Facile synthesis of binary PtRu nanoflowers for advanced electrocatalysts toward methanol oxidation

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.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Synthesis of PtRu alloy nanofireworks as effective catalysts toward glycerol electro-oxidation in alkaline media

Electro-oxidation of glycerol is a key anodic reaction in direct alcohol fuel cell (DAFCs). Exploring the cost-effective nanocatalysts for glycerol oxidation reaction (GOR) is very important for the development of DAFC, but it is still challenging. In this paper, nanofirework-like PtRu alloy catalyst was successfully synthesized and used for GOR in alkaline medium. Thanks to the unique nanofirework-like structure and synergetic effects, the activity and stability of the as-prepared PtRu alloy nanofireworks (NFs) toward GOR were significantly improved relative to Pt NFs. In particular, the peak current density of GOR catalyzed by the optimized Pt₁Ru₃ NFs catalyst reached 2412.0 mA mg^-1, surpassing that of commercial Pt/C catalyst. This work has important guidance for the design of advanced anode electrocatalysts for fuel cells.

One-Pot Microwave-Assisted Synthesis of Graphene-Supported PtCoM (M = Mn, Ru, Mo) Catalysts for Low-Temperature Fuel Cells

In this study, one-pot microwave-assisted synthesis was used to fabricate the graphene (GR)-supported PtCoM catalysts where M = Mn, Ru, and Mo. The catalysts with the molar ratios of metals Pt:Co:Mn, Pt:Co:Ru, and Pt:Co:Mo equal to 1:3:1, 1:2:2, and 7:2:1, respectively, were prepared. Catalysts were characterized using Transmission Electron Microscopy (TEM). The electrocatalytic activity of the GR-supported PtCoMn, PtCoRu, and PtCoMo catalysts was evaluated toward methanol oxidation in an alkaline medium employing cyclic voltammetry and chrono-techniques. The most efficient electrochemical characteristics demonstrated the PtCoMn/GR catalyst with a current density value of 144.5 mA cm−2, which was up to 4.8 times higher than that at the PtCoRu(1:2:2)/GR, PtCoMo(7:2:1)/GR, and bare Pt/GR catalysts.

Insights into the morphology and composition effects of one-dimensional CuPt nanostructures on the electrocatalytic activities and methanol oxidation mechanism by in situ FTIR

Morphology modulation and surface structure-controlled synthesis are two effective ways to tune the electrocatalytic activities of metal nanomaterials. Pt-based binary or ternary metal nanostructures have become a class of promising catalysts toward the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) for direct methanol fuel cells. Herein to reveal the morphology and surface structure effects of one-dimensional (1D) Pt-based nanostructures on their electrocatalytic properties, two types of 1D CuPt nanowires (CuPt NWs) and CuPt nanotubes (CuPt NTs) with tunable surface structures and compositions were fabricated using a convenient and easy strategy. It was found that among all the studied samples, CuPt2.22 NWs exhibited the highest efficiency catalytic performances for both the ORR and MOR in an acidic electrolyte. For the ORR, CuPt2.22 NWs exhibited an onset potential (Eonset) of 0.749 V and a half-wave potential (E1/2) of 0.577 V, which are more positive than those of the commercial Pt/C (0.668 V and 0.558 V). On the other hand, CuPt2.22 NWs show a specific activity of 20.76 mA cm-2 and a mass activity of 0.171 mA μgPt-1 for the MOR, which are 7.75 and 1.82 times, respectively, larger than those of Pt/C (2.679 mA cm-2 and 0.094 mA μgPt-1). Meanwhile, the reaction mechanism of the MOR on CuPt2.22 NWs was examined by in situ FTIR. From the enhanced IR absorption, the linear- and bridge-adsorbed CO intermediates can be determined during the methanol oxidation on CuPt2.22 NWs, from which the MOR proceeds through a dual reaction pathway. This work reveals that rationally tuning the electronic structures of 1D metal nanomaterials by well-controlling the composition and surface morphology on the nanoscale could greatly enhance the catalytic properties, which are very important for their application in fuel cells.

Monodisperse thiourea functionalized graphene oxide-based PtRu nanocatalysts for alcohol oxidation

Addressed herein, thiourea functionalized graphene oxide-based PtRu nanocatalysts (PtRu@T/GO) has been synthesized and characterized by several techniques and performed for methanol oxidation reactions as novel catalysts. In this study, graphene oxide (GO) was functionalized with thiourea (T/GO) in order to obtain monothiol functionalized graphene and increase the stability and activity of the nanocatalysts. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), TEM (transmission electron microscopy) and high-resolution transmission electron microscopy (HR-TEM) were used for characterization of the prepared nanocatalysts. The results obtained from these techniques showed that the prepared nanocatalysts were in a highly crystalline form, well dispersed on T/GO, very small in size and colloidally stable. The average size of the synthesized nanocatalysts determined by TEM analysis was found to be 3.86 ± 0.59 nm. With HR-TEM analysis, the atomic lattice fringes of the nanocatalysts were calculated to be 0.23 nm. After the full characterization of the prepared nanocatalysts, they were tried for the methanol oxidation reaction (MOR) and it was observed that 97.3% of the initial performance was maintained even after 1000 cycles while exhibiting great catalytic activity and stability with the help of T/GO. Thus, the arranged nanocatalysts displayed great heterogeneous catalyst characteristics for the methanol oxidation response.

Electrocatalytic enhancement of platinum and palladium metal on polydopamine reduced graphene oxide support for alcohol oxidation

The objective of our work is to improve low-temperature fuel cell catalysts by increasing the surface area to augment the efficiency of catalytic reactions. Reduced graphene oxide (rGO) supports were prepared by adding N-containing derivatives of polydopamine (PDA) and loading of Pt and Pt-based metal alloy nanoparticles were accomplished for catalyst preparation. To study the effects of surface modification on catalyst activity, the GO surfaces modified by addition of PDA (PDA-rGO) were richer in oxygen- and nitrogen-containing functional groups, which reduced the number of graphene defects. Reduction of metals (M = Pt, Pd, Pt_xPd_y where x and y = 1-3) by NaBH₄ produced M/GO (metal on GO) and M/PDA-rGO (metal on PDA-rGO) catalysts. Examination of morphology and chemical composition confirmed that the existence of particle size on M/PDA-rGO catalysts was smaller than that on M/GO catalysts in agreement with calculated electrochemically active surface areas (ECSA). Electrochemical analysis was conducted to evaluate the catalyst activity and stability. The prepared catalysts had significantly greater surface areas as a result of association between the metal nanoparticles and the oxygen and nitrogen functional groups on the rGO supports. The catalysts also exhibited lower onset potentials and greater current intensities, I_f/I_b values, and long-term stabilities for methanol and ethanol oxidation compared with those of commercial PtRu/C. Moreover, the diameter of the Nyquist plot of the catalysts on PDA-rGO were smaller than that of the catalysts M/GO. The results suggest that variation of the Pt_xPd_y atomic ratio on carbon nanocomposites is an encouraging means of enhancing electrocatalytic performance in direct alcohol fuel cell applications.