PtCu Alloy Research Articles

Wavy PtCu alloy nanowire networks with abundant surface defects enhanced oxygen reduction reaction

Bimetallic platinum-copper (Pt-Cu) alloy nanowires have emerged as a novel class of fuel cell electrocatalysts for oxygen reduction reaction (ORR) due to their intrinsic high catalytic activity and durability, but preparing such electrocatalysts with clean surface via facile method is still a challenge. Herein, PtCu alloy with nanowire networks (NWNs) structure is obtained by a simple modified polyol method accompanied with a salt-mediated self-assembly process in a water/ethylene glycol (EG) mixing media. The formation mechanism of PtCu NWNs including the morphological evolution and the relevant experimental parameters has been investigated systematically. We propose that a micro-interface in H2O-EG media formed with the assistance of disodium dihydrogen pyrophosphate (Na2H2P2O7) and its unique nature of coordinating with Pt2+ or Cu2+ play critical roles in the formation of NWNs. When tested as ORR catalyst, the PtCuNWNs/C exhibits much higher activity and durability than that of PtNWNs/C and commercial Pt/C, even exceeding the target of DOE in 2020. The excellent performance of PtCuNWNs/C could be attributed to the unique structure of NWNs with 2.4 nm ultrathin wavy nanowires and plentiful surface defects and the modified electronic effect caused by alloying with Cu atoms.

Ni(OH)2 Decorated Pt-Cu Octahedra for Ethanol Electrooxidation Reaction.

Here we report the synthesis of 9 nm Ni(OH)2 decorated Pt-Cu octahedra (Ni(OH)2-PtCu) in one-pot synthesis for ethanol oxidation reaction (EOR) electrocatalysis in acidic electrolyte. To prepare Ni(OH)2-PtCu octahedra, CO gas was directly introduced in a reaction process as selective capping agents on the PtCu(111) facet. Ni(OH)2 was naturally deposited on the Pt-Cu octahedra during the synthesis. Carbon supported Ni(OH)2-PtCu (Ni(OH)2-PtCu/C) as an EOR catalyst showed enhanced CO tolerance due to the existence of oxophilic Ni(OH)2 on the surface of Pt-Cu, facilitating water dissolution to produce OH adsorption and to promote complete CO oxidation to CO2. In addition, Pt-Cu alloy composition also showed improvement of CO tolerance because of modified d-band structure of the Pt atoms, thereby weakening the binding strength of CO on the catalysts. Therefore, the Ni(OH)2-PtCu/C showed enhanced EOR activity and durability compared to the Pt-Cu octahedra and commercial Pt/C counterparts.

In-Situ Monitoring of Both Pt and Cu Dissolved from Pt-Cu Alloys Using Channel Flow Multi Electrode

Introduction Polymer electrolyte fuel cell (PEFC) is considered to be clean energy conversion device due to its low operating temperature and portability. Previously, Pt is used as cathode catalyst in PEFC, because Pt exhibits high catalytic activity for oxygen reduction reaction (ORR). Since Pt is limited resources and high cost, Pt alloy catalysts should be developed instead of Pt catalysts. Pt-Cu alloys exhibit greater catalytic activity for ORR than Pt, 1 however, Pt-Cu alloys would degrade under PEFC operating conditions. Therefore, we need to clarify dissolution mechanism of Pt-Cu alloys. In our previous work, we established channel flow double electrode (CFDE) for in-situ detection of Pt, and we proposed dissolution mechanism of Pt under simulating PEFC operating condition using CFDE. 2 In this study, we firstly improved CFDE to in-situ detect both Pt and Cu dissolved from Pr-Cu alloys, and then dissolution behavior of Pt-Cu alloys has been investigated by using this technique. Experimental In order to determine detection potential (E CE) of Cu2+ dissolved from Pt-Cu alloys, we prepared various concentration (0, 0.1, 0.5, 1.0 mM) of CuSO4, whose pH was adjusted to around 0.5 by adding H2SO4. Under laminar flow condition of the electrolyte (10 cm s-1), Au electrode was subjected to cathodic polarization at 298 K in Ar-purged these solutions. Potential range of the experiment from open circuit potential (OCP) to −0.2 V vs. SHE at 1 mV s-1. In order to confirm quantitativity of E CE determined by the cathodic polarization experiments, dissolved Cu2+ was detected on downstream Au collector electrode during anodic polarization of upstream Cu working electrode using channel flow cell. Au collector electrode potentiostatically polarized at (E CE=) 0, −0.1, and −0.2 V in Ar-purged 0.5 M H2SO4, when the working electrode anodically polarized from OCP to 1.0 V at 2 mV s-1. Results and Discussion Diffusion limiting current of residual oxygen was observed between 0.2 − −0.1 V in the cathodic polarization curve in 0 mM CuSO4 (Cu2+ free). And then, cathodic current increased by hydrogen evolution reaction (HER) below −0.1 V. On the other hand, cathodic current observed in the solution containing more than 0.1 mM CuSO4 was higher than that in 0 mM CuSO4. This is caused by the following reaction on the Au electrode: Cu2+ + 2e- → Cu. In addition, Cu2+ reduction current almost increased proportionally to Cu2+ concentration below −0.15 V. However, this concentration-dependent current overlapped with HER current. Therefore, quantitative determination of E CE for Cu2+ detection needs further experiments. Cu working current (i WE) exponentially increased with increasing potential from the OCP, and reached almost constant value (0.1 A cm-2). During this anodic polarization, Au collector current (i CE) at E CE = 0, −0.1, and −0.2 V shows similar trend in the i WE. After subtracting residual current from the i CE, we calculated dissolution current (i Diss.) using collection number (N = 0.38). When E CE was 0 V, i WE was not completely match i Diss. during the polarization, which means that E CE = 0 V is not quantitative potential for Cu2+ detection. On the contrary, i WE almost equals to i Diss. at E CE = −0.1, and −0.2 V. Hence, Cu2+ dissolved from Cu is quantitatively detected on Au electrode at E CE < −0.1 V. Reference 1. P. Strasser, S. Koh, and J. Greeley, Phys. Chem. Chem. Phys., 10, 3670 (2008). 2. Z. Wang, E. Tada, and A. Nishikata, J. Electrochem. Soc., 161 (4), F380 (2014).

Development of Porous Structured PtCu/C Catalyst Via Sputtering Method for Efficient Oxygen Reduction Reaction.

Polymer exchange membrane fuel cell (PEMFCs) is expected to be the promising candidate as the future clean energy sources. Especially, it is considered that the PEMFCs are suitable for applying to the transportation because of its various advantages such as high-power density, easy scale up and immediate response to change in the demand for power. However, due to the high cost of fuel cell system, it is difficult to commercialize of fuel cell automobiles. The system cost is usually depending on the usage of PGM catalyst in MEA. Herein, PtCu/C catalyst were synthesized by using sputtering method to reduce the amount of Pt which is occupying a large portion of the system cost. First, various ratio of PtCu nanoparticles were carried out onto the powder substrate by adjusting the sputter gun power. After then nanoparticles were transferred to carbon. Through the heat treatment and acid treatment, we can get mesoporous structured PtCu/C catalysts. This PtCu alloy catalyst shows similar or higher oxygen reduction reaction activity then that of commercial Pt/C even though the amount of Pt is much lower.

(Invited) Characterization and Functional Improvement of Nanoporous Metals

Dealloying of binary AgAu and ternary AgAuPt alloys has been proven to yield nanoporous metals (NPG and NPG-Pt) that are promising candidates as catalysts and smart materials. The alloy is exposed to electrolytic conditions at which it is favorable for one metal to dissolve, leaving behind a nanoporous network that is enriched in the other more noble metal(s) [1-2]. The structural stability, and catalytic activity of nanoporous metals are mainly affected by aspects including structural evolution, surface area stability and nanoscale composition. Achieving a deeper realization of the mechanisms that govern the nanoscale behavior in this material at such small scale is vital for pushing forward this class of materials to industrial applications. Thus, high-resolution characterization could be used to improve the already existing insights into the formation and tunability of nanoporous metals. Atom probe tomography (APT) of as-dealloyed and thermally coarsened NPG/NPG-Pt was enabled by inner-pore potentiostatic deposition of Cu (Fig 1) [3]. The recently demonstrated ability of complete infiltration of NPG/NPG-Pt with Cu brings attention to the peculiar electrochemical properties of NPG that are worth further consideration. A previous investigation by Lee et al. [4] on the electrodeposition of Cu onto nanoporous Pt, made by dealloying of CuPt alloys, revealed a sub-potential deposition regime that lies between the UPD (underpotential deposition) and the equilibrium deposition regimes. The sub-potential deposition regime was attributed to the curvature of the nanoporous Pt surface. We report a deeper understanding of the complete infiltration of NPG and NPG-Pt with potentiostatically electrodeposited Cu from acidic solutions of copper sulfate. The main parameters controlling the extent of filling are shown to include ligament /pore sizes, the concentration of Cu2+ ions in solution and the electrochemical parameters of the deposition. The crystallographic structure of Cu and its relation to that of the NPG substrate is also studied at high resolution. The infiltration of NPG and NPG-Pt at significant depths serves to highlight their interesting electroactive properties, and the great prospects that lie in using NPG as a template for growth of 3D nanostructures. Fig 1. Schematic of the electrochemical process by which NPG samples are formed and prepared for APT sample fabrication. From bulk AgAuPt alloy (a) selective dissolution of Ag creates a dealloyed layer of NPG-Pt (b). Consolidation of this open-cell network for APT sample preparation is then achieved by electrodeposition of Cu (c).

Nanoporous platinum-copper flowers for non-enzymatic sensitive detection of hydrogen peroxide and glucose at near-neutral pH values.

Multimodal nanoporous PtCu flowers(np-PtCu) were prepared via a two-step dealloying strategy under mild conditions. The np-PtCu alloy possesses an interconnected flower-like network skeleton with multiscale pore distribution. This material was placed on a glassy carbon electrode where it shows outstanding detection performance towards hydrogen peroxide and glucose in near-neutral pH solutions. It can be attributed to the specific structure in terms of interconnected nanoscaled ligaments, rich pore openings and a synergistic alloying effect. Figures of merit for detection H2O2 assay include (a) a working voltage of 0.7V (vs. the reversible hydrogen electrode); (b) a wide linear response range (from 0.01 to 1.7mM), and (c) a low detection limit (0.1μM). The respective data for the glucose assay are (a) 0.4V, (b) 0.01-2.0mM, and (c) 0.1μM. The method is not interfered in the presence of common concentrations of dopamine, acetaminophen and ascorbic acid. Graphical abstract Multimodal nanoporous (np) PtCu alloy was prepared via a two-step dealloying strategy under mild conditions. Np-PtCu exhibits superior electrocatalytic activity. The assay is highly sensitive, selective, and it allows for along-term detection of H2O2 and glucose.

Deep eutectic solvent-assisted synthesis of highly efficient PtCu alloy nanoclusters on carbon nanotubes for methanol oxidation reaction

Deep eutectic solvents are promising in the green synthesis of advanced functional materials owing to their several distinct advantages including good solubility, wide electrochemical window, high conductivity, low cost, nontoxicity and tolerance to humidity. Herein, we report a novel green protocol to design the hybrid PtCu nanoclusters on multi-walled carbon nanotubes in deep eutectic solvents medium without adding any surface controlling agent. Subsequently, the structure, elemental composition and electrocatalytic aspects of the as-synthesized nanohybrids are characterized by transmission electron microscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopic features and electrochemical investigations. Typically, the synthesis medium plays a key role to control the dispersion of Pt-based nanoparticles and to enhance the electronic transfer interaction among the catalytic nanoparticles and support material. On other hand, the addition of alloyed Cu not only further decreases the crystallite size of catalytic particles but also results in the formation of cluster nanostructure with the coarse surface. Moreover, the methanol oxidation electrocatalytic activity of the as-fabricated material is clearly composition dependent, their maximum mass activity (Pt/Cu mass ratio 1:0.25) is about 2.5 times that of the carbon nanotubes-supported monometallic Pt catalyst. And it also presents the good CO-tolerance ability and evident long-term electrochemical durability. This study suggests that the synthesis strategy in deep eutectic solvents is of great importance to design and fabricate the high-performance electrocatalysts for fuel cells applications.

The Combination of Bipolar Electrolytic and Galvanic Method to Synthesize CuPt Nano-Alloy Electrocatalyst for Direct Ethanol Fuel Cell

CuPt nano alloy-particles were successfully synthesized by a combination of the methods of bipolar electrolytic and galvanic replacement. Cu2O nanoparticles prepared by a bipolar electrolytic method were used as the sacrificial templates for galvanic replacement reactions with H2PtCl6 solutions. The size of Cu2O nanoparticles was optimized by changing the electrolytic parameters to obtain fine nanoparticles. SEM and TEM analyses showed that Cu2O nanoparticles were grown in a crystal shape with a grain size of about 100 nm. The XRD results indicated that Cu2O nanoparticles were grown in a face-centered cubic structured crystal. The effects of the amount of H2PtCl6 solution on the structure, morphology, composition and electrocatalysis of CuPt were investigated. The phase analysis by XRD showed the presence of CuPt crystalline phases with a rhomb-centered structure. The SEM images indicated that the crystalline shape of Cu2O was turned into a spherical shape with the size expanded to 140 nm after galvanic reaction. The absorption analysis showed that there was one absorption peak at a wavelength of 500 nm for Cu2O while no absorption peak was observed for CuPt alloys. Additionally, compositional analysis by EDX showed that the main components of the alloys were Cu and Pt. The presence of O on the samples indicated that the galvanic reactions were not complete. The cyclic voltammetry measurement showed that CuPt nano alloy-particles exhibit better ethanol oxidation in an alkali medium compared with bare Pt.

Dragon fruit-like Pt-Cu@mSiO2 nanocomposite as an efficient catalyst for low-temperature ethanol steam reforming

The critical problem facing catalysts for the LT-ESR is deactivation owing to sintering of the active metal and carbon deposition. To solve this problem, a dragon fruit-like Pt-Cu@mSiO2 catalyst for LT-ESR reaction has been successfully fabricated by a facile encapsulation strategy. Structural and morphological analysis shows that the Pt-Cu@mSiO2 nanocomposite (approximately 400 nm) has a uniform dragon fruit-like structure, with well crystallized Pt-Cu alloy nanoparticles (about 50 nm) embedded in the mSiO2. Benefiting from the unique components and architectural features, the dragon fruit-like Pt-Cu@mSiO2 nanocomposite with optimal Pt/Cu ratio present superior performance than that of Pt@mSiO2, Cu@mSiO2 and supported Pt-Cu/mSiO2 catalysts in terms of activity, H2 selectivity, and stability in the LT-ESR reaction. Moreover, the synergistic effect of platinum and copper can substantially decrease the CO concentration. It is crucial that the mesoporous SiO2 shell not only make the embedded Pt-Cu alloy nanoparticles easily accessible but also effectively prevent leaching and aggregation of active sites as well as spatially suppress the carbon deposition on the active surface, thus maintain a good catalytic activity during the 150 h stability test at 400 °C.

Insights into thermal annealing of highly-active PtCu3/C Oxygen Reduction Reaction electrocatalyst: An in-situ heating transmission Electron microscopy study

Thermal annealing processes for supported Pt-based nanoparticles are usually developed based on iterative empirical findings resulting from ex-situ characterization of pre- and post-annealed samples. Such an approach, however, offers limited insight into processes occurring during the heating step. In this work, we first exemplify typical findings that are accessible by ex-situ investigation using typical conventional techniques such as transmission electron microscopy (TEM), X-ray diffraction (XRD), and thin film – rotating disc electrode (TF-RDE). As a model system we select a well-researched Pt-Cu alloy which, as demonstrated, offers exciting new insights into the dynamics occurring during heat treatment on the nano-to-atomic scale. This dynamics can be viewed by upgrading the ex-situ findings with a high resolution TEM imaging in combination with carefully designed in-situ heating protocol. This way one can directly observe the particle growth mechanisms during heat treatment. Such direct observations, in turn, provide new understanding of morphology-performance correlations in alloys. For example, it is shown that the enhanced activity of the present PtCu3/C electrocatalyst is due to Cu enrichment during heat treatment. This enrichment, however, is only possible due to the presence of relatively large excess CuO needle-like particles left over from the previous double passivation galvanic displacement step. Very importantly, we further show that the mechanism of Cu enrichment at elevated temperatures involves migration of Cu single atoms via the carbon support. At moderate temperatures (up to 500 °C), other effects have also been observed such as reshaping into a sphere-like shape as well as ordering of the crystal lattice which could not occur without enrichment of the initial Pt-Cu nanoparticles with Cu. In that region, Cu enrichment is also responsible for the initial growth of PtCu nanoparticles. By contrast, upon heating till 800 °C, the growth is mainly due to coalescence. Ostwald ripening, on the other hand, does not seem to play a significant role in the increase in the nanoparticle size. The new general insights can be readily extended to various other similar alloy systems.

Synthesis and Characterization of Nitrogen Doped Reduced Graphene Oxide (N-rGO) Supported PtCu Anode Catalysts for Direct Methanol Fuel Cell.

Incomplete methanol oxidation and rapid activity degradation of electro-catalysts are key barriers to successful commercialization of direct methanol fuel cell (DMFC). To address these problems, we report the synthesis of platinum-copper (PtCu) alloy nanoparticles supported on nitrogen doped reduced graphene oxide (N-rGO) as the anode catalyst for the efficient electro-oxidation of methanol. Catalysts with varying molar ratios of PtCu were fabricated using impregnation reduction method and their electrochemical performance was compared with the commercially available Pt/C (20 wt%) anode catalyst. The electro-catalytic activity of the synthesized PtCu (1:2)/N-rGO catalyst was found to be much higher to those that observed for Pt/N-rGO and Pt/C catalyst as revealed by cyclic voltammetry, electrochemical impedance spectroscopy and electron transfer measurements. The enhanced electrochemical activity of PtCu (1:2)/N-rGO catalyst is not only attributed to strong interfacial interaction between the nitrogen group of N-rGO and PtCu active metal phase but also to the altered electronic structure of Pt as a result of Cu alloying. This reduces the adsorption of CO and OH- species on Pt surface, thereby creating more Pt active sites for methanol electro-oxidation; thus faster kinetics is exhibited. These results indicate the potential application of PtCu/N-rGO catalyst as an anode material in a DMFC.

PtCu nanoframes as ultra-high performance electrocatalysts for methanol oxidation

Despite tremendous progress has been achieved in the past two decades, the lack of high-performance catalysts suitable for long-term operation remains a great challenge in realizing the commercial application of direct methanol fuel cell technology. Here, we reported a simple approach for one-pot synthesis of PtCu alloy nanoframes along with their exciting electro-catalytic performance for methanol oxidation. PtCu alloys with highly-open nanoframe structures have been achieved in presence of a structure-directing agent like polyvinyl pyrrolidone (PVP) and reducing solvent like sodium borohydride. Such PtCu alloy nanoframes show tremendous improvement in the methanol electrooxidation with a highest mass activity of 1.64 A mgPt−1 (much lower onset potential compared to Pt alone), which is believed to be much higher compared to that of the commercial Pt/C catalyst and most of the literature reports, indicating a better alloy formation and highly active sites created by highly open nanoframes structures.

Morphology-Controlled Pt Alloy Nanoparticles for Oxygen Reduction Reaction

Proton-exchange membrane (PEM) fuel cell, which can provide clean electricity with high efficiency, is essential for improving the sustainability of our society. Since oxygen reduction reaction (ORR) limits the performance of PEM fuel cells, precious platinum catalyst is crucial in the cathode electrode. Recently, Pt and its alloy nanoparticles (NPs) with controlled morphology have been attracted to reduce the amount of Pt loading. For example, nano-frames, nao-rods, nano-plates, etc. have been reported. As reduction rate and/or stability of a chemical reaction from ionic to metallic state play a key role to synthesize morphology-controlled NPs, in 233rd ECS meeting, we have shown a control technique of oxidation-reduction potential (ORP). However, the controllable range of ORP was revealed to be narrow, which suggests that controllability of the reduction rate needs to be extended. In order to delay the reduction rate for morphology control of Pt alloy NPs, solid precursor instead of ionic counterpart is hopeful. Herein, ammonium hexachloroplatinate which is generated in recycling process is chosen as Pt precursor. The ammonium hexachloroplatinate hardly dissolves in aqueous ammonium chloride solution, whereas it is known to dissolve well in water. In the present work, we demonstrate a facile synthesis method of morphology-controlled Pt alloy NPs by using solid Pt precursor. The ammonium hexachloroplatinate was chemically reduced with Cu ions on carbon support. Synthetic solution was adjusted to be water or ammonium chloride solution, and the samples were labelled as without-NH4Cl and with-NH4Cl, respectively. Transmission electron microscope (TEM) observation revealed that, in the without-NH4Cl, highly dispersed small NPs were deposited on carbon support. On the other hand, in the with-NH4Cl, catalytic NPs were obviously larger than those in the without-NH4Cl, and the morphology was not spherical but plate-like. X-ray diffraction (XRD) profiles indicated that crystal phases of both samples were mainly composed of Pt-Cu alloy crystal. ORR catalytic activities were measured for the small Pt alloy NPs (without-NH4Cl), the plate-like Pt alloy NPs (with-NH4Cl) and commercial Pt. Compared to the commercial Pt, electrochemical active surface area (ECSA) of the without-NH4Cl was almost the same and that of the with-NH4Cl was relatively smaller. This hierarchy is corresponding to particle diameters obtained by the TEM observation. Mass activities of our samples were higher than the commercial Pt, especially, the without-NH4Cl showed a 2-fold increase. The with-NH4Cl exhibited 4 times higher specific activity. Therefore, plate-like Pt alloy NPs will achieve drastically higher mass activity if ECSA is improved. In order to explain the ORR catalytic activities of the synthetic samples, a model of structure of the catalytic NPs was constructed (see Figure). The with-NH4Cl has larger diameter of the catalytic NPs, which indicates more atoms are located at the core of the particles. Since Pt atoms at the core are catalytically inactive, with-NH4Cl showed smaller ECSA than the without-NH4Cl. However, at the same time, the without-NH4Cl has more Cu atoms at the surface, and exposed Cu atoms are easy to leach out during potential scans in acidic solution. In Pt alloy catalysts, transition metals including Cu exhibit an important synergistic effect. When Cu atoms combine with Pt atoms, electronic state of surface Pt changes and surface adsorption energy is tuned, which contributes to an enhancement of ORR catalytic activity. As a result, with-NH4Cl which has larger diameter inhibited leaching of Cu atoms at the core, and sustained the synergistic effect to enhance specific activity. Moreover, plate-like morphology of the with-NH4Cl can be another factor of the high specific activity by selective exposure of active facet. It is reported that Pt nano-plates selectively expose active facet and exhibit high specific activity. In conclusion, we adjusted concentration of ammonium chloride in aqueous synthetic solution to control reduction rate of Pt and morphology of Pt alloy NPs supported on carbon. Highly dispersed small Pt alloy NPs were synthesized in water, whereas plate-like Pt alloy NPs which showed high specific activity were synthesized in aqueous ammonium chloride solution. However, when the concentration of ammonium chloride is excess, the chemical reduction of Pt is inhibited and synthetic yield decreases. Thus, the addition amount of ammonium chloride requires careful consideration. Figure 1

Ferroxidase-like and antibacterial activity of PtCu alloy nanoparticles

Many metal nanoparticles are reported to have intrinsic enzyme-like activities and offer great potential in chemical and biomedical applications. In this study, PtCu alloy nanoparticles (NPs), synthesized through hydrothermal treatment of Cu2+ and Pt2+ in an aqueous solution, were evaluated for ferroxidase-like and antibacterial activity. Electron spin resonance (ESR) spectroscopy and colorimetric methods were used to demonstrate that PtCu NPs exhibited strong ferroxidase-like activity in a weakly acidic environment and that this activity was not affected by the presence of most other ions, except silver. Based on the color reaction of salicylic acid in the presence of Fe3+, we tested the ferroxidase-like activity of PtCu NPs to specifically detect Fe2+ in a solution of an oral iron supplement and compared these results with data acquired from atomic absorption spectroscopy and the phenanthroline colorimetric method. The results showed that the newly developed PtCu NPs detection method was equivalent to or better than the other two methods used for Fe2+ detection. The antibacterial experiments showed that PtCu NPs have strong antibacterial activity against Staphylococcus aureus and Escherichia coli. Herein, we demonstrate that the peroxidase-like activity of PtCu NPs can catalyze H2O2 and generate hydroxyl radicals, which may elucidate the antibacterial activity of the PtCu NPs against S. aureus and E. coli. These results showed that PtCu NPs exhibited both ferroxidase- and peroxidase-like activity and that they may serve as convenient and efficient NPs for the detection of Fe2+ and for antibacterial applications.

Nickel-Ion-Oriented Fabrication of Spiny PtCu Alloy Octahedral Nanoframes with Enhanced Electrocatalytic Performance

Metal cation is an emerging type of morphology controlling agency in nanoscience, but has rarely been used in fabrication of hollow structures. Herein, with the addition of Ni2+ ion, PtCu alloy oct...

The Construction of Pt-based Catalyst Based on Exquisite Cu-doped CeO2 Nanotubes for Methanol Electrooxidation

The novel Cu-doped CeO2 (Ce1‐xCuxO2‐δ) nanotubes as a superior co-catalyst have been primarily fabricated by coupling reflux with thermolysis methods. Then scanning electron microscopy and transmission electron microscopy reveal that the length of nanotube ranges from 200 nm to 700 nm and its diameter is about 80 nm, and interestingly, these nanotubes can orderly build up into the unique 3D nanobundles. After depositing Pt nanoparticles onto the hybrid support consisted of Vulcan XC-72R and Ce1‐xCuxO2‐δ, a few PtCu alloys appear on the surface of Ce1‐xCuxO2‐δ nanotubes. Afterwards, correlative evaluations declare clearly that Pt/C-Ce0.8Cu0.2O2‐δ catalyst possesses better electrocatalytic performance and CO resistance, and its electrochemical specific surface area (ECSA) is as high as 142.9 m2·g‐1, which is one of the best outcomes reported up to now. The fortified catalytic performance of Pt/C-Ce0.8Cu0.2O2‐δ may be because the introduction of Cu atom improves the electric conductivity and oxygen vacancy of CeO2, moreover, the hollow structure of nanotubes is beneficial to enhance the charge transfer and ECSA. Therefore, this study not only confirms an extremely handy pathway to synthesize the particular structure, but also offers more possibilities for the development of efficient electrocatalyst in methanol oxidation.

CO-assisted ex-situ chemical activation of Pt-Cu/C oxygen reduction reaction electrocatalyst

In the future, low-temperature proton exchange membrane fuel cells (PEMFC), together with batteries, are expected to compete and eventually replace conventional combustion engines in the automotive industry. Currently, the most promising strategy towards cost-effective and highly-active oxygen reduction reaction (ORR) electrocatalysts seems to be alloying of Pt with less expensive and less noble 3d transition metals (Cu, Co and Ni, …). A crucial issue to be resolved in the near future is, however, to bridge the gap between the remarkable activities measured on the laboratory scale with thin film rotating disk electrode (TF-RDE) and the industrial membrane electrode assembly (MEA). In the case of Pt-Cu alloy, one of the major reasons for this difficulty is inadequate removal of unstable Cu or in other words, improper ‘activation’. Inadequately removed Cu can act as an impurity by poisoning the Pt surface via the well-known underpotential deposition (UPD) interaction, resulting in the inhibition of ORR performance. Due to highly favourable experimental conditions, in-situ electrochemical activation (in-situ EA) in TF-RDE setup masks many of the issues one experiences when trying to do the same ex-situ. Thus, matching the ORR performance obtained after in-situ EA with ex-situ CA in the case of Pt-Cu system has not been properly addressed so far. Based on a deeper understanding of in-situ EA of our in-house designed Pt-Cu/C electrocatalyst we here demonstrate development of carbon monoxide (CO) assisted ex-situ CA method. By using this gram scale ex-situ CA method, we for the first time show that a Pt-Cu system can achieve very high ORR performances in TF-RDE setup without any need for the use of in-situ EA.

Engineering the electronic structure of single atom Ru sites via compressive strain boosts acidic water oxidation electrocatalysis

Single-atom precious metal catalysts hold the promise of perfect atom utilization, yet control of their activity and stability remains challenging. Here we show that engineering the electronic structure of atomically dispersed Ru1 on metal supports via compressive strain boosts the kinetically sluggish electrocatalytic oxygen evolution reaction (OER), and mitigates the degradation of Ru-based electrocatalysts in an acidic electrolyte. We construct a series of alloy-supported Ru1 using different PtCu alloys through sequential acid etching and electrochemical leaching, and find a volcano relation between OER activity and the lattice constant of the PtCu alloys. Our best catalyst, Ru1–Pt3Cu, delivers 90 mV lower overpotential to reach a current density of 10 mA cm−2, and an order of magnitude longer lifetime over that of commercial RuO2. Density functional theory investigations reveal that the compressive strain of the Ptskin shell engineers the electronic structure of the Ru1, allowing optimized binding of oxygen species and better resistance to over-oxidation and dissolution. While Ru-based electrocatalysts are among the most active for acidic water oxidation, they suffer from severe deactivation. Now, Yuen Wu, Wei-Xue Li and co-workers report a core–shell Ru1–Pt3Cu catalyst with surface-dispersed Ru atoms for a highly active and stable oxygen evolution reaction in acid electrolyte.

Monodisperse CuPt alloy nanoparticles assembled on reduced graphene oxide as catalysts in the transfer hydrogenation of various functional organic groups

We present herein a new nanocatalyst, namely binary CuPt alloy nanoparticles (NPs) supported on reduced graphene oxide (CuPt‐rGO), as a highly active heterogeneous catalyst for the transfer hydrogenation (TH) protocol that is demonstrated to be applicable over the reduction of various unsaturated organic compounds (olefins, aldehydes/ketones and nitroarenes) in aqueous solutions at room temperature. CuPt alloy NPs were synthesized by the co‐reduction of metal (II) acetylacetonates by borane‐tert‐butylamine (BTB) complex in hot oleylamine (OAm) solution and then assembled on reduced graphene oxide (rGO) via ultrasonic‐assisted liquid phase self‐assembly method. The structure of yielded CuPt NPs and CuPt‐rGO nanocatalyst were characterized by TEM, XRD and ICP‐MS. The activity of Cu7Pt3‐rGO nanocatalysts were then tested for the THs that were conducted in a commercially available high‐pressure tube using water as sole solvent and ammonia borane as a hydrogen donor at room temperature. The presented catalytic TH protocol was successfully applied over nitroarenes, olefines and aldehydes/ketones, and all the tested compounds were converted to corresponding reduction products with the yields reaching up to 99% under ambient conditions. Moreover, the Cu7Pt3‐rGO nanocatalyst was also reusable in the TH by providing 99% yield after five consecutive runs in TH of nitrobenzene as an example.

CuPt Alloy Thin Films for Application in Spin Thermoelectrics

Spin thermoelectrics represents a new paradigm of thermoelectricity that has a potential to overcome the fundamental limitation posed by the Wiedmann-Franz law on the efficiency of conventional thermoelectric devices. A typical spin thermoelectric device consists of a bilayer of a magnetic insulator and a high spin-orbit coupling (SOC) metal coated over a non-magnetic substrate. Pt is the most commonly used metal in spin thermoelectric devices due to its strong SOC. In this paper, we found that an alloy of Cu and Pt can perform much better than Pt in spin thermoelectric devices. A series of CuPt alloy films with different Pt concentrations were deposited on yttrium iron garnet (YIG) films coated gadolinium gallium garnet (GGG) substrate. Through spin Seebeck measurements, it was found that the Cu0.4Pt0.6/YIG/GGG device shows almost 3 times higher spin Seebeck voltage compared to Pt/YIG/GGG under identical conditions. The improved performance was attributed to the higher resistivity as well as enhanced spin hall angle of the CuPt layer.