Epitaxial growth of zigzag PtAu alloy surface on Au nano-pentagrams with enhanced Pt utilization and electrocatalytic performance toward ethanol oxidation reaction

One-pot synthesis of Au-M@SiO2 (M = Rh, Pd, Ir, Pt) core-shell nanoparticles as highly efficient catalysts for the reduction of 4-nitrophenol

The conversion of p-nitrophenol (4-NP) to p-aminophenol (4-AP) is of great significance for pharmaceutical and material manufacturing. In this work, Au-M@SiO2 (M = Rh, Pd, Ir, Pt) nanoparticles (NPs) with core-shell structures, which are expected to be excellent catalysts for the transformation of 4-NP to 4-AP, were synthesized by a facile one-pot one-step method. The structure and composition of the NPs were characterized through transmission electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Au-M@SiO2 (M = Rh, Pd, Ir, Pt) core-shell NPs showed excellent catalytic activity in the reduction of 4-NP, which is superior to most catalysts reported in the previous literature. The enhanced catalytic activity of Au-M@SiO2 core-shell NPs is presumably related to the bimetallic synergistic effect. This study provides a simple strategy to synthesize core-shell bimetallic NPs for catalytic applications.

Self-Assembled Pt/MoCx/MWCNTs Nano Catalyst for Ethanol Electrooxidation of Fuel Cells

Direct ethanol fuel cells (DEFCs) have attracted more and more attention because of their unique advantages such as low cost and low toxicity. However, sluggish C-C bond cleavage during the ethanol electrooxidation reaction (EOR) in acidic media results in a lower energy yield and gravely hinders the commercialization of DEFCs. Therefore, it is very necessary to develop an anode catalyst with high performance, high stability and low cost to solve this problem. In this paper, Pt/MoC_x/MWCNTs nanocomposites with different mass ratios of PtMo were obtained through a molecular self-assembly technology. The structure and morphology of Pt/MoC_x/MWCNTs nanocomposites were characterized by several techniques such as XRD, FESEM, XPS, etc. The electrochemical performance and stability of Pt/WC_x/MWCNTs electrocatalysts toward EOR were investigated in acid electrolytes. The results show that PtMo exists in the form of alloy. The size of Pt/MoC_x nanoparticles is very uniform with an average size of ∼24 nm. The Pt/MoC_0.25/MWCNTs exhibits excellent electrocatalytic activities with an electrochemically active surface area of 37.1 m² g⁻¹, a peak current density of 610.4 mA mg_Pt⁻¹ and a steady-state current density of 39.8 mA mg_Pt⁻¹ after 7,200 s, suggesting that the Pt/MoC_0.25/MWCNTs is a very promising candidate for application in EOR of DEFCs.

Electrocatalysis of gold-based nanoparticles and nanoclusters

Gold (Au)-based nanomaterials, including nanoparticles (NPs) and nanoclusters (NCs), have shown great potential in many electrocatalytic reactions due to their excellent catalytic ability and selectivity. In recent years, Au-based nanostructured materials have been considered as one of the most promising non-platinum (Pt) electrocatalysts. The controlled synthesis of Au-based NPs and NCs and the delicate microstructure adjustment play a vital role in regulating their catalytic activity toward various reactions. This review focuses on the latest progress in the synthesis of efficient Au-based NP and NC electrocatalysts, highlighting the relationship between Au nanostructures and their catalytic activity. This review first discusses the parameters of Au-based nanomaterials that determine their electrocatalytic performance, including composition, particle size and architecture. Subsequently, the latest electrocatalytic applications of Au-based NPs and NCs in various reactions are provided. Finally, some challenges and opportunities are highlighted, which will guide the rational design of Au-based NPs and NCs as promising electrocatalysts.

Hollow Multiple Noble Metallic Nanoalloys by Mercury-Assisted Galvanic Replacement Reaction for Hydrogen Evolution

Hollow multimetallic noble nanoalloys with high surface area/volume ratio, abundant active sites, and relatively effective catalytic activity have attracted considerable research interest. Traditional noble nanoalloys fabricated by hydro-/solvothermal methods usually involve harsh synthetic conditions such as high temperatures and intricate processing. We proposed a simple and mild strategy to synthesize platinum- and palladium-decorated hollow gold-based nanoalloys by the galvanic replacement reaction (GRR) at room temperature using hollow gold nanoparticles as templates and mercury as an intermediate. The hollow gold nanoparticles were essential for increasing the number of surface-active sites of the obtained multimetallic nanoalloys, and the introduction of mercury can eliminate the influence of the electrochemical potential of Pt/Pd with Au in the GRRs, increase alloying degrees, and maintain the nanoalloys that exhibit the hollow nanostructures. The structural characterizations of the hollow nanoalloys were studied by means of high-angle annular dark-field scanning transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. On the basis of the electrochemical catalytic measurements, the platinum-exposed nanoalloys were found to have excellent electrocatalytic activities. Especially in the presence of palladium, owing to the synergistic effect, the quaternary AuHgPdPt hollow nanoalloy displayed a low overpotential of 38 mV at 10 mA cm^-2 with a small Tafel slope of 56.23 mV dec^-1 for the alkaline hydrogen evolution reaction. In addition, this approach not only expands the application range of the galvanic replacement reaction but also provides new ideas for the preparation of multialloys and even high-entropy alloys at room temperature.

Recent advances in formic acid electro-oxidation: from the fundamental mechanism to electrocatalysts

Direct formic acid fuel cells have attracted significant attention because of their low fuel crossover, high safety, and high theoretical power density among all the proton-exchange membrane fuel cells. Much effort has been devoted to the study of formic acid oxidation, including the reaction processes and electrocatalysts. However, as a model reaction, the anodic electro-oxidation process of formic acid is still not very clear, especially regarding the confirmation of the intermediates, which is not helpful for the design and synthesis of high-performance electrocatalysts for formic acid oxidation or conducive to understanding the reaction mechanisms of other small fuel molecules. Herein, we briefly review the recent advances in investigating the mechanism of formic acid electro-oxidation and the basic design concepts of formic acid oxidation electrocatalysts. Rather than an exhaustive overview of all aspects of this topic, this mini-review mainly outlines the progress of this field in recent years.

Trimetallic Ru@AuPt core-shell nanostructures: The effect of microstrain on CO adsorption and electrocatalytic activity of formic acid oxidation

It is desirable to unravel the correlation between the geometric and electronic structures and the activity and further prepare high-performance electrocatalysts. Here in this paper, trimetallic Ru@Au-Pt core-shell nanoparticles were prepared by sequential ethanol reduction method, and further subject to characterization of X-ray diffraction, high angle annular dark field transmission electron microscopy, X-ray photoelectron spectroscopy and electrochemical CO stripping. Further analysis based on Williamson-Hall method revealed that the Au/Pt atomic ratio and shell thickness result in apparent variation of micro-strain and CO binding energy of Ru@AuPt nanoparticles, where the CO oxidation peak potential showed an inverted volcano-shape dependence on the microstrain of the metal nanoparticles while the catalytic activity towards electrooxidation of formic acid is linearly dependent on the micro-strain. The best Ru@Au-Pt catalyst delivers a specific activity of 4.14 mA cm^-2, which is 52 times that of Pt/C, respectively. This study indicated that the microstrain and stacking fault of metal nanoparticles might be a good descriptor for the catalytic activity and may shed light the rational design, synthesis and surface engineering towards the high-performance electrocatalyst.

Controlled Overgrowth of Five-Fold Concave Nanoparticles into Plasmonic Nanostars and Their Single-Particle Scattering Properties

Growth of anisotropic nanostructures enables the manipulation of optical properties across the electromagnetic spectrum by fine morphological tuning of the nanoparticles. Among them, stellated metallic nanostructures present enhanced properties owing to their complex shape, and hence, the control over the final morphology becomes of great importance. Herein, a seed-mediated method for the high-yield production of gold_rich-copper concave branched nanostructures and their structural and optical characterization is reported. The synthesis protocol enabled excellent control and tunability of the final morphology, from concave pentagonal nanoparticles to five-fold branched nanoparticles, named "nanostars". The anisotropic shape was achieved via kinetic control over the synthesis conditions by selective passivation of facets using a capping agent and assisted by the presence of copper chloride ions, both having a crucial impact over the final structure. Optical extinction measurements of nanostars in solution indicated a broad spectral response, hiding the properties of the individual nanostars. Hence, single-particle scattering measurements of individual concave pentagonal nanoparticles and concave nanostars were performed to determine the origin of the multiple plasmon bands by correlation with their morphological features, following their growth evolution. Finite-difference time-domain calculations delivered insights into the geometry-dependent plasmonic properties of concave nanostars and their packed aggregates. Our results uncover the intrinsic scattering properties of individual nanostars and the origin of the broad spectral response, which is mostly due to z-direction packed aggregates.

Monodispersed bimetallic platinum-copper alloy nanospheres as efficient catalysts for ethylene glycol electrooxidation

Designing and fabricating highly active and efficient catalysts are of vital importance for the practical applications of direct ethylene glycol fuel cells (DEGFCs). In this study, we employ a feasible one-pot synthetic method to construct highly monodispersed PtCu nanospheres (NSs) as high-efficiency anode electrocatalysts for DEGFCs. Interestingly, the optimized carbon supported Pt₁Cu₁ NSs can display the highest mass activity of 2146.9 mA mg^-1 in 1 M KOH + 1 M EG solution under the scan rate of 50 mV s^-1, which is 1.9 times higher than that of commercial Pt/C catalysts. This is ascribed to the favorable electronic effect between Pt and Cu, which is beneficial for ethylene glycol oxidation reaction (EGOR) in fuel cells. Meanwhile, such monodispersed Pt₁Cu₁ NSs can also exhibit excellent durability, where the Pt₁Cu₁ catalyst retains 62.6% of the initial value after the cyclic voltammetry of 500 cycles. This work not only provides a significant approach for designing catalysts for fuel cells, but also constructs a novel class of active and stable electrocatalysts for EGOR.

Shape-control of one-dimensional PtNi nanostructures as efficient electrocatalysts for alcohol electrooxidation

Bimetallic one-dimensional (1D) nanostructures such as nanowires (NWs) and nanorods (NRs), serving as high-efficiency anode electrocatalysts, have attracted extensive attention in the past decade. However, the precise design and synthesis of 1D Pt-based nanocrystals with tunable morphology and size still remain an arduous challenge. Driven by this, we report a facile yet efficient strategy for the first time to prepare PtNi ultrafine NWs (UNWs), sinuous NWs (SNWs) and ultrashort NRs (UNRs) by adjusting the amount of citric acid, ascorbic acid and glucose. Detailed analysis of their electrocatalytic properties has indicated that the as-obtained PtNi SNWs exhibit the most outstanding electrocatalytic activity toward ethylene glycol oxidation reaction (EGOR) and glycerol oxidation (GOR), 4.5 and 4.3 times higher in mass activity as well as 4.3 and 3.9 times higher in specific activity compared with the commercial Pt/C catalyst. The as-prepared PtNi SNWs are also more stable than the commercial Pt/C catalyst after successive durability tests. The proposed method provides insight into more rational designs of bimetallic nanocatalysts with 1D architectures and the as-synthesized PtNi catalysts with improved electrocatalytic performance assist in promoting the further development of direct alcohol fuel cells (DAFCs).

Insight of holey-graphene in the enhancing of electrocatalytic activity as supporting material

An ideal supporting material improves both activity and durability of noble metal nanoparticles in electrocatalytic reactions. Graphene possesses a high transport rate of electrons in-plane, a low cost, and stability, but, the restacking of graphene layers trap noble metal nanoparticles and make them inaccessible to reactants and results in reduced catalytic activity. Here, holey-graphene as the supporting materials for Pt nanoparticle catalysts is deeply investigated in the electrocatalytic reaction of methanol oxidation. The holey-graphene can be scalable to synthesize using our simple method described herein. The holes on the holey-graphene layer promote the access of reactants with Pt nanoparticle catalysts compared with carbon black and graphene when used as supporting materials. Density functional theory calculations and molecule dynamic simulation further explain the function of holey-graphene in the promotion of electrocatalytic activity. Holey-graphene may open extraordinary possibilities as a supporting material for electrocatalysts.

Oxygen Reduction Reaction and Hydrogen Evolution Reaction Catalyzed by Pd–Ru Nanoparticles Encapsulated in Porous Carbon Nanosheets

Developing bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for enhancing the energy transfer efficiency of metal–air batteries and fuel cells, as well as producing hydrogen with a high purity. Herein, a series of Pd–Ru alloyed nanoparticles encapsulated in porous carbon nanosheets (CNs) were synthesized and employed as a bifunctional electrocatalyst for both ORR and HER. The TEM measurements showed that Pd–Ru nanoparticles, with a size of approximately 1–5 nm, were uniformly dispersed on the carbon nanosheets. The crystal and electronic structures of the PdxRu100−x/CNs series were revealed by powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The as-prepared samples exhibited effective ORR activity in alkaline media and excellent HER activity in both alkaline and acid solutions. The Pd50Ru50/CNs sample displayed the best activity and stability among the series, which is comparable and superior to that of commercial 10% Pd/C. For ORR, the Pd50Ru50/CNs catalyst exhibited an onset potential of 0.903 V vs. RHE (Reversible Hydrogen Electrode) and 11.4% decrease of the current density after 30,000 s of continuous operation in stability test. For HER, the Pd50Ru50/CNs catalyst displayed an overpotential of 37.3 mV and 45.1 mV at 10 mA cm−2 in 0.1 M KOH and 0.5 M H2SO4, respectively. The strategy for encapsulating bimetallic alloys within porous carbon materials is promising for fabricating sustainable energy toward electrocatalysts with multiple electrocatalytic activities for energy related applications.

Hollow Ag44Pt56 nanotube bundles with high electrocatalytic performances for hydrogen evolution and ethylene glycol oxidation reactions

It is a main challenge to synthesize highly efficient and durable nanocatalysts towards hydrogen evolution reaction (HER) and alcohol oxidation reaction in energy conversion and storage. Herein, a green wet-chemical approach was developed to directly prepare hollow Ag₄₄Pt₅₆ nanotube bundles (H-Ag₄₄Pt₅₆ NTBs), utilizing 5-azacytosine as a structure-directing agent. The obtained electrocatalyst displayed superior catalytic activity and durability for HER in acid media, and the great improvement in catalytic performance for ethylene glycol oxidation reaction (EGOR) in the alkaline electrolyte, outperforming home-made Ag₃₄Pt₆₆ nanoparticles (NPs), Ag₇₀Pt₃₀ NPs, and commercial Pt/C catalysts. The high electrocatalytic characters are mainly attributed to the special nanostructures and the synergetic effects between the bimetals.