Facile synthesis of hierarchical dendritic PtPd nanogarlands supported on reduced graphene oxide with enhanced electrocatalytic properties

Electrocatalytic ethanol oxidation reaction: recent progress, challenges, and future prospects

Direct ethanol fuel cells (DEFCs) have been widely considered as a feasible power conversion technology for portable and mobile applications. The economic feasibility of DEFCs relies on two conditions: a notable reduction in the expensive nature of precious metal electrocatalysts and a simultaneous remarkable improvement in the anode's long-term performance. Despite the considerable progress achieved in recent decades in Pt nanoengineering to reduce its loading in catalyst ink with enhanced mass activity, attempts to tackle these problems have yet to be successful. During the ethanol oxidation reaction (EOR) at the anode surface, Pt electrocatalysts lose their electrocatalytic activity rapidly due to poisoning by surface-adsorbed reaction intermediates like CO. This phenomenon leads to a significant loss in electrocatalytic performance within a relatively short time. This review provides an overview of the mechanistic approaches during the EOR of noble metal-based anode materials. Additionally, we emphasized the significance of many essential factors that govern the EOR activity of the electrode surface. Furthermore, we provided a comprehensive examination of the challenges and potential advancements in electrocatalytic EOR.

Carbon-Supported Noble-Metal Nanoparticles for Catalytic Applications—A Review

Noble-metal nanoparticles (NMNPs), with their outstanding properties, have been arousing the interest of scientists for centuries. Although our knowledge of them is much more significant today, and we can obtain NMNPs in various sizes, shapes, and compositions, our interest in them has not waned. When talking about noble metals, gold, silver, and platinum come to mind first. Still, we cannot forget about elements belonging to the so-called platinum group, such as ruthenium, rhodium, palladium, osmium, and iridium, whose physical and chemical properties are very similar to those of platinum. It makes them highly demanded and widely used in various applications. This review presents current knowledge on the preparation of all noble metals in the form of nanoparticles and their assembling with carbon supports. We focused on the catalytic applications of these materials in the fuel-cell field. Furthermore, the influence of supporting materials on the electrocatalytic activity, stability, and selectivity of noble-metal-based catalysts is discussed.

Modification of Palladium Nanocrystals with Single Atom Platinum via an Electrochemical Self-Catalysis Strategy for Efficient Formic Acid Electrooxidation

Single atom alloys (SAA) have recently drawn increased attention due to their unique structure, high atomic utilization, and fascinating catalytic performance. However, their controllable synthesis still presents a challenge. This study proposes an electrochemical self-catalysis (ESC) strategy to synthesize Pd@Pt/C SAA catalysts, that is, depositing Pt atoms on Pd nanocrystals through in situ decomposition of sodium formate. The relationship between composition and structure of Pd@Pt/C is distinguished through a combination of electrochemical analysis, sphere-corrected scanning transmission electron microscopy, and X-ray adsorption spectra. That relationship evolved from SAA to a sea-island structure and even a core-shell structure with composition-controllable atomic ratios, highlighting the great diversity and convenience of this method in nanostructure construction. The Pd@Pt/C SAA catalyst showed excellent catalytic activity to formic acid oxidation with a peak current density of 5.2 A/mg^metal, which is about 18.6 times that of the commercial Pd/C. density functional theory calculations revealed that the enhanced activity was due to the "passivation" of Pd sites near the Pt single atoms, which attenuated the adsorption of CO. Based on electrochemical principles, this ESC strategy was also expanded to prepare a series of Pd-based SAA, including Pd-Au, Pd-Ir, and Pd-Bi.

Highly Enhanced Electrocatalytic Performances with Dendritic Bimetallic Palladium-Based Nanocrystals

The exploration of efficient nanocatalysts with high activity and stability towards water electrolysis and fuel cell applications is extremely important for the advancement of electrochemical reactions. However, it remains challenging. Controlling the morphology of bimetallic Pd–Pt nanostructures can be a great way to improve their electrocatalytic properties compared with previously developed catalysts. Herein, we synthesize bimetallic Pd–Pt nanodendrites, which consist of a dense matrix of unsaturated coordination atoms and high porosity. The concentration of cetyltrimethylammonium chloride was significant for the morphology and size of the Pd–Pt nanodendrites. Pd–Pt nanodendrites prepared by cetyltrimethylammonium chloride (200 mM) showed higher activities towards both the hydrogen evolution reaction and methanol oxidation reaction compared to their different Pd–Pt nanodendrite counterparts, commercial Pd, and Pt catalysts, which was attributed to numerous unsaturated surface atoms in well-developed single branches.

A comprehensive and critical review of the recent progress in electrocatalysts for the ethanol oxidation reaction

The human craving for energy is continually mounting and becoming progressively difficult to gratify. At present, the world's massive energy demands are chiefly encountered by nonrenewable and benign fossil fuels. However, the development of dynamic energy cradles for a gradually thriving world to lessen fossil fuel reserve depletion and environmental concerns is currently a persistent issue for society. The discovery of copious nonconventional resources to fill the gap between energy requirements and supply is the extreme obligation of the modern era. A new emergent, clean, and robust alternative to fossil fuels is the fuel cell. Among the different types of fuel cells, the direct ethanol fuel cell (DEFCs) is an outstanding option for light-duty vehicles and portable devices. A critical tactic for obtaining sustainable energy sources is the production of highly proficient, economical and green catalysts for energy storage and conversion devices. To date, a broad range of research is available for using Pt and modified Pt-based electrocatalysts to augment the C2H5OH oxidation process. Pt-based nanocubes, nanorods, nanoflowers, and the hybrids of Pt with metal oxides such as Fe2O3, TiO2, SnO2, MnO, Cu2O, and ZnO, and with conducting polymers are extensively utilized in both acidic and basic media. Moreover, Pd-based materials, transition metal-based materials, as well as transition metal-based materials are also points of interest for researchers nowadays. This review article delivers a broad vision of the current progress of the EOR process concerning noble metals and transition metals-based materials.

Effect of Pd on the Electrocatalytic Activity of Pt towards Oxidation of Ethanol in Alkaline Solutions

The understanding of electrocatalytic activity and poisoning resistance properties of Pt and Pd nanoparticles, recognized as the best electrocatalysts for the ethanol oxidation reaction, is an essential step for the commercialization of direct ethanol fuel cells (DEFCs). In this paper, mono and bimetallic Pt and Pd nanoparticles with different atomic ratios have been synthesized to study their electrocatalytic properties for an ethanol oxidation reaction in alkaline solutions. The different nanoparticles were physiochemically characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The electrochemical characterization was performed by cyclic voltammetry and chronoamperometry measurements. The electrochemical measurements indicate that Pt nanoparticles have much higher electrocatalytic activity for ethanol oxidation than Pd nanoparticles. The studies with bimetallic PtPd nanoparticles showed a significant impact of their composition on the ethanol oxidation. Thus, the highest electrocatalytic activity and poisoning resistance properties were obtained for Pt3Pd2 nanoparticles. Moreover, this study demonstrates that the poisoning of the catalyst surface through ethanol oxidation is related to the prevalence of the acetaldehyde–acetate route and the polymerization of acetaldehyde through aldol condensation in the alkaline media.

Convenient Synthesis of 3D Fluffy PtPd Nanocorals Loaded on 2D h-BN Supports as Highly Efficient and Stable Electrocatalysts for Alcohol Oxidation Reaction

Fuel cells hold great promise for clean and sustainable energy, whereas their widespread commercialization strongly depends on the development of highly efficient and stable electrocatalysts. Herein, three-dimensional fluffy PtPd nanocorals (NCs) loaded on two-dimensional (2D) hexagonal boron nitride (h-BN) supports were successfully achieved by a simple one-step strategy based on ultraviolet (UV) laser-excited photochemical reaction. As for alcohol oxidation reaction, the h-BN/PtPd NCs with unique nanoporous surface provide more enhanced electrocatalytic performances than many previous nanocatalysts, owing to abundant active sites and plentiful charge-transfer channels formed on high electrode-electrolyte contact area. Especially, the mass activity of h-BN/PtPd NCs is about 962.8 mA mg_PtPd ^-1 in methanol oxidation reaction in alkaline solution, which can be maintained at ∼274.9 mA mg_PtPd ^-1 (28.6% of the initial one) even after a 5 × 10⁴ s durability test. The present work not only offers an advanced electrocatalyst for long-term fuel cells but also provides a versatile route for construction of complex metallic nanocomposites on 2D supports, holding great potential for diverse energy-related applications.

Nanocatalysts for Electrocatalytic Oxidation of Ethanol

The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol-based fuel cell, highly active electrocatalysts are required to break the C-C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet-chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet-chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro-oxidation. As potential alternatives to noble metals, non-noble-metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Recent Progress in Graphene-Based Noble-Metal Nanocomposites for Electrocatalytic Applications

The fast industrialization process has led to global challenges in the energy crisis and environmental pollution, which might be solved with clean and renewable energy. Highly efficient electrochemical systems for clean-energy collection require high-performance electrocatalysts, including Au, Pt, Pd, Ru, etc. Graphene, a single-layer 2D carbon nanosheet, possesses many intriguing properties, and has attracted tremendous research attention. Specifically, graphene and graphene derivatives have been utilized as templates for the synthesis of various noble-metal nanocomposites, showing excellent performance in electrocatalytic-energy-conversion applications, such as the hydrogen evolution reaction and CO₂ reduction. Herein, the recent progress in graphene-based noble-metal nanocomposites is summarized, focusing on their synthetic methods and electrocatalytic applications. Furthermore, some personal insights on the challenges and possible future work in this research field are proposed.

Electrochemical sensor for facile detection of trace N-nitrosodiphenylamine based on poly(diallyldimethylammonium chloride)-stabilized graphene/platinum nanoparticles

A simple and sensitive electrochemical sensor for the detection of trace N-nitrosodiphenylamine was constructed based on PDDA-stabilized graphene/platinum nanoparticles.

Porous PtPd alloy nanotubes: towards high performance electrocatalysts with low Pt-loading

Porous PtPd alloy nanotubes with Pt contents down to 5 at% are powerful, Pt-lean electrocatalysts.

Engineering of Hollow PdPt Nanocrystals via Reduction Kinetic Control for Their Superior Electrocatalytic Performances

Synthesis of hollow metal nanocrystals (NCs) is greatly attractive for their high active surface areas, which gives rise to excellent catalytic activity. Taking PdPt alloy nanostructure as an example, we designed a synthetic tactic for the preparation of hollow metal nanostructures by delicate control over the difference in the reduction kinetic of metal precursors. At a high reduction rate difference, the Pd layer forms from H₂PdCl₄ and is subsequently etched, leading to the formation of a hollow space. A solid PdPt structure is achieved when the reduction rate of Pd and Pt precursor is comparable. Obviously, the hollow space and composition are tunable as well by adjusting the reduction rate difference. More importantly, the prepared hollow PdPt nanostructures exhibit a branched outer, porous wall, and rough hollow interior. The branched outer and rough hollow interior provide the higher density of unsaturated atoms, whereas the porous wall serves as channels connecting the inner, outer, and reactive agents. Moreover, the periodic self-consistent density function theory suggests that the d-band theory density of state of the PdPt nanoalloys is upshifted in comparison to the monometallic component, which will beneficial for improvement in their catalytic performances. Electrocatalytic tests reveal that the PdPt bimetallic NCs, especially for Pt₃₂Pd₆₈ nanostructures, show excellent catalytic activity and stability toward methanol oxidation reaction owing to their special structures as well as compositions.

Synthesis of Pt-Pd Bimetallic Porous Nanostructures as Electrocatalysts for the Methanol Oxidation Reaction

Pt-based bimetallic nanostructures have attracted a great deal of attention due to their unique nanostructures and excellent catalytic properties. In this study, we prepared porous Pt–Pd nanoparticles using an efficient, one-pot co-reduction process without using any templates or toxic reactants. In this process, Pt–Pd nanoparticles with different nanostructures were obtained by adjusting the temperature and ratio of the two precursors; and their catalytic properties for the oxidation of methanol were studied. The porous Pt–Pd nanostructures showed better electrocatalytic activity for the oxidation of methanol with a higher current density (0.67 mA/cm²), compared with the commercial Pt/C catalyst (0.31 mA/cm²). This method provides one easy pathway to economically prepare different alloy nanostructures for various applications.

Highly Ordered Hierarchical Pt and PtNi Nanowire Arrays for Enhanced Electrocatalytic Activity toward Methanol Oxidation

Highly ordered hierarchical Pt and PtNi nanowire arrays were prepared using CdS hierarchical nanowire arrays (HNWAs) as sacrificial templates and demonstrated high electrochemical active surface areas. For the resulting Pt HNWAs sample, the peak current for methanol oxidation at +0.74 V was almost 1 order of magnitude higher than that of Pt solid nanowire arrays prepared in a similar manner but without the use of CdS template, and the addition of a Ni cocatalyst effectively enhanced the tolerance against CO poisoning. The results demonstrated that highly ordered Pt and PtNi HNWAs may be exploited as promising anode catalysts in the application of direct methanol fuel cells.

Pd-on-Au Supra-nanostructures Decorated Graphene Oxide: An Advanced Electrocatalyst for Fuel Cell Application

We report a very easy and effective approach for synthesizing unique palladium-on-gold supra-nanostructure (Au@Pd-SprNS)-decorated graphene oxide (GO) nanosheets. The SprNSs comprising Au nanorods as core and a unique close-packed assembly of tiny anisotropic Pd nanoparticles (NPs) as shell were homogeneously distributed on the GO surface via electrostatic self-assembly. Compared with the traditional one-pot method for synthesis of metal NPs on GO sheets, the size and shape of core-shell Au@Pd SprNSs can be finely controlled and uniformly distributed on the GO carrier. Interestingly, this Au@Pd-SprNSs/GO nanocomposite displayed high electrocatalytic activities toward the oxidation of methanol, ethanol, and formic acid, which can be attributed to the abundance of intrinsic active sites including high density of atomic steps, ledges and kinks, Au-Pd heterojunctions and cooperative action of the two metals of the SprNSs. Additionally, uniform dispersion of the SprNSs over the GO nanosheets prevent agglomeration between the SprNSs, which is of great significance to enhance the long-term stability of catalyst. This work will introduce a highly efficient Pd-based nanoelectrocatalyst to be used in fuel cell application.

Enhanced electrochemical performance of cobalt oxide nanocube intercalated reduced graphene oxide for supercapacitor application

We investigated different molar concentrations of cobalt precursor intercalated reduced graphene oxide (rGO) as possible electrode materials for supercapacitors.

Fabrication of Pd/P nanoparticle networks with high activity for methanol oxidation

The as-prepared Pd/P nanoparticle networks efficiently exhibit electrocatalytic activity and stability for methanol oxidation.

Unconventional synthesis of Cu–Au dendritic nanowires with enhanced electrochemical activity

Cu–Au dendritic nanowires were obtained in high yield with enhanced electrochemical activity and potential application in glucose detection.

One-pot solvothermal synthesis of bimetallic yolk–shell Ni@PtNi nanocrystals supported on reduced graphene oxide and their excellent catalytic properties for p-nitrophenol reduction

Bimetallic yolk–shell Ni@PtNi NC-rGO were facilely prepared by a one-pot solvothermal method, which exhibited enhanced catalytic performance for p-nitrophenol reduction.

Synthesis of Cu3P nanocubes and their excellent electrocatalytic efficiency for the hydrogen evolution reaction in acidic solution

A novel Cu₃P product with excellent electrocatalytic activity toward HER was prepared through an efficient two-step strategy.

Engineering noble metal nanomaterials for environmental applications

Besides being valuable assets in our daily lives, noble metals (namely, gold, silver, and platinum) also feature many intriguing physical and chemical properties when their sizes are reduced to the nano- or even subnano-scale; such assets may significantly increase the values of the noble metals as functional materials for tackling important societal issues related to human health and the environment. Among which, designing/engineering of noble metal nanomaterials (NMNs) to address challenging issues in the environment has attracted recent interest in the community. In general, the use of NMNs for environmental applications is highly dependent on the physical and chemical properties of NMNs. Such properties can be readily controlled by tailoring the attributes of NMNs, including their size, shape, composition, and surface. In this feature article, we discuss recent progress in the rational design and engineering of NMNs with particular focus on their applications in the field of environmental sensing and catalysis. The development of functional NMNs for environmental applications is highly interdisciplinary, which requires concerted efforts from the communities of materials science, chemistry, engineering, and environmental science.

Facile synthesis of three-dimensional Pt-Pd alloyed multipods with enhanced electrocatalytic activity and stability for ethylene glycol oxidation

A facile one-pot solvothermal method was developed for the fabrication of well-defined three-dimensional highly branched Pt-Pd alloyed multipods, using ethylene glycol as a solvent and a reducing agent, along with N-methylimidazole as a structure-directing agent, without any seed, template, or surfactant. The as-prepared nanocrystals exhibited a relatively large electrochemically active surface area, improved electrocatalytic activity and superior stability for ethylene glycol oxidation in alkaline media, compared with commercial Pt black and Pd black, making them promising electrocatalysts in fuel cells.

One-step melamine-assisted synthesis of graphene-supported AuPt@Au nanocrystals for enhanced catalytic reduction of p-nitrophenol

Core–shell AuPt@Au NCs/rGO was facilely prepared by a one-step melamine-assisted method, which exhibited enhanced catalytic performance for p-nitrophenol reduction.

Facile large-scale synthesis of Au–Pt alloyed nanowire networks as efficient electrocatalysts for methanol oxidation and oxygen reduction reactions

A rapid one-pot wet-chemical method was developed for large-scale preparation of surface-clean AuPt alloyed nanowire networks with the assistance of N-methylimidazole as a structure-directing agent and a weak stabilizing agent.

Facile synthesis of porous bimetallic alloyed PdAg nanoflowers supported on reduced graphene oxide for simultaneous detection of ascorbic acid, dopamine, and uric acid

A simple, in situ reduction method was developed for synthesis of PdAg NFs/rGO nanocomposite, which displayed improved electrocatalytic performances for simultaneous detection of AA, DA, and UA.

Ethanol electro-oxidation on nanoworm-shaped Pd particles supported by nanographitic layers fabricated by electrophoretic deposition

Different morphologies of nanographitic flake coatings used as catalyst supports for nanoworm-shaped palladium (Pd) were fabricated via the electrophoretic deposition (EPD) of dispersed nanographitic flakes in isopropyl alcohol.

Facile synthesis of PdPt@Pt nanorings supported on reduced graphene oxide with enhanced electrocatalytic properties

In this work, a facile one-pot wet-chemical method was developed for the self-assembly of PdPt@Pt nanorings via in situ reduction of [PdCl4](2-) and [PtCl6](2-) at room temperature, which are simultaneously dispersed on reduced graphene oxide (rGO; denoted as PdPt@Pt/rGO). Hexadecylpyridinium chloride was demonstrated as a shape-directing agent and formic acid as a reducing agent during the reaction process. The as-prepared PdPt@Pt/rGO exhibited enhanced electrocatalytic activity and better stability for oxygen reduction reaction and ethanol oxidation reaction in acid media, compared with PtPd/rGO, Pt/rGO, Pd/rGO, Pt black, and Pt/C catalysts.