that they serve as reducing agents and dispersants, and Pd nanoparticles are tightly anchored to graphene. The size and dispersion of Pd particles are improved when supercritical carbon dioxide (scCO₂) is used because it has gaslike diffusivity and near-zero surface tension, which results in excellent wettability between the scCO₂ and the carbon surface. The prepared sc-Pd NPs/GR/SPCE shows excellent activity toward glycerol oxidation compared to composites not fabricated by scCO₂ processes. This study demonstrates the potential of using this scCO₂-assisted protocol combined with deep eutectic solvents to further construct nanoparticles/graphene composites.

Bimetallic alloy and semiconductor support synergistic interaction effects for superior electrochemical catalysis

The design and fabrication of economically viable anode catalysts for the methanol oxidation reaction (MOR) have been challenging issues in direct methanol fuel cells (DMFCs) over the decades. In this work, a composite electrochemical catalyst of Pd-coupled Ag and ZnO for the possible replacement of expensive Pt catalysts in DMFCs is successfully prepared. The as-made Pd@Ag/ZnO exhibits specific activity, which is 1.8-fold, 2.8-fold, and 4.6-fold higher than that of a Pd/ZnO catalyst, 20% Pd/C catalyst and Pd black, respectively. The improvement of the catalytic mechanism is likely due to the synergistic interaction between Pd@Ag and ZnO. The density functional theory (DFT) calculation results confirm that Ag doped into Pd weakens the adsorption of CO, dramatically improving the capability to resist CO poisoning.

Supercritical Fluid-Facilitated Exfoliation and Processing of 2D Materials

Since the first intercalation of layered silicates by using supercritical CO2 as a processing medium, considerable efforts have been dedicated to intercalating and exfoliating layered two-dimensional (2D) materials in various supercritical fluids (SCFs) to yield single- and few-layer nanosheets. Here, recent work in this area is highlighted. Motivating factors for enhancing exfoliation efficiency and product quality in SCFs, mechanisms for exfoliation and dispersion in SCFs, as well as general metrics applied to assess quality and processability of exfoliated 2D materials are critically discussed. Further, advances in formation and application of 2D material-based composites with assistance from SCFs are presented. These discussions address chemical transformations accompanying SCF processing such as doping, covalent surface modification, and heterostructure formation. Promising features, challenges, and routes to expanding SCF processing techniques are described.

Optimized Synthesis of Nitrogen and Phosphorus Dual-Doped Coal-Based Carbon Fiber Supported Pd Catalyst with Enhanced Activities for Formic Acid Electrooxidation

Development of a Pd-based catalyst with highly active and durable properties for formic acid oxidation reaction at the anode remains an important matter of interest in the research community. Herein, we have designed novel coal-based carbon fibers (Coal-CFs) with dicyandiamide (DCD) as nitrogen (N) source, triphenylphosphine (TPP) as phosphorus (P) source dual-doped to support Pd catalysts (Pd/NP-Coal-CFs(DCD/TPP)), which exhibit superior catalytic performance toward formic acid oxidation reaction. Mass activity of formic acid oxidation of Pd/NP-Coal-CFs(DCD/TPP) catalyst is 536.6 mA·mg^-1_Pd, which is 2.5 times higher than that of Pd/Coal-CFs catalyst. The higher specific surface areas, exclusive electron transport path, and the high synergistic interaction of N and P are the favorable phenomena for catalytic performance. The addition of coal not only increases the abundant defects sites but also makes the utilization of coal with high added value. This N and P dual-doped catalyst inspires an idea for promoting applications in practical fuel cells.

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.

Dendritic unzipped carbon nanofibers enable uniform loading of surfactant-free Pd nanoparticles for the electroanalysis of small biomolecules

Illustration of the mechanisms of SCNF and preparation of Pd/GNF composites and Pd/GNF sensors for the simultaneous determination of small biomolecules.

Cellulose as a Scaffold for Self-Assembly: From Basic Research to Real Applications

Cellulose has received a tremendous amount of attention both in academia and industry owing to its unique structural features, impressive physical-chemical properties, and wide applications. This natural polymer is originally used for packaging, paper, lightweight composites, and so forth and is now being developed for various new areas, such as antibacterial treatment, catalysis, water purification and separation, and biological and environmental analysis. In the current article, we summarize the recent developments in the self-assembly of cellulose with various species including metal ions and metal and metal oxide nanoparticles. Then we highlight several key application areas of cellulose-based composites by reviewing the recent representative literature in each area. A significant part of this review demonstrates some exciting innovations for a wide range of practical applications of cellulose-based composites. Some challenges are also discussed with a view toward future developments.

Mussel-Inspired Polydopamine-Functionalized Graphene as a Conductive Adhesion Promoter and Protective Layer for Silver Nanowire Transparent Electrodes

For the scalable fabrication of transparent electrodes and optoelectronic devices, excellent adhesion between the conductive films and the substrates is essential. In this work, a novel mussel-inspired polydopamine-functionalized graphene/silver nanowire hybrid nanomaterial for transparent electrodes was fabricated in a facile manner. Graphene oxide (GO) was functionalized and reduced by polydopamine while remaining stable in water without precipitation. It is shown that the polydopamine-functionalized GO (PFGO) film adhered to the substrate much more easily and more uniformly than the GO film. The PFGO film had a sheet resistance of ∼3.46 × 10(8) Ω/sq and a transparency of 78.2%, with excellent thermal and chemical stability; these characteristics are appropriate for antistatic coatings. Further reduced PFGO (RPFGO) as a conductive adhesion promoter and protective layer for the Ag nanowire (AgNW) significantly enhanced the adhesion force between AgNW networks and the substrate. The RPFGO-AgNW electrode was found to have a sheet resistance of 63 Ω/sq and a transparency of 70.5%. Moreover, the long-term stability of the RPFGO-AgNW electrode was greatly enhanced via the effective protection of the AgNW by RPFGO. These solution-processed antistatic coatings and electrodes have tremendous potential in the applications of optoelectronic devices as a result of their low production cost and facile processing.

Nitrogen-doped graphene/tungsten oxide microspheres as an electro-catalyst support for formic acid electro-oxidation

Tungsten trioxide (WO₃) spheres decorated with nitrogen-doped graphene (NRGO–WO₃) were synthesized by applying the spray-drying procedure and characterized for their ability to serve as an electro-catalyst support for formic acid electro-oxidation.