Carbon-supported Pt−Co alloy nanoparticle catalysts of nominal atomic composition but with different alloying extents were prepared via a modified Watanabe process by employing microwave heating. Their structure was studied by X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) techniques. Transmission electron microscopy (TEM) images indicated that the in-house-prepared Pt−Co alloy nanoparticles (sample-1 and sample-2) were well dispersed on the surface of the carbon support with narrow particle size distribution which is consistent with XRD grain size values. The catalyst composition obtained from XAS was nearly the same as that of the nominal value (1:1). The alloying extent values of Pt calculated from XAS measurements for sample-2 is similar to that of the commercial E-tek Pt−Co/C. This observation demonstrates the practical viability of our preparation protocol for Pt−Co/C catalysts. A comparative study was made for the oxygen reduction reaction (ORR) using a thin-film rotating disk electrode method to evaluate the catalytic behavior of Pt−Co/C and Pt/C catalyst with similar metal loadings and particle sizes. As compared to the Pt/C catalyst, the bimetallic Pt−Co/C of sample-2 exhibited an enhancement factor of 3 in mass activity at 0.95 V toward ORR. The enhancement in activity of sample-2 is similar in magnitude to that of the commercial E-tek Pt−Co/C catalyst. It is found that that the samples possessing a high alloying extent of Pt in the cluster enhances the activity of the bimetallic Pt−Co/C toward ORR. This observation confirms that the alloying extent of Pt is an important parameter by which one can have control over the fine-tuning of the catalytic activities of bimetallic nanoclusters. This activity enhancement may originate from the favorable electronic effects of a well mixed alloy underneath a thin “Pt-rich skin” structure of the Pt−Co bimetallic nanoparticles. This kind of thin “Pt-rich skin” is created by the dissolution of Co oxide on Pt−Co bimetallic nanoparticles while washing in acidic electrolyte before being subjected to ORR.

The exploration of MoS 2 based catalyst has been growing over the recent years, mainly focusing on finetuning the metallic phases for improved catalytic activity in the hydrogen evolution reaction (HER). Considering the synthesis of MoS 2 , the 2H phase (trigonal prismatic, D 3h ) is more stable than the 1T phase (octahedral, Oh). Still, with the increased electronic conductivity, hydrophilic nature, and the presence of electrochemically active basal planes, the 1T phase shows enhanced catalytic activity compared to the 2H phase which shows semiconducting nature with only edge sites being active. So far, one of the best ways to synthesize 1T-MoS 2 is the alkali metal exfoliation, but a setback to this method is that there are many issues like intercalation of alkali ions, self-heating, and pyrophoric nature associated with it. Moreover it requires undesirable and expensive organic solvent to produce 1T phase. The aqueous phase synthesis of 1T-MoS 2 is still hampered by the low extent of 1T enrichment and reproducibility. Here, in contrast, by the introduction of Santa Barbara Amorphous-15 (SBA-15) as a template, the selective formation of the 1T phase in MoS 2 over 90% has been achieved. This is the very first observation of phase selectivity behavior of SBA-15 for the entire layered materials. Moreover, the reproducibility of this methodology is also ensured by repeating the experiment 14 times. Besides, the storage stability of the 1T-MoS 2 at room temperature (RT) has been analyzed by storing it at RT over 30 days, which is essential for commercialize the methodology. Therefore, this reporting methodology resolving all the existing problems in aqueous phase synthesis of 1T-MoS 2 such as enhancement in the 1T phase, reproducibility, room temperature storage stability, and large scale production. This templatedriven 1T-MoS 2 has demonstrated an excellent activity, and to attain 10 mA cm −2 , it required just 252 mV with a low Tafel slope value of 45 mV/decade. These findings will pave a way to other similar 2D materials for selective enrichment in the 1T phase, which is the more desirable phase for energy storage and conversion devices at present.

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In this work, five types of MnO 2 nanostructres (nanowires, nanotubes, nanoparticles, nanorods, and nanoflowers) were synthesized with a fine control over their α-crystallographic form by hydrothermal method. The electrocatalytic activities of these materials were examined toward oxygen reduction reaction (ORR) in alkaline medium. Numerous characterizations were correlated with the observed activity by analyzing their crystal structure (TGA, XRD, TEM), material morphology (FE-SEM), porosity (BET), inherent structural nature (IR, Raman, ESR), surfaces (XPS), and electrochemical properties (Tafel, Koutecky−Levich plots and % of H 2 O 2 produced). Moreover, X-ray absorption near-edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS) analysis were employed to study the structural information on the MnO 2 coordination number as well as interatomic distance. These combined results show that the electrocatalytic activities are significantly dependent on the nanoshapes and follow an order nanowire > nanorod > nanotube > nanoparticle > nanoflower. α-MnO 2 nanowires possess enhanced electrocatalytic activity compared to other shapes, even though the nanotubes possess a much higher BET surface area. In the ORR studies, α-MnO 2 nanowires displayed Tafel slope of 65 mV/decade, n-value of 3.5 and 3.6% of hydrogen peroxide production. The superior ORR activity was attributed to the fact that it possesses active sites composed with two shortened Mn− O bonds along with a Mn−Mn distance of 2.824 Å, which provides an optimum requirement for the adsorbed oxygen in a bridge mode favoring the direct 4 electron reduction. In accordance with the first principles based density functional theory (DFT), the enhancement in ORR activity is due to the less activation energy needed for the reaction by the (211) surface than all other surfaces.

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The chemical state and formation mechanism of Pt-Ru nanoparticles (NPs) synthesized by using ethylene glycol (EG) as a reducing agent and their stability have been examined by in situ X-ray absorption spectroscopy (XAS) at the Pt L III and Ru K edges. It appears that the reduction of Pt(IV) and Ru(III) precursor salts by EG is not a straightforward reaction but involves different intermediate steps. The pH control of the reaction mixture containing Pt(IV) and Ru(III) precursor salts in EG to 11 led to the reduction of Pt(IV) to Pt(II) corresponding to [PtCl 4 ] 2-whereas Ru III Cl 3 is changed to the [Ru(OH) 6 ] 3-species. Refluxing the mixture containing [PtCl 4 ] 2-and [Ru(OH) 6 ] 3-species at 160°C for 0.5 h produces Pt-Ru NPs as indicated by the presence of Pt and Ru in the first coordination shell of the respective metals. No change in XAS structural parameters is found when the reaction time is further increased, indicating that the Pt-Ru NPs formed are extremely stable and less prone to aggregation. XAS structural parameters suggest a Pt-rich core and a Ru-rich shell structure for the final Pt-Ru NPs. Due to the inherent advantages of the EG reduction method, the atomic distribution and alloying extent of Pt and Ru in the Pt-Ru NPs synthesized by the EG method are higher than those of the Pt-Ru/C NPs synthesized by a modified Watanabe method.

Bimetallic alloy nanoparticles consisting of two noble metals Pt-Ag supported on carbon with a variable dimension were successfully prepared by ethylene glycol (EG) synthesis method. This work highlights the viability of EG synthesis methodology yielding a range of particle size from 1.2 to 3.1 nm with 1:1 atomic composition but with different alloying extents by a simple control over the solution pH of the preparation medium. The physical properties of resultant Pt-Ag/C nanoparticles such as size, structure, composition, coordination, and alloying extent parameters as well as d-band unfilled states of Pt atom were systematically studied by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), transmission emission microscopy (TEM), and X-ray absorption spectroscopy (XAS) techniques. Both EDX and XAS analysis confirmed that the catalyst composition was nearly the same as that of the nominal value. It was realized that the lower preparation pH produces the Pt-Ag/C with larger dimension, wider particle size distribution (PSD), and worse alloying extent associated with lower d-band unfilled states. At higher preparation pH yields Pt-Ag/C particles of smaller size, narrower PSD, and better alloying extent along with higher d-band unfilled states. Increasing the d-band unfilled states of the bimetallic Pt-Ag/C nanoparticles leads to a negative shift in CO oxidation peak potential at identical experimental conditions. The observed d-band unfilled state of the Pt atom in the Pt-Ag/C nanoparticles may be due to the resultant of the two opposite effects, namely, the electron donation by Ag and the size effect of the Pt-Ag nanoparticles. The electron donation ability of Ag is believed to associate with the alloying extent of Ag and/or Pt atoms in the Pt-Ag nanoparticles, and a possible explanation was drawn on the basis of their charge transfer index scale values.

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