A strategy for fabricating porous PdNi@Pt core-shell nanostructures and their enhanced activity and durability for the methanol electrooxidation

Cyanogel-Induced Synthesis of RuPd Alloy Networks for High-Efficiency Formic Acid Oxidation

For direct formic acid fuel cells (DFAFC), palladium (Pd)-based alloy catalysts with competitive morphology and elemental composition are essential to boost the performance of the formic acid oxidation reaction (FAOR) in the anode zone. Herein, we design and synthesize RuPdx alloy nano-network structures (ANs) via the facile wet-chemical reduction of Pd-Ru cyanogel (Pdx [Ru(CN)6]y·aH2O) as an effective electrocatalyst for the FAOR. The formation of Pd-Ru cyanogel depends on the facile coordination of K2PdCl4 and K3 [Ru(CN)6]. The unique structure of cyanogel ensures the presentation of a three-dimensional mesoporous morphology and the homogeneity of the elemental components. The as-prepared RuPd3 ANs exhibit good electrocatalytic activity and stability for the FAOR. Notably, the RuPd3 ANs achieve a mass-specific activity of 2068.4 mA mg−1 in FAOR, which shows an improvement of approximately 16.9 times compared to Pd black. Such a competitive FAOR performance of RuPd3 ANs can be attributed to the advantages of structure and composition, which facilitate the exposure of more active sites, accelerate mass/electron transfer rates, and promote gas escape from the catalyst layer, as well as enhance chemical stability.

Zinc-Coordination Polymer-Derived Porous Carbon-Supported Stable PtM Electrocatalysts for Methanol Oxidation Reaction

Porous carbon (PC) is obtained by carbonizing a zinc-coordination polymer (MOF-5) at 950 °C and PtM (M = Fe, Co, Ni, Cu, Zn) nanoparticles (NPs), which are deposited on PC using the polyol method. Structural and morphological characterizations of the synthesized materials are carried out by powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM), and the porosity was determined using a N2 adsorption/desorption technique. The results revealed that PtM NPs are alloyed in the fcc phase and are well dispersed on the surface of PC. The electrochemical results show that PtM/PC 950 catalysts have higher methanol oxidation reaction (MOR) performances than commercial Pt/C (20%) catalysts. After 3000 s of chronoamperometry (CA) test, the MOR performances decreased in the order of Pt1Cu1/PC 950 > Pt1Ni1/PC 950 > Pt1Fe1/PC 950 > Pt1Zn1/PC 950 > Pt1Co1/PC 950. The high MOR activities of the synthesized catalysts are attributed to the effect of M on methanol dissociative chemisorption and improved tolerance of Pt against CO poisoning. The high specific surface area and porosity of the carbon support have an additional effect in boosting the MOR activities. Screening of the first row transition metals (d 5+n , n = 1, 2, 3, 4, 5) alloyed with Pt binary catalysts for MOR shows that Pt with d 8 (Ni) and d 9 (Cu) transition metals, in equivalent atomic ratios, are good anode catalysts for alcohol fuel cells.

Sustainable NO removal and its sensitive monitoring at room temperature by electrogenerated Ni (I) electron mediator

Online monitoring of gas pollutants in the gas phase at room temperature using an electrochemical macro gas flow sensor is challenging and important for the pollutant treatment process. In this work, for the first time, we tried to explore the homogeneous and heterogeneous application of Ni(II) (CN)₄^2- in the KOH environment for the removal and monitoring of toxic nitric oxide gas. The homogeneous electrogenerated Ni(I) (CN)₄^3- was effectively removing the toxic nitric oxide gas by electro scrubbing method and the novel Ni(II) (CN)₄^2- and KOH modified electrode used for heterogeneous sensor application with high sensitivity, and reliability toward Nitric oxide gas. The sensor showed enhanced gas diffusion and high sensitivity. Scanning electron microscopy and X-ray diffraction confirmed the modification of the carbon felt electrode. In a high concentrated KOH environment, the active mediator stabilized the sensor for a long time compared to the neutral environment. The Ni(II) (CN)₄^2- fabricated carbon felt was used to monitor the concentration of nitric oxide gas pollutant; the calculated sensitivity was approximately -0.33 mA ppm^-1 cm^-2. The current increased linearly with increasing nitric oxide concentration up to 12 ppm and was validated by online gas chromatography. The developed electrochemical gas flow sensor successfully monitored the unremoved nitric oxide gas at the exit from the MER electro-scrubbing process; the concentration was calculated using a calibration plot.

Boosting Oxygen Electroreduction over Strained Silver

Manipulating the strain effect of Ag without any foreign metals to boost its intrinsic oxygen reduction reaction (ORR) activity is intriguing, but it remains a challenge. Herein, we developed a class of Ag-based electrocatalysts with tunable strain structures for efficient ORR via ligand-assisted competitive decomposition of Ag-organic complexes (AgOCs). Benefiting from the superior coordination capability, 4,4'-bipyridine as a ligand triggered a stronger competition with NaBH₄ for Ag ions during reduction-induced decomposition of AgOCs in comparison with the counterparts of the pyrazine ligand and the NO₃^- anion, which moderately modulated the compressive strain structure to upshift the d-band center of the catalyst and increase the electron density of Ag. Accordingly, the O₂ adsorption was obviously improved, and the stronger repulsion effect between the Ag sites and the 4e ORR product, i.e., the electron-rich OH^-, was generated to promote the desorption of OH^- via the Ag-OH bond cleavage, which enabled more Ag sites to be regenerated after ORR. Both of these led to an enhancement to the intrinsic ORR activity of the Ag-based catalyst. This competitive decomposition of metal-organic complex strategy would provide a facile method to design other catalysts with the well-tuned strain structures for energy conversion and heterocatalysis.

Phase transition and thermal stability of epitaxial PtSe2 nanolayer on Pt(111)

This work relates to direct synthesis of the two-dimensional (2D) transition metal dichalchogenide (TMD) PtSe₂ using an original method based on chemical deposition during immersion of a Pt(111) surface into aqueous Na₂Se solution. Annealing of the sample induces significant modifications in the structural and electronic properties of the resulting PtSe₂ film. We report systematic investigations of temperature dependent phase transitions by combining synchrotron based high-resolution X-ray photoemission (XPS), low temperature scanning tunnelling microscopy (LT-STM) and low energy electron diffraction (LEED). From the STM images, a phase transition from TMD 2H-PtSe₂ to Pt₂Se alloy monolayer structure is observed, in agreement with the LEED patterns showing a transition from (4 × 4) to (√3 × √3)R30° and then to a (2 × 2) superstructure. This progressive evolution of the surface reconstruction has been monitored by XPS through systematic de-convolution of the Pt4f and Se3d core level peaks at different temperatures. The present work provides an alternative method for the large scale fabrication of 2D transition metal dichalchogenide films.

LEED, STM and XPS techniques were used to systematically study a temperature-dependent phase transition on a PtSe₂ film grown on the surface of Pt(111) by a chemical deposition method.

Pt-Ni@PC900 Hybrid Derived from Layered-Structure Cd-MOF for Fuel Cell ORR Activity

Fuel cell technology is the supreme alternate option for the replacement of fossil fuel in the current era. Pt alloys can perform well as fuel cell electrodes for being used as catalytic materials to perform the very notorious oxygen reduction reaction. In this regard, first, a layered metal-organic framework with empirical formula [C₈H₁₀CdO₇] _n ·4H₂O is synthesized and characterized using various experimental and theoretical techniques. Then, a nanostructured porous carbon material with a sheet morphology (PC900) having a high BET surface area of 877 m² g^-1 is fabricated by an inert-atmosphere thermal treatment of the framework upon heating up to 900 °C. Pt and Ni nanoparticles are embedded into PC900 to prepare a homogenized hybrid functional material, i.e., Pt-Ni@PC900. The Pt-Ni@PC900 hybrid is proved to be an excellent ORR catalyst in terms of half-wave potential and limiting current density with 7% Pt loading compared with the commercially available 20% Pt/C catalyst. Pt-Ni@PC900 also shows stability of current up to 12 h with only a very small variation in current. This work highlights the importance of Pt alloys in future large-scale commercial applications of fuel cells.

Fast Hydrogenation and Dehydrogenation of Pt/Pd Bimetal Decorated over Nano-Structured Ag Islands Grown on Alumina Substrates

This study reports the fast hydrogenation and dehydrogenation of ultra-thin discrete platinum/palladium (Pt/Pd) bimetal over nano-structured Ag islands grown on rough alumina substrate by a RF magnetron sputtering technique. The morphology of Ag nanoislands was optimized by RF magnetron sputtering and rapid thermal annealing process. Later, Pt/Pd bimetal (10/10) nm were deposited by RF magnetron sputtering on the nanostructured Ag islands. After the surface morphological optimization of Ag nanoislands, the resultant structure Pt/Pd@Ag nanoislands at alumina substrate showed a fast and enhanced hydrogenation and dehydrogenation (20/25 s), response magnitude of 2.3% (10,000 ppm), and a broad detection range of 500 to 40,000 ppm at the operating temperature of 120 °C. The superior hydrogenation and dehydrogenation features can be attributed to the hydrogen induced changes in the work function of Pt/Pd bimetal which enhances the coulomb scattering of percolated Pt/Pd@Ag nanoislands. More importantly, the atomic arrangements and synergetic effects of complex metal alloy interfacial structure on Ag nanoislands, supported by rough alumina substrate incorporate the vital role in accelerating the H₂ absorption and desorption properties.

Ultrathin Metallic Nanowire-Based Architectures as High-Performing Electrocatalysts

Fuel cells (FCs) convert chemical energy into electricity through electrochemical reactions. They maintain desirable functional advantages that render them as attractive candidates for renewable energy alternatives. However, the high cost and general scarcity of conventional FC catalysts largely limit the ubiquitous application of this device configuration. For example, under current consumption requirements, there is an insufficient global reserve of Pt to provide for the needs of an effective FC for every car produced. Therefore, it is absolutely necessary in the future to replace Pt either completely or in part with far more plentiful, abundant, cheaper, and potentially less toxic first row transition metals, because the high cost-to-benefit ratio of conventional catalysts is and will continue to be a major limiting factor preventing mass commercialization. We and other groups have explored a number of nanowire-based catalytic architectures, which are either Pt-free or with reduced Pt content, as an energy efficient solution with improved performance metrics versus conventional, currently commercially available Pt nanoparticles that are already well established in the community. Specifically, in this Perspective, we highlight strategies aimed at the rational modification of not only the physical structure but also the chemical composition as a means of developing superior electrocatalysts for a number of small-molecule-based anodic oxidation and cathodic reduction reactions, which underlie the overall FC behavior. In particular, we focus on efforts to precisely, synergistically, and simultaneously tune not only the size, morphology, architectural motif, surface chemistry, and chemical composition of the as-generated catalysts but also the nature of the underlying support so as to controllably improve performance metrics of the hydrogen oxidation reaction, the methanol oxidation reaction, the ethanol oxidation reaction, and the formic acid oxidation reaction, in addition to the oxygen reduction reaction.

Microwave-Assisted Synthesis of Highly Dispersed PtCu Nanoparticles on Three-Dimensional Nitrogen-Doped Graphene Networks with Remarkably Enhanced Methanol Electrooxidation

A well-dispersed PtCu alloy nanoparticles (NPs) on three-dimensional nitrogen-doped graphene (PtCu/3D N-G) electrocatalyst has been successfully synthesized by a conventional hydrothermal method combined with a high-efficiency microwave-assisted polyol process. The morphology, composition, and structures are well-characterized by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy. Cyclic voltammograms illustrate that the as-prepared PtCu/3D N-G electrocatalyst possesses the larger electrochemical active surface area, lower onset potential, higher current density, and better tolerance to CO poisoning than PtCu NPs on reduced graphene oxide and XC-72 carbon black in acid solution. In addition, long-time chronoamperometry reveals that the PtCu/3D N-G catalyst exhibits excellent stability even longer than 60 min toward acid methanol electrooxidation. The remarkably enhanced performance is related to the combined effects of uniformly interconnected three-dimensional porous graphene networks, nitrogen doping, modified Pt alloy NPs, and strong binding force between Pt alloy NPs and 3D N-G structures.

PdCo/Pd-Hexacyanocobaltate Hybrid Nanoflowers: Cyanogel-Bridged One-Pot Synthesis and Their Enhanced Catalytic Performance

Elaborate architectural manipulation of nanohybrids with multi-components into controllable 3D hierarchical structures is of great significance for both fundamental scientific interest and realization of various functionalities, yet remains a great challenge because different materials with distinct physical/chemical properties could hardly be incorporated simultaneously into the synthesis process. Here, we develop a novel one-pot cyanogel-bridged synthetic approach for the generation of 3D flower-like metal/Prussian blue analogue nanohybrids, namely PdCo/Pd-hexacyanocobaltate for the first time. The judicious introduction of polyethylene glycol (PEG) and the formation of cyanogel are prerequisite for the successful fabrication of such fascinating hierarchical nanostructures. Due to the unique 3D hierarchical structure and the synergistic effect between hybrid components, the as-prepared hybrid nanoflowers exhibit a remarkable catalytic activity and durability toward the reduction of Rhodamine B (RhB) by NaBH₄. We expect that the obtained hybrid nanoflowers may hold great promises in water remediation field and beyond. Furthermore, the facile synthetic strategy presented here for synthesizing functional hybrid materials can be extendable for the synthesis of various functional hybrid nanomaterials owing to its versatility and feasibility.

Highly Porous Carbon Derived from MOF-5 as a Support of ORR Electrocatalysts for Fuel Cells

The development of highly competent electrocatalysts for the sluggish oxygen reduction reaction (ORR) at cathodes of proton-exchange membrane fuel cells (PEMFCs) is extremely important for their long-term operation and wide applications. Herein, we present highly efficient ORR electrocatalysts based on Pt/Ni bimetallic nanoparticles dispersed on highly porous carbon obtained via pyrolysis of a metal-organic framework MOF-5. In comparison to the commercial Pt/C (20%), the electrocatalyst Pt-Ni/PC 950 (15:15%) in this study exhibits a pronounced positive shift of 90 mV in Eonset. In addition, it also demonstrates excellent long-term stability and durability during the 500-cycle continue-oxygen-supply (COS) accelerating durability tests (ADTs). The significantly improved activity and stability of Pt-Ni/PC 950 (15:15%) can be attributed to the Pt electron interaction with Ni and carbon support as has been proved in X-ray and microscopic analysis.

Ultrafine Pt nanoparticle decoration with CoP as highly active electrocatalyst for alcohol oxidation

Ultrafine Pt nanoparticles decorated with CoP provide a promising bifunctional electrocatalyst for alcohol oxidation.

PtCu nanodendrite-assisted synthesis of PtPdCu concave nanooctahedra for efficient electrocatalytic methanol oxidation

PtPdCu alloy concave nanooctahedra show superior electrocatalytic activity and durability for the methanol oxidation reaction.