pH effect on electrocatalytic reduction of CO2 over Pd and Pt nanoparticles

Adsorbed hydrogen participates in electrocatalytic reduction of CO₂ and competitive hydrogen evolution reaction (HER) simultaneously, and its reaction pathway greatly affects the activity and selectivity of CO₂ reduction. In this work, we investigate pH effect on electrocatalytic reduction of CO₂ over Pd and Pt nanoparticles (NPs) with a similar size in a pH range from 1.5 to 4.2. Pt NPs completely contribute to HER in the pH range. Over Pd NPs, Faradaic efficiency for CO production at − 1.19 V (vs. reversible hydrogen electrode) varies from 3.2% at pH of 1.5 to 93.2% at pH of 4.2, and current density for CO production reaches maximum at pH of 2.2. The significant enhancement of Faradaic efficiency and current density for CO production over Pd NPs at high pH values is attributed to decreased kinetics of hydrogen evolution reaction by increasing hydrogen binding energy and lowered adsorption affinity of CO-like intermediate compared to Pt.     

Electrocatalytic O2 reduction at glassy carbon electrodes modified with dendrimer-encapsulated Pt nanoparticles

Platinum dendrimer-encapsulated nanoparticles (DENs) were prepared within fourth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers and immobilized on glassy carbon electrodes using an electrochemical coupling strategy. X-ray photoelectron spectroscopy, electron microscopy, and electrochemical experiments confirmed that the Pt DENs were about 1.4 nm in diameter and that they remained within the dendrimer following surface immobilization. The resulting Pt DEN films were electrocatalytically active for the oxygen reduction reaction. The films were also robust, surviving up to 50 consecutive cyclic voltammograms and sonication.     

Enhancement of the electrocatalytic activity of Pt nanoparticles in oxygen reduction by chlorophenyl functionalization

Chlorophenyl-stabilized platinum nanoparticles (1.85 nm) exhibited electrocatalytic activity for oxygen reduction up to 3 times higher than that of commercial Pt/C catalysts. Similar enhancement was observed with naked Pt/C functionalized by the same chlorophenyl fragments, suggesting the important role of organic capping ligands in the manipulation of nanoparticle electrocatalytic performance.     

Electrochemical study of nitrobenzene reduction using novel Pt nanoparticles/macroporous carbon hybrid nanocomposites

Novel Pt nanoparticles (PN) ensemble on macroporous carbon (MPC) hybrid nanocomposites (PNMPC) were prepared through a rapidly and simple one-step microwave-assisted heating procedure. The obtained PNMPC was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA) and electrochemical methods. The electrochemical reduction of nitrobenzene (NB) was thoroughly investigated at the PNMPC modified glassy carbon (GC) electrode, and the catalytic rate constant was calculated to be 3.14 × 10⁴ M⁻¹ s⁻¹ for NB. A sensitive NB sensor was developed based on the PNMPC/GC electrode, which showed a wide linear range (1–200 μM), low detection limit (50 nM), high sensitivity (6.93 μA μM⁻¹), excellent anti-interference ability and good stability. And moreover, the electrode was successfully applied to the determination of NB in real samples.     

壳聚糖修饰的Pt纳米粒子

以氯铂酸为前驱体,硼氢化钠为还原剂,壳聚糖为保护剂,通过化学还原法,在室温条件下制备了Pt纳米粒子.透射电镜(TEM)显示纳米粒子的粒径在28.5nm左右,X-射线衍射(XRD)表明纳米粒子的晶型为面心立方结构,X-光电子能谱(XPS)和红外(FTIR)证实了壳聚糖包覆在纳米粒子表面,热重分析(TGA)表明纳米粒子表面的壳聚糖含量大约为52.8％.     

Effect of particle size on the kinetics of the electrocatalytic oxygen reduction reaction catalyzed by Pt dendrimer-encapsulated nanoparticles

Platinum dendrimer-encapsulated nanoparticles (DENs) containing an average of 55, 100, 147, 200, and 240 atoms were prepared within sixth-generation, hydroxyl-terminated, poly(amidoamine) dendrimers. These DENs were immobilized on glassy carbon electrodes, and the effect of particle size on the kinetics of the oxygen reduction reaction (ORR) was quantitatively evaluated using rotating disk voltammetry. The total areas of the Pt DENs were determined by electrochemical CO stripping and hydrogen desorption, and the results were found to be in reasonable agreement with calculated values. The largest particles exhibited the highest specific activities for the ORR.     

Shape-dependent catalytic properties of Pt nanoparticles

Tailoring the chemical reactivity of nanomaterials at the atomic level is one of the most important challenges in catalysis research. In order to achieve this elusive goal, fundamental understanding of the geometric and electronic structure of these complex systems at the atomic level must be obtained. This article reports the influence of the nanoparticle shape on the reactivity of Pt nanocatalysts supported on γ-Al(2)O(3). Nanoparticles with analogous average size distributions (～0.8-1 nm), but with different shapes, synthesized by inverse micelle encapsulation, were found to display distinct reactivities for the oxidation of 2-propanol. A correlation between the number of undercoordinated atoms at the nanoparticle surface and the onset temperature for 2-propanol oxidation was observed, demonstrating that catalytic properties can be controlled through shape-selective synthesis.     

Dendrimer-encapsulated Pt nanoparticles on mesoporous silica for glucose detection

A hybrid system of mesoporous silica (MS) particle incorporated with poly(amidoamine) dendrimer-encapsulated platinum nanoparticles (Pt-DENs) was constructed in a neutral aqueous solution through electrostatic interaction. The MS/Pt-DENs composite particles immobilized with glucose oxidase (GOx) were used to modify a glassy carbon electrode for detecting the electrocatalytic response to the reduction of glucose. Pt-DENs can improve the conductivity of MS and enhance the electron transfer between redox centers in enzymes and electrode surfaces. The structure of composite particles and the performance of MS/Pt-DEN-modified electrodes were characterized by transmission electron microscopy, N₂ sorption characterization method, electrochemical impedance spectroscopy, cyclic voltammetry and amperometric measurements. The MS/Pt-DENs/GOx-modified electrodes, which had a fast response of GOx less than 3?s, could be used for the determination of glucose ranging from 0.02 to 10?mM. The detection limits were 4???M at signal-to-noise ratio of 3.     

Polyoxometalate-stabilized Pt nanoparticles and their electrocatalytic activities

The synthesis of long-term stable polyoxometalate (POM)-stabilized Pt nanoparticles (NPs) is described here. By means of controlled bulk electrolysis, the reduced POM anions, SiW(12)O(40)(4-) (or SiW(12)) and H(2)W(12)O(40)(6-) (or H(2)W(12)), respectively, served the dual role of reductant and protecting/stabilizing ligand for the Pt NPs. Transmission electron microscopy (TEM) images confirmed the formation of 3 to 4 nm sized Pt NPs, which coincidently was in the same size range of the commercial Pt black that was used as a reference. Elemental XPS analyses showed W/Pt ratios of 0.12 for the SiW(12)- and 0.18 for the H(2)W(12)-stabilized Pt NPs, but found no evidence of the presence of Cl(-) anion in the samples. Controlled electrochemical (EC), UV-Vis, and IR data provided unambiguous evidence for the structural integrity of the POM anions on the Pt NP surface. CO stripping, methanol oxidation reaction (MOR), and oxygen reduction reaction (ORR) were used to assess their electrocatalytic activities. It was found that both SiW(12)- and H(2)W(12)-stabilized Pt NPs showed enhanced activities in MOR and ORR as compared to that of Pt black, with the latter having higher enhancement. These observations clearly demonstrated that the stabilizing POM anions have a profound influence on the electrocatalytic activity of the underlying Pt NPs.     

Polymer-mediated synthesis of highly dispersed Pt nanoparticles on carbon black

A new method was developed to prepare highly dispersed Pt nanoparticles on carbon black to use as proton exchange membrane (PEM) fuel cell catalysts. This method involves using a polymer, poly(vinylpyrrolidone) (PVP), to prevent particle aggregation and thereby reduce nanoparticle sizes to achieve high dispersion. It was found that Pt nanoparticles mediated by PVP are smaller than those obtained without PVP and have a narrower size distribution. Well-dispersed Pt nanoparticles with metal loadings from 5 to 35 wt % were obtained on carbon black (Vulcan XC-72R). It was found that well-dispersed Pt nanoparticles on carbon black could be synthesized at a PVP monomers-to-Pt atoms ratio of 0.1 under our experimental conditions. Larger amounts of PVP did not produce smaller nanoparticles, but rather reduced the Pt mass loading on carbon black. The morphology of the Pt nanoparticles that were supported on carbon black was characterized with transmission electron microscopy and X-ray diffraction. Their active surface areas were determined using cyclic voltammetry in a sulfuric acid solution. High Pt dispersion was obtained for the catalysts synthesized with PVP mediation, even at Pt loadings up to 35 wt %. The catalysts prepared with PVP mediation generally showed larger active specific areas than did those prepared without PVP.     

Hydrogen peroxide reduction on single platinum nanoparticles

Understanding oxygen reduction, key to much of electrochemical energy transformation technology, crucially requires exploration of the role of hydrogen peroxide as a possible intermediate especially on catalysts such as Pt which can bring about the 4e reduction of O₂ to water. We reveal that at the single nanoparticle scale the direct platinum catalysed reduction of hydrogen peroxide is found – even at high overpotentials – not to be controlled by the rate mass-transport of the reagents to the interface but by a surface limited process. Further under alkaline (pH 12.3) and near mass-transport free conditions, the single nanoparticle hydrogen peroxide reduction rate goes through a maximum at potentials comparable to the surface deposition of hydrogen (H_upd) with the highest reaction rate occurring when the surface is partially covered in hydrogen.

At the single platinum nanoparticle scale the hydrogen peroxide reduction reaction is a surface limited process.     

Electrodeposition of Se on carbon-supported Pt nanoparticles by cyclic voltammetry

Cyclic voltammetry (CV) is a powerful and popular electrochemical technique widely used to study the surface structure of materials through the electrochemical behaviors. Herein CV is utilized to study the electrochemical deposition of selenium (Se) on carbon black-supported Pt nanostructures. We synthesized carbon-loaded platinum nanoparticles (Pt/C) by microwave method and studied the electrochemical behavior of selenium on them. Through the experiment of changing the reverse potential, the corresponding relationship between the Se deposition peak and stripping peak was clarified and the deposition and stripping process of Se was proposed. Meanwhile, we synthesized cubic and octahedral nanocrystals of Pt, and used CV to study the Se deposition on these nanosctructures supported by carbon. It was found that the relative intensity of UPD peaks on Pt is different, as Pt_cube@C is dominated by (100) and Pt_oct@C electrode is dominated by (111) while Pt@C falls in between.

     

Enhanced activity for oxygen reduction reaction on "Pt3Co" nanoparticles: direct evidence of percolated and sandwich-segregation structures

Atomically resolved structures and compositions of Pt alloy nanoparticles were obtained using aberration-corrected high-angle dark field imaging, which was correlated to specific ORR activity based on a Pt surface area. The enhanced specific ORR activity (approximately 2 times relative to Pt) of acid-treated "Pt3Co" nanoparticles can be related to composition variations at the atomic scale and the formation of percolated Pt-rich and Pt-poor regions within individual particles. Upon annealing, we show direct evidence of surface Pt sandwich-segregation structures, which correspond to a specific ORR activity approximately 4 times relative to Pt.     

Formation of nanoparticles in water-in-oil microemulsions controlled by the yield of hydrated electron: the controlled reduction of Cu2+

In the water-in-oil (W/O) microemulsions based on nonionic surfactants, i.e., Brij 30, Brij 56, or Triton X-100, the omega value (molar ratio of water to surfactant), anion, and surfactant could remarkably affect the radiolytic reduction of Cu2+ and the morphologies of the reduction products simultaneously. The addition of toluene or naphthalene could transform the reduction products from copper to cuprous oxide in the Brij 56-based microemulsion, and the efficiency of naphthalene was obviously higher than that of toluene. After the effects of pH value and cosurfactant were excluded, it could be concluded that the effects of the omega value, the anion, and the structure of the surfactant on the yield of hydrated electrons (eaq-) play a key role in the radiolytic reduction of Cu2+. It was also suggested that the morphology of the reduction product may be controlled by the yield of eaq-.     

Enhanced electrocatalytic oxygen reduction through electrostatic assembly of Pt nanoparticles onto porous carbon supports from SnCl2-stabilized suspensions

Monodisperse Pt nanoparticles with atomic structures that span the cluster to crystal transition have recently been synthesized in electrostatically stabilized, aqueous-based suspensions. In the present study, the anionic charge from the stabilizing SnCl(2) sheath adsorbed on the surface of these particles is used for the first time to assemble Pt directly onto porous carbon supports via electrostatic assembly. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) reveals that these assemblies have substantially higher Pt-C dispersions than obtained from precipitation methods commonly used for commercial electrocatalyst systems. Energy dispersive spectroscopy (EDS) and inductively coupled plasma-mass spectrometry (ICP-MS) are used to determine that loadings of 10-30% by weight Pt (particle packing fractions from 0.05 to 0.25) are obtained through a single electrostatic application of these particles on Vulcan carbon, depending on particle size. The highest average oxygen reduction reaction (ORR) mass activity obtained using this approach is 90.4 A/g(Pt) at 0.9 V vs RHE in 0.1 M perchloric acid is with 1-2 nm particles that exhibit a transitional atomic structure. This activity compares to an average value of 74.0 A/g(Pt) obtained from densely packed electrostatic layer-by-layer (LbL) assemblies of unsupported particles and 36.7 A/g(Pt) commercial Vulcan electrocatalyst from Tanaka Kikinzoku Kogyo (TKK). Enhanced activity is observed with electrostatic assembly of any particle size on Vulcan relative to unsupported or commercial electrocatalyst with comparable durability. Such enhanced activity is attributed to improved reactant accessibility to the catalyst surface due to the increase in particle dispersion. An extinction coefficient of 7.41 m(2)/g at 352 nm is obtained across the entire cluster to crystal transition from 20 atom clusters to 2.9 nm single crystal nanoparticles, indicating that observed variation in ORR activity with particle size may be associated primarily with changes in atomic surface structure as opposed to the metallic character of the nanoparticles as assessed by UV-vis spectroscopy.     

Ultrasmall Pt2Sr alloy nanoparticles as efficient bifunctional electrocatalysts for oxygen reduction and hydrogen evolution in acidic media

Electrocatalytic oxygen reduction reaction(ORR) and hydrogen evolution reaction(HER) in acidic media are vital for the applications of renewable energy electrolyzers.However,the low mass activity of noble Pt urgently needs to be improved due to the strong binding energetics of oxygen species(*O) with Pt sites.Here we report fine PtxSr alloy(～2 nm) supported on N-doped carbon(NC) pyrolyzing from ZIF-8 as bifunctional electrocatalysts toward ORR and HER in acidic media.The representative Pt_2<...     

Pt@Ag/Pt复合型纳米颗粒的合成与表征

通过吸附在铂纳米颗粒表面的氢交替还原硝酸银和氯铂酸,得到了复合型纳米颗粒Pt@Ag／Pt,用紫外-可见吸收光谱（UV-Vis）、透射电子显微镜（TEM）、X-射线衍射（XRD）对其进行了表征。通过氢化催化苯甲醛反应,由于Pt与Ag双金属间的协同效应,其催化活性较纯铂好。     

Characterization of Pt nanoparticles deposited onto carbon nanotubes grown on carbon paper and evaluation of this electrode for the reduction of oxygen

Multiwalled carbon nanotubes (MWCNTs) were grown on the fibers of a commercial porous carbon paper used as carbon-collecting electrodes in fuel cells. The tubes were then covered with Pt nanoparticles in order to test these gas diffusion electrodes (GDEs) for oxygen reduction in H2SO4 solution and in H2/O2 fuel cells. The Pt nanoparticles were characterized by cyclic voltammetry, transmission electron microscopy, and X-ray photoelectron spectroscopy. The majority of the Pt particles are 3 nm in size with a mean size of 4.1 nm. They have an electrochemically active surface area of 60 m2/g Pt for Pt loadings of 0.1-0.45 mg Pt/cm2. Although the electroactive Pt surface area is larger for commercial electrodes of similar loadings, Pt/MWCNT electrodes largely outperform the commercial electrode for the oxygen reduction reaction in GDE experiments using H2SO4 at pH 1. On the other hand, when the same electrodes are used as the cathode in a H2/O2 fuel cell, they perform only slightly better than the commercial electrodes in the potential range going from approximately 0.9 to approximately 0.7 V and have a lower performance at lower voltages.