Optimizing the Size of Platinum Nanoparticles for Enhanced Mass Activity in the Electrochemical Oxygen Reduction Reaction

High oxygen reduction (ORR) activity has been for many years considered as the key to many energy applications. Herein, by combining theory and experiment we prepare Pt nanoparticles with optimal size for the efficient ORR in proton‐exchange‐membrane fuel cells. Optimal nanoparticle sizes are predicted near 1, 2, and 3 nm by computational screening. To corroborate our computational results, we have addressed the challenge of approximately 1 nm sized Pt nanoparticle synthesis with a metal–organic framework (MOF) template approach. The electrocatalyst was characterized by HR‐TEM, XPS, and its ORR activity was measured using a rotating disk electrode setup. The observed mass activities (0.87±0.14 A mg_Pt^?1) are close to the computational prediction (0.99 A mg_Pt^?1). We report the highest to date mass activity among pure Pt catalysts for the ORR within similar size range. The specific and mass activities are twice as high as the Tanaka commercial Pt/C catalysis.     

Ultrasmall and uniform Pt3Au clusters strongly suppress Ostwald ripening for efficient ethanol oxidation

Clean and uniform Pt₃Au clusters decorated on graphene (Pt₃Au@PDDA-G) with an average size as small as 2.1 nm were successfully synthesized, offering higher catalytic activity and stability toward ethanol oxidation than that of Pt₃Au@G and commercial Pt/C, respectively. The catalytic enhancement mechanism of Pt₃Au@PDDA-G was proposed and discussed, and this work demonstrated that the uniformly distributed Pt₃Au clusters could strongly suppress Ostwald ripening to retain their original crystals size and morphology for highly catalytic properties.     

Waste Banana Stem Utilized for Biosynthesis of Silver and Gold Nanoparticles and Their Antibacterial and Catalytic Properties

The present work presented a synthesis of silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) using the aqueous extract of waste banana stem (WBS), Musa paradisiaca Linn. The reduction and formation of MNPs have been characterized by several analysis techniques such as X-ray diffraction (XRD), Fourier transmission infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM). The techniques showed that average particle size of WBS-AgNPs and WBS-AuNPs in crystalline nature was in ranges of 7–13 nm and 11–14 nm, respectively. The synthesized nanoparticles were used to evaluate antibacterial activity and catalysis. The WBS-AgNPs showed strong antibacterial activity against B. subtilis and E. coli. The largest zone of inhibition against B. subtilis (14.2 mm) and E. coli (9.3 mm) was found at concentrations of 4.0 ppm and 2.0 ppm, respectively. The excellent catalytic application of both the nanoparticles for the reduction of 4-nitrophenol was confirmed via study on their kinetics. The normalized kinetic constants (k_nor) of WBS-AgNPs and WBS-AuNPs were found to be 1.72?×?10^–3 s^?1 mg^?1 and 2.45?×?10^–3 s^?1 mg^?1, respectively.

     

Microwave-irradiated synthesized platinum nanoparticles/carbon nanotubes for oxidative determination of trace arsenic(III)

Platinum nanoparticles/carbon nanotubes (Pt_nano/CNTs) were rapidly synthesized by microwave radiation, and applied for the oxidative determination of arsenic(III). The transmission electron microscopy (TEM) revealed the size of synthesized Pt nanoparticles with nominal diameter of 15 ± 3 nm. Pt_nano/CNTs modified glassy carbon electrode (Pt_nano/CNTs/GCE) exhibited better performance for arsenic(III) analysis than that of Pt nanoparticles modified GCE (Pt_nano/GCE) by electrochemical deposition or Pt foil electrode. Excellent reproducibility of the Pt_nano/CNTs/GCE was obtained with the relative standard deviation (RSD) of 3.5% at 20 repeated analysis of 40 μM As(III), while the RSD was 9.8% for Pt_nano/GCE under the same conditions. The limit of determination (LOD) of the Pt_nano/CNTs/GCE was 0.12 ppb, which was 1–2 orders of magnitude lower than that of Pt_nano/GCE or Pt foil electrode.     

Pulsed electrodeposition of Pt nanoclusters on carbon nanotubes modified carbon materials using diffusion restricting viscous electrolytes

A simple method for achieving high dispersion and small platinum nanoparticles down to only 2 or 3 nm on structured carbon supports (carbon nanotubes-modified PAN-based carbon fiber and carbon nanotubes-modified graphite foil) is presented. Pulsed electrodeposition of Pt nanoparticles was performed at increased viscosity of the H₂PtCl₆ containing electrolyte by addition of glycerol. The catalyst nanoparticle size can be controlled by varying the amount of glycerol added into the aqueous H₂PtCl₆ solution, and adjusting the number of the potential pulses. The shape and size of the Pt nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy. The electrocatalytic properties of Pt nanoparticles with respect to O₂ and H₂O reduction were investigated by means of cyclic voltammetry, and the improved catalytic activity of the Pt nanoparticles/carbon nanotubes surfaces could be proved.     

3-D composite electrodes for high performance PEM fuel cells composed of Pt supported on nitrogen-doped carbon nanotubes grown on carbon paper

The 3-D composite electrodes consisting of Pt nanoparticles supported on nitrogen-doped carbon nanotubes (CN_x) grown directly on carbon paper were successfully prepared. The effect of the nitrogen atom incorporation in carbon nanotubes (CNTs) on the Pt nanoparticle dispersion and catalytic activities for the oxygen reduction reaction has been investigated. Compared to regular CNTs, highly dispersed Pt nanoparticles with smaller size (2–3 nm) and higher electrochemical Pt surface area as well as higher fuel cell performance were obtained for CN_x.     

Synergistic enhancement of formic acid electro-oxidation on PtxCuy co-electrodeposited binary catalysts

A propitious binary catalyst composed of Pt and Cu which were electrodeposited simultaneously onto a glassy carbon (GC) substrate was recommended for the formic acid (FA) electro-oxidation reaction (FAOR); the principal anodic reaction in the direct FA fuel cells (DFAFCs). The simultaneous co-electrodeposition of Pt and Cu in the catalyst provided an opportunity to tune the geometric functionality of the catalyst to resist the adsorption of poisoning CO at the Pt surface that represented the major impediment for DFAFCs marketing. The catalytic activity of the catalyst toward FAOR was significantly influenced by the (Pt⁴⁺/Cu²⁺) molar ratio of the electrolyte during electrodeposition, which also affected the surface coverage of Pt and Cu in the catalyst. Interestingly, with a molar (Pt⁴⁺/Cu²⁺) ratio of (1:4), the catalyst sustained superior (3.58 compared to 0.65 obtained at the pristine Pt/GC catalyst) activity for FAOR, concurrently with up to four-times (0.73 compared to 0.18 obtained at the pristine Pt/GC catalyst) improvement in the catalytic tolerance against CO poisoning. This associated, surprisingly, a negative shift of ca. 336 mV in the onset potential of FAOR, in an indication for the competitiveness of the catalyst to minimize superfluous polarizations in DFAFCs. Furthermore, it offered a better (ended up with 20% loss in the activity) stability for continuous (1 h) electrolysis than pristine Pt/GC catalyst (the loss reached 35%). The impedance and CO stripping measurements together excluded the electronic element but confirmed the geometrical influence in the catalytic enhancement.     

Magnetically separable tea leaf mediated nickel oxide nanoparticles for excellent photocatalytic activity

Synthesis of nanoparticles having low chemical toxicity has been interest of researchers for decades. Utilization of plant phytochemicals as reducing agent is now a globally recognized alternative technique for environmental friendly and low-cost production of nanoparticles. This work reports a facile green synthesis protocol of Nickel Oxide nanoparticles (NiO NPs) using fresh tea leaf extract. The synthesized nanoparticles have been characterized through various analytical techniques like Powder XRD (P-XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The XRD results reveal the formation of crystalline nickel oxide nanoparticles. FTIR spectrum displays the existence of different polyphenolic groups over NiO NPs surface. TEM and SEM images indicate the formation of slightly agglomerated spherical nanoparticles with particle size 3–5 ​nm. The nanoparticles were used towards the photocatalytic degradation of both cationic, anionic dyes and their mixtures under optimum conditions in the presence of UV light irradiation. More than 95% degradation was observed for all the dye solutions with 30 ​mg ​L^-1 catalytic dose. Moreover, the degradation efficiency of the nanoparticle was studied by altering various parameters like pH, initial dye concentration and amount of catalytic dose. Pseudo first order kinetic model was employed in all the reactions. A detailed mechanism and kinetics of the all the reactions were studied. Interestingly, the catalyst showed excellent recyclability up-to 4th cycles with very low catalytic activity loss.     

Bimetallic Cluster Provides a Higher Activity Electrocatalyst for Methanol Oxidation

The cluster complex Pt₂Ru₄(CO)₁₈ was used as a precursor to prepare a 60 wt% 1:2 Pt:Ru nanoparticles on carbon (PtRu/C) for use as an electrocatalyst for methanol oxidation. This bimetallic carbonyl cluster complex was found to provide smaller, more uniform bimetallic nanoparticle that exhibited higher electrocatalytic activity than a 60 wt% 1:1 Pt:Ru commercial catalyst from E-Tek. Using bimetallic cluster precursors simplifies the synthetic procedures by reducing the need for high temperature reduction and assures a more intimate mixing of the two different metals. Transmission electron microscopy (TEM) images of the catalyst obtained from the cluster precursor showed bimetallic nanoparticles having a narrow size range of 2–3 nm that were dispersed uniformly over the surface of the support. Images of the commercial catalyst showed particles 3–4 nm in diameter that tended to agglomerate near the edges of the carbon support particles. Cyclic voltammograms of methanol oxidation from the two catalysts showed significantly higher activity for the cluster-derived catalyst. The onset potential for methanol oxidation for the cluster-derived catalyst was approximately 170 mV lower than that of the commercial catalyst at 100 A/g Pt, and approximately 250 mV lower at 400 A/g Pt. ^* This report is dedicated to Prof. Günter Schmid on the occasion of his 70th birthday.     

Development of Pt-Co catalysts supported on carbon nanotubes using the polyol method—tuning the conditions for optimum properties

Pt alloys with transition metals supported on carbon substrates are used as improved cathode electrocatalysts for fuel cells. Enhanced catalytic activity is attributed to the structure (Pt-Pt bond distance) and/or electronic effect (Pt d-electron vacancy). This work focuses on the development of Pt₃Co/f-MWCNT catalysts (functionalized multiwalled carbon nanotubes [f-MWCNT]) using ethylene glycol as the dispersing and reducing agent. The aim is to in parallel achieve fine dispersion, quantitative deposition and alloy formation. As described herein, the pH value of the reaction suspension has a critical effect on the composition and morphology of the synthesized nanoparticles. High pH values favor the formation of Pt₃Co alloy, nevertheless negatively influencing the dispersion. A discussion is made on the reduction/deposition mechanism and how to control the conditions to result in optimum properties.     

Technical electrodes catalyzed with PtRu on mesoporous ordered carbons for liquid direct methanol fuel cells

This paper presents the behavior of ordered mesoporous carbon (OMC)-supported catalysts as anodes for direct methanol fuel cells (DMFC), fed with an aqueous methanol solution. OMC samples were prepared by the nanocasting method from a polymerized furan resin using mesoporous silica as a template. Pt and PtRu nanoparticles were supported on OMC with high dispersion, the particle size being 2.4 nm at PtRu loading of 15 wt.%. The resulting catalysts were analyzed using carbon monoxide stripping voltammetry, cyclic voltammetry, and chronoamperometry in three-electrode experiments and recording cell voltage vs. current density curves in practical DMFC. It was found that PtRu-catalyzed technical electrodes exhibited good activity towards methanol electrooxidation in half-cell experiments under fuel-cell-relevant conditions. Specifically, Pt₈₅Ru₁₅/OMC catalyst showed the highest catalytic enhancement compared to Pt/OMC for the steady-state electrooxidation of methanol at 60 °C and 0.5 V, by a factor of 22 in 2-M MeOH solution. DMFC single cells yielded an open-circuit voltage of 0.625 V at 60 °C. Polarization curves indicate that DMFC with OMC-supported Pt₈₅Ru₁₅ catalyst at the anode exhibited the best performance.     

Antibacterial Activity of Light-Activated Silicone Containing Methylene Blue and Gold Nanoparticles of Different Sizes

Methylene Blue and methylene blue-gold nanoparticle mixtures were encapsulated in a silicone polymer using a swell-encapsulation-shrink technique. The antibacterial properties of the materials, when tested against Escherichia coli and Staphylococcus epidermidis, and exposed to laser light (660 nm), were significantly affected by both the presence and size of Au nanoparticles. Bacterial inactivation data were analysed using the Weibull inactivation model. For both E. coli and S. epidermidis the value of the parameter, indicating the time required to achieve the first log₁₀ reduction in the viable count, decreased when Au nanoparticles of ca 2 nm diameter were present. Larger Au nanoparticles (diameters of 5 and 20 nm) in combination with methylene blue were also embedded in silicone. The values of these materials increased with nanoparticle diameter, indicating a reduction in antibacterial activity. In all cases E. coli had higher values than S. epidermidis.     

Size-selective Pt siderophores based on redox active azo-aromatic ligands

We demonstrate a strategy inspired by natural siderophores for the dissolution of platinum nanoparticles that could enable their size-selective synthesis, toxicological assessment, and the recycling of this precious metal. From the fabrication of electronics to biomedical diagnosis and therapy, PtNPs find increasing use. Mitigating concerns over potential human toxicity and the need to recover precious metal from industrial debris motivates the study of bio-friendly reagents to replace traditional harsh etchants. Herein, we report a family of redox-active siderophore-viz. π-acceptor azo aromatic ligands (L) that spontaneously ionize and chelate Pt atoms selectively from nanoparticles of size ≤6 nm. The reaction produces a monometallic diradical complex, Pt^II(L˙⁻)₂, isolated as a pure crystalline compound. Density functional theory provides fundamental insights on the size dependent PtNP chemical reactivity. The reported findings reveal a generalized platform for designing π-acceptor ligands to adjust the size threshold for dissolution of Pt or other noble metals NPs. Our approach may, for example, be used for the generation of Pt-based therapeutics or for reclamation of Pt nano debris formed in catalytic converters or electronic fabrication industries.

Biofriendly recycling of Pt is enabled by ligands that size-selectively dissolve nanoclusters.     

Platinum–titanium intermetallic nanoparticle catalysts for oxygen reduction reaction with enhanced activity and durability

A facile method to prepare Pt–Ti intermetallic nanoparticles supported on carbon was developed. Starting from a commercial Pt/C catalyst, TiO₂ layers were formed on the Pt/C then thermal annealing under a reducing condition successfully produced intermetallic Pt–Ti nanoparticles with an average size of 4.2 nm. The intermetallic Pt–Ti/C showed enhanced activity and durability for oxygen reduction reaction due to the change in electronic structure and less aggregation.     

Relationship between Pt particle size and catalyst activity for catalytic oxidation of ultrahigh‐concentration formaldehyde

The effects of particle size and kinetics of Pt/activated carbon (AC) catalysts on catalytic oxidation of formaldehyde (HCHO) were investigated. AC, f‐SiO₂ and MCM‐41 were used as supports to prepare low‐Pt‐content catalysts using H₂ reduction. Pt/AC catalyst shows the highest activity with the largest Pt particle size. By contrast, 0.1 wt% Pt/AC reduced using KBH₄ has much higher activity than that reduced using H₂, which can oxidize HCHO completely over 6000 ppm at 60°C in a fixed bed reactor. Transmission electron microscopy and X‐ray photoelectron spectroscopy results indicate that Pt/AC‐KBH₄ has larger Pt particles and lower valence state than Pt/AC‐H₂, which may be attributed to the ligand effect between Pt⁴⁺ and the AC support. The result of O₂ temperature‐programmed oxidation suggests that highly dispersed Pt⁴⁺ ions have stronger interaction with AC support and thus are harder to be reduced by H₂. Furthermore, Pt/AC is structure‐sensitive and larger‐sized Pt particles result in a high conversion of HCHO. Investigation of kinetics indicated that it is a zero‐order reaction for such a high HCHO concentration condition for Pt/AC‐KBH₄.     

Pd/Co双金属纳米颗粒的制备及催化制氢性能

采用聚乙烯吡咯烷酮(PVP)保护的化学共还原法制备了Pd/Co双金属纳米颗粒, 研究了PVP及还原剂(NaBH₄)的用量、金属盐浓度、金属比例等对Pd/Co双金属纳米颗粒催化NaBH₄制氢性能的影响. 透射电子显微镜(TEM)的结果表明, 所制备的Pd/Co双金属纳米颗粒的平均粒径在1.5-2.8 nm之间. Pd/Co双金属纳米颗粒(BNPs)的催化活性远高于Pd与Co单金属纳米颗粒的活性; 当Pd/Co的理论原子比为1/9时, 双金属纳米颗粒的催化活性最高可达15570 mol·mol^-1·h^-1 (文中纳米颗粒的催化活性均为每摩尔Pd的活性). 密度泛函理论(DFT)的计算结果表明, Pd原子与Co原子之间发生电荷转移, 使得Pd原子带负电而Co原子带正电, 荷电的Pd和Co原子进而成为催化反应的活性中心. 所制备的Pd/Co双金属纳米颗粒具有很好的催化耐久性, 即使重复使用5次后, 该催化剂仍具有较高的催化活性, 且使用后的纳米颗粒催化剂也没有出现团聚现象. 双金属纳米颗粒催化NaBH₄水解反应的活化能约为54 kJ·mol^-1.     

Fabrication and catalytic properties of Pt and Ru decorated TiO2⧹CNTs catalyst for methanol electrooxidation

Highly ordered anodic titania nanotube arrays provide a large surface area for electrodepositing nickel nanoparticles which are used as the catalyst for carbon nanotube growth. Pt and Ru nanoparticles, approximately 3 nm in diameter, are uniformly electrodeposited on the as synthesized titania-supported carbon nanotubes (CNTs), constructing a novel catalyst for electrocatalytic oxidation of methanol. An enhanced and stable catalytic activity is obtained due to the uniformly dispersed Pt and Ru nanoparticles, and the large CNT network facilitating the electron transfer between the adsorbed methanol molecules and the catalyst substrate. An oxidation peak current density of 55 mA/cm² is achieved at a low Pt load of 0.126 mg/cm² with a Pt/Ru mole ratio of 1:1.     

A Self-Assembled Fmoc-Diphenylalanine Hydrogel-Encapsulated Pt Nanozyme as Oxidase- and Peroxidase-Like Breaking pH Limitation for Potential Antimicrobial Application

Nanomaterials with oxidase- and peroxidase-like activities have potential in antibacterial therapy. The optimal activity of most nanozymes occurred in acidic pH (3.0–5.0), while the pH in biological systems is mostly near neutral. Herein, a general system using 9-fluorenylmethoxycarbonyl-modified diphenylalanine (Fmoc-FF) hydrogel for enhancing oxidase- and peroxidase-like activities of Pt NPs and other typical enzyme-like nanomaterials at neutral or even alkaline pH is proposed. In this system, Fmoc-FF hydrogel provides an acidic microenvironment for Pt NPs due to hydrogen protons (H⁺) produced by the dissociation of F at neutral pH. As a result, Pt NPs exhibits 6-fold enhanced oxidase-like and 26-fold peroxidase-like activity after being encapsulated into Fmoc-FF hydrogel at pH 7.0. Based on outstanding enzymatic activities and the antibacterial activity of Fmoc-FF hydrogel itself, Pt-Fmoc-FF hydrogel realizes excellent antibacterial effect. This design provides a universal strategy to break pH limitation of nanozymes and promotes the biological applications of nanozymes.     

Inorganic and organometallic chemistry of PtIII complexes having a delocalized PtIII—PtIII bond

Amidate-bridged dinuclear Pt^III complexes having a Pt^III—Pt^III bond react with ketones and alkenes. In the reaction with alkenes in water, 1,2-diols are obtained. In the reactions with conjugated dienes, stereospecific 1,4-diols are formed selectively. A kinetic study revealed that at each intermediate step of the reaction with alkenes the electronic state of the Pt—Pt bond changes between Pt^III—Pt^III and Pt^II—Pt^IV and stabilizes the reaction intermediates.     

Carbon-supported ultrafine Pt nanoparticles modified with trace amounts of cobalt as enhanced oxygen reduction reaction catalysts for proton exchange membrane fuel cells

To accelerate the kinetics of the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells, ultrafine Pt nanoparticles modified with trace amounts of cobalt were fabricated and decorated on carbon black through a strategy involving modified glycol reduction and chemical etching. The obtained Pt₃₆Co/C catalyst exhibits a much larger electrochemical surface area (ECSA) and an improved ORR electrocatalytic activity compared to commercial Pt/C. Moreover, an electrode prepared with Pt₃₆Co/C was further evaluated under H₂-air single cell test conditions, and exhibited a maximum specific power density of 10.27 W mg_Pt^?1, which is 1.61 times higher than that of a conventional Pt/C electrode and also competitive with most state-of-the-art Pt-based architectures. In addition, the changes in ECSA, power density, and reacting resistance during the accelerated degradation process further demonstrate the enhanced durability of the Pt₃₆Co/C electrode. The superior performance observed in this work can be attributed to the synergy between the ultrasmall size and homogeneous distribution of catalyst nanoparticles, bimetallic ligand and electronic effects, and the dissolution of unstable Co with the rearrangement of surface structure brought about by acid etching. Furthermore, the accessible raw materials and simplified operating procedures involved in the fabrication process would result in great cost-effectiveness for practical applications of PEMFCs.