Ru-assisted synthesis of Pd/Ru nanodendrites with high activity for ethanol electrooxidation

Sustainable Ammonia Electrosynthesis from Nitrate Wastewater Coupled to Electrocatalytic Upcycling of Polyethylene Terephthalate Plastic Waste

Integrating the nitrate reduction reaction (NO₃RR) with polyethylene terephthalate (PET) hydrolysate oxidation to construct the nitrate/PET hydrolysate coelectrolysis system holds a great promise of realizing the simultaneous upcycling of nitrate wastewater and PET plastic waste, which, however, is still an almost untouched research area. Herein, we develop an ultralow content of Ru-incorporated Co-based metal-organic frameworks as a bifunctional precatalyst, which can be in situ reconstructed to Ru-Co(OH)₂ at the cathode and Ru-CoOOH at the anode under electrocatalytic environments, and function as real active catalysts for the NO₃RR and PET hydrolysate oxidation, respectively. With a two-electrode nitrate/PET hydrolysate coelectrolysis system, the current density of 50 mA cm^-2 is achieved at a cell voltage of only 1.53 V, realizing the simultaneous production of ammonia and formate at a lower energy consumption. This study provides a concept for the construction of coelectrolysis systems for upcycling of nitrate wastewater and PET plastic waste.

Organic Hybrid Antimoniotungstate Layered Ionic Crystal: Synthesis, Structure, and Interlayer-Confined Proton Conduction

A synchronous crystal- and microstructure-dependent strategy was implemented to synthesize the organic hybrid antimoniotungstate layered ionic crystal Na_5.5H_6.5[(SbW₉O₃₃)₂{WO₂(OH)}₂{WO₂}RuC₇H₃NO₄]·36H₂O, and the layered structure was constructed through the Na⁺ bridged sheet and the hydrogen-bonded layers. It displayed an effective proton conductivity of 2.97 × 10^-2 S cm^-1 at 348 K and 75% RH, owing to the complete interlayer confined hydrogen-bond network formed by the hydrogens of interlayer crystal waters, organic ligands ({RuC₇H₃NO₄}²⁺, {C₇H₃NO₄} is formed by the hydrolysis of pyridine 2,5-dicarboxylic acid (C₇H₅NO₄)), and acidic protons (H⁺), along with the interlayer domain as a transport channel. Furthermore, the hydrogen-bond network originating from interlayer organic ligands and acidic protons was more stable at a higher temperature of 423 K, preserving a high conductivity of 1.99 × 10^-2 S cm^-1.

Noble metal nanodendrites: growth mechanisms, synthesis strategies and applications

Inorganic nanodendrites (NDs) have become a kind of advanced nanomaterials with broad application prospects because of their unique branched architecture. The structural characteristics of nanodendrites include highly branched morphology, abundant tips/edges and high-index crystal planes, and a high atomic utilization rate, which give them great potential for usage in the fields of electrocatalysis, sensing, and therapeutics. Therefore, the rational design and controlled synthesis of inorganic (especially noble metals) nanodendrites have attracted widespread attention nowadays. The development of synthesis strategies and characterization methodology provides unprecedented opportunities for the preparation of abundant nanodendrites with interesting crystallographic structures, morphologies, and application performances. In this review, we systematically summarize the formation mechanisms of noble metal nanodendrites reported in recent years, with a special focus on surfactant-mediated mechanisms. Some typical examples obtained by innovative synthetic methods are then highlighted and recent advances in the application of noble metal nanodendrites are carefully discussed. Finally, we conclude and present the prospects for the future development of nanodendrites. This review helps to deeply understand the synthesis and application of noble metal nanodendrites and may provide some inspiration to develop novel functional nanomaterials (especially electrocatalysts) with enhanced performance.

Thermo-responsive palladium-ruthenium nanozyme synergistic photodynamic therapy for metastatic breast cancer management

Reactive oxygen species (ROS) have become an effective "weapon" for cancer therapy due to their strong oxidation and high anti-tumor activity. Photodynamic therapy (PDT) is one of the classical methods to induce reactive oxygen species. Therefore, an ultraminiature palladium ruthenium alloy (sPdRu) and Ru(II) were combined with thermally responsive phase change materials (PCMs). Polypyridyl-complex (RCE) co-encapsulation was performed to obtain thermally responsive nanoparticles (PdRu-RCE@PCMNPs) for multimodal synergistic anti-breast cancer therapy. On the one hand, the thermosensitive PCM protective layer can realize the slow release of sPdRu, and then catalyze the production of oxygen from tumor endogenous H₂O₂ to perform RCE-mediated PDT. At the same time, sPdRu further increased ROS levels through peroxidase (POD) activity. On the other hand, sPdRu has high photothermal conversion efficiency and can be effectively used for photothermal therapy and photodynamic therapy. Importantly, PdRu-RCE@PCM NPs not only can effectively inhibit primary tumor growth, but also can inhibit tumor metastasis. In addition, due to the effective accumulation of sPdRu and RCE, PdRu-RCE@PCM NPs also show excellent fluorescence and photothermal imaging capabilities of tumors, which can be used for tumor tracing and evaluation of treatment. Accordingly, PdRu-RCE@PCM NPs are useful in treating primary tumors and inhibiting tumor metastasis.

One Stone Two Birds: Unlocking the Synergy between Amorphous Ni(OH)2 and Pd Nanocrystals toward Ethanol and Formic Acid Oxidation

Even though extensive efforts have been devoted to mixing Pd nanocrystals with Ni(OH)₂ for the enhanced synergy, it remains a great challenge to incorporate nanosized Ni(OH)₂ species on the Pd electrode and reveal their synergy. Herein, we present spongelike Pd nanocrystals with the modification of amorphous Ni(OH)₂ species. The catalyst configuration is first considered by compositing Pd with Ni(OH)₂ species to optimize the Pd-Pd interatomic distance and then constructing a strongly coupled interface between Pd nanostructures and Ni(OH)₂ species. For the ethanol oxidation reaction (EOR) and the formic acid oxidation reaction (FAOR), Pd-Ni(OH)₂ composites exhibit an impressive mass activity of 4.98 and 2.65 A mg_Pd^-1, respectively. Most impressively, there is no significant decrease in the EOR activity during five consecutive cycles (50 000 s). A series of CO-poisoning tests have proved that the enhanced EOR and FAOR performances involve synergy between Pd nanostructures and Ni(OH)₂ species.

Synthesis of PtRu alloy nanofireworks as effective catalysts toward glycerol electro-oxidation in alkaline media

Electro-oxidation of glycerol is a key anodic reaction in direct alcohol fuel cell (DAFCs). Exploring the cost-effective nanocatalysts for glycerol oxidation reaction (GOR) is very important for the development of DAFC, but it is still challenging. In this paper, nanofirework-like PtRu alloy catalyst was successfully synthesized and used for GOR in alkaline medium. Thanks to the unique nanofirework-like structure and synergetic effects, the activity and stability of the as-prepared PtRu alloy nanofireworks (NFs) toward GOR were significantly improved relative to Pt NFs. In particular, the peak current density of GOR catalyzed by the optimized Pt₁Ru₃ NFs catalyst reached 2412.0 mA mg^-1, surpassing that of commercial Pt/C catalyst. This work has important guidance for the design of advanced anode electrocatalysts for fuel cells.

B,N-Doped PdRu Aerogels as High-Performance Peroxidase Mimics for Sensitive Detection of Glucose

Among plentiful porous nanomaterials, noble metal aerogels taken as nanozymes attract broad attention in sensing applications with their distinct enzyme mimic functions. In the catalytic field, the heteroatom doping strategy is a kind of way with great promise in improving the enzyme mimic activity of noble metal aerogels. In this experiment, we find a type of creative materials that were prepared by the fast and simple method. Due to the unique porous structure and synergetic effect from doped atoms, PdRu aerogels co-doped with boron and nitrogen (B, N-PdRu aerogels) were prepared using NH₃BH₃ as a reductant, which present improved peroxidase mimicking activity. With the existence of H₂O₂, the oxidation of 3,3',5,5'-tetramethylbenzidine was catalyzed by B, N-PdRu aerogels fairly efficiently, whose solution would be a blue appearance at optimum absorption wavelength 652 nm. Thus, by the tandem reaction bound to the enzyme glucose oxidase, the B, N-PdRu aerogels can be used for the sensitive determination of glucose. The new method has a good linear detection effect for glucose in the range of 10 μM to 2 mM. The minimum limit of detection can reach as low as 6 μM. This work will contribute to research on the rational design of metal aerogels based on the heteroatomic doping strategy and enhance the corresponding performance for a variety of applications.

Ordered PdCu-Based Core-Shell Concave Nanocubes Enclosed by High-Index Facets for Ethanol Electrooxidation

Crystal phase engineering is a powerful strategy for regulating the performance of electrocatalysts toward many electrocatalytic reactions. Herein we demonstrate that Au@Pd₁Cu concave nanocubes (CNCs) with an ordered body-centered cubic (bcc) PdCu alloy shell enclosed by many high active high-index facets can be adopted as highly active yet stable electrocatalysts for the ethanol oxidation reaction (EOR). These CNCs are more efficient than other nanocrystals with a disordered face-centered cubic (fcc) PdCu alloy surface and display high mass and specific activities of 10.59 A mg_pd^-1 and 33.24 mA cm^-2, which are 11.7 times and 4.1 times higher than those of commercial Pd black, respectively. Our core-shell CNCs also exhibit robust durability with the weakest decay in activity after 250 potential-scanning cycles, as well as outstanding antipoisoning ability. Alloying with Cu and the ordered bcc phase surface can provide abundant OH_ads species to oxidize carbonaceous poison to avoid catalyst poisoning, and the exposed high-index facets on the surface can act as highly catalytic sites.

Two-Dimensional Palladium-Copper Alloy Nanodendrites for Highly Stable and Selective Electrochemical Formate Production

Pd is the only metal that can catalyze electrochemical CO₂ reduction to formate at close-to-zero overpotential. It is unfortunately subjected to severe poisoning by trace CO as the side product and suffers from deteriorating stability and selectivity with increasing overpotential. Here, we demonstrate that alloying Pd with Cu in the form of two-dimensional nanodendrites could enable highly stable and selective formate production. Such unique bimetallic nanostructures are formed as a result of the rapid in-plane growth and suppressed out-of-plane growth by carefully controlling a set of experimental parameters. Thanks to the combined electronic effect and nanostructuring effect, our alloy product catalyzes CO₂ reduction to formate with remarkable stability and selectivity under the working potential as cathodic as -0.4 V. Our results are rationalized by computational simulations, evidencing that Cu atoms weaken the *CO adsorption and stabilize the *OCHO adsorption on neighboring Pd atoms.

A comprehensive and critical review of the recent progress in electrocatalysts for the ethanol oxidation reaction

The human craving for energy is continually mounting and becoming progressively difficult to gratify. At present, the world's massive energy demands are chiefly encountered by nonrenewable and benign fossil fuels. However, the development of dynamic energy cradles for a gradually thriving world to lessen fossil fuel reserve depletion and environmental concerns is currently a persistent issue for society. The discovery of copious nonconventional resources to fill the gap between energy requirements and supply is the extreme obligation of the modern era. A new emergent, clean, and robust alternative to fossil fuels is the fuel cell. Among the different types of fuel cells, the direct ethanol fuel cell (DEFCs) is an outstanding option for light-duty vehicles and portable devices. A critical tactic for obtaining sustainable energy sources is the production of highly proficient, economical and green catalysts for energy storage and conversion devices. To date, a broad range of research is available for using Pt and modified Pt-based electrocatalysts to augment the C2H5OH oxidation process. Pt-based nanocubes, nanorods, nanoflowers, and the hybrids of Pt with metal oxides such as Fe2O3, TiO2, SnO2, MnO, Cu2O, and ZnO, and with conducting polymers are extensively utilized in both acidic and basic media. Moreover, Pd-based materials, transition metal-based materials, as well as transition metal-based materials are also points of interest for researchers nowadays. This review article delivers a broad vision of the current progress of the EOR process concerning noble metals and transition metals-based materials.

Biomimetic two-dimensional nanozymes: synthesis, hybridization, functional tailoring, and biosensor applications

Biological enzymes play important roles in mediating the biological reactions in vitro and in vivo due to their high catalytic activity, strong bioactivity, and high specificity; however, they have also some disadvantages such as high cost, low environmental stability, weak reusability, and difficult production. To overcome these shortcomings, functional nanomaterials including metallic nanoparticles, single atoms, metal oxides, alloys, and others have been utilized as nanozymes to mimic the properties and functions of natural enzymes. Due to the development of the synthesis and applications of two-dimensional (2D) materials, 2D nanomaterials have shown high potential to be used as novel nanozymes in biosensing, bioimaging, therapy, logic gates, and environmental remediation due to their unique physical, chemical, biological, and electronic properties. In this work, we summarize recent advances in the preparation and functionalization, as well as biosensor and immunoassay applications of various 2D material-based nanozymes. To achieve this aim, first we demonstrate the preparation strategies of 2D nanozymes such as chemical reduction, templated synthesis, chemical exfoliation, calcination, electrochemical deposition, hydrothermal synthesis, and many others. Meanwhile, the structure and properties of the 2D nanozymes prepared by conjugating 2D materials with nanoparticles, metal oxides, biomolecules, polymers, ions, and 2D heteromaterials are introduced and discussed in detail. Then, the applications of the prepared 2D nanozymes in colorimetric, electrochemical, fluorescent, and electrochemiluminescent sensors are demonstrated.

Recent Progress of Ultrathin 2D Pd-Based Nanomaterials for Fuel Cell Electrocatalysis

Pd- and Pd-based catalysts have emerged as potential alternatives to Pt- and Pt-based catalysts for numerous electrocatalytic reactions, particularly fuel cell-related reactions, including the anodic fuel oxidation reaction (FOR) and cathodic oxygen reduction reaction (ORR). The creation of Pd- and Pd-based architectures with large surface areas, numerous low-coordinated atoms, and high density of defects and edges is the most promising strategy for improving the electrocatalytic performance of fuel cells. Recently, 2D Pd-based nanomaterials with single or few atom thickness have attracted increasing interest as potential candidates for both the ORR and FOR, owing to their remarkable advantages, including high intrinsic activity, high electron mobility, and straightforward surface functionalization. In this review, the recent advances in 2D Pd-based nanomaterials for the FOR and ORR are summarized. A fundamental understanding of the FOR and ORR is elaborated. Subsequently, the advantages and latest advances in 2D Pd-based nanomaterials for the FOR and ORR are scientifically and systematically summarized. A systematic discussion of the synthesis methods is also included which should guide researchers toward more efficient 2D Pd-based electrocatalysts. Lastly, the future outlook and trends in the development of 2D Pd-based nanomaterials toward fuel cell development are also presented.

The fabrication composite material of bimetallic micro/nanostructured palladium–platinum alloy and graphene on nickel foam for the enhancement of electrocatalytic activity

A composite of micro/nanostructured palladium–platinum alloy, reduced graphene oxide and polydopamine on nickel foam was obtained by a chemical immersion method and anneal method with high catalytic efficiency for the ethanol oxidation.

Synthesis of Bimetallic PdAg Nanoparticles and Their Electrocatalytic Activity toward Ethanol

Palladium-based bimetallic nanoparticles (NPs) have been studied as important electrocatalysts for energy conversion due to their high electrocatalytic performance and the less usage of the noble metal. Herein, well-dispersed PdAg NPs with uniform size were prepared via oil bath accompanied with the hydrothermal method. The variation of the Ag content in PdAg NPs changed the lattice constant of the face-centered cubic alloy nanostructures continuously. The Pd/Ag molar ratio in the PdAg alloy NPs affected their size and catalytic activity toward ethanol electrooxidation. Experimental data showed that PdAg NPs with less Ag content exhibited better electrocatalytic activity and durability than pure Pd NPs owing to both the small size and the synergistic effect. PdAg-acac-4 with the Pd/Ag molar ratio of 4 : 1 in the start system possessed the highest catalytic current density of 2246 mA/mg for the electrooxidation of ethanol. The differences in the morphology and electrocatalytic activity of the as-made PdAg NPs have been discussed and analyzed.

CO direct esterification to dimethyl oxalate and dimethyl carbonate: the key functional motifs for catalytic selectivity

The direct esterification of CO involves processes using CO as the starting material and ester chemicals as products. Dimethyl oxalate (DMO) and dimethyl carbonate (DMC) are two different products of the direct CO esterification reaction. However, the effective control of the reaction pathway and direct synthesis of DMO and DMC are challenging. In this review, we summarize the recent research progress on the direct esterification of CO to DMO/DMC and reveal the functional motifs responsible for the catalytic selectivity. Firstly, we discuss the microstructure of catalysts for the direct esterification of CO to DMO and DMC, including the valence state and the aggregate state of Pd. Then, the influence of characteristics of the support on the selectivity is analyzed. Importantly, the aggregate state of the active component, Pd is deemed as a vital functional motif for catalytic selectivity. The isolated Pd is conducive for the formation of DMC, while the aggregated Pd is beneficial for the formation of DMO. This review will provide rational guidance for the direct esterification of CO to DMO and DMC.

Shewanella oneidensis MR-1 self-assembled Pd-cells-rGO conductive composite for enhancing electrocatalysis

Biosynthesized noble metal nanoparticles (NPs) as promising green catalysts for electrochemical application has invited a lot of attention. However, effective electron transfer between biosynthesized NPs and electrode remains a challenge due to the uncontrollable and poor conductive property of cell substrates. In this study, graphene oxide (GO) was introduced into a bio-Pd synthesis process governed by Shewanella oneidensis MR-1, which was demonstrated to be simultaneously reduced with Pd(II) and transformed to reduced GO (rGO), resulting in the formation of a Pd-cells-rGO composite. Compared to the control without rGO (Pd-cells), the electrochemical conductivity of Pd-cells-rGO composite increased from almost zero to 196 μS cm^-1, indicating the rGO facilities the electron transport across the composite. Electrochemical characterizations revealed the electrochemical active surface area (ECSA) of Pd in Pd-cells-rGO was enlarged by increasing the amount of rGO in the composite, clearly indicating that the conductive network created by rGO enable the Pd NPs receive electrons from electrode and become electrochemical active. A considerable enhancement of electrocatalytic activity was further confirmed for Pd-cells-rGO as indicated by 36.7- and 17.2-fold increase (Pd-cells-rGO with Pd/GO ratio of 5/1 vs Pd-cells) of steady state current density toward hydrogen evolution and nitrobenzene reduction at -0.7 V and -0.55 V vs Ag/AgCl, respectively. We also compared the electrocatalytic performance with MWCNTs hybrids Pd-cells-CNTs. It was found that the association of Pd, cells and rGO creates an interactive and synergistic environment to allow higher conductivity and catalytic activity under the same amount of carbon nanomaterial. The strategy developed in this work activates a highly reactive NPs and proposed a designable protocol for enhancing electrocatalytic activity of biocatalysts.

Synthesis of Palladium-Based Crystalline@Amorphous Core-Shell Nanoplates for Highly Efficient Ethanol Oxidation

Phase engineering of nanomaterials (PEN) offers a promising route to rationally tune the physicochemical properties of nanomaterials and further enhance their performance in various applications. However, it remains a great challenge to construct well-defined crystalline@amorphous core-shell heterostructured nanomaterials with the same chemical components. Herein, the synthesis of binary (Pd-P) crystalline@amorphous heterostructured nanoplates using Cu_{3- χ} P nanoplates as templates, via cation exchange, is reported. The obtained nanoplate possesses a crystalline core and an amorphous shell with the same elemental components, referred to as c-Pd-P@a-Pd-P. Moreover, the obtained c-Pd-P@a-Pd-P nanoplates can serve as templates to be further alloyed with Ni, forming ternary (Pd-Ni-P) crystalline@amorphous heterostructured nanoplates, referred to as c-Pd-Ni-P@a-Pd-Ni-P. The atomic content of Ni in the c-Pd-Ni-P@a-Pd-Ni-P nanoplates can be tuned in the range from 9.47 to 38.61 at%. When used as a catalyst, the c-Pd-Ni-P@a-Pd-Ni-P nanoplates with 9.47 at% Ni exhibit excellent electrocatalytic activity toward ethanol oxidation, showing a high mass current density up to 3.05 A mg_Pd ^-1 , which is 4.5 times that of the commercial Pd/C catalyst (0.68 A mg_Pd ^-1 ).

Electron injection effect in In2O3 and SnO2 nanocrystals modified by ruthenium heteroleptic complexes

In this work, the optical characteristics and conductivity under photoactivation with visible light of hybrids based on nanocrystalline SnO2 or In2O3 semiconductor matrixes and heteroleptic Ru(ii) complexes were studied. The heteroleptic Ru(ii) complexes were prepared based on 1H-imidazo[4,5-f][1,10]phenanthroline and 2,2'-bipyridine ligands. Nanocrystalline semiconductor oxides were obtained by chemical precipitation with subsequent thermal annealing and characterized by XRD, SEM and single-point BET methods. The heteroleptic Ru(ii) complexes as well as hybrid materials were characterized by time-resolved luminescence and X-ray photoelectron spectroscopy. The results showed that the surface modification of SnO2 nanoparticles with heteroleptic ruthenium complexes led to an increase in conductivity upon irradiation with light appropriate for absorption by organometallic complexes. In the case of In2O3, the deposition of Ru(ii) complexes resulted in a decrease in conductivity, apparently due to the special structure of the surface layer of the semiconductor.

Bimetallic alloy and semiconductor support synergistic interaction effects for superior electrochemical catalysis

The design and fabrication of economically viable anode catalysts for the methanol oxidation reaction (MOR) have been challenging issues in direct methanol fuel cells (DMFCs) over the decades. In this work, a composite electrochemical catalyst of Pd-coupled Ag and ZnO for the possible replacement of expensive Pt catalysts in DMFCs is successfully prepared. The as-made Pd@Ag/ZnO exhibits specific activity, which is 1.8-fold, 2.8-fold, and 4.6-fold higher than that of a Pd/ZnO catalyst, 20% Pd/C catalyst and Pd black, respectively. The improvement of the catalytic mechanism is likely due to the synergistic interaction between Pd@Ag and ZnO. The density functional theory (DFT) calculation results confirm that Ag doped into Pd weakens the adsorption of CO, dramatically improving the capability to resist CO poisoning.

Manipulating the surface composition of Pt–Ru bimetallic nanoparticles to control the methanol oxidation reaction pathway

Here, we achieve surface composition by precisely manipulating bimetallic Pt–Ru alloys from Pt-skin-rich to Ru-skin-rich materials and report that the MOR pathway can be controlled by tuning the location and content of Ru on the Pt–Ru alloy surface.

Interface engineering of Ni5P2 nanoparticles and a mesoporous PtRu film heterostructure on Ni foam for enhanced hydrogen evolution

Engineering of multicomponent heterostructures can yield exceptional functionalities and enhance electrocatalytic activities by a synergistic effect. Herein, Ni₅P₂ nanoparticle-decorated mesoporous PtRu film on Ni foam (Ni₅P₂-mPtRu/NF) has been synthesized via a facile two-step strategy. Ni₅P₂-mPtRu/NF possesses a well-developed continuous mesoporous structure and strong electronic interaction between Ni₅P₂ and PtRu, exhibiting an enhanced electrocatalytic performance towards an alkaline hydrogen evolution reaction (HER). Ni₅P₂-mPtRu/NF achieves a current density of 10 mA cm^-2 at an overpotential of 28.8 mV and a low Tafel slope of 56.5 mV dec^-1, and has excellent durability. This work provides a promising pathway for developing self-supported mesoporous multicomponent heterostructures as efficient electrocatalysts for an alkaline HER.

Nanocatalysts for Electrocatalytic Oxidation of Ethanol

The use of ethanol as a fuel in direct alcohol fuel cells depends not only on its ease of production from renewable sources, but also on overcoming the challenges of storage and transportation. In an ethanol-based fuel cell, highly active electrocatalysts are required to break the C-C bond in ethanol for its complete oxidation at lower overpotentials, with the aim of increasing the cell performance, ethanol conversion rates, and fuel efficiency. In recent decades, the development of wet-chemistry methods has stimulated research into catalyst design, reactivity tailoring, and mechanistic investigations, and thus, created great opportunities to achieve efficient oxidation of ethanol. In this Minireview, the nanomaterials tested as electrocatalysts for the ethanol oxidation reaction in acid or alkaline environments are summarized. The focus is mainly on nanomaterials synthesized by using wet-chemistry methods, with particular attention on the relationship between the chemical and physical characteristics of the catalysts, for example, catalyst composition, morphology, structure, degree of alloying, presence of oxides or supports, and their activity for ethanol electro-oxidation. As potential alternatives to noble metals, non-noble-metal catalysts for ethanol oxidation are also briefly reviewed. Insights into further enhancing the catalytic performance through the design of efficient electrocatalysts are also provided.

Monodisperse ordered indium-palladium nanoparticles: synthesis and role of indium for boosting superior electrocatalytic activity for ethanol oxidation reaction

The slow kinetics of ethanol oxidation reaction (EOR) has limited its widespread use for fuel cells. Bimetallic catalysts with optimized surface compositions can considerably govern rate-determining steps through selectivity for CH3COOH formation or by facilitating the adsorption of OHadsvia the bifunctional effect of an alloy to increase the EOR's kinetic rates. Here, we reported monodisperse ordered In-Pd nanoparticles as new bimetallic high-performance catalysts for EOR. In-Pd nanoparticles, i.e., In3Pd2 and In3Pd5 were prepared using arrested precipitation in solution, and their composition, structures, phase and crystallinity were confirmed using a variety of analyses including TEM, XPS, EDS and XRD. In-Pd nanoparticles were loaded on carbon black (Vulcan XC-72) as electrocatalysts for EOR in alkaline media. In3Pd2 and In3Pd5 nanoparticles exhibited 5.8 times and 4.0 times higher mass activities than commercial Pd/C, which showed that the presence of indium greatly boosts electrocatalytic reactivity for EOR of Pd catalysts. This performance is the best among those of bimetallic nanoparticles reported to date. Such high performance of In-Pd nanoparticles may be attributed to the following two reasons. First, In-Pd nanoparticles exhibited excellent CO anti-poison ability, as confirmed by CO striping experiments. Second, as revealed by DFT calculations of metals with OHads adsorption, In atoms on In3Pd2 surface exhibited the lowest energy (-1.659 eV) for OHads adsorption as compared to other common oxophilic metals including Sn, SnPt, Ag, Ge, Co, Pb, and Cu. We propose that the presence of indium sites promoted efficient free OH radical adsorption on indium sites and resulted in a faster reaction rate of acetate formation from acetaldehyde (the rate determining step for EOR on Pd sites). Finally, a single direct ethanol fuel cell (DEFC) with Pd/C anode was prepared. Compared to the results for a commercial Pd/C anode, the open circuit voltage (OCV) of In3Pd2/C improved by 0.25 V (from 0.64 to 0.89 V) and the power density improved by ∼80% (from 3.7 to 6.7 mW cm-2), demonstrating its practical uses as Pt or Pd catalyst alternatives for DEFC.

Black Phosphorus-Graphene Heterostructure-Supported Pd Nanoparticles with Superior Activity and Stability for Ethanol Electro-oxidation

Rational design supporting material for palladium (Pd)-based catalyst can maximize its electrocatalytic performance for ethanol oxidation reaction (EOR) catalyst in alkaline condition. Utilizing the unique two-dimensional structures and outstanding physicochemical property of graphene and black phosphorus (BP), herein, we proposed and designed a black phosphorus-graphene heterostructure for supporting Pd nanoparticles. Through merely ball-milling of activated graphene (AG) and black phosphorus (BP), the AG-BP hybrid with a linkage of P-C bonding is used as supports of Pd. The obtained Pd/AG-BP hybrid exhibits ultrahigh electrochemical activity toward EOR. Remarkably, it can achieve a high mass peak current density of ∼6004.53 and ∼712.03 mA mg_Pd^-1 before and after the durability tests of 20 000s on EOR, which are ∼7.19 and 80 times higher than those of commercial Pd/C. The experimental analysis and density-functional-theory calculation show that Pd becomes more positive with electrons transfer from Pd to AG-BP supports and is liable to absorb the OH radicals for removing CO_ads intermediate to release active sites on EOR, together with the excellent ability to generate additional OH militants after combining with the AG-BP heterostructure.

Ternary N, S, and P-Doped Hollow Carbon Spheres Derived from Polyphosphazene as Pd Supports for Ethanol Oxidation Reaction

Ethanol oxidation reaction (EOR) is an important electrode reaction in ethanol fuel cells. However, there are many problems with commercial ethanol oxidation electrocatalysts today, such as poor durability, poor anti-CO poisoning ability, and low selectivity for C–C bond cleavage. Therefore, it is very meaningful to develop a high-performance EOR catalyst. Herein, we designed ternary N, S, and P-doped hollow carbon spheres (C–N,P,S) from polyphosphazene (PCCP) as Pd supports for EOR. Using SiO2 spheres as the templates, the PCCP was first coated on the surfaces of SiO2 spheres by in situ polymerization. Through high-temperature pyrolysis and hydrofluoric acid-etching, the hollow PCCP has a large surface area and porous structure. After loading Pd nanoparticles (NPs), the Pd/C–N, P, S catalysts with Pd NPs decorated on the surfaces of C–N, P, S can achieve a high mass peak current density of 1686 mA mgPd−1, which was 2.8 times greater than that of Pd/C. Meanwhile, the Pd/C–N, P, S catalyst also shows a better stability than that of Pd/C after a durability test of 3600s.

Hollow Ag44Pt56 nanotube bundles with high electrocatalytic performances for hydrogen evolution and ethylene glycol oxidation reactions

It is a main challenge to synthesize highly efficient and durable nanocatalysts towards hydrogen evolution reaction (HER) and alcohol oxidation reaction in energy conversion and storage. Herein, a green wet-chemical approach was developed to directly prepare hollow Ag₄₄Pt₅₆ nanotube bundles (H-Ag₄₄Pt₅₆ NTBs), utilizing 5-azacytosine as a structure-directing agent. The obtained electrocatalyst displayed superior catalytic activity and durability for HER in acid media, and the great improvement in catalytic performance for ethylene glycol oxidation reaction (EGOR) in the alkaline electrolyte, outperforming home-made Ag₃₄Pt₆₆ nanoparticles (NPs), Ag₇₀Pt₃₀ NPs, and commercial Pt/C catalysts. The high electrocatalytic characters are mainly attributed to the special nanostructures and the synergetic effects between the bimetals.

An etching-assisted route for fast and large-scale fabrication of non-layered palladium nanosheets

To date, great progress has been made in the shape-controlled synthesis of noble-metal nanocrystals. However, there still exists a major gap between academic studies and industrial applications due to the inability to produce nanocrystals in large quantities while retaining their uniformity. To help fill this gap, herein, we provide a new route to scale up and accelerate the production of non-layered palladium nanosheets (Pd NSs) by incorporating etching while retaining effective capping during the synthesis. The key to this rapid synthesis is the etching induced by selected etchants (e.g., Fe3+/Fe2+, Cl-/O2, Br-/O2, and I-/O2). Specifically, this synthesis can be accomplished within 3 min, reaching a yield as high as 7.2 g L-1 h-1. The thickness of Pd NSs can be tuned to 1.6, 2.0, 2.3, and 3.5 nm by controlling the etching and reducing rates via choosing different type of etchants. Moreover, these non-layered Pd NSs are fabricated in an aqueous solution without the addition of any organic compounds; therefore, the surface of these NSs is extremely clean. When used as a catalyst for the formic acid oxidation reaction, the as-prepared non-layered Pd NSs exhibit a mass activity as high as 1350 mA mg-1, which is 3.7 times higher than that of commercial Pd/C, due to their much larger electrochemical surface area (66.2 m2 g-1, which is 2.7 times higher than that of commercial Pd/C).

2D PdAg Alloy Nanodendrites for Enhanced Ethanol Electroxidation

The development of highly active and stable electrocatalysts for ethanol electroxidation is of decisive importance to the successful commercialization of direct ethanol fuel cells. Despite great efforts invested over the past decade, their progress has been notably slower than expected. In this work, the facile solution synthesis of 2D PdAg alloy nanodendrites as a high-performance electrocatalyst is reported for ethanol electroxidation. The reaction is carried out via the coreduction of Pd and Ag precursors in aqueous solution with the presence of octadecyltrimethylammonium chloride as the structural directing agent. Final products feature small thickness (5-7 nm) and random in-plane branching with enlarged surface areas and abundant undercoordinated sites. They exhibit enhanced electrocatalytic activity (large specific current ≈2600 mA mgPd-1) and excellent operation stability (as revealed from both the cycling and chronoamperometric tests) for ethanol electroxidation. Control experiments show that the improvement comes from the combined electronic and structural effects.

Facile construction of fascinating trimetallic PdAuAg nanocages with exceptional ethylene glycol and glycerol oxidation activity

Highly open metallic nanocages represent a novel class of nanostructures for advanced catalytic applications in direct liquid fuels cells due to their specific capability of providing easy access to reactants in both internal and external active sites and also desirable electronic structures for the adsorption of molecules, which render superior catalytic performances. However, to date, the rational design of trimetallic nanocages with tunable compositions remains a challenge. Herein, we demonstrate a facile method combining seed mediated and galvanic replacement for the preparation of unique trimetallic Pd-Au-Ag nanocages catalysts with tunable compositions. A series of controlled experiments reveal that the reaction time plays a crucial role in affecting the morphology of the final product. Importantly, the newly-generated Pd-Au-Ag nanocages are high-performance electrocatalysts for the oxidation of both ethylene glycol and glycerol with mass activities of 7578.2 and 5676.1 mA mg^-1, respectively, which are far superior to that of commercial Pd/C. We firmly believe that the strategy and enhanced electrocatalysts developed in this study can be well applied to boost the commercial development of fuel cell technologies.

Hollow AuxAg/Au core/shell nanospheres as efficient catalysts for electrooxidation of liquid fuels

One plausible approach to endow nanocrystals with both enhanced catalytic activity and stability for the electrooxidation of liquid fuels is to chemically control the crystal structures of nanoparticles. To date, core-shell and alloy structures have been demonstrated to offer generally two precious opportunities to design highly efficient nanocatalysts for the electrooxidation reaction of organic molecules. We herein combine these two advantages and develop a general method to successfully synthesize hollow Au_xAg/Au core/shell nanospheres with a high yield approaching 100% via a combined seed mediated and galvanic replacement method. The results from the electrochemical measurements have revealed that this as-obtained hollow Au_xAg/Au core/shell nanosphere exhibited considerably high electrocatalytic performance towards ethylene glycol and glycerol oxidation with mass activity of 4585 and 3486 mA mg_Au^-1, which were 5.3- and 5.8-fold higher than that of pure Au. We trust this strategy may be extended to the syntheses of other multimetallic nanocatalysts with such fascinating nanostructures and the as-obtained hollow Au_xAg/Au core/shell nanospheres can be well applied to serve as highly desirable anode catalysts for the electrooxidation of ethylene glycol and glycerol.

Cactus-Like Hollow Cu2-x S@Ru Nanoplates as Excellent and Robust Electrocatalysts for the Alkaline Hydrogen Evolution Reaction

The development of Pt-free electrocatalysts for the hydrogen evolution reaction (HER) recently is a focus of great interest. While several strategies are developed to control the structural properties of non-Pt catalysts and boost their electrocatalytic activities for the HER, the generation of highly reactive defects or interfaces by combining a metal with other metals, or with metal oxides/sulfides, can lead to notably enhanced catalytic performance. Herein, the preparation of cactus-like hollow Cu_2-x S@Ru nanoplates (NPs) that contain metal/metal sulfide heterojunctions and show excellent catalytic activity and durability for the HER in alkaline media is reported. The initial formation of Ru islands on presynthesized Cu_1.94 S NPs, via cation exchange between three Cu⁺ ions and one Ru³⁺ , induces the growth of the Ru phase, which is concomitant with the dissolution of the Cu_1.94 S nanotemplate, culminating in the formation of a hollow nanostructure with numerous thin Ru pillars. Hollow Cu_2-x S@Ru NPs exhibit a small overpotential of 82 mV at a current density of -10 mA cm^-2 and a low Tafel slope of 48 mV dec^-1 under alkaline conditions; this catalyst is among state-of-the-art HER electrocatalysts in alkaline media. The excellent performance of hollow Cu_2-x S@Ru NPs originates from the facile dissociation of water in the Volmer step.

Single-Atomic Ruthenium Catalytic Sites on Nitrogen-Doped Graphene for Oxygen Reduction Reaction in Acidic Medium

The cathodic oxygen reduction reaction (ORR) is essential in the electrochemical energy conversion of fuel cells. Here, through the NH₃ atmosphere annealing of a graphene oxide (GO) precursor containing trace amounts of Ru, we have synthesized atomically dispersed Ru on nitrogen-doped graphene that performs as an electrocatalyst for the ORR in acidic medium. The Ru/nitrogen-doped GO catalyst exhibits excellent four-electron ORR activity, offering onset and half-wave potentials of 0.89 and 0.75 V, respectively, vs a reversible hydrogen electrode (RHE) in 0.1 M HClO₄, together with better durability and tolerance toward methanol and carbon monoxide poisoning than seen in commercial Pt/C catalysts. X-ray adsorption fine structure analysis and aberration-corrected high-angle annular dark-field scanning transmission electron microscopy are performed and indicate that the chemical structure of Ru is predominantly composed of isolated Ru atoms coordinated with nitrogen atoms on the graphene substrate. Furthermore, a density function theory study of the ORR mechanism suggests that a Ru-oxo-N₄ structure appears to be responsible for the ORR catalytic activity in the acidic medium. These findings provide a route for the design of efficient ORR single-atom catalysts.