Effect of the iridium oxide thin film on the electrochemical activity of platinum nanoparticles

Electro-Design of Bimetallic PdTe Electrocatalyst for Ethanol Oxidation: Combined Experimental Approach and Ab Initio Density Functional Theory (DFT)-Based Study

An alternative electrosynthesis of PdTe, using the electrochemical atomic layer deposition (E-ALD) method, is reported. The cyclic voltammetry technique was used to analyze Au substrate in copper (Cu²⁺), and a tellurous (Te⁴⁺) solution was used to identify UPDs and set the E-ALD cycle program. Results obtained using atomic force microscopy (AFM) and scanning electron microscopy (SEM) techniques reveal the nanometer-sized flat morphology of the systems, indicating the epitaxial characteristics of Pd and PdTe nanofilms. The effect of the Pd:Te ratio on the crystalline structure, electronic properties, and magnetic properties was investigated using a combination of density functional theory (DFT) and X-ray diffraction techniques. Te-containing electrocatalysts showed improved peak current response and negative onset potential toward ethanol oxidation (5 mA; -0.49 V) than Pd (2.0 mA; -0.3 V). Moreover, DFT ab initio calculation results obtained when the effect of Te content on oxygen adsorption was studied revealed that the d-band center shifted relative to the Fermi level: -1.83 eV, -1.98 eV, and -2.14 eV for Pd, Pd₃Te, and Pd₃Te₂, respectively. The results signify the weakening of the CO-like species and the improvement in the PdTe catalytic activity. Thus, the electronic and geometric effects are the descriptors of Pd₃Te₂ activity. The results suggest that Pd₂Te₂ is a potential candidate electrocatalyst that can be used for the fabrication of ethanol fuel cells.

Noble Metal-Based Multimetallic Nanoparticles for Electrocatalytic Applications

Noble metal-based multimetallic nanoparticles (NMMNs) have attracted great attention for their multifunctional and synergistic effects, which offer numerous catalytic applications. Combined experimental and theoretical studies have enabled formulation of various design principles for tuning the electrocatalytic performance through controlling size, composition, morphology, and crystal structure of the nanoparticles. Despite significant advancements in the field, the chemical synthesis of NMMNs with ideal characteristics for catalysis, including high activity, stability, product-selectivity, and scalability is still challenging. This review provides an overview on structure-based classification and the general synthesis of NMMN electrocatalysts. Furthermore, postsynthetic treatments, such as the removal of surfactants to optimize the activity, and utilization of NMMNs onto suitable support for practical electrocatalytic applications are highlighted. In the end, future direction and challenges associated with the electrocatalysis of NMMNs are covered.

Effective immobilization of nanoscale Pd on a carbon hybrid for enhanced electrocatalytic performances: stabilization mechanism investigations

The grand challenge inhibiting the use of electrocatalysts is the degradation of active species which results in poor durability and long-term performances. Studying the origin of active metal particle stabilization mechanisms by using supports and the immobilization-induced changes of active particles is of significant importance. This study describes the preparation of Pd nanoparticles supported by carbon hybrid NPG-CN, revealing that the mass and specific activities (1987 A g-1 Pd and 28.7 A m-2) of this catalyst for formic acid oxidation significantly exceed those of commercial Pd/C, and excellent stability and enhanced CO-poisoning tolerance properties are obtained. The origin of this behavior is probed by surface analytical techniques and identical-location transmission electron microscopy (IL-TEM), and the enhanced activity of Pd/NPG-CN is ascribed to the electronic effect of the substrate, the high content of surface metallic Pd0, and the reduced extent of active Pd leaching and physical ripening during the FOA process compared with commercial Pd/C. In addition, theoretical calculations demonstrate that NPG-CN can efficiently trap Pd atoms, which accumulate and form Pd clusters at trapping (nucleation) sites.

Sensitive electrochemical detection of nitric oxide based on AuPt and reduced graphene oxide nanocomposites

Since nitric oxide (NO) plays a critical role in many biological processes, its precise detection is essential toward an understanding of its specific functions. Here we report on a facile and environmentally compatible strategy for the construction of an electrochemical sensor based on reduced graphene oxide (rGO) and AuPt bimetallic nanoparticles. The prepared nanocomposites were further employed for the electroanalysis of NO using differential pulse voltammetry (DPV) and amperometric methods. The dependence of AuPt molar ratios on the electrochemical performance was investigated. Through the combination of the advantages of the high conductivity from rGO and highly electrocatalytic activity from AuPt bimetallic nanoparticles, the AuPt-rGO based NO sensor exhibited a high sensitivity of 7.35 μA μM(-1) and a low detection limit of 2.88 nM. Additionally, negligible interference from common ions or organic molecules was observed, and the AuPt-rGO modified electrode demonstrated excellent stability. Moreover, this optimized electrochemical sensor was practicable for efficiently monitoring the NO released from rat cardiac cells, which were stimulated by l-arginine (l-arg), showing that stressed cells generated over 10 times more NO than normal cells. The novel sensor developed in this study may have significant medical diagnostic applications for the prevention and monitoring of disease.

Understanding nanoparticle porosity via nanoimpacts and XPS: electro-oxidation of platinum nanoparticle aggregates

The porosity of platinum nanoparticle aggregates (PtNPs) is investigated electrochemically via particle-electrode impacts and by XPS. The mean charge per oxidative transient is measured from nanoimpacts; XPS shows the formation of PtO and PtO₂ in relative amounts defined by the electrode potential and an average oxidation state is deduced as a function of potential. The number of platinum atoms oxidised per PtNP is calculated and compared with two models: solid and porous spheres, within which there are two cases: full and surface oxidation. This allows insight into extent to which the internal surface of the aggregate is 'seen' by the solution and is electrochemically active.

An exploration of the use of Au submonolayer decorated Pd7Ir nanoparticles as a highly active electrocatalyst for the ethanol oxidation reaction in alkaline media

An activity promotion over 130% from the use of Au submonolayer on carbon supported Pd₇Ir nanoparticles as highly active electrocatalyst for EOR.

Localization of platinum nanoparticles on inner walls of mesoporous hollow carbon spheres for improvement of electrochemical stability

Mesoporous hollow carbon spheres with Pt nanoparticles (NPs) loaded on their inner walls (Pt@HC-meso) have been designed and prepared through a dual-templating method. The core-shell structured Pt/SiO₂@micelle-polydopamine (PDA) precursor is obtained by first depositing Pt NPs on silica spheres and then coating them with the carbon precursor of PDA and diblock copolymer micelles as soft templates. The subsequent carbonization and KOH etching convert the micelle-PDA shells into mesoporous carbon and remove the silica cores, respectively. Thus, the Pt NPs are subjected to calcination and left on the inner walls. The fabricated Pt@HC-meso achieved high electrocatalytic performance and outstanding stability in catalyzing methanol oxidation. We infer that the mesoporous carbon shells not only provide accessible diffusion pathways for the reactants, but also protect the inner Pt NPs from collision with Pt NPs in other hollow carbon spheres. Each hollow carbon sphere with Pt NPs inside can be regarded as an independent nanoreactor. Moreover, observations of the morphology have proved that the calcined Pt NPs avoid a second aggregation during the electrocatalytic process and maintain long-term stability.

Exploring nanoparticle porosity using nano-impacts: platinum nanoparticle aggregates

Nano-impacts of porous nanoparticles reveal the extent to which the internal surfaces can contribute to electrocatalysis.

Directly-grown and square-patterned arrays of metal oxide nanowires for high-performance catalyst support platforms

This research reports novel and efficient electrocatalyst support systems. Tin dioxide nanowires grown directly on current collecting substances are introduced as high-performance support platforms. For this propose, palladium or platinum catalysts are impregnated on these nanowire scaffolds and exhibit improved electrocatalytic performance for methanol oxidation in alkaline and acidic environments. These nanowire support platforms could be demonstrated to maximize the electrocatalytic activity because of the effective charge transport provided by the direct connection between the nanowire supports and current collectors. More significantly, grid-patterned nanowire arrays grown directly on current collectors are, for the first time, demonstrated as a milestone to enhance the electrocatalytic performance. The empty space between the patterned nanowire arrays acts as a channel to facilitate the electrolyte diffusion. The metal catalysts incorporated into the patterned nanowire supports show an 8-fold improvement in the catalytic performance for methanol electrooxidation, most likely because of the synergetic effects of the enhanced charge transport and mass transfer attributed to the structural advantages of the patterned nanowire array supports.

Electrocatalysis and photoelectrochemistry based on functional nanomaterials

Catalysis plays a key role in chemical production, energy processing, air purification, water treatment, food processing, and the life sciences. Nanostructured materials with high surface areas and some unique properties have received widespread interest in electrocatalysis and photocatalysis. Recently, the author’s research team has designed and studied a variety of novel functional nanomaterials. This review article is derived from the author’s 2013 Canadian Catalysis Lectureship Award Lecture and focuses primarily on the electrocatalytic activities of platinum- and palladium-based nanomaterials and the development of TiO2-based nanostructured photocatalysts. Palladium possesses several exceptional properties that may enable promising applications in hydrogen detection, purification, and storage. The significant roles of palladium-based nanomaterials in facilitating the growth of a hydrogen economy are addressed. As platinum-based catalysts are vital to the development of fuel cells and sensors, the design of high-performance platinum-based electrocatalysts is highlighted. Additionally, TiO2 is considered to be one of the most promising photocatalysts due to its nontoxicity, high stability, and cost effectiveness. The modification of TiO2 nanomaterials to achieve visible light response is discussed as well. It is anticipated that the development of advanced functional nanostructured catalysts will further improve the efficiency and reduce the cost of electrochemical and photochemical processes, making them more attractive in addressing the pressing global energy and environmental issues.

PtIr-WO3 nanostructured alloy for electrocatalytic oxidation of ethylene glycol and ethanol

In this article, we characterized tungsten oxide-decorated carbon-supported PtIr nanoparticles and tested it for the electrooxidation reactions of ethylene glycol and ethanol. Phase and morphological evaluation of the proposed electrocatalytic materials are investigated employing various characterization techniques including X-ray diffraction (XRD) and transmission electron microscopy (TEM). Electrochemical diagnostic measurements such as cyclic voltammetry, chronoamperometry, and linear sweep voltammetry revealed that the tungsten oxide-modified PtIr/Vulcan nanoparticles have higher catalytic activity for ethylene glycol and ethanol electrooxidation than that of PtIr/Vulcan. A significant enhancement for electrooxidation of CO-adsorbate monolayers occurred in the presence of a transition metal oxide relative to that of pure PtIr/Vulcan electrocatalyst. The likely reasons for this are modification on the Pt center electronic structure and/or increasing the population of reactive oxo groups at the PtIr/Vulcan electrocatalytic interface in different potential regions.

New deposition technique for metal films containing inorganic fullerene-like (IF) nanoparticles

This study describes a new method for fabrication of thin composite films using physical vapor deposition (PVD). Titanium (Ti) and hybrid films of titanium containing tungsten disulphide nanoparticles with inorganic fullerene-like structure (Ti/IF-WS2) were fabricated with a modified PVD machine. The evaporation process includes the pulsed deposition of IF-WS2 by a sprayer head. This process results in IF-WS2 nanoparticles embedded in a Ti matrix. The layers were characterized by various techniques, which confirm the composition and structure of the hybrid film. The Ti/IF-WS2 shows better wear resistance and a lower friction coefficient when compared to the Ti layer or Ti substrate. The Ti/IF films show very good antireflective properties in the visible and near-IR region. Such films may find numerous applications, for example, in the aerospace and medical technology.

Relevance of electronic effects on the yield of CO2 from methanol oxidation

The yields of products of methanol oxidation (HCHO, HCOOH, and CO(2)) were studied for carbon-supported PtRu nanoparticles having different amounts of alloyed and oxide phases. It is demonstrated that the increase in the Pt 5d-band vacancy enhances the production of CO(2), which is not directly related with the catalytic activity for CO oxidation. Results prove the relevant role of oxides and, at the same time, shed some new light on mechanistic aspects of methanol oxidation on PtRu nanocatalysts. It is also demonstrated that extrapolating from the behavior of smooth surfaces to nanoparticle systems is not always valid.

Nanocatalysis and prospects of green chemistry

Designing and developing ideal catalyst paves the way to green chemistry. The fields of catalysis and nanoscience have been inextricably linked to each other for a long time. Thanks to the recent advances in characterization techniques, the old technology has been revisited with a new scope. The last decade has witnessed a flood of research activity in the field of nanocatalysis, with most of the studies focusing on the effect of size on catalytic properties. This led to the development of much greener catalysts with higher activity, selectivity and greater ease of separation from the reaction medium. This Minireview describes the emerging trends in the field of nanocatalysis with implications towards green chemistry and sustainability.

Synthesis and electrocatalytic activity of photoreduced platinum nanoparticles in a poly(ethylenimine) matrix

Monodisperse polymer-mediated platinum (Pt) nanoparticles (NPs) have been synthesized by photoreduction in the presence of poly(ethylenimine) (PEI), a hyperbranched polymer. The formation process of the Pt NPs is pursued by UV-vis spectroscopy, and the formation mechanism is discussed. The morphology and size of the Pt NPs were characterized by transmission electron microscopy (TEM). TEM imaging shows that the Pt NPs' average diameter is 2.88 +/- 0.53 nm. The PEI/Pt NPs were immobilized on glassy carbon electrodes, and the electrocatalytic activity of the catalysts was investigated by cyclic voltammetry. PEI/Pt NPs exhibit very high catalytic activity for a methanol oxidation reaction. PEI/Pt NPs on glassy carbon electrodes are robust, showing good tolerance to poisoning even after many cycles. The electrocatalytic activity of PEI/Pt NPs compares favorably with other polymer-mediated Pt NPs. The results indicate that PEI is an appropriate complexing reducing agent for the photochemical production of Pt NPs and a good capping agent, allowing immobilization of the NPs on the working electrode.